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Appendix E Environmental Protection Agency Program and Region Responses to Questions from the Committee In January 2007 the NRC committee sent EPA a list of questions (see below) to gather additional information on their risk assessment practices. EPA responses were provided by the Office of Air and Radiation (OAR); Office of Prevention, Pesticides, and Toxic Substances (OPPTS), Region 2; and the Office of Solid Waste and Emergency Response (OSWER); and the Office of Water (OW). The EPA responses do not represent the views of the committee on these issues. QUESTIONS FOR EPA FROM THE NRC COMMITTEE Give an example of a risk assessment from your office that you would consider an example of âbest practice,â and an example of a risk assessment that you think could have been improved (and if so, how). What improvement in EPA risk assessment practices would you find particularly helpful in the short term (2-5 years) and in the longer term (10-20 years)? If these improvements were to be implemented, how do you foresee the changes impacting your office? Please describe the risk assessment paradigm(s) used by your office. Do these paradigms adequately address environmental problems faced by the country? If not, how might current paradigms be modified or new paradigms identified to address these problems? Describe problems that arise when using risk assessment to support regulatory decision making. Do you encounter similar problems when using risk assessment in non-regulatory decisions? Please provide specific examples to illustrate your points. How would you recommend improving the presentation of EPA risk assessments for decision-making? 367
368 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT How have you addressed and communicated uncertainty in risk assessments? Please discuss the adequacy of default assumption choices, and efforts to use alternatives to these default assumptions. Please describe the ways in which children and potentially unique or vulnerable populations are specifically considered in your officeâs risk assessments. Please provide examples. AGENCY RESPONSES TO QUESTIONS Office of Air and Radiation (OAR) Current Practice â¢ Statutory basis/current approach and paradigms for risk assessment (specific to each program office) - Examples and best practices - Gaps and problems â¢ Uncertainty analysis - Examples - Communication of risk and uncertainty â¢ Sensitive and vulnerable subpopulations (e.g., children, elderly, tribes, endangered species) - Examples of physical attributes and unique exposures that impact risk - Problems and challenges â¢ Challenges for risk assessment in a regulatory process - Examples - Problems and challenges General Comment The 2004 Agency document âAn Examination of EPA Risk Assessment Principles and Practicesâ (EPA 2004a) provides a good resource for understanding the Agency as well as OARâs approach to risk assessment. Consistent to the focus of the NAS committee charge this response does not address ecological risk assessment. Protection of ecosystems from adverse impacts from of air pollution is an important mission of our Office and we could provide additional information in this area if requested. There are two programs within OAR that best illustrate the use of risk assessment in our Office. First, are assessment activities that support the development of national ambient air quality standards (NAAQS) for the 6 âcriteriaâ air pollutants, and, second, those conducted in consideration of emissions controls for hazardous air pollutants (HAPs or air toxics). National Ambient Air Quality Standards (NAAQS) The âcriteriaâ air pollutants are the six pollutantsâozone, particulate matter, carbon monoxide, nitrogen dioxide, sulfur dioxide and leadâthe presence of which in the ambient air results from numerous or diverse sources, and for which there are established public health concerns at historic ambient levels. These pollutants have been extensively studied
APPENDIX E 369 over time and health-based National Ambient Air Quality Standards (NAAQS) have been developed for each. Human exposure and/or health risk assessments and ecological risk as- sessments are performed during the periodic reviews of these standards. The process under which exposure and/or risk assessments are performed for the cri- teria pollutants is largely driven by statutory language and legislative history and involves substantial external peer and public review. Each NAAQS review includes a full review of the underlying scientific database which supports the quantitative exposure and/or risk as- sessments (for an example, see the Air Quality Criteria for Ozone and Other Photochemical Oxidants [EPA 2008a]). The health-effects databases for criteria pollutants are generally very rich and include: epidemiological studies of normal exposures to the ambient mix of air pollutants, controlled-human exposure studies, and animal studies (short- and long-term exposures). Risk assessments for criteria air pollutants also benefit from extensive exposure related information including monitoring data and well developed exposure models. Hazard characterization involves a weight-of-evidence approach, using all relevant in- formation and considering the nature and severity of effects, patterns of human exposure, nature and size of sensitive populations, the kind and degree of uncertainties, and the con- sistency or coherence across all types of available evidence. âDoseâ-response evaluations are based on the nature of available evidence from human studies, generally with no discern- able thresholds (effects observed at current ambient concentrations). For example, for PM, ambient concentration-response functions are employed, for ozone, exposure-response and concentration-response relationships are used and for CO and lead, internal dose-metrics are used. When ambient concentration-response functions are used, simulations of âjust meetingâ alternative standards are used to examine levels of risk. When exposure or internal dose-response metrics are used, exposure modeling is relied upon that includes air quality monitoring/modeling and simulations of âjust meetingâ alternative standards, pollutant concentrations within relevant microenvironments (home, yard, car, office), amount of time in different microenvironments and level of exertion (time-activity and breathing rate data), population demographics (census data, commuting patterns), probabilistic assessment (in- cluding uncertainty and variability), and sensitivity analyses. This modeling provides the abil- ity to identify, and characterize exposure distributions for sensitive and/or at risk groups. Risk characterization for criteria pollutants includes both qualitative and quantitative approaches. There is an integration of evidence on acute and chronic health effects (strengths, weaknesses, uncertainties). Expert judgments are made on adversity of effects (severity, dura- tion, frequency). There are qualitative and quantitative assessments of population exposures of concern and/or risks to public health. The risk characterizations are primarily based on available evidence from human studies and âreal-worldâ air quality and exposure analyses; no need for traditional âuncertaintyâ or âsafetyâ factors. Risk assessments and characterizations for criteria pollutants, while considering the gen- eral population, include focus on the susceptible and/or the more highly exposed subpopu- lations (e.g., asthmatics and children are groups focused on in the current ozone NAAQS review). However, exposures and risks do not focus on maximum exposed individuals or maximum individual risk given the legislative history indicating that standards are to protect most of the sensitive population group but not the most sensitive individual. Uncertainty in criteria pollutant risk assessments is routinely addressed using proba- bilistic assessment (including uncertainty and variability) and sensitivity analyses. For an example of the type of exposure and risk assessments conducted for the NAAQS reviews see the final OAQPS Staff Paper for Ozone (EPA 2008b) and the human exposure, health risk assessment, and exposure, risk and impacts assessment for vegetation technical support documents (EPA 2008c).
370 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT Risk assessments for criteria pollutants generally include quantitative sensitivity analy- ses of exposure and health risk estimates as mentioned above, and also include qualitative discussion of contributing uncertainties. Key Issues and Challenges Key issues and challenges in carrying out quantitative risk assessments for criteria pol- lutants have included: (1) how to appropriately reflect and characterize model uncertainty, especially with respect to the shape and location of concentration-response relationships for which epidemiological studies are often failing to discern population thresholds, even at ambient levels approaching background levels; and (2) how to appropriately address and consider multi-pollutant health effect models and to disentangle the likely interaction among air pollutants, many of which are correlated and come from common sources (e.g., combustion of fossil fuels) in causing various health effects. In the area of exposure analysis, these challenges include how to use the human activity data base which consists of over 20,000 individual daily diaries to construct human activity sequences over months or an entire year. There is very little longitudinal data, so it is difficult to know if we are appropriately taking into account the repeated activities that individuals engage in. There also are few exposure field studies that include representative population sampling that would allow evaluation of the regulatory exposure models used by EPA in its NAAQS assessments. In addition, there are challenges in determining how âjust meetingâ hourly or daily standards will affect the overall distribution of pollutant concentrations across all hours and days. For non-threshold pollutants, the choice of method used in simu- lating attainment can have potentially large impacts on the estimated risks. Hazardous Air Pollutants The hazardous air pollutants (HAPs or âair toxicsâ) are 187 substances listed in CAA (e.g., benzene, methylene chloride, cadmium compounds, etc.) which have been associated with, or for which data suggest, the potential for serious adverse health and/or environmen- tal effects, and for which there are specific source-based statutory requirements. Although several HAPs have substantial health and/or ecological effects data bases, most others have very limited data, much of it based solely on knowledge of health effects on exposed animals rather than humans. HAPs are regulated through source-oriented technology and risk-based emissions standards. HAP risk assessments are performed for consideration of risk-based emissions standards (residual risk standards) for source categories for which technology-based controls have already been applied (a good example of which may be found in the docket supporting the proposed residual risk rule for the source category called âHalogenated Solvent Cleanersâ (look in ICF International 2006). Rather than focusing on the risks associated with expo- sure to an individual chemical, these risk assessments commonly examine cumulative risks associated with exposures resulting from the combination of pollutants emitted by a par- ticular type of industry. By statutory language and regulatory history, these risk assessments include both a maximum individual risk (i.e., presuming an individual were exposed to the maximum level of a pollutant for a lifetime), as well as a characterization of a representa- tive population risk. HAP risk assessments may also be performed for other programmatic purposes. For example, national-scale assessments have been performed based on the 1996 and 1999 emissions inventories as part of the National Air Toxics Assessment (NATA) activities (EPA
APPENDIX E 371 2002a, 2003a). As another example, risk assessments may be performed to support deci- sions on petitions to list or delist individual HAPs or source categories from Clean Air Act regulatory consideration. The scope of HAP risk assessments varies with the characteristics of the pollutants and sources being assessed. Inhalation and, as appropriate, other routes of exposure are assessed, and both chronic and acute time scales are considered. Ecological risks are also considered for residual risk decision-making. Routinely, a tiered approach is employed for efficiency, with lower tiers using simpler, more conservative tools and assumptions to identify important sources and pollutants, and higher tiers using more refined tools and site-specific data to determine where emission controls may be appropriate. Lower-tier risk assessments generally support decisions not to regulate or assist decisions to focus resources on a small number of stressors and sources for next iteration. They alone generally do not support decisions to mandate additional control of emissions. Such decisions, which can have significant economic implications, usually require more refined assessment. Hazard and dose-response assessments for HAPs generally rely on the most current existing assessments that have undergone scientific peer review and public review. The dose- response metrics used are acute or chronic reference concentrations (RfCs), and cancer inha- lation unit risk (IUR) estimates. The sources for these values include U.S. EPA (e.g., IRIS), U.S. ATSDR, California EPA, etc. The common qualities across the sources employed are: development under a defined scientific process, use of independent external peer review, and a reflection of the state of knowledge at the time of the assessment. Risk assessments for HAPs routinely include, as a first step, derivation of risk estimates for conservative exposure scenarios (e.g., continuous lifetime exposure). Where this first step suggests risks in a range of potential concern, more refined assessments which utilize more of the available data are performed. The most refined assessments attempt to provide a probabilistic distribution of risk (including uncertainty and variability) and sensitivity analy- ses. The use of probabilistic assessments is currently limited to certain exposure assessment variables (i.e., those describing daily activity and long-term migration behaviors), and does not typically include variables describing emission rates, release conditions, meteorology, fate and transport, or dose-response. Consideration of the most exposed receptors (individuals) is accomplished by estimat- ing chronic exposures at the Census block level and acute exposures at the offsite location with the highest 1-hour concentration. OAR in its HAPs assessment is a user of Hazard/ Dose response information (e.g., such as that produced under the IRIS program). Thus, consideration of sensitive subpopulations is considered in so far as it is explicitly built into the dose-response metrics that EPA uses to estimate risk (i.e., where data supporting such distinctions are available). Unit risk estimates typically incorporate protective low-dose extrapolation assumptions and are based on statistical upper confidence limits. Reference concentrations employ uncertainty factors that account for differences among species, within human populations, and database deficiencies (e.g., failure to identify no-effect doses and absence of chronic studies). These uncertainty factors are intended to ensure that the refer- ence concentration represents an exposure that is likely to be without appreciable risk of adverse effects in human populations, including sensitive sub-populations. Risk assessments for HAPs may include quantitative sensitivity analyses of exposure as mentioned above, and also include qualitative discussion of contributing uncertainties. However, the dose response information provided in IRIS (or other sources of dose response information) typically does not have information suitable quantitative analysis of either uncertainty or variability.
372 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT Key Issues and Challenges Key issues and challenges in carrying out risk assessments for hazardous air pollutants include both lack of data and how to appropriately reflect and characterize uncertainty and variability in assessments. As described above, risk assessments for the HAP program decisions routinely address multiple pollutant exposure and risk for multiple similar sources. Limitations associated with current assessments may contribute to uncertainties in resultant risk estimates. Examples of these are listed below as areas where improvements in risk assessment methods, tools or inputs might lead to reduced uncertainty in risk estimates. â¢ As described above, the single greatest challenge in risk analysis for most hazard- ous air pollutants is the need to rely primarily on animal or limited human data for the development of hazard and dose response assessments. The interpretation and implications of such data for potential risk is typically one of the greatest sources of uncertainty in such assessments. â¢ One of the significant sources of uncertainty to risk assessments is the source char- acterization, including emissions estimates. This is particularly true for source categories that have large numbers of sources and where ârepresentativeâ data may not exist. For modeling purposes, source data should include site-specific release parameter/characterization infor- mation as well as better source emission estimates. For example, such parameters include map coordinates, release heights and temperatures, emissions data measured or estimated (and approved) directly by the facilities, annual and maximum hourly emission rates, and quantitative estimates of the uncertainties associated with each. â¢ We are limited in methods to consider the effects on source-specific exposure of longer-term population mobility. While such data on migration behavior on a local scale are available, they have not been developed into tools or analyses that are readily applicable to our risk assessment methods. â¢ Atmospheric deposition data, which would contribute to improved/enhanced assess- ment of non-inhalation exposures and risk, are limited. â¢ Methods for estimating and presenting uncertainty in a manner easily understood by decision makers are limited. â¢ Use of the Agencyâs traditional exposure-response assessments (e.g., cancer unit risk factors and RfCs) contribute to our limitations with regard to incorporating quantitative uncertainty and variability of response into risk estimates. â¢ Limitations with regard to spatial coverage of air toxics monitoring networks affect performance evaluation capabilities for local-scale air modeling used in HAP risk assessments. â¢ Our ability to evaluate mixtures and potential interactions (other than that provided under EPAâs current mixtures guidance) is limited. â¢ Because of the number of hazardous air pollutants emitted from the many sources considered and the time required for updating the hazard and dose-response assessments, the development of those updated assessments can not kept up with the need to make regulatory decisions. Thus, OAR is often confronted with making such decisions with out the benefit of final IRIS assessments.
APPENDIX E 373 Future Directions: Addressing Gap, Limitations, and Needs Both the Criteria and Hazardous air pollutant program operate under the risk assessment paradigm developed by the NRC in its 1983 âRed Bookâ report. The overall approach to risk assessment in the Hazardous Air pollutant program has also been guided by the 1994 NRC report, âScience and Judgment,â which, for example, outlined a tiered approach to the assessment of risk from toxics air emissions from affected sources. We believe the basic paradigm for risk assessment remains sound. In developing recommendations for improvements, we ask that the Committee consider that the agency must operate within mandated timeframes and growing resource constraints. Thus, any guidance on prioritization of recommendations or on those circumstances where potentially more resource intensive approaches are suggested, would be useful. The âkey issues and challengesâ discussions in Part I of this submission (for both the NAAQS process and hazardous air pollutants) provide useful insight into areas where the Committee might focus in looking at future directions and needs. In addition to those points we would add the following few comments: The issue of needed data and tools for improving NAAQS assessments are to some extent addressed in the NAAQS review process. Of particular note is the role played by our external scientific review group, the Clean Air Scientific Advisory Committee (CASAC), that explic- itly identifies policy-relevant research needs to improve our capabilities for the next cycle of review. This has led to a continuous improvement in our assessment capabilities. Within the NAAQS program the application of additional methods for uncertainty analysis (e.g. expert elicitation) has particular promise in this program. However, the Agency is still in an early stage of considering how best to incorporate such approaches into its as- sessments, where appropriate, and how to consider such assessments relative to data driven assessments. Whatever approaches are adopted to characterize uncertainties, it is important to communicate how much weight to accord across the distribution of exposure and/or risk estimates, and not simply provide lower and upper uncertainty bounds. Office of Prevention, Pesticides and Toxic Substances (OPPTS) Current Practice: Risk Assessment at the EPA Statutory Basis/Current Approach and Paradigms for Risk Assessment (Specific ro Each Program Office) A response to this question can be found at our websites (EPA 2008d,e) along with current practices and recommendations to improve risk assessment (EPA 2002b, 2007a, 2008f). Very briefly, as an example, the passage of the 1996 Food Quality Protection Act re- quires that EPA consider, among other things, the best available data and information on the following: aggregate exposure to the pesticide (including exposure from food, water, and residential pesticide uses to a single pesticide), cumulative effects from other pesticides sharing a common mechanism of toxicity (including exposure from food, water, and resi- dential pesticide uses to a multiple pesticides), whether there is an increased susceptibility from exposure to the pesticide to infants and children, and whether the pesticide produces an effect in humans similar to an effect produced by a naturally occurring estrogen, or other endocrine effects. Like other EPA offices, OPPTS relies on the basic 4 component NAS paradigm from the
374 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT Red Book/Science and Judgment) (NRC 1983, 1994) in assessing aggregate and cumulative risks (hazard, dose response, exposure assessment and risk characterization). OPPTS fol- lows EPA approaches for risk assessment described in Agency risk assessment guidelines. In order to reduce the application of default assumptions and default uncertainty/extrapolation factors, in the areas of animal to human extrapolation and high to low dose extrapola- tion, OPPTS has used physiologically based pharmacokinetic (PBPK) models, data-derived uncertainty factors, and mode of action data, and human biomonitoring data in their risk assessments. OPPTS has been a leader in developing and implementing newer and sophisti- cated approaches and tools such as probabilistic methods for assessing exposures in food, water, and from residential pathways. Key examples of the implementation of all of these approaches include the Organophosphate Pesticide (OP) and N-methyl carbamate cumulative risk assessments (EPA 2002c, 2007b), PFOA draft risk assessment (EPA 2005a), and draft lead risk assessment (EPA 2007c). It should be noted that not all assessments need to be of the same depth and scope. We use an iterative and tiered process that considers exposure and sensitivity analyses to balance resources against the need to refine the assessment and reduce uncertainty where appropriate. Uncertainty Analysis OPPTS uses sensitivity analyses in the exposure component of risk assessments, par- ticularly in those assessments that inform or support potentially consequential actions (e.g., pesticides and major industrial compounds). As noted below, OPPTS is working closely with ORD to develop more advanced methods of quantitative uncertainty analysis (e.g., 2-dimen- sional Monte Carlo). For example, OPPTS and ORD are planning to discuss science issues surrounding the implementation of 2-dimensional Monte Carlo into ORDâs SHEDs model (Stochastic Human Exposure and Dose Simulation Model) with the FIFRA Science Advisory Panel in 2007. Current methods for the hazard component provide some quantitative mea- sure of experimental data variability. For example, in the cumulative risk assessments for the OP and N-methyl carbamate pesticides, OPPTS quantified upper and lower confidence bounds on potency estimates for each chemical. For those risk assessments that utilize PBPK models, uncertainty/sensitivity analysis of the input parameters can be performed. Currently, however, uncertainty due to missing toxicological data is qualitatively described and estab- lished methods for quantifying that uncertainty are lacking. Sensitive and Vulnerable Subpopulations (e.g., Children, Elderly, Tribes, Endangered Species) A response to this question can be extracted from NCEAâs Framework for Childrenâs Health Risk Assessment (EPA 2006) and the RAF document on the RfD/RfC methodology (EPA 2002b) which OPPTS uses as guidance. For pesticides, it should be noted however, that the FQPA includes the statutory requirement of an additional 10X safety factor to protect infants and children. This 10X factor can only be reduced or removed if it is determined that the hazard and exposure analyses are protective of infants and children. OPPâs guidance for implementing the FQPA factor can also be found via the web (EPA 2002d). OPP also assesses the potential effect of pesticides to non-target species, including feder- ally listed threatened and endangered species (listed species) and habitat deemed critical to their survival. The assessment is conducted consist with scientific methodology described in EPAâs Overview Document (EPA 2004b) and endorsed by the U.S. Fish and Wildlife Service
APPENDIX E 375 and National Marine Fisheries Service (FWS/NMFS 2004). This assessment results in an âeffects determinationâ for a speciesâa determination of whether a particular pesticideâs use has âno effect,â is ânot likely to adversely affect,â or is âlikely to adversely affectâ the listed species on a geographically specific basis. Consistent with Departments of Interior and Commerce regulations governing federal agency responsibilities relative to listed species, EPA consults with the U.S. Fish and Wildlife Service and National Marine Fisheries Service (the Services), as appropriate, for any determination other than âno effect.â Consultation and resulting input from the Services, informs OPPs decision on whether changes to the pesticideâs registration are necessary to ensure protection of federally listed threatened or endangered species and their critical habitat. Challenges for Risk Assessment in a Regulatory Process There are many challenges for risk assessment in a regulatory process. One key issue is the training of staff to implement new tools (e.g., MOA analyses) and prepare risk charac- terizations that provide transparent weight of evidence analyses. Another one is account- ing for missing toxicological data via quantitative uncertainty analyses and to move the evaluation of toxicological effects into probabilistic and multi- endpoint analyses. Lastly, an important overall direction for OPPTS is to improve and refine how we integrate all avail- able and relevant toxicology, human studies/epidemiology, biomonitoring, and exposure information into a paradigm that balances resources with the needs of the risk assessment (i.e., sustainable). Future Directions: Addressing Gap, Limitations, and Needs Issues to Be Addressed: Needed Improvements and Recommendations Short-term: 2-5 years OPPTS is working closely with ORD to develop more advanced methods of quantitative uncertainty analysis (e.g., 2-dimensional Monte Carlo) and incorporating these into exposure models. As knowledge expands, these methods will need further refinement and improve- ments. There is a need to continue to promote the development of PBPKmodels and other approaches which allow for the replacement of default assumptions uncertainty/extrapola- tion and to develop methods to quantify uncertainty and variability for the hazard/effects component of risk assessment. Long-term: 10-20 years Replacement or reduction of animal testing and moving toward an âintegratedâ risk paradigm by improving QSAR approaches, developing methods for interpreting and incor- porating âomicsâ data, in silico, etc approaches into risk analyses. Address Media-Specific Needs for Risk Assessment, For Example: Do Current Paradigms Adequately Address Environmental Problems Faced by the Country? See above response to short and long term needs. OPPTS continues to develop and use alternatives to defaults by incorporating PBPK modeling and data derived uncertainty fac-
376 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT tors, mode of action data, probabilistic exposure modeling, and biomonitoring data. For example, As an alternative to the RfD, OPPTS also uses characterization of risk for specific age groups and evaluates exposures across different durations of exposure (e.g., single day to lifetime). REGION 2 AND THE OFFICE OF SOLID WASTE AND EMERGENCY RESPONSE Introduction This report is primarily based on Chapter 5 of EPAâs Office of the Science Advisorâs Staff Paper titled: âRisk Assessment Principles and Practicesâ (EPA 2007a). The Chapter provides information regarding current practices for site and chemical specific risk assess- ments in EPAâs Office of Solid Waste and Emergency Response (OSWER). As described on the OSWER homepage (EPA 2008g): OSWER provides policy, guidance and direction for the Agencyâs solid waste and emergency response programs. We develop guidelines for the land disposal of hazardous waste and underground storage tanks. We provide technical assistance to all levels of government to establish safe practices in waste management. We administer the Brownfields program which supports state and local governments in redeveloping and reusing potentially contaminated sites. We also manage the Superfund program to respond to abandoned and active hazardous waste sites and accidental oil and chemical releases as well as encourage innovative technolo- gies to address contaminated soil and groundwater. This chapter provides a perspective on site-specific risk assessments conducted within the Superfund program. Current Practice Statutory Basis/Current Approach and Paradigms for Risk Assessment (Specific to Each Program Office) The Superfund Program To understand the Superfund program and its application in OSWER and the Regions it is important to first take a look at the legislation that governs this regulatory program. The Comprehensive Environmental Response Compensation and Liability Act (CERCLA) was enacted in 1980 and is commonly referred to as the Superfund program. The Act was amend- ed in 1986 under the Superfund Amendments and Reauthorization Act of 1986. These laws require that action selected to remedy hazardous waste sites be protective of human health and the environment. The National Oil and Hazardous Substances Pollution Contingency Plan, or NCP, establishes the overall approach for determining appropriate remedial action at Superfund sites across the country and mandates that a risk assessment is performed to characterize current and potential threats to human health and the environment (40 CFR Â§ 300.430 (d)(4)). The preamble to the NCP (55 Fed. Reg. 8709) provides more detail on the general goals and approach for Superfund risk assessments. The Superfund process involves a number of steps as shown in Figure E-1 from site discovery, listing on the National Priorities List (NPL), Remedial Investigation and Feasibil- ity Study (RI/FS), Record of Decision (ROD) to final NPL deletion. Within the Superfund program, the range of activities at sites includes Removal Actions where actions are neces- sary in a short timeframe and longer remedial investigations of complex sites. This discus-
APPENDIX E 377 FIGURE E-1â Community involvement activities at NPL sites. Source: EPA 2001a. sion will concentrate primarily on the latter type of investigation, i.e., sites that are on the NPL. Currently, across the country, there are 1,557 current and deleted sites on the NPL. The NPL is the list of national priorities among the known releases or threatened releases of hazardous substances, pollutants, or contaminants throughout the United States and its territories. The NPL is intended primarily to guide the EPA in determining which sites war- rant further investigation. Further details regarding the Superfund program are available on the Superfund homepage (EPA 2008h). At each site risk assessments are developed to assess both human health and ecological risks during the RI/FS. The risk information is used to determine whether remedial action is needed at the site. All decisions at Superfund sites must meet the nine criteria provided in Table E-1. The Threshold Criteria that must be met at all sites are protection of public health and the environment and meeting the Applicable or Relevant and Appropriate Requirements (ARARs) or statutory requirements. Risk assessment plays a critical role in determining that these criteria are met. Risk Assessment in the Superfund Program The Superfund program uses risk assessment to determine whether remedial action is necessary at a specific site and to determine the levels of remedial action where actions are required. The program protects human health and the environment from current and potential future threats posed by uncontrolled hazardous substances releases. Decisions at Superfund sites involve consideration of cancer risks, non-cancer health hazards, and site- specific information associated with both current and future land use conditions. Consider- ation of future land use and future risks is included in the risk assessment because CERCLA mandates that remedies are protective in the long-term. The human health and ecological risk assessments developed at sites follow peer-re- viewed guidelines, policies and guidance specific to the OSWER program as well as those for the Agency. The OSWER documents regarding risk assessment are available online (EPA
378 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT Table E-1 Nine Evaluation Criteria for Superfund Remedial Alternatives THRESHOLD CRITERIA Overall protection of human health and the environment determines whether an alternative eliminates, reduces, or controls threats to public health and the environment through institutional controls, engineering controls, or treatment. Compliance with ARARs evaluates whether the alternative meets federal and state environmental statutes, regulations, and other requirements that pertain to the site, or whether a waiver is justified. PRIMARY BALANCING CRITERIA Long-term effectiveness and permanence considers the ability of an alternative to maintain protection of human health and the environment over time. Reduction of toxicity, mobility, or volume of contaminants through treatment evaluates an alternativeâs use of treatment to reduce the harmful effects of principal contaminants, their ability to move in the environment, and the amount of contamination present. Short-term effectiveness considers the length of time needed to implement an alternative and the risks the alternative poses to workers, residents, and the environment during implementation. Implementability considers the technical and administrative feasibility of implementing the alternative, including factors such as the relative availability of goods and services. Cost includes estimated capital and annual operation and maintenance costs, as well as present worth cost. Present worth cost is the total cost of an alternative over time in terms of todayâs dollar value. Cost estimates are expected to be accurate within a range of +50% to -30%. MODIFYING CRITERIA State acceptance considers whether the state agrees with the EPAâs analyses and recommendations, as described in the RI/FS and Proposed Plan. Community acceptance considers whether the local community agrees with EPAâs analyses and preferred alternative. Comments received on the Proposed Plan are an important indicator of community acceptance. 2008i). The guidance provides an overall approach to developing risk assessments at a wide variety of sites across the country. The site specific risk assessments include assessment of contamination in multiple media (air, surface and groundwater, soil, fish, etc.) that occurs during the Remedial Investigation phase where the nature and extent of contamination are determined. Typically, site-specific risk assessments evaluate exposures to multiple chemi- cals through multiple routes of exposure (i.e., ingestion, inhalation, dermal contact, etc.). Receptors evaluated at sites include young children, adolescents, and adults depending and the current and future landuse. Within the Superfund program we follow the basic risk assessment paradigm developed in the 1983 Framework document, i.e. the four steps of hazard identification, dose response assessment, exposure analysis, and risk characterization. Over the years, this paradigm has been expanded to include Problem Formulation, communication with risk managers, and early and continuous community involvement. On a site-specific basis evaluations regarding exposures and the availability of site-specific information (i.e., site-specific chemical sam- pling, activity patterns, creel surveys, etc.) are evaluated for inclusion in the risk assessment. For toxicity values, Superfund primarily relies on EPAâs National Center for Environmental Assessment (NCEA) and the Superfund Technical Support Center assessments. A typical Superfund site does not exist. Sites range from small contaminated parcels where groundwater and soil are impacted to large contaminated river systems or lakes that cover hundreds of miles. In general, most sites include multiple media, multiple chemicals, and multiple exposure pathways that are evaluated to determine the risks to the Reason-
APPENDIX E 379 ably Maximally Exposed individual or RME individual. The RME individual is defined as someone who is exposed to the highest exposure that is reasonably expected to occur at a Superfund site. As described in the National Contingency Plan, the regulation under which the Superfund program acts, the RME will result in an overall exposure estimate that is conservative but within a realistic range of exposures. Under this policy, EPA defines âreasonable maximumâ such that only potential exposures that are likely to occur will be included in the assessment of exposures. The Super- fund program has always designed its remedies to be protective of all individuals and envi- ronmental receptors that may be exposed to a site; consequently, EPA believes it is important to include all reasonably expected exposures in its risk assessmentsâ¦. Uncertainty Analysis, Default Assumptions, Use of Alternatives, Probabilistic Risk Assessment and Communication of Risk, and Evaluation of Alternative Remediation Strategies and Superfund Process Post Remedial Investigation Uncertainty Analysis. Within the Superfund program uncertainty in the risk assessments is addressed by discussing risks to the Reasonably Maximally Exposed Individual and the Central Tendency or average exposed individual. As described above, decisions are based on the RME individual. The presentation of the risks to the RME and CTE individual provides a bounding estimate of risks. In addition, site-specific risk assessment provide a qualitative discussion of uncertainties such as data limitations, where toxicity data is missing, where risk is potentially overestimated based on the data i.e., a screening level assessment, and discuss the impacts of these risk estimates. Risks are typically compared to the risk range identified in the National Contingency Plan or NCP, the Superfund regulation. Default Assumptions Risk assessments incorporate both default assumptions and site-specific information. The supplemental guidance document, âStandard Default Exposure Factorsâ (OSWER Directive 9285.6-03, March 25, 1991), presents the Superfund programâs default exposure factors for calculating RME exposure estimates (EPA 1991a). This guidance was developed in response to requests that EPA make Superfund risk assessments more transparent and their assump- tions more consistent. However, the guidance clearly states that the defaults should be used where âthere is a lack of site-specific data or consensus on which parameter to choose, given a range of possibilities.â These default exposure assumptions are supplemented with data from the Exposure Factors Handbook (EPA 1997a), and Child Specific Exposure Factors Handbook (EPA 2002e) where EPA compiled and analyzed scientific literature on exposure to develop ranges of exposure variables for risk assessments. Table E-2 (EPA 2004a, Table 5-1) presents examples of default exposure values and the percentile of the population the values represent, as well as the peer reviewed studies sup- porting these assumptions. The RME approach uses default values designed to estimate the exposure of a high-end individual in the 90th percentile of exposure or above (EPA 1992). Consistent with this guidance, relevant default assumptions for various activity levels and age groups are used for drinking water consumption rates, soil ingestion rates, residence times, body weight, and inhalation rates. The table illustrates the range of percentilesâsome defaults included the 50th percentile (e.g., body weight), 80th, 90th, and 95th percentiles. Although the Superfund program routinely uses default assumptions to assess the risk to the RME individual at many sites, the characteristics of the surrounding population change from site to site. For example, the distributions of individual residence times will
380 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT Table E-2â Examples of Default Exposure Values With Percentiles Exposure Pathway Percentile Source of Data Drinking water consumption: 90th Approximately a 90th percentile value (EPA 2000). 2 liters/day Soil ingestion rate for children: 65th Analyses and distributions constructed by Stanek 200 mg/day and Calabrese (1995a,b, 2000) places the 200 mg ingestion rate around the 65th percentile of average daily intakes throughout the year. The Stanek and Calabrese analyses suggests that ingestion rates for children in the top 10% (i.e., the high end) of the distribution would be greater than 1,000 mg/day. Residence duration: 30 years 90th 80th For home owners, farms, and rural populations; 30 90thâ95th years is greater than the 95th percentile residence time for renters and urban populations. Body weight: 70 kg 50th For males and females 18 to 75 years old (NCHS 1987) Source: EPA 2004a, p. 100, Table 5-1. vary depending on whether the site is located in a rural or an urban area. Individuals in rural communities are likely to have longer residence times than individuals in urban communities. Thus, a default value of 30 years may fall at the 80th percentile for farmers but above the 95th percentile for renters in an urban setting. The extent to which a single default value will impact the final exposure estimate depends on the values and variabilities of all the parameters used to estimate exposure. The goal is to estimate an individual exposure that actually occurs and is above the 90th percentile. In some cases, use of default assumptions may produce an estimate near the 90th percentile; in others, the estimate may be higher in the range. In general, Superfundâs default factors are designed to be reasonably protective of the majority of the exposed population. The assumptions used in Superfundâs risk assessments are consistent with the 90th percentile or above and the Agencyâs exposure assessment guidelines (EPA 1992). Default exposure factors used to assess the RME are a mix of aver- age and high-end estimates (see Table E-1). The use of these default exposure assumptions does not automatically result in an overestimation of exposures. The Principles and Practices Document (EPA 2004a) provides several other examples that may be of interest to the reader regarding exposure assumptions. Probabilistic Risk Assessment Guidance Development of the OSWER probabilistic risk assessment guidance illustrates the process used in the Superfund program to develop guidance to address uncertainty (EPA 2001b). In that case, Superfund identified the emerging science, developed an EPA workgroup to evalu- ate the available science and its application within the Superfund program, released the draft guidance document for public comment, and conducted an external peer review before the document was completed. The guidance document provides program-specific information regarding the conduct of probabilistic risk assessments and supplements the earlier policy on this issue (EPA 1997b). In addition, EPA has developed training courses on the application of this methodology within the Superfund program. To date, probabilistic risk assessment
APPENDIX E 381 methods have been used or are being developed at several sites to evaluate exposures in rela- tion to both cancer risks and non-cancer health hazards (TAM Consultants, Inc. 2000). For example, at one regional site, a point estimate was presented along with the results from a probabilistic risk assessment to provide a comparison of results. As part of the com- munity involvement, results from both assessments were shared and the results discussed regarding the relative impacts of varying exposure assumptions in a probabilistic assessment on the decision. The Region presented the data incorporating the point estimate and show- ing that when other exposure assumptions were used the risk remained above the risk range described for Superfund above. We found that it was important to work with the community before the final risk results from both the point estimate and probabilistic assessment were presented to highlight this tool and its application (i.e., what kind of data was used, why this technique was included, how the results of the deterministic and probabilistic risk assessment were comparable, and how this information is used in the decision-making process). Evaluation of Alternative Remedial Strategies Risk assessment is one of several tools used to inform risk management decisions. Risk managers weigh a number of factors, including uncertainties in exposure and risk estimates, when developing health and environmental protective decisions. EPA considers a variety of alternatives to protect human health and the environment at sites and evaluates them by considering the balancing criteria and modifying criteria presented in Table E-1 (i.e., long- term effectiveness, use of treatment, short-term effectiveness, implementability, and cost). EPA then proposes a protective, cost-effective remedy that is, compliant with the Applicable or Relevant and Appropriate Requirements (ARAR), which it may modify based on state and public comments (see also CERCLA Â§ 121, 42 U.S.C. Â§ 9621 and 40 CFR Â§ 300.430[e]). CERCLA establishes a preference for remedial actions in which treatment permanently and significantly reduces the volume, toxicity, or mobility of the hazardous substances, pollutants, and contaminants is a principal element [CERCLA Â§ 121 (b)(1)]. This paragraph goes on to require a consideration of permanent solutions and alternative treatment technologies or resource recovery technologies in the remedy selection process. CERCLA also directs Superfund to consider long-term maintenance costs, potential for future remedial actions if the remedy should fail. CERCLA Â§ 121(b)(1) also establishes as one of the fundamental remedy selection criteria that we select remedies that âutilize permanent solutions and alternatives to treatment technologies or resource recovery technologies to the maximum extent practicable.â For evaluating and selecting remedies, the NCP at 40 CRFÂ§ 300.430 (e) (9) (C) [long-term effectiveness and permanence ] and (D) [reduction of toxic- ity, mobility, or volume through treatment] require consideration of âmagnitude of residual risk...;â âadequacy and reliability of controls such as containment systems and institutional controls..;â â...the degree to which alternative employ recycling or treatment that reduces toxicity, mobility, or volume..;â â...the amount of hazardous material that will be destroyed, treated or recycled...;â â...the type and quantity of treatment residuals considering the persis- tence, toxicity, mobility, and propensity to bioaccumulate...;â âthe degree to which treatment reduces the inherent hazards posed by principal threats at the site.â EPA initiatives are also looking at cross-program coordination in EPAâs Land Revitaliza- tion Office, to return contaminated land to safe and beneficial uses (EPA 2007d).
382 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT Superfund Process Following Remedial Investigation Following the completion of the Remedial Investigation (RI) during which the risk assess- ment is conducted, EPA develops a feasibility study (FS) that evaluates remedial alternatives for action at the site (EPA 1988). Among other objectives, the FS evaluates the risks in the absence of remedial actions or institutional controls. This provides a baseline for compari- son with other remedial alternatives. The FS includes the development of Remedial Action Objectives, including Preliminary Remediation Goals (PRGs) that are developed based on the RME exposure assumptions used in the risk assessment. The PRGs provide concentration levels that are protective of the RME individual who is currently exposed or may be exposed in the future. EPAâs guidance âThe Role of the Baseline Risk Assessmentâ provides further information regarding risk management decisions on sites (EPA 1991b). During the FS, remedial alternatives are developed to achieve the program goals through a variety of different methods, generally including containment and treatment alternatives. The alternatives reflect the scope and complexity of the site problem. The Superfund program evaluates these alternatives using nine criteria described by the NCP (see Table E-1). The criteria address protectiveness, effectiveness, implementability, and acceptability issues. The criteria were derived from remedy selection criteria provided by Congress in SARA 121. The detailed analysis consists of an assessment of the individual alternatives against each of the nine evaluation criteria and a comparative analysis focusing upon the relative performance of each alternative against those criteria. In addition to viable remedial alternatives, EPA evaluates a no-action remedial alternative at all sites. The no-action alternative provides a baseline for comparison of the various alternatives that are appropriate for a specific site. All of this information is provided in a Proposed Plan, which is released with the RI/FS for public review and comment. EPA provides opportunities for community involvement and public review of this infor- mation. A public meeting is held to discuss the proposed remedial alternatives and to obtain comments. Public comments are addressed at the meeting and in the Response to Comments that is developed as part of the Record of Decision (ROD). The ROD identifies remedial actions that have been selected for the site. Following the ROD, EPA begins the remedial design process and the implementation of construction. Depending on the nature of the remedial actions and the amount of time required to complete the construction, EPA may conduct 5-year reviews to determine the protectiveness of the remedy (EPA 2001c). Throughout this process, information is shared with the community regarding the progress of the remedial actions. Sensitive and Vulnerable Subpopulations (e.g., Children, Elderly, Tribes, Endangered Species) Children A common question asked of EPA is why Superfund risk assessments evaluate âdirt eat- ing kidsâ: Why should Superfund sites be cleaned up to levels such that children can safely âeatâ the soil there? Actually, EPA does not typically assume that children are eating the dirt; rather, EPA assumes that they are exposed to contaminants through the course of normal activities of play on the ground, exposure to dust in the home, and incidentally through mouthing behavior (EPA 1996, 2005b). It is commonly observed that young children suck their thumbs or put toys and other objects in their mouths. This behavior occurs especially among children from 1 to 3 years
APPENDIX E 383 old (Charney et al. 1980; Behrman and Vaughan 1983). This âhand-to-mouthâ exposure is well documented in the scientific literature for children under 6, and is especially prevalent among children 1Â½ to 3 years old, a critical period for brain development. This time period is of special concern regarding potential exposure, since children may be at special risk of exposure to specific chemicals, e.g., lead (CDC 1991). Superfund experience has taught us that children do incur exposures to contaminated soil, as is evident at lead-contaminated sites in which elevated blood levels occur in children residing at those sites (EPA 1996, 2005b). Scientists agree that because of this behavior, children may incidentally or accidentally take in soil and dust (Calabrese et al. 1989; Davis et al. 1990; van Wijnen et al. 1990). Where children are likely to be exposed to contaminated soils (in residential areas, for example), it is appropriate for EPA to evaluate potential risks and set cleanup levels that will protect children for this widely recognized pathway of exposure, especially during this sensitive developmental period in the childâs lifetime. The basis of EPAâs default soil ingestion rate is generally a point of contention. EPA has developed soil ingestion rates that are used as âdefault exposure assumptionsâ for adults and children. For young children (6 years or younger), the Superfund program default value is 200 milligrams of soil and dust ingested per day (EPA 1991a, 1996). EPAâs risk estimates address the âincidentalâ ingestion that might occur when a child puts a hand or toy in his or her mouth, or eats food that has touched a dusty surface. Although this default assump- tion is often presented as an overly conservative value, the amount (200 milligrams per day) represents a small amount of soil ingested. It is less than 1/100 of an ounce (or one-fifth of the contents of a single-serving packet of sugar) a day. This peer reviewed value is applied in estimates of RME exposures (EPA 1989a, 1991a, 1997a). In Superfund risk assessments, this soil ingestion rate for young children is combined with site-specific assumptions about exposure frequency (days per year) to estimate an average intake over the 6-year exposure period. Exposure frequency varies depending on site-specific current and future land uses. Soil ingestion studies report daily averages; the amount of soil ingested cannot be prorated on an hourly basis. Also, soil ingestion is episodic in nature and dependent upon a childâs activity patterns, so prorating by time is not always appropriate. This is a common misapplication of soil ingestion rates in risk assessment. Some children deliberately eat soil and other non-food items (a behavior known as pica). Pica behavior has been identified in children at rates of up to 5,000 milligrams per day (Calabrese et al. 1991; ATSDR 1996, 2001). The Agency for Toxic Substances and Disease Registry uses this pica ingestion rate when calculating Environmental Media Evaluation Guides, which are used to select contaminants of concern at hazardous waste sites (ATSDR 1996). EPA itself does not routinely address this form of exposure unless site-specific in- formation is available. The default soil ingestion rate of 200 milligrams per day applied in Superfund risk assessments is intended to ensure reasonable protection of children in cases where they are likely to become exposed to contaminated soils and dust associated with a Superfund site. At sites, depending on land use consideration may also be given to evaluating risks to adolescent trespasser. The adolescent trespasser is typically older than the young child de- scribed above (i.e., 10 to 18 years) and has shorter exposure frequency and duration than the young child resident. Sensitive Populations Assessment of fish consumption patterns is an area where young children and sensitive subpopulations may be exposed to contaminants. In some cases site-specific surveys have
384 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT been conducted to evaluate the consumption patterns for specific populations that the pub- lished surveys do not capture. These surveys found considerably higher consumption rates among these populations than if the standard default assumptions from the 1997 Exposure Factors Handbook were used (EPA 1997a). For example, a 3Â½-year site-specific creel survey (Toy et al. 1996) included information on whether or not adults harvested fish and shellfish from Puget Sound. The survey included 190 adults and 69 children between the ages of 0 and 6. The study found that tribal seafood consumption rates were considerably higher than Exposure Factors Handbook values. Among the Squaxin, the average consumption rate was 72.8 grams per day and the 90th percentile ingestion rate was 201.6 grams per day. Among the Tulalips, the average consumption rate was 72.7 grams per day and the 90th percentile was 192.3 grams per day. Other site-specific consumption surveys found similar differences in consumption rates (Chiang 1998; EPA 2001d; Sechena et al. 2003). In cases where EPA has conducted individual surveys to identify fish consumption rates, EPA has found it important to include the community in the process (EPA 1999a). EPA and other agencies (both private and governmental) have spent considerable resources and time to plan and implement these studies. The surveys (Chiang 1998; EPA 2001d; Sechena et al. 2003) were all conducted using one-on-one interviews, as opposed to creel or mail surveys. The people conducting the interviews were always specially trained members of the ethnic group or community being surveyed. Challenges for Risk Assessment in the Regulatory Process The challenges faced in developing risk assessments include: Communication of Complex Scientific Concepts This was an issue identified by Bill Farland when he was with the Agency. Within the Superfund program there is extensive communication with the community regarding the remedial investigation, risk assessment, remedial actions, and Superfund process. One of the challenges that is faced at all sites is the explanation of complex scientific concepts such as hydrodynamic modeling, groundwater issues, changes in the understanding of the toxicity of chemicals, and application of ranges of toxicity values. Training of Risk Assessors/Risk Managers in New Scientific Advancements With the advances in areas such as genomics, other âomics,â nanotechnology, under- standing of mutagenic modes of action, and all of the emerging areas of science there are new challenges in training staff in these emerging areas, especially risk managers who are often more accustomed to addressing engineering concepts and questions. The challenge is how to provide adequate background information in these areas and bring both risk assessors and managers up to speed with consideration of the current time and resource constraints. The use of the Hazardous Waste Clean-Up Information (CLU-IN) Web Site provides information about innovative treatment and site characterization technologies to the hazardous waste remediation community; web based seminars, annual meetings, conference calls etc. have proven effective and are continuing to be used. Another part of this challenge is knowing what to do with the information that is developed. For example, using genomics to deter- mine that some member of a population at a site may be particularly susceptible does not indicate a regulatory response to that information is appropriate or necessary. In some cases, there may not be the regulatory authority to act or to do the population sampling necessary
APPENDIX E 385 to determine biomarkers. Typically, the Agency for Toxic Substances and Disease Registry (ATSDR) is responsible for taking clinical samples. Lack of Toxicity Data At sites, there are typically a number of chemicals that can not be assessed quantitatively in the assessment based on a lack of peer-reviewed toxicity values. Typically these chemicals are addressed qualitatively in the risk assessment. Development of peer-reviewed toxicity data to include in the quantification of cancer risks and non-cancer health hazards obviously is quite important in the development of risk assessments. Future Directions: Addressing Gaps, Limitations, and Needs Issues to be Addressed in the Short Term (2-5 years) and the Long Term (10-20 years) Overarching challenges for EPA including OSWER are to address the need to reach regulatory conclusions in a timely and cost effective manner with limited data and limited resources for analyses. In addition, EPA needs to develop transparent, clear, consistent, and reasonable presentations and procedures to support and explain its analyses. Briefly noted here are a few key areas. Planning and Scoping Over the last several years, as noted in the EPA Staff Paper, EPA has increasingly empha- sized the importance of identifying as early as possible in our processes, through dialogue between risk assessors and risk managers, the scope and level of effort that is appropriate for a planned assessment. And that this may need to be done repeatedly. It seems likely that greater reliance on these interactions and efforts will play an increasingly important role as assessments continue to grow in complexity, and in the amount of review and scrutiny that they may receive. Toxicity Data In the Superfund program, we rely on NCEA including the Integrated Risk Information System (IRIS) and the Superfund Technical Support Section as the source for toxicity values. Typically, regions do not develop site-specific toxicity values. OSWER has defined a hierar- chy for using other toxicity values when these are not available (EPA 2003b). In brief, such sources should be the most current, with a basis that is transparent and publicly available, and that has been peer reviewed. Sources for these toxicity values include California toxicity values, ATSDR minimal risk levels, and others. In the absence of toxicity values we rely on a qualitative discussion of the uncertainties in the risk assessment. The current developments in the areas of Informatics, gene arrays and related areas hold the possibility of improving our understanding of Quantitative Structure Activity Relation- ships (QSAR) and so to reduce uncertainty, to help bound potential toxicity values and to reduce the need to conduct toxicity tests to support those values. In addition, as noted above, this is another area where early identification of data gaps and needs would allow for the possibility of data generation to support the assessment.
386 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT Short-Term Exposures Toxicity values and analyses are needed for short-term and mid-term exposures. These toxicity values are important in Removal Actions at sites. Mixtures Typically at Superfund sites we evaluate exposures to multiple chemicals through mul- tiple pathways. EPA program offices and regional risk assessors have a great need for both assessment information and risk assessment methods to evaluate human health and ecological risks from exposure to chemical mixtures. Exposure Assumptions Superfund recognizes the most accurate way to characterize potential site-specific expo- sures to populations around Superfund sites would be to conduct a detailed census of each site considering both current and future land uses. Theoretically, this should involve inter- viewing all potentially exposed individuals regarding their lifestyles, daily patterns, water usage, consumption of local fish and game and procedures, working locations and exposure conditions while collecting environmental samples. Although site-specific data are collected on environmental media (e.g., soil, groundwater air, etc.) as appropriate during the Remedial Investigation, such collection has significant limitations. The three almost insurmountable difficulties are time, expense and intrusion on privacy. In the absence of site-specific infor- mation, Superfund relies on the Standard Default Exposure Factors and the Exposure Fac- tors Handbook as sources for exposure information for use at sites. The Exposure Factors Handbook and its updates have been very important sources of information on exposures to a variety of populations (i.e., children, anglers, and others) through multiple media. The recent addition of the Child-specific Handbook has also been helpful in understanding risks to sensitive populations such as children. Because we assess future potential risks, we often want information that can not be directly measured such as potential changes in behavior following remediation of an area. Probabilistic Risk Assessment Superfund has developed peer-reviewed specific guidance for conducting site-specific probabilistic risk assessment. At all sites, both the RME and CTE (or average exposures) are evaluated to provide a range of risks and inform the risk management decision. The RME, however, under the NCP is the basis for the decision. In some cases, site-specific as- sessments have used the tiered approach in the guidance beginning with a deterministic risk assessment and then progressing to a more refined technique such as the one dimensional and two dimensional analysis. At the present time, site-specific probabilistic risk assessments have been conducted at several sites to examine exposure assessments. Superfund is currently working on the Risk Assessment Forum project to look at the application and use of probabilistic risk assessment in decision making. The project is also looking at ways to better communicate the application of these techniques to risk managers to help identify areas where this technique is more applicable.
APPENDIX E 387 Improving Communication Consistent with EPA Superfund goals of improving the transparency of the process, the methods for summarizing risk information are found in the RAGS Part D (EPA 2001e). Superfund continues to update guidance documents to improve the transparency of risk information. With the advancements in science described above, there are new challenges associated with the summarization and presentation of data. With advances in Geographic Informa- tion Systems it is possible to demonstrate areas within and exceeding specific risk ranges. Current ongoing activities to digitize data locations with samples will facilitate the process of process of providing this data for further analysis.. EPA guidance and educational materials help illustrate the ways that citizens can be involved in the risk assessment process (EPA 1999a,b). For example: Community-specific information on fishing preferences helped to identify exposure areas for sampling and fish species consumed by people who fish in a contaminated bay. Information from farmers on pesticide applications helped EPA determine why certain contaminants were present in an aquifer. Discussions with farmers about certain harvesting practices helped EPA refine ex- posure models and assumptions at another site (EPA 1999b). EPA uses a range of communication tools to include the community in the Superfund process. These include newsletters, fact sheets, site-specific home pages, public meetings, public availability sessions, and 1-800- numbers to contact EPA staff. EPA strives to com- municate information about the RI, the results of the risk assessment, proposed actions at the site, and the proposed and final decisions for remedial actions. The Record of Decision (ROD) includes a responsiveness summary that addresses comments including those from the community. During the period of the remedial action, communication with the community continues, including updates during the 5-year review process. OFFICE OF WATER (OW) Current Practice Statutory Basis/Current Approach and Paradigms for Risk Assessment (Specific to Each Program Office) Office of Water (OW) follows the 1983 paradigm for human health risk assessments for chemicals and radiation, as explicated in the published U.S. EPA Risk Assessment Guidelines and other Agency guidance. OW also does assessment of human health risk from microbial disease, from consum- ing drinking water, using water for recreation, and consuming aquatic organisms, and from contact with waste water. The paradigm for microbial risk assessment involving host/para- site interactions is still evolving. There is an EPA Risk Assessment panel that is developing Guidelines based on a proposed framework and collaboration with other Agencies. And important component of the microbial disease assessment is risk/risk tradeoff, such as was considered in the development of linked drinking water regulations for limitation of microbes and disinfection by-products. Lastly, OW engages in ecological risk assessment, following the paradigm published in the Guidelines for Ecological Risk Assessment (Figure E-2) (EPA 1998). The Risk Assessment âStaff Paperâ (EPA 2004a) compiles many of the general and specific risk assessment practices used by OW.
388 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT Ecological Risk Assessment Planning (Risk Assessor/ Problem Formulation Risk Manager/ Iterate Process, Monitor Results As Necessary: Acquire Data, Interested Parties Dialogue) Characterization Characterization of Exposure of Effects Analysis Risk Characterization Communicating Results to the Risk Manager Risk Management and Communicating Results to Interested Parties Figure E-2â The framework for ecological risk assessment (Modified from EPA 1998). Figure E-2.eps Office of Water operates under several pieces of enabling legislation. We have obliga- tions under the following: â¢ Safe Drinking Water Act (Amended 1996) â¢ Clean Water Act â¢ Food Quality Protection Act (1996) (FQPA) â¢ Beaches Environmental and Coastal Health Act (BEACH Act) (2000) â¢ Coastal Zone Management Act â¢ Endangered Species Act FQPA amended the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) in 1996; this was specifically to highlight risks to children from pesticides. As pesticides are found in drinking water source waters, OW adopts the risk assessments done under FQPA by the Office of Pesticides Programs, at least as far as hazard identification and dose response; exposure assessment will differ given the purview of the legislation under which the risk assessment is conducted. The BEACH act is a 2000 amendment to the Clean Water Act (CWA). These changes set new requirements for recreational criteria and standards for coastal areas and the Great Lakes. The Endangered Species Act requires that EPA engage in consultation with the U.S. Fish and Wildlife Service on any actions which may affect endangered plant or animal species. The major pieces of enabling legislation for water programs are the CWA and the Safe
APPENDIX E 389 Does the contaminant adversely affect Regulate with public health? NPDWR Is the contaminant known or likely to occur in PWSs with a frequency and at levels posing a threat to public health? Will regulation of the contaminant present a meaningful opportunity for health risk reduction? Figure E-3â Conditions for regulation under SDWA 1996. Figure E-3.eps Drinking Water Act (SDWA) as amended in 1996. SDWA deals with all uses of water from the tap, but only tap water (albeit from source to last public connection). Under SDWA, EPA establishes a list of chemical and microbial contaminants for potential regulation. EPA is obliged to revise this list on a regular basis; furthermore, EPA must make regulatory deci- sions on five agents on the list every five years. The bases for regulation are illustrated in Figure E-3. In order to regulate a contaminant in drinking water, EPA must establish the following: the contaminant can adversely affect public health; the contaminant occurs or is likely to occur in public water systems at levels that can affect public health; and there is a meaningful opportunity for public health improvement as a result of the regulation. In answering these questions OW conducts quantitative risk assessments to determine nonenforceable Maximum contaminant level goals (MCLGs). OW then sets enforceable Maximum contaminant levels (MCLs) as close as technically feasible to the MCLGs after taking costs into consideration. SDWA also requires that EPA conduct a Health Risk Reduction and Cost Analysis (HRCCA) for each proposed rule. There are seven elements of the HRRCA 1. Quantifiable and non-quantifiable health risk reduction benefits; 2. Quantifiable and non-quantifiable health risk reduction benefits form reduction in co-occurring contaminants; 3. Quantifiable and non- quantifiable costs; 4. Incremental costs and benefits; 5. Effects of the contaminant on the general population as well as sensitive subpopula- tions including infants, children, pregnant women, the elderly, individuals with a history of serious illness or others that may be at greater risk; 6. Any increase in health effects as a result of compliance including co-occurring contaminants;
390 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT 7. The quality and extent of information, the uncertainties in the analyses and factors with respect to the degree and nature of the risk. After completion of the HRCCA, analysis of technical feasibility of contaminant control, and determining appropriate monitoring, OW may propose and promulgate a National Primary Drinking Water Rule (NPDWR). These rules must be reviewed every six years by OW to determine if there is sufficient reason (e.g. new data, new risk assessment methods) to revise the rule. The CWA provides broad outlines for controlling discharges to ambient waters from point sources of pollution and diffuse sources of contamination (e.g. run-off from agricultural lands, mining sites, etc). CWA requires that States and authorized Tribes designate uses for waterbodies (such as drinking water source water, fishable/swimable waterbody). The States then are required to take specific actions to ensure that those uses are attained; such as setting standards, issuing permits, defining total maximum daily loads of a contaminant to a water body. Under CWA, OW publishes ambient water quality criteria (AWQC) for both human health and aquatic life. These are risk assessments that the States and Tribes may choose to adopt; EPA determines whether State or Tribal standards are scientifically justified. In deriving national AWQC, OW follows EPA published methodologies including the Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health (EPA 2000), and the Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and Their Uses (EPA 1985). The latter document is being updated. The Human Health Methodology is being expanded through Technical Support Documents. A series of technical documents deals with bioaccumulation through aquatic food webs, as human health criteria specifically identify consumption of con- taminated seafood as a pathway in exposure assessment. The Human Health Methodology also describes the concept of relative source contribution (RSC), a method for apportioning the âallowable riskâ such as an RfD over all plausible routes of exposure. OW also applies the RSC in calculating MCLGs under SDWA. For example in the risk assessment for chlo- roform, inhalation of vapors and concentrations in foods were considered in developing the MCLG. Ultimately the EPA default process had to be used in the chloroform RSC, as there were insufficient data on which to base a specific value. Other examples of best practices can be seen in the economic analyses in support of NPDWRs such as the 2005 Long Term 2 Enhanced Surface Water Treatment Rule (LT2) and the 2006 Groundwater Rule (GWR). Both of these rules were based on assessment of human risk from a variety of microbial contaminants including protozoa, bacteria and viruses. Uncertainty Analysis Regarding the presentation of alternative risk estimates SDWA says the following: The Administrator shall, in a document made available to the public in support of a regulation promulgated under this section, specify, to the extent practicable: 1. Each population addressed by any estimate of public health effects; 2. The expected risk or central estimate of risk for the specific populations; 3. Each appropriate upper-bound or lower-bound estimate of risk â¦ (OW; SDWA Â§ 300g-1 (b)(3)). OW describes areas of uncertainty and variability in the risk assessment documents
APPENDIX E 391 supporting our regulatory and other risk management decisions. Some of these analyses in- cluded quantitative estimates of uncertainty and variability; this is most commonly done for exposure data. Recent economic analyses done in support of SDWA include assessments of uncertainty in occurrence or exposure data (for example, LT2, the arsenic NPDWR, GWR). Discussion of uncertainty in dose response assessment was published in the context of these rules as well. In addition OW discussed uncertain the effectiveness of drinking water treat- ment (LT2) as well as uncertainty in the measurements or indicators used in risk-targeted regulatory strategies (LT2 and GWR). These analyses are peer-reviewed and subject to public comment before publication of the final economic analysis. OW has published sensitivity analyses and presentations of alternative risk estimates; for example in the Regulatory Impact Analysis (RIA) supporting the Arsenic NPDWR. Note that the preamble to this rule also included an extensive discussion of uncertainty in the dose response data and modeling. OW has also used published uncertainty analyses; for example, the assessment of variability in pharmacokinetic parameters presented by NRC (2000) was incorporated into the reference dose for methylmercury used in the AWQC (EPA 2001f). OW uses default procedures and assumptions as indicated in EPA documents including the 2005 Cancer Guidelines and Supplemental Guidance (EPA 2005c,d) and the Staff Paper (EPA 2004a). OW has also published analyses that permit the use of distributional ap- proaches to exposure assessment; for example, analyses of Continuing Study of Food Intake by Individuals (CSFII) data on consumption of water from public water systems, in beverages and so on. This report also supports the use of 2l/day for adult exposure assessment as a reasonable default when distributional approaches are not warranted (EPA 2004c). Sensitive and Vulnerable Subpopulations (e.g., Children, Elderly, Tribes, Endangered Species) The SDWA Amendments mandate that EPA consider risks to groups within the general population that are identified as being at greater risk of adverse health effects; these include children, the elderly, and people with serious illness (Safe Drinking Water Act ). To this end OW includes consideration of appropriate susceptible populations in the risk assessment documents supporting risk management. This is always described in the preamble to regula- tions (for, example Disinfection By-products Stage 1). For example specific consideration of immunocompromised persons was highlighted in the Long Term Enhanced Surface Water Treatment Rules. OW specifically recommends that States and authorized Tribes use waterbody specific population and exposure data in their derivation of criteria and standards. OW recommends use of default exposure factors only in absence of any relevant data (EPA 2000). OW is conscious of Native American and other traditional lifestyles that may result in exposure parameters different from those considered to be the norm. The American Indian Environ- mental Office (AEIO/OW) and EPA Tribal Science Council are among the groups pursuing these issues. Challenges for Risk Assessment in a Regulatory Process Under the SDWA, costs vs. benefits of regulation are a factor in the choice to regulate or not as well as in the limits set by an MCL. An illustration of the methods and challenges of benefits assessment is the RIA for the arsenic NPDWR. It should be noted that identified but not quantified, and quantified but not monetized, benefits are difficult to characterize and compare with monetized benefits. Given that the standard non-linear low dose extrapola-
392 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT tion procedure, calculation of an RfD, does not provide an estimate of risk, this is a major challenge. In the GWR economic analysis, OW made the case using a semi-quantitative approach that monetized benefits might be more than five-fold greater than those used, if bacterial disease could be better quantified. Under the Clean Water Act, OW publishes AWQC for human health; these risk assess- ments do not consider the cost or technological feasibility of meeting these criteria. However, demonstration of quantifiable, monetized benefits has become increasingly important in the acceptance of any risk management choice. The problem of assessing benefits of an ecosystem remains a very serious one. The major problem in conduct of OW risk assessments is insufficient resources. Chief among the resource lack is the lack of data. None of the enabling legislation for water pro- grams provide a means to require that ecological or health effect data be generated. OW can establish requirements for monitoring of various kinds, depending on the law, but there is no way to acquire health effects data. There is further a requirement in SDWA that data serving as the basis for regulation be peer-reviewed and publicly available. OW risk assess- ments are most often limited by paucity of usable data on health effects and occurrence of contaminants in food and water. Data to support microbial dose response assessment are lacking and are likely not to be forthcoming. New human challenge studies are extremely unlikely to be conducted, and even if available may not be usable by EPA given recent restrictions on use of human stud- ies. Those studies that are complete may not be applicable to assessment of exposure in the general population for these reasons. â¢ The studies administered laboratory strains of microbes; that is healthy infectious organisms grown or concentrated from specific hosts. Environmental organisms are of more diverse origin and may be more or less potent than laboratory strains. â¢ Challenge studies are conducted in healthy volunteers, usually one gender, and only of a limited age range (typically 20-50). Another challenge in assessing microbial pathogens is lack of data and models on second- ary transmission. Dynamic disease transmission modeling is developing as a useful tool. Time is also a limited resource. SDWA risk assessments must be done to deadlines for regulation proposal, promulgation and review. For both CWA and SDWA actions, there are often court-ordered deadlines to be met. OW may not delay these actions to await data generation or method development. Under SDWA OW is concerned with contaminant mixtures in drinking water in response to requirements of the Safe Drinking Water Act Amendments of 1996, including mixtures of DBPs and of Contaminant Candidate List chemicals (e.g., organotins, pesticides, metals, pharmaceuticals). Information and methods are being developed to better evaluate the toxic mode of action, the risk posed by drinking water mixtures, exposure estimates for mixtures via multiple routes, and the relative effectiveness of advanced treatment technologies (EPA 2003c,d). Whole-mixture studies are routinely used in ecological risk assessments. The Agency has developed subchronic toxicity tests for whole aqueous effluents and for contaminated ambient waters, sediments, and soils (EPA 1989b, 1991c, 1994a). Furthermore, the effects of mixtures in aquatic ecosystems are evaluated using bioassessment techniques that are equivalent to epidemiology, but more readily employed (Barbour et al. 1999). Similar bio- assessment methods are sometimes used at Superfund sites (EPA 1994b). These empirical approaches to assessing ecological risks from mixtures are employed in National Pollutant
APPENDIX E 393 Discharge Elimination System permitting and the development of Total Maximum Daily Loads, and are often used in Superfund baseline ecological risk assessments. Many uncertainty analyses account for parameter uncertainty, but ignore model uncer- tainty. When only one model can reasonably explain or be fit to the data, then there is need only to account for uncertainty in that specific modelâs parameter values. For example, a dose-response relationship might be known to be exponential, and data are used to esti- mate and characterize uncertainty about the exponential modelâs single parameter (r). If it is uncertain whether the model is exponential, beta-Poisson, or some other form, then the data are used to characterize uncertainty about the model as well as the modelsâ parameter values. In OWâs GWR and LT2 rules, model uncertainty was explored in sensitivity analyses; these showed that the choice of model did not significantly alter the results. Dealing with model uncertainty may be a significant challenge in future analyses under these conditions: (a) data do not clearly point to a single preferred model; or (b) the regulatory outcome or estimate is sensitive to model choice. Future Directions: Addressing Gaps, Limitations, and Needs The 1983 NRC paradigm for human health risk assessment for chemicals and radiation remains adequate. The 1998 paradigm for ecological risk assessment remains adequate. We look forward to a federal peer-reviewed, published microbial risk assessment paradigm. Water programs need improved dose response methods, in particular for microbial disease causing agents. While OW would like to see increased use of data from âomicâ technologies, there is an enormous amount of work in that field to be done before such use will be either practi- cal or will stand the test of the courts. Probably the first accepted use of âomicsâ in water programs will be in microbial source tracking and in rapid detection of contaminants (rather than in risk assessment). Improved and accepted methods for quantifying ecological benefit, and human health benefits (beyond value of a statistical life), will be immediately useful. Means to assess the utility and the lessons learned from various types of uncertainty analyses will be immediately useful, as will improved methods for communicating uncertainty to both decision makers and the (litigious) public. The major limitations in applying any new risk assessment methods will be lack of data (particularly health and ecological effects data); and degree of acceptance of new methods by stakeholders. References ATSDR (Agency for Toxic Substances and Disease Registry). 1996. ATSDR Public Health Assessment Guidance Manual. Agency for Toxic Substances and Disease Registry, Atlanta, GA. ATSDR (Agency for Toxic Substances and Disease Registry). 2001. Summary Report for the ATSDR Soil-Pica Workshop, June 2000, Atlanta, GA. Prepared by Eastern Research Group, Lexington, MA. Contract No. 205- 95-0901. Task Order No. 29. March 20, 2001 [online]. Available: http://www.atsdr.cdc.gov/NEWS/soilpica. html [accessed Jan. 30, 2008]. Barbour, M.T., J. Gerritsen, B.D. Snyder, and J.B. Stribling. 1999. Rapid Bioassessment Protocols for Use in Streams and Wadeable Rivers: Periphyton, Benthic Macroinvertebrates and Fish, 2nd Ed. EPA 841-B-99-002. Office of Water, U.S. Environmental Protection Agency, Washington, DC [online]. Available: http://www.epa.gov/ owow/monitoring/rbp/ [accessed Jan. 31, 2008]. Behrman, L.E., and V.C. Vaughan, III. 1983. Nelson Textbook of Pediatrics, 12 Ed. Philadelphia, PA: W.B. Saunders.
394 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT Calabrese, E.J., R. Barnes, E.J. Stanek, III, H. Pastides, C.E. Gilbert, P. Veneman, ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ X.R. Wang, A. Lasztity, and P.T. Kostecki. 1989. How much soil do young children ingest: An epidemiologic study. Regul. Toxicol. Pharmacol. ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ 10(2):123-137. Calabrese, E.J., E.J. Stanek, and C.E. Gilbert. 1991. Evidence of soil-pica behavior and quantification of soil inges- tion. Hum. Exp. Toxicol. 10(4):245-249. CDC (Centers for Disease Control and Prevention). 1991. Preventing Lead Poisoning in Young Children. 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Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and Their Uses. EPA 822/R-85-100. U.S. Environmental Protection Agency, Office of Research and Development, Environmental Research Laboratories, Duluth, MN, Narragansett, RI, and Corvallis, OR [online]. Available: http://www.epa.gov/waterscience/criteria/85guidelines. pdf [accessed Jan. 30, 2008]. EPA (U.S. Environmental Protection Agency). 1988. Guidance for Conducting Remedial Investigations and Fea- sibility Studies under CERCLA. Interim Final. OSWER Directive 9355.3-01. EPA/540/G-89/004. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC. October 1988 [online]. Available: http://rais.ornl.gov/homepage/GUIDANCE.PDF [accessed Jan. 30, 2008]. EPA (U.S. Environmental Protection Agency). 1989a. Risk Assessment Guidance for Superfund, Vol. 1. Human Health Evaluation Manual (Part A). EPA/540/1-89/02. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC. December 1989 [online]. Available: http://www.epa. ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ gov/oswer/riskassessment/ragsa/pdf/rags-vol1-pta_complete.pdf [accessed Jan. 30, 2008]. ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ EPA (U.S. Environmental Protection Agency). 1989b. Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms, 2nd Ed. EPA 600/4-89/001. Environmental Moni- toring Systems Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH. EPA (U.S. Environmental Protection Agency). 1991a. Risk Assessment Guidance for Superfund, Vol. I: Human Health Evaluation Manual, Supplemental Guidance, âStandard Default Exposure Factors.â Interim Final. OSWER Directive 9285.6-03. PB91-921314. 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Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms, 4th Ed. EPA-600/4-90/027. Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC. September 1991. EPA (U.S. Environmental Protection Agency). 1992. Guidelines for Exposure Assessment. EPA/600/Z-92/001. Risk Assessment Forum, U.S. Environmental Protection Agency, Washington, DC. May 1992 [online]. Available: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=15263 [accessed Oct. 10, 2007]. EPA (U.S. Environmental Protection Agency). 1994a. ECO Update: Catalog of Standard Toxicity Tests for Ecologi- cal Risk Assessment. EPA 540-F-94-013. Pub. 9345.0-051. Office of Solid Waste and Emergency Response, Washington, DC. Intermittent Bulletin 2(2) [online]. Available: http://www.epa.gov/swerrims/riskassessment/ ecoup/pdf/v2no2.pdf [accessed Jan. 30, 2008]. EPA (U.S. Environmental Protection Agency). 1994b. 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APPENDIX E 395 EPA (U.S. Environmental Protection Agency). 1996. Soil Screening Guidance: Userâs Guide, 2nd Ed. OSWER Pub. 9355.4-23. EPA540/R-96/018. Office of Solid Waste and Emergency Response, Washington, DC. July 1996 [online]. Available: http://www.epa.gov/superfund/health/conmedia/soil/pdfs/ssg496.pdf [accessed Jan. 30, 2008]. EPA (U.S. Environmental Protection Agency). 1997a. Exposure Factors Handbook, Vols. 1-3. EPA/600/P-95/002F. Office of Research and Development, National Center for Environmental Assessment, U.S. Environmen- tal Protection Agency, Washington, DC [online]. Available: http://www.epa.gov/ncea/efh/ [accessed June 3, 2007]. EPA (U.S. Environmental Protection Agency). 1997b. Policy for Use of Probabilistic Analysis in Risk Assessment at the U.S. Environmental Protection Agency. U.S. Environmental Protection Agency, Washington, DC. May 15, 1997 [online]. ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ Available: http://www.epa.gov/osa/spc/pdfs/probpol.pdf [accessed June 3, 2007]. ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ EPA (U.S. Environmental Protection Agency). 1998. Guidelines for Ecological Risk Assessment. EPA/630/R-95/002F. Risk Assessment Forum, U.S. Environmental Protection Agency, Washington, DC [online]. Available: http:// cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=12460 [accessed June 3, 2007]. EPA (U.S. Environmental Protection Agency). 1999a. Risk Assessment Guidance for Superfund: Vol. IâHuman Health Evaluation Manual (Supplement to Part A): Community Involvement in Superfund RiskAassessments. EPA 540-R-98-042. 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Available: http://www.epa.gov/superfund/commu- nity/pdfs/pipeline.pdf [accessed Feb. 1, 2008]. EPA (U.S. Environmental Protection Agency). 2001b. Risk Assessment Guidance for Superfund (RAGS), Volume III, Part A: Process for Conducting Probabilistic Risk Assessment. EPA 540-R-02-002. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC [online]. Available: http://www. epa.gov/oswer/riskassessment/rags3a/ [accessed Oct 10, 2007]. EPA (U.S. Environmental Protection Agency). 2001c. Comprehensive Five-Year Review Guidance. EPA 540- R-01-007. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC. June 2001 [online]. Available: http://www.epa.gov/superfund/accomp/5year/guidance.pdf [accessed Jan. 31, 2008]. EPA (U.S. Environmental Protection Agency). 2001d. Record of Decision: Alcoa (Point Comfort)/Lavaca Bay Site Point Comfort, TX. CERCLIS #TXD008123168. Superfund Division, Region 6, U.S. Environmental Protection Agency. December 2001 [online]. Available: http://www.epa.gov/region6/6sf/pdffiles/alcoa_lavaca_ final_rod.pdf [accessed Jan. 31, 2008]. EPA (U.S. Environmental Protection Agency). 2001e. Risk Assessment Guidance for Superfund: Vol. IâHuman Health Evaluation Manual (Part D, Standardized Planning, Reporting, and Review of Superfund Risk As- sessments). Final. Publication 9285.7-47. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC [online]. Available: http://www.epa.gov/oswer/riskassessment/ragsd/tara. htm [accessed Oct. 11, 2007]. EPA (U.S. Environmental Protection Agency). 2001f. Water Quality Criterion for the Protection of Human Health: Methylmercury. Final. EPA-823-R-01-001. Office of Water, Office of Science and Technology, U.S. Environmental Protection Agency, Washington, DC. January 2001 [online]. 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396 SCIENCE AND DECISIONS: ADVANCING RISK ASSESSMENT EPA (U.S. Environmental Protection Agency). 2002c. Organophosphate Pesticides: Revised Cumulative Risk Assess- ment. Office of Pesticide Programs, U.S. Environmental Protection Agency. June 10, 2002 [online]. Available: http://www.epa.gov/pesticides/cumulative/rra-op/ [accessed Feb. 4, 2008]. EPA (U.S. Environmental Protection Agency). 2002d. Determination of the Appropriate FQPA Safety Factor(s) in Tolerance Assessment. Office of Pesticide Programs, U.S. Environmental Protection Agency, Washington, DC. February 28, 2002 [online]. Available: http://www.epa.gov/oppfead1/trac/science/determ.pdf [accessed Jan. 25, 2008]. EPA (U.S. Environmental Protection Agency). 2002e. Child-Specific Exposure Factors Handbook. Interim Report. EPA-600-P-00-002B. National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC. September 2002 [online]. Available: http://cfpub. epa.gov/ncea/cfm/recordisplay.cfm?deid=5514 [accessed Feb. 1, 2008]. EPA (U.S. Environmental Protection Agency). 2003a. Technology Transfer Network 1999 National-Scale Air Tox- ics Assessment: 1999 Assessment Result [online]. Available: http://www.epa.gov/ttn/atw/nata1999/nsata99. html [accessed Aug. 19, 2008]. EPA (U.S. Environmental Protection Agency). 2003b. Human Health Toxicity Values in Superfund Risk Assess- ments. OSWER Directive 9285.7-53. Memorandum to Superfund National Policy Managers, Regions 1-10, from Michael B. Cook, Director /s/ Office of Superfund Remediation and Technology Innovation, Office of Solid Waste and Emergency Response, U.S. Environmental Protection Agency, Washington, DC. Decem- ber 5, 2003 [online]. Available: http://www.epa.gov/oswer/riskassessment/pdf/hhmemo.pdf [accessed Feb. 1, 2008]. EPA (U.S. Environmental Protection Agency). 2003c. Developing Relative Potency Factors for Pesticide Mixtures: Biostatistical Analyses of Joint Dose-Response. EPA/600/R-03/052. National Center for Environmental As- sessment, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH. September 2003. EPA (U.S. Environmental Protection Agency). 2003d. The Feasibility of Performing Cumulative Risk Assess- ments for Mixtures of Disinfection By-Products in Drinking Water. EPA/600/R-03/051. National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH. June 2003 [online]. Available: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=56834 [accessed Jan. 31, 2008]. EPA (U.S. Environmental Protection Agency). 2004a. An Examination of EPA Risk Assessment Principles and Prac- tices. EPA/100/B-04/001. Office of the Science Advisor, U.S. Environmental Protection Agency, Washington, DC [online]. Available: http://www.epa.gov/OSA/pdfs/ratf-final.pdf [accessed June 3, 2007]. EPA (U.S. Environmental Protection Agency). 2004b. Overview of the Ecological risk Assessment Process in the Office of Pesticide Programs: Endangered and Threatened Species Effects Determinations. Office of Prevention, Pesticides and Toxic Substances, Office of Pesticides Programs, U.S. Environmental Protection Agency, Wash- ington, DC. September 23, 2004 [online]. Available: http://www.epa.gov/oppfead1/endanger/consultation/ ecorisk-overview.pdf [accessed Feb. 1, 2008]. EPA (U.S. Environmental Protection Agency). 2004c. Estimated Per Capita Water Ingestion and Body Weight in the United StatesâAn Update. EPA-822-R-00-001. Office of Water, Office of Science and Technology, U.S. Environmental Protection Agency, Washington, DC. October 2004 [online]. Available: http://www.epa.gov/ waterscience/criteria/drinking/percapita/2004.pdf [accessed Jan. 31, 2008]. EPA (U.S. Environmental Protection Agency). 2005a. Draft Risk Assessment of the Potential Human Health Effects Associated with Exposure to Perfluorooctanoic Acid and Its Salts. Office of Pollution Prevention and Toxics, U.S. Environmental Protection Agency. January 4, 2005 [online]. Available: http://www.epa.gov/oppt/pfoa/ pubs/pfoarisk.pdf [accessed Feb. 4, 2008]. EPA (U.S. Environmental Protection Agency). 2005b. Integrated Exposure Uptake Biokinetic Model for Lead in Children (IEUBKwin v1.0 build 264). Software and Usersâ Manuals, U.S. Environmental Protection Agency, Washington, DC. December 2005 [online]. Available: http://www.epa.gov/superfund/lead/products.htm [ac- cessed Jan. 31, 2008]. EPA (U.S. Environmental Protection Agency). 2005c. Guidelines for Carcinogen Risk Assessment. EPA/630/P- 03/001F. Risk Assessment Forum, U.S. Environmental Protection Agency, Washington, DC. March 2005 [online]. Available: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=116283 [accessed Feb. 7, 2007]. 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Available: http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_ cr_cd.html [accessed Aug. 19, 2008]. EPA (U.S. Environmental Protection Agency). 2008b. Ozone (O3) Standards Documents from Review Completed in 2008âStaff Papers. Technology Transfer Network National Ambient Air Quality Standards, U.S. Environ- mental Protection Agency [online]. Available: http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_cr_sp.html [accessed Aug. 19, 2008]. EPA (U.S. Environmental Protection Agency). 2008c. Ozone (O3) Standards Documents from Review Completed in 2008âTechnical Documents. Technology Transfer Network National Ambient Air Quality Standards, U.S. Environmental Protection Agency [online]. Available: http://www.epa.gov/ttn/naaqs/standards/ozone/ s_o3_cr_td.html [accessed Aug. 19, 2008]. EPA (U.S. Environmental Protection Agency). 2008d. Office of Pollution, Prevention and Toxics, U.S. Environmen- tal Protection Agency [online]. Available: http://www.epa.gov/oppt/ [accessed Feb. 1, 2008]. 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