The California Department of Pesticide Regulation (DPR) conducts human health risk assessments as part of its mission to ensure the protection of workers and public health in the state. The risk assessments identify potential health hazards posed by pesticides, characterize dose–response relationships, and estimate exposure to characterize potential risks to humans. Over the last decade, advances in methods of scientific and technical analysis have led to improvements in the risk-assessment process that have made them more rigorous, transparent, and useful to risk managers. In light of the advances, DPR arranged for an independent peer review of the agency’s risk-assessment practices to ensure that they are scientifically and technically credible.
DPR asked the National Research Council to conduct the independent review. In response to the request, the National Research Council convened the Committee to Review California’s Risk-Assessment Process for Pesticides to determine whether DPR’s processes of hazard identification, exposure assessment, dose–response analysis, and risk characterization are consistent with best practices, such as those outlined in recent National Research Council reports. The committee also was asked to evaluate the methods used for setting priorities among pesticides for risk assessment and to identify possible options for improving efficiency and productivity.
SETTING PRIORITIES AMONG PESTICIDES
Over 300 pesticides are candidates for risk assessment in California because of concerns about their potential adverse health effects. They include new pesticides and state-registered pesticides that are undergoing re-evaluation because a potential health hazard has been identified. A priority-setting process is used by DPR to focus its resources on pesticides that pose the greatest risks to human health. The process involves establishing a list of candidate pesticides for risk assessment; screening and categorizing them into groups of high, medium, and low priority; and identifying and ranking the top 10 candidates for risk assessment. Four advisory panels are involved in the categorization, ranking, and review of the priorities at various stages of the process. Criteria used by the panels to set priorities fall into categories of physical and chemical properties, toxicity data, and potential for exposure. Reports of pesticide-related illnesses are also considered.
The screening process used by DPR to categorize pesticides into high-, medium-, and low-priority groups is practical given the large number of pesticides that DPR must consider. The criteria used to select the top 10 pesticides for risk assessment are reasonable and help to minimize the possibility that humans will incur excess risk during the time required to complete the assessment and make risk-management decisions. Strengths of the process include public consultation on the priority lists and the involvement of scientific review and stakeholder groups in the selection process. Periodic re-evaluation of the high-, medium-, and low-priority lists and annual selection of 10 pesticides for risk assessment are also commendable.
Although the committee generally supports DPR’s priority-setting process, it identified several improvements that will help to make the process more transparent and defensible. First,
better documentation of the evidence used to place pesticides into high, medium, and low categories is needed. Second, a more structured and objective ranking process is needed to ensure that DPR is focusing on the most important compounds. The current processes used to select the top 10 pesticides from the high-priority list of candidates are fairly subjective and depend on the expertise and knowledge of the persons conducting the reviews. Although documents describing the selection of the top candidates are available, the discussions are qualitative and do not explain how consideration of the criteria led to the ultimate ranking of the 10 pesticides. A more formal approach would make the rankings more defensible, ensure that a consistent ranking approach is applied, help outside parties to understand how priorities are established, and provide a baseline description of the methods that would be used if DPR decides to make modifications in the future.
Recommendations:
• DPR should update its documentation of its priority-setting process to provide more details so that the public can understand the process better. Flow diagrams would be helpful in documenting the steps in the process, identifying the staff and peer-review groups involved in each step, and indicating the opportunities for public input.
• DPR should provide more explicit documentation and support for how pesticides are categorized into groups of high, medium, and low priority.
• DPR should develop a more objective and structured approach for ranking high-priority pesticides so that others could reasonably reproduce the rankings. One option to consider is the development of a scoring system to weight the different factors. Such a scheme could provide greater transparency in illustrating how the 10 high-priority candidates for risk assessments were selected. If such a scheme were developed, it would be important to have it peer-reviewed before implementation.
RISK-ASSESSMENT METHODS AND PRACTICES
Problem Formulation
Two of the goals of recent advances in risk assessment were to improve transparency of analyses and judgments and to increase the utility of risk assessment for decision-makers. Important steps in achieving those goals are problem formulation and scoping. The 2009 National Research Council report Science and Decisions: Advancing Risk Assessment advocates that those steps be performed in consultation with decision-makers because it is critically important for the people who perform the risk assessment to understand the questions being asked and the decisions to be made by risk managers. Under the statutes within which DPR operates, it might be possible to develop a general catalog of the decisions and the options for making them. Such a catalog would help to ensure that the decisions and options are clearly set forth and that the set of considerations applied to each problem is consistent. Many of the committee’s concerns about improving California’s risk-assessment process for pesticides would be lessened if there were a description of problem formulation for each assessment, including a conceptual model and analysis plan that outlined the technical details for conducting the assessment. There should continue to be separation between risk assessors and managers with respect to any influence on the outcome of the assessment, but joint planning in the early stages of the process to identify and formulate the needs of risk-managers is likely to improve both the relevance and the efficiency of the assessment.
Risk-Assessment Methods and Guidance
The committee reviewed guidance documents provided by DPR on how it performs various aspects of its risk assessments. Three of the more recently completed pesticide risk assessments (those of chloropicrin, carbaryl, and methyl iodide) were considered in depth, as were summaries of the 11 most recent risk-characterization documents. Overall, the committee found that DPR’s risk-characterization documents are comprehensive and follow established risk-assessment practices but that DPR’s risk-assessment guidance documents do not yet reflect recommendations made in recent in National Research Council reports. The bulk of the assessments duplicate much of the work of the US Environmental Protection Agency (EPA). For example, similar critical effects are identified, the same studies are considered, and comparable approaches are used by the two agencies. However, differences between DPR and EPA at multiple stages of the risk assessments, including the ultimate reference values derived, were fairly common. In the more recent cases, DPR’s reference values were lower than EPA’s. Overall, however, the differences were usually small and almost always within an order of magnitude of each other. The differences are due to reasonable differences in scientific interpretation and judgment and generally fall within the level of uncertainty that is inherent in modern risk assessments. Thus, the committee questions whether the extensive effort needed to conduct a comprehensive risk assessment independently of EPA is justified in light of DPR’s resources. In the committee’s judgment, there are considerable benefits to harmonizing approaches among DPR, EPA, and other relevant agencies with respect to hazard identification and dose–response analysis for most pesticides.
Under DPR’s current paradigm, it appears to take several years for a risk assessment to be made final. If DPR could rely more on EPA’s evaluations for hazard identification and dose–response assessment, more of its resources could be directed to exposure assessment. Exposure assessments performed by DPR provide the greatest benefit when they introduce state-specific considerations into the risk-assessment process, so the collection of more California-specific information would be valuable.
Recommendations:
• DPR should review the legislative mandates under which it works to determine whether an independent and comprehensive evaluation of pesticides is required in every case in which a risk assessment is performed. If no new and compelling toxicology data have been generated since an EPA assessment was conducted and if there is no reason to believe that the EPA assessment is seriously flawed, DPR could rely on EPA’s assessment to identify the critical studies for hazard identification, interpretation of the dose–response data, and derivation of reference values. That would permit DPR to focus its efforts on California-specific issues, to tailor its risk assessments to its needs, to complete them more quickly, and to complete more of them in a timely fashion.
• When an independent assessment is warranted, DPR should incorporate problem formulation and other relevant elements recommended in the 2009 National Research Council report Science and Decisions: Advancing Risk Assessment into its risk-assessment process. An important consideration is that risk managers should be consulted in the problem-formulation stage so that a risk assessment can be designed to address the decisions that need to be made by managers and other stakeholders. Consideration should be given to whether a general set of problems and risk-management options could be formulated to use as a starting point in problem formulation.
• DPR should update its risk-assessment guidance documents regularly and perhaps develop additional reference materials to reflect the most current risk-assessment practices. DPR should provide better documentation of the guidance to be followed, ensure that the bases of selection and application of default assumptions are explicitly set forth, and that the guidelines
are followed in practice. The guidance should draw from the work of EPA, the California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment, and other relevant agencies. That will help to standardize and streamline reviews and evaluation approaches and will promote consistency among the assessment teams and contributors. Key subjects for which new guidance should be considered include incorporation of human variation in susceptibility to cancer, risks to susceptible subpopulations, and the types of evidence and justification necessary to permit departure from defaults.
California Data to Inform Priority-Setting and Risk Assessment
DPR supplements its exposure assessments with California-specific information, which the committee judges to be the most valuable contribution to DPR’s risk-assessment process. California routinely collects data on agricultural and other pesticide uses, air concentrations of some pesticides, residue data, and reports of human pesticide-related illnesses. California’s Pesticide Use Reporting (PUR) program is recognized as one of the most comprehensive in the nation. The program requires that pesticide use in the state be reported monthly, but this requirement applies only to agricultural uses, not to home-and-garden use or most industrial and institutional uses. The California Air Resources Board collects measurements of ambient concentrations of pesticides that are deemed toxic air contaminants.
Another important program is the Pesticide Illness Surveillance Program, which collects information on pesticide-related illnesses. The program is probably capturing only a moderate percentage of cases, because the submission of a case report depends on a person’s being seen by a physician, a physician’s recognizing that the illness is pesticide-related, and the physician’s taking the action necessary to report the case. However, case reports are a useful indicator of potential hazard and are used by DPR in setting priorities among pesticides for risk assessment.
Recommendations:
• Consideration should be given to expanding the PUR requirements to include all licensed pesticide appliers; these would include those who perform applications for nonagricultural purposes in homes, institutions, and industries if licensed appliers are not already required to do so. The resulting data would help to fill gaps in information about exposure in these types of pesticide uses.
• If resources allow, PUR data should be reviewed in relation to air-monitoring data and pesticide-illness surveillance data to determine whether any patterns are evident and to judge the accuracy of exposure assumptions or models.
• Consideration should be given to improving the reporting of cases of pesticide-related illness, for example, by improving the training of physicians, expanding the means by which cases can be reported, searching electronic health records, and possibly expanding the use of biomarkers.
