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A Set of Scientific Issues Being Considered by the Agency in Connection with
EPA's Corn Cluster Ecological Risk Assessment

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A Meeting of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel (SAP) completed review of a set of scientific issues regarding the Agency's Corn Cluster Ecological Risk Assessment. The review was conducted in an open meeting held in Arlington, Virginia, on May 29-31, 1996. The meeting was chaired by Dr. Ernest E. McConnell. In addition, Mr. James Fairchild (National Biological Service, Columbia, Missouri), Dr. Elwood Hill (Gardnersville, Nevada, NBS-Retired), Ms. Jane Hughes (Carolina Ecotox, Inc., Durham, N.C.), Dr. Christopher Ingersoll (NBS, Columbia, MO), Dr. Ronald Kendall (Clemson University, S.C.) recused himself from the proceedings on the corn cluster risk assessment, Dr. Donald Munson (Washington College, Chestertown, MD), Dr. Barry Wilson (University of California, Davis, CA) served as Ad Hoc experts to the FIFRA SAP.

Public notice of the meeting was published in the Federal Register on May 1, 1996.

Oral statements were received from:

Written statements were provided by:


The Panel addressed the specific questions raised by the Agency and, where necessary, offers additional recommendations for improvement. In consideration of all matters brought out during the meeting and careful review of all documents presented by the Agency, the Panel unanimously submits the following report.



The Panel commends the Agency on its ambitious pilot study to develop methodology to rank the environmental risks of chemicals that have similar uses. As instructed, the Panel's review is not concerned with the specifics of the several chemicals; it focuses on the science underlying the risk assessment process and its decisions.

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Having complimented the Agency on its decision to establish a relative risk project, the Panel also suggests that its name "Corn Cluster" is confusing. Several members of the Panel expected to review a multifactorial approach to assessing the risks of several chemicals, either alone or as mixtures. To avoid such misunderstandings, the Panel recommends a name such as "___Risk ranking Project:___" be chosen. This has the added advantage of applying to more than one crop or ecological situation. (e.g.,Pesticide Risk Ranking: Corn; Pesticide Risk Ranking: Wheat)

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Field Testing

The Panel finds that, regardless of the efforts undertaken by the Agency to adhere to the New Paradigm approach, field testing is necessary to move beyond gross First Tier decisions. The New Paradigm guidelines themselves recommend field testing when existing data bases fail to provide data sufficient for probabilistic risk assessments. In the case of the pesticides used on corn and other field crops, further work is needed to clarify exposures, validate toxicities and establish site specific and bench mark data for species critical to the regulatory decision making process. Therefore, although the Panel recognizes the intent of previous task forces to reduce expensive field testing and applauds their efforts, we strongly urge the Agency to reinstate critical field testing (and related mesocosm studies) of chemicals both to monitor chemical use, to test paradigms and modeling algorithms and to obtain base line data on the interactions between chemicals, habitats and toxicities to birds, small mammals, aquatic organisms and other appropriate wildlife. Although some of this needed field research can be done by the private sector, EPA scientists need to take the lead.

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Relevance to the New Paradigm

The Panel views the "Corn Cluster" and "Carbofuran" projects as first steps towards the application of the New Paradigm approach to Terrestrial Ecotoxicology. The power of the New Paradigm approach is it moves beyond single point deterministic derived statements of risk to probabilistic statements of risk and mitigation based upon the sum total of laboratory and field findings. Its weaknesses are in the assumptions and data bases applied. In the studies presented for its review, the Panel is surprised that steps recommended by the New Paradigm Task Force (See, for example, the Aquatic Dialogue Group: Pesticide Risk Assessment and Mitigation, 1994 booklet) were not followed more closely, and/or that gaps in the process were not more clearly identified. For example, there is a clear statement in the recommendations as to the importance of dose-response data and slopes of the curves in the assessment process. Identifying where data is lacking to provide a sound scientific basis to the risk statements generated provides a continuing impetus for Agency scientists to stay abreast of advances in disciplines critical to their tasks, provides guidance to Agency, academic and industry scientists on experiments and designs considered critical by the Agency, and, provides a way to judge the relative reliability of the risks calculated. In the Corn Cluster Project the data gaps are such that the Agency is still trapped in a deterministic mode rather than providing rough probabilistic assessments for the chemicals concerned. For these reasons, the Panel recommends that the Agency prepare an evaluation of the extent to which the Corn Cluster risk analysis meets the guidelines of the New Paradigm, and how and why the Agency has had to depart from them.

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Corn Cluster Project Gaps

Specific matters that need further testing in the Corn Cluster Project include the reliability of estimating exposures from AI values, the vexing problem of establishing toxicity of granular, flowable and other formulations and devising reliable mediations to their adverse effects, the use of sentinel species and most sensitive species as compared to more probabilistic approaches, establishing when and where laboratory and mesocosm experiments can be extrapolated to full field situations and the introduction of dose-response data and their slopes directly into the modeling process. Such matters play large roles in the suggestions of the Panel and the criticisms and suggestions received from the registrants and scientists from other agencies. One way to accomplish this is to provide more funds for EPA research, general reviews and work of Agency scientists.

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Task Force

A second suggestion is to establish a task force of Agency, registrants and academia representatives to review proposals of the complexity of projects such as the "Carbofuran" and Corn Cluster Reports before they reach the SAP. In essence, a Terrestrial or a renewed Avian-Ecology Dialogue Group comparable to the Aquatic Dialogue Group. A major charge of such a committee would be to harmonize the approaches, conditions recommended and research base examined within the Agency, establishing a common format to the process of developing and presenting appropriate guidelines for the various experimental procedures necessary to evaluate a given chemical formulation or use. The Task Force should also identify procedures for the Agency to follow in liberalization of guideline requirements when specific chemical uses under review clearly will not affect certain ecotypes and wildlife populations.

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Specific Concerns

  1. Objectives and Justifications

    Although several reasons for undertaking the Corn Cluster Project are given in the text (e.g., avoidance of decisions that shift uses from one chemical to another without considering relative risks, harmonization of risk assessment processes) the Panel had difficulty finding and agreeing on them. The Panel suggests that the reasons for the Corn Cluster Project (including its applicability to the New Paradigm Process) be clearly stated and justified early on in the document.

  2. Generality of the Approach

    One could argue that the efforts of the Agency scientists would have been wasted if the approach taken was applicable only to chemicals of high toxicity applied on single crops. The Panel suggests that the Agency discuss the uses of the approach for other chemicals and situations. For example, would the approach taken in the examination of the four high toxicity chemicals in the Corn Cluster be appropriate for other agents such as DDT and other chlorinated hydrocarbons, pyrethroids, or even carbaryl (a carbamate)? What modifications would be necessary in the weight of evidence parameters?

    A strength of the approach is its intent to provide relative risks. The weaknesses are both practical and theoretical. There are extensive data gaps, and poorly validated parameters that are being applied in the absence of better data which softens the numbers. In addition, the lack of stressing probabilistic models will make it difficult to move from qualitative deterministic statements to more quantitative probabilistic ones. For example, to proceed from LD50 considerations to establishing the risk that 10 percent of the population will be severely affected by a certain treatment and in consideration of differences in toxic mechanisms and likelihood of exposure, potential for chemical-stressor interactions; such an approach is not scientifically defensible.

  3. Strengths and weaknesses of presenting overall risk

    The Panel thinks that the Agency has not provided a powerful enough analysis to estimate overall risk; at best a relative ranking based on selected tests can be achieved. One important advantage of comparing chemicals is that the approach is standardized and no single chemical gets the benefit of a parameter not considered in the study of another, but to what extent is different toxic mechanism and likelihood of exposure considered?

    The Panel is not persuaded that there are scientific reasons for taking opportunistic qualitative reports and using them to generate quantitative risks. Incident data are very important in establishing that the chemicals concerned have adverse effects, but other effects may also be considered. Therefore, incident reports should be used mainly to justify further investigations that must be tailored to the specific chemical formulation and uses.

  4. Role of Environmental Fate

    In a similar vein the Panel would like to know what risks would have been generated if the environmental fate parameters were not similar for the chemicals compared? In other words, how disparate a set of circumstances can be compared and still derive scientifically sound relative risks by the "cluster" (and by extrapolation, the New Paradigm) approach?

  5. Risk Quotient

    The Panel would like to know the scientific justifications for comparing the Risk Quotient to the LOC. There are scientific questions as to the validity of both parts of the ratio. In particular, what is the justification for establishing an EEC based solely on application rates? Has the suggestion to establish exposure based on AI been validated beyond the initial work of almost 25 years ago? How does this use of AI fit with the concern for establishing the relative risks of different formulations? And, in terms of probabilistic risk assessment, should one not be thinking of a curve of AI versus exposure? Routes of exposure may be very important in this determination. Limiting the exposures to ingestion may not be scientifically sound (for example, many graminivorous precocial birds engage in repeated dusting activities which increases routes of exposure to include at least inhalation and percutaneous).

  6. Endpoints

    1. Are the endpoints of the risk assessment process fully validated and adequate to the task? Should a full risk assessment include data for the entire growth cycle of the crop? Indeed, is focusing on planting an appropriate approach since such a "worst case" analysis excludes species that may be affected at other stages of the growing cycle of the plants and animals.

    2. As mentioned elsewhere in the report the Panel thinks it a mistake to remain bound to mortality as the major end point for the data input into the risk assessment process. The cost of this convenience may be immense in establishing risks and embarking on mitigation especially when the goal is to proceed from individual toxicity measurements to understanding population effects. Parameters such as biomarkers of effect (e.g., cholinesterases, P450 levels, hormone levels, reproductive indices and birth abnormalities) should be built-in as endpoints with a process for adding new end points and removing old ones as toxic mechanisms are better defined and understood.

  7. Species

    Why are invertebrates, fish and birds studied while mammals, reptiles, amphibians, and critical forage insects, all important parts of the food chains, ignored? Will there be special attention given in the future to nesting altricial birds, multiple routes of exposures and chemical interactions (including chemical-chemical and chemical-physiological stressor)?

  8. Environmental Fate and Risk Assessment Models

    How up-to-date are the environmental fate models? What research has been done to validate them with site-specific information? Are the risk assessment models applied consistent with the probabilistic approach and represent state-of-the art modeling science?

  9. Feeding Studies

    The Panel suggests that carefully designed feeding studies will be necessary (if they have not been done previously) to validate the risk parameters chosen. For example, what if a breeding animal is exposed to a given toxic challenge for the first time at different stages of the reproductive cycle? Behavior may be affected differently.

  10. Cost Effectiveness

    Was one of the reasons for the relative risk "cluster" approach cost-effectiveness? The Panel is not assured of the cost-effectiveness of examining several chemicals at one time. Has any consideration been given to establishing data on mixtures or at least the conduct of simultaneous studies to tease out the most and least toxic from their total toxicities?

  11. Dose-Response Slopes

    The Panel suggests that the shallowness or steepness of the dose-response of the chemicals should play an important role in the weight of evidence of toxicity as discussed in other sections of the Panel's response. Indeed, such slopes play an integral part in the probabilistic approach recommended in the New Paradigm reports. Determination of LOC and NOEL from standard lethality curves has many technical weakness; especially in the area of reproducibility. Special studies must be designed for these important data points.

  12. New Paradigm

    The extent to which the Guidelines and the science subsumed under the phrase "New Paradigm" is applied in the Corn Cluster efforts leads some on the Panel to think that (to paraphrase G.B. Shaw) the trouble with the New Paradigm, like Christianity, is that it has not yet been practiced. The Panel finds that the way the "New Paradigm" is being applied in these cases is not yet sufficient to carry out the tasks.

  13. Listed Species

    What is the role of Federally Listed Species data in the weight of evidence process? The Panel had no comments.

  14. Weight of Evidence

    The Panel recommends that, at a minimum, the weight of evidence parameters include at least:

    1. Validated Risk Quotients
    2. Chemical Properties
    3. Use Parameters
    4. Formulations
    5. Field Studies
    6. Incident Data
    7. Slopes of the Dose-Response-Curves to adequately provide a Tier I assessment.

    In addition, the Panel also recommends that the Risk Quotient be reexamined as to its theoretical justification and field test validation.

  15. Individual Species

    Several Panel members observed that the individual risk assessments for the chemicals revealed high levels of toxicity to birds and other animals that may warrant future action, regardless of their relative rankings in the Cluster. Also, what importance should be placed on potential exposure of Federally "Listed Species"?

  16. Aquatic Studies

    As these four chemicals can be applied in estuarine habitats, it would be of considerable value to have information on the effects of the chemicals on estuarine organisms, particularly fish. The use of controlled experimental regimens, specifically mesocosms, lend themselves elegantly to this kind of investigation. Many estuarine fishes (e.g. minnows) attain sexual maturity in relatively brief periods of time. Information on tissue developmental changes due to chronic and/or acute exposures to the chemical would be of extreme value.

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In closing this last presentation of the meeting, the Panel once again compliments the Agency on their efforts in this ambitious undertaking even though the Panel does not consider the task completed. Considering the complexity of the situation, the extensive comments and offers to interact with the Agency on the part of the registrants, the Panel recommends that the Agency take the lead in further collaborative study on this matter stressing obtaining or generating the data permitting them to move from deterministic to probabilistic assessments of risk and mitigation.

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Certified as an accurate report of Findings:

Larry C. Dorsey
Designated Federal Official

FIFRA Scientific Advisory Date: ( July 1, 1996)

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