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Executive Summary When groundwater pollution emerged as a public issue in the late 1970s, major documented sources of contamina- tion were generally associated with the disposal of manufacturing wastes. By the early 1980s, several incidents of groundwater contamination resulting from the field application of pesticides had been confirmed. The most widespread problems involved the insecticides/ nematocides aldicarb (Temik) and DBCP (dibromochloro- propane). Early findings led to monitoring for other pesticides, and several additional active ingredients have now been detected In groundwater in at least a dozen states. Groundwater contamination from field-applied pesti- cides was against entirely unexpected, particularly since the pesticides being found in groundwater included those generally assumed to degrade or volatilize rapidly. When the first incidents were documented, pesticide manufac- turers and regulatory officials had little pertinent baseline data on groundwater quality to assess the scope of emerging pry. Responses to positive findings were necessarily ad hoc. Those early responses and experiences, data recently generated on groundwater contamination, and the current technical and polity status of the issue are the subjects of this investigation. The report reviews diverse activities in four states related to the detection in groundwater of residues from field-applied pesticides. These activities include hydrogeologic investigations; regulatory actions, including monitoring and cleanup; recommended changes in agricultural management practices, including irrigation and pest management; and various research initiatives, including development of new analytic chemistry techniques. Information from state 1
2 and local sources was supplemented and put into a national context with information based on interviews with federal regulatory officials and agrichemical company representatives. The report presents a series of vignettes illustrating a wide range of variables associated with the contamina- tion of groundwater by the agricultural use of pesti- cides. The cases reviewed are not detailed enough to characterize completely the current status of groundwater in the four states reviewed, nor are they necessarily representative of other states with significantly different agricultural activities. Nevertheless, the experiences in these four states suggest a number of generalizations concerning groundwater quality research needs, federal and state regulatory actions, and agricultural management practices associated with pesticide use. RESPONSES TO GROUNDWATER CONTAMINATION When pesticides were first detected In groundwater, no formal or informal regulatory mechanisms were in place to respond. As a result, programs to detect pesticides in groundwater and to remedy problems of contamination were largely ad hoc. Several patterns of response across states emerged, indicating opportunities to share knowledge and possibly coordinate activities. In other cases, inconsistent decisions between states indicate areas needing research and possible reassessment. Detection and Monitoring The detection of ald~carb in groundwater in Suffolk County, New York, first led to expanded local monitoring and then To programs to test for that pesticide in the groundwaters of other states where it was used. This sequence of looking for pesticides in groundwater has been repeated several times. Detection of DBCP in a limited number of wells in California led to a much more extensive statewide monitoring program. Positive findings in California convinced other states to under- take monitoring in areas where DBCP had been in use, leading to more positive findings. Until recently, programs for monitoring pesticides in groundwater tended to develop incrementally, covering
3 only one or a few suspect pesticides in particular areas Bence, most early monitoring is of limited use for developing a statistically reliable data base on the presence of pesticide residues in groundwater. In the four states visited, relatively comprehensive monitoring in major agricultural production regions has been conducted for a limited set of active ingredients. These include for California--DBCP; New York (Suffolk County only)--aldicarb, 1,2-dibromoethane (EDB), carbofuran, carbaryl, oxamyl, methomyl, and 1,2-dichloropropane; Wisconsin--aldicarb; and Florida--aldicarb and EDB. The monitoring has been funded and conducted by various parties, including the U.S. Environmental Protection Agency (EPA), state or local agencies, and pesticide producers (for example, Union Carbide Corporation for aldicarb). . Responses to Contamination Where residues have been found, actions to protect the public health and to prevent further contamination have been adopted largely on an ad hoc basis. Consequently, the levels of residues in groundwater that trigger concern and remedial actions are not always consistent from state to state. For example, Wisconsin and Florida have set health guidelines for aldicarb at 10 parts per billion (ppb), whereas New York has set its health guide- line for aldicarb at 7 ppb. The EPA's Office of Pesti- cide Program's Acceptable Daily Intake (ADI) for aldicarb is 0.003 mg/kg/day, and its recommended drinking water Health Advisory Level is 30 ppb; the EPA'S Office of Drinking Water's ADI for aldicarb is 0.001 mg/kg/day, and its proposed Health Advisory Level is 10 ppb. The National Research Council Committee on Drinking Water and Health is currently reviewing the toxicology data on aldicarb to see if a revision is warranted. Where wells supplying drinking water contain residues in excess of applicable standards, remedial actions have included supplying bottled water, installing granulated activated carbon filters, extending community water supplies to households with contaminated wells, capping contaminated wells, and drilling new wells. Some remedial actions have been funded by pesticide manufac- turers (for example, Union Carbide and FMC Corporation on Long Island) and applicators (State of Florida, for state-applied EDB).
4 Regulation of Pesticides Immediate actions to prevent further groundwater con- tamination have included bans on certain pesticides, at least temporarily, and use restrictions designed to minimize the possibility of contamination. Restrictions on the timing, method, site, and rate of application have been adopted for aldicarb in both Florida and Wisconsin. In Suffolk County, New York, a 1-year experimental program that restricted the conditions of aidicarb use indicated that even these steps were insufficient to keep groundwater contamination levels below health guidelines Accordingly, the use of aldicarb is no longer permitted in Suffolk and Nassau counties. NEEDS AND PROBLEMS . Efforts to respond to the presence of field-applied pesticides in groundwater have highlighted a series of needs and problems. The first set of needs concerns the information necessary to determine the nature and scope of groundwater contamination by pesticides: How wide- spread is the leaching of pesticides to groundwater? What chemical and hydrogeologic factors determine the likelihood of leaching? What is the toxicological significance of residues detected in groundwater? The second set of needs concerns the institutional and policy capabilities to respond to the problem. And the third set deals with adjustments in agricultural management necessitated by the potential for pesticides to leach to groundwater. Understanding the Nature and Scope of the Problem Some 200 pesticides are in common use' and a wide range of hydrogeologic conditions affect the suscepti- bility of groundwaters to contamination. Clearly, it is impracticable to sample every aquifer and test for every pesticide. Rather, efficient monitoring of resources depends on the establishment of systematic procedures for sampling and testing and the collection of data that can be used to identify critical site/pesticide combinations.
s Monitoring Screening and analytic techniques If a particular pesticide is known to be present in groundwater, sampling and analysis for that single pesticide may be appro- priate, despite the relatively high costs per sample tested. But for routine screening of groundwater (or drinking water), existing analytic techniques capable of detecting more than one compound tend to be expensive, time-consuming, limited to certain pesticide classes, and/or lacking in sensitivity. The development of improved multiresidue analytic screens for pesticides in water would enhance monitoring efficiency. According to researchers interviewed, such a development should be possible at_a reasonable cost within a few Years. The Food and Drug Administration (FDA), for example, uses multiresidue analytic methods capable of.detecting up to 125 active ingredients in a.single test in :. its food residue testing Programs. Several chemists suggested that the FDA's analytic methods could be adapted for use in monitoring pesticide residues in water. Any detection of residues should be confirmed by appropriately sensitive tests, preferably by.a :.- separate analytic procedure' before actions based on their presence are taken. Sampling protocols. Some state and federal programs to sample groundwater have been conducted in the absence of formal, established protocols concerning selection of test wells, collection and handling of samples, and development of quality assurance/quality control programs. The establishment of scientifically based sampling protocols would not only improve data quality and ~ . ~ . . . . comparability , but also f acilitate the training of technicians taking and handling samples. Data Needs Four sets of data are urgently needed to identify the potential for groundwater contamination and to develop , .,
6 appropriate pesticide use restrictions to protect ground- water. These are (1) the characteristics of a pesticide that determine the probability of its leaching to ground- water; (2) the complementary characteristics of the soil, the unsaturated (vadose) zone, and aquifer that determine the probability of a leachate reaching the groundwaves; (3) the locations where pesticides of concern are used and in what quantities; and (4) the locations of poten- tially vulnerable aquifers. The comparison of patterns of pesticide use with patterns of aquifer vulnerability would delimit areas of concern, and knowledge of the chemical and hydrologic mechanisms contributing to leaching would permit appropriate regulations to be formulated on how and where such pesticides should be applied. Moreover, because cropping and pesticide use patterns shift--sometimes dramatically in just a few years--the nature of and analytic protocols for monitoring programs must be continuously modified to retain the ability to detect emerging problems. Environmental fate data. Several or those interviewed commented on the need for the development and dissemina- tion of information concerning the environmental fate characteristics of pesticides. This need is broadly recognized, and basic information is being sought. Consequently, in spring 1984, the EPA requested pesticide registrants to supply data on the potential for groundwater contamination by 84 pesticides thought to pose a hazard to groundwater. A1SO, EPA has requested groundwater data for more than 50 other pesticide active ingredients as part of its registration standards program. These requests for data on the environmental fate of pesticides in relation to groundwater involve essentially all currently registered pesticides believed to pose a threat to groundwater. In addition, some states, including Florida, Wisconsin, and California, specifically authorize state-level pesticide regulatory bodies to require any additional data needed to assess particular local problems. Also, the interviews revealed that some pesticide producers are making marketing decisions based on the potential for groundwater contamination. Defining characteristics of susceptible sites. Despite the many differences among the four states visited, several hydrologic variables clearly influence
7 the potential for groundwater contamination, including the porosity, organic matter content, and pa of the soil and the depth, confinement, and recharge areas of aqui- fers. Particularly susceptible areas are characterized by sandy soils, shallow water tables, and special hydro- geologic conditions that expose aquifers to inf iltration by surface contaminants. Many areas with special susceptib well known, but continued and addition~i:reg~r~ p the conditions that make aquifers vulnerable to con- . . lamination by pesticides should be given a high priority. Models to describe the potential leaching of chemicals to groundwater exist, but their applicability to field conditions remains uncertain. Controlled field studies provide tests of such modes, but much more testing is required before the general applicability of models in the field can be assessed with confidence. Delineating vulnerable areas. Enough is already known - about critical soil and aquifer conditions, however, to permit identification of broadly vulnerable areas. Work to characterize susceptible areas is ongoing in all four states, both to specify particular problems (for example, aldicarb migration studies in New York, Wisconsin, and Florida) and to identify geographic areas where ground- water would be at high risk of pesticide contamination (for example, in heavily farmed regions of California with a rising water table). Crucial hydrogeologic conditions can be so site-specific, however, that the thorough identification and delineation of sensitive regions could be a highly resource-intensive activity. There are, for example, approximately 460 groundwater basins in California, and, within each of those, extensive variations may affect the potential for pesticides to leach to groundwater. Pesticide use data. A lack of historical pesticide . . use data has hindered identification of potential con- tamination problems. Furthermore, current pesticide use data are seldom adequate (they are either incomplete or too aggregated) to identify specific areas of high risk. The absence of up-to-date and accurate pesticide use data is particularly troublesome in susceptible regions where pesticides may be newly introduced to replace products restricted because of previous groundwater contamination. .
8 Because of the need for pesticide use data groundwater monitoring and Protection programs, as well as for other environmental and Public health purposes' restrictions in current regulatory law and procedures on the public dissemination of such data may need reevaluation. In summary, a key finding that emerged from this project is the high priority that should be placed on (1) research on the environmental fate characteristics of pesticides and of hydrologic conditions favoring pesticide contamination of groundwater; (2) the develop- ment of data on the location of areas highly susceptible to groundwater contamination; and (3) the generation of data on the use of pesticides in detail sufficient to pinpoint loadings in susceptible areas. Such data would more clearly focus the scope of the problem; allow limited resources to be directed at specific, high-risk areas; and support appropriate pesticide use restric- tions. Furthermore, increased effort should be applied to the development and validation of models predicting the environmental fate and transport of pesticides in the vadose zone before the use of these models in regulatory program-= is accepted or rejected. Point Source Contamination With some local exceptions, residues in groundwater from field application of pesticides tend to be restricted to perched groundwater and the upper levels of unconfined aquifers. Bowever, contamination may be more extensive, migrate more deeply, or reach conf ined aquifers, particularly when the source of the residues is more concentrated or the integrity of an aguifer's conf ining layer is pierced. Concentrated point sources of pesticides include manufacturing and formulating sites, applicator loading and mixing sites, and chemiga- tion systems--each of which has on occasion been associ- ated with contamination. Procedures for identifying and preventing point source threats of pesticide contamination to ground- water need evaluation.
9 Health Assessment Where pesticide residues are detected in groundwater, the practical problem arises of determining what residue concentrations should trigger regulatory actions. The Importance of this challenge is growing rapidly and will continue to grow in step with the development of increasingly sensitive analytic techniques and with expanding coverage in monitoring programs. _ Health standards. The EPA has set few maximum contaminant levels (MCL) or health advisories. often states have set their own MCLs, health advisory levels, action levels, and guidelines; and even though they may rely on data generated by the federal government, the lack of formally set levels can lead to inconsistent state standards. Local and state officials and agrichemica} represen- I_ . . tatives interviewed consistently voiced strong . . . sentiments regarding the need for the EPA to be more aggressive in setting aPuroPriate~HCLs or health - advisories for pesticides (and other chemicals) in; water. ~ . In support of their calls for federal leadership' these officials and representatives cited the resources required to assess health effects; the fact that the EPA, at least in the pesticide program, already requires the submission of data regarding health effects from which advisories should be able to be calculated; the problem of inconsistent state and local actions; and the need to mitigate public distress. Treatment technologies. Where groundwater used as drinking water has been contaminated with pesticide residues in excess of applicable standards, various remedial actions have been adopted. The cost-effectiveness of different remedial actions appears to be highly site specific and deserves~more research and evaluation. Less costly, long-term solutions for domestic application are especially needed. . _ . .
10 Institutional and Policy Capabilities to Respond to the Problem Because groundwater protection is a relatively new environmental issue, it lacks a developed body of law, established institutions, and formal administrative policies and procedures. Laws, institutions, and policies are developing at the federal level and in many states, but at varying rates and degrees. For example, Florida and Wisconsin have new groundwater protection laws that differ in many ways, including the provisions addressing monitoring, regulatory responsibilities, relationships between groundwater and surface water, and funding mechanisms. This undeveloped nature of groundwater law, institu- tions, and policy encourages continued ad hoc responses to perceived problems. Consequently, several key issues concerning pesticide use and groundwater quality remain unresolved: · It appears probable that in some regions little can be done to prevent agricultural chemicals from leaching to groundwater unless agricultural production practices are substantially modified or curtailed. In such cases, it is critical to determine what level of residue can be accepted without undue risk to public health and to relate this level to agricultural management practices in the region. · Where drinking-water wells are already contaminated by pesticides, only ad hoc remedies may be available. Who should bear the responsibility and costs for mitigating contamination in cases where the source of pollution is known needs to be clarified, and the appropriate responses of users, manufacturers, and landowners in cases where the source of contamination is unknown need to be established. · The lack of federally set MCLs or other health advisories for pesticides in water is widely perceived as a critical impediment to local and state health protection programs. Overcoming constraints to the issuance of health advisories and other quantitative standards and focusing federal scientific resources more effectively on developing such standards are hign- priority needs. · The lack of clear policies for the respective state and federal roles in funding and carrying out such research, and for coordination between research in the
11 public and private sectors, remains a critical institu- tional shortcoming that deserves continued attention. IMPLICATIONS FOR AGRICULTURE The unexpected presence in groundwater of residues from previously acceptable and sanctioned agricultural uses of pesticides has already had significant local impacts on agriculture in several major farm states. Aldicarb, for example, is no longer approved for use in Suffolk County, New York, and the taming and quantity approved for use in Wisconsin and Florida are restricted on a crop-by-crop and geographic basis. Many of those interviewed believed that such case-by-case, site-by-site restrictions are feasible and warranted, although there are concerns regarding the feasibility and administrative costs of such an approach in light of the generally complex and often cumbersome regulatory tools currently available at the state and federal levels. There is also considerable concern that public apprehensions about groundwater contamination will grow to the point where statewide or national bans will become politically expedient, even in cases where pesticide contamination is a controllable, localized phenomenon. These concerns have Implications for agricultural management practices as well as for pesticide avail- ability and use. The development of regulatory restraints and the growing sensitivity of pesticide producers to the problem (and to potential liability) suggest that directions for pesticide use will increasingly be written with an eye toward avoiding groundwater problems. Pesticide use restrictions--along or in combination with adjustments in other agricultural management practices--have been the primary approach to addressing contamination problems. This study raises questions about how users can..be.st be.informed offend . . .. trained in improved practices, tangling from Antigua- . ted pest management to calibration of application ~` equipment, and how the adoption of improved Practices can be fostered, monitored, and., if necessary, enforced. Adjustments in crop management and tillage practices in some areas may be the most efficient means of . ..
12 avoiding groundwater problems, especially where nematode control is required. Since soil conditions favoring nematodes tend also to allow for the ready movement of water and solutes through the vadose zone, and since nematocides by design tend to be highly water soluble and thus easily leach below the root zone, the adoption of new cultivars or adjust- ments in cropping patterns to minimize nematode problems may be necessary to avoid groundwater problems in some areas. Integrated pest management (IPM) Programs have significant potential to reduce Pesticide use and thus the Possibility of contamination. More emphasis is needed on IPM for nematodes and other Pests of the root zone and for sites and crops associated with vulnerable hydrologic areas. Irrigation efficiency and water management affect the Potential for agricultural chemicals to leach to groundwater. pesticide leaching is closely related to the site- specif ic chemical and physical properties of the vadose zone. Return-flow water management and drainage discharge practices may also contribute to groundwater contamination (for example, the discharge of wastewaters into inactive wells, which is of concern in California) and need to be assessed. Groundwater Protection needs associated with the complete process of manufacturing, formulating, ~ - transporting, delivering, and applying agricultural pesticides should be assessed, and~appropriate management standards developed where necessary. The influence of irrigation on CONCLUSION Overall, the emergence of the problem of pesticide . residues in groundwater adds a new dimension to the whole array of public health, environmental protection, pesti- cide innovation and marketing, and agricultural manage- ment. The interviews conducted and documents collected during this project indicate that new information is being integrated into ongoing programs and activities, though not always promptly and coherently. Not surprisingly, variations in approach have arisen from
13 special local conditions, different interests involved, and lack of federal leadership in key areas. The most urgent actions needed to address groundwater problems arising from field-applied pesticides appear to be · Federal determination of health-based standards for pesticides in water; · The development of improved, multiresidue analytic tools for screening groundwater for pesticides at the parts-per-billion to parts-per-trillion range; · The development of a systematic monitoring program; · The development of improved models of pesticide behavior and fate in soils, the vadose zone, and aquifers, and assessment of their validity under field conditions; · The development of data on environmental fate and pesticide use patterns, in conjunction with local hydro- geologic conditions, at a level of specificity adequate to identify areas especially vulnerable to groundwater contamination and to develop site-specific restrictions on pesticide use; and o The integration of groundwater resource considera- tions into an array of agricultural management practices and choices, including cropping, tillage, irrigation, and pest management.
