PROTECTION EPA is considering the risks of residues from insecticides like this one being sprayed on a lettuce field in New Mexico.
PESTICIDES
on the regulatory outcomes. Stakeholders need to be able to interpret the document "with a full understanding of its assumptions and the uncertainties introduced by making those assumptions," said Margaret Stasikowski, director of OPP's Health Effects Division. Both the environmental community and CropLife America (formerly the American Crop Protection Association), which represents pesticide manufacturers, praise EPA for the enormous amount of work it did to produce this document. "EPA has never tried anything this complex before," says Ray McAllister, vice president for science and regulatory affairs at CropLife America. "It had fewprecedents to draw on." "The agency is to be praised for developing the most sophisticated analysis ever," says Charles Benbrook, a consultant in Sandpoint, Idaho. "It is time to change how a few pesticides are used on a few crops and get rid of this risk," he adds. However, environmental and industry representatives have voiced some criticisms of choices EPA made in developing the assessment. The methods used in the complex cuscientific methods. Several key science and science policy decisions that affect the eval- mulative assessment are difficult to explain, uation of risk have not yet been made, she yet crucial for understanding the criticisms explained. Therefore, "we are not yet ready and outcomes. Anna Lowit, a toxicologist to draw firm conclusions from the docu- in OPP's Health Effects Division, described ment" about all the risks posed by organo- how the toxicities of the individual organophosphates are combined. First, a relative phosphates, she continued. However, EPAhas come to several gen- potency factor for each chemical—that is, eral conclusions, Rossi said. One is that its relative ability to inhibit cholinesterase— organophosphate residues in drinking wa- is calculated by comparing it to an index ter are not a major contributor to the risks. chemical, methamidophos, a pesticide with Another is that "although most indoor us- well-understood toxicity es of organophosphates have been eliminated" through regulatory actions over the IN THE ASSESSMENTp a method called past few years, "some remaining uses may the benchmark dose 10 (BMD10) was used pose risks of concern" and therefore may as a measure ofrelative potency This is the have to be restricted, she explained. As dose of pesticide that reduces cholinesmore uses are banned by further regulato- terase activity 10% relative to the backry action, she said, EPA will incorporate ground level in specific animal tests. the resulting risk reductions into the cu- BMD10 replaces the traditional toxicologmulative assessment. Exposures and risks ical approach, which uses no observed adfrom pesticide residues on food are still be- verse effect levels (NOAELs). NOAELs ing evaluated. The document indicates that vary according to the actual dose levels some food uses may cause excess risk for tested, so they are not very useful for comthe most highly exposed children, she said. parative purposes, Lowit said. After calculating the relative potency THE MAIN PURPOSE of the technical factors for all the chemicals in the assessbriefing was to create a common under- ment, the residues of each chemical are standing of the methods used in the doc- multiplied by that chemicals relative poument so there can be meaningful dialogue tency factor for each exposure of interest,
ASSESSING RISK FOR ORGANOPHOSPHATES
Higher safety factors, cumulative exposures complicate setting acceptable tolerance levels BETTE HILEMAN, C&EN WASHINGTON
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HE 1996 FOOD QUALITY PRO-
tection Act (FQPA) directs the Environmental Protection Agency to consider the combined effects to human health from all pesticides that share a common mechanism oftoxicity. It also requires EPA to simultaneously consider all routes of exposure from food, drinking water, and indoor uses. Since all of the organophosphate pesticides have a common mode of action— that is, they are all cholinesterase inhibitors —EPA has been working hard on an assessment of the combined risks posed by the entire group. In early December 2001, EPA released its preliminary assessment of the cumulative risks from organophosphate pesticides. OnJan. 15, it held a public meeting to explain the technical aspects of the document and solicit comments on its methods and parameters. At the meeting, Lois Rossi, director of the Special Review & Reregistration Division at EPAs Office of Pesticide Programs (OPP), explained that because this is the first time anyone has attempted to assess the total risks posed by a group ofpesticidesfrommultiple sources through multiple pathways, EPA had to develop new HTTP://PUBS.ACS.ORG/CEN
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sured residues that were illegally high in its analysis of risks from pesticide residues in food. "I understand that the illegal residues should not be there, but they are real. We should be looking at this in a real-world way," he says. The statute clearly directs the agency to evaluate risks as they The other pesticides evaluated in the appear in the diet, he notes. risk assessment document are acephate, azinphos-methyl, bensulide, chlorethoxyOver the past fewyears, Croplife Amerfos, chlorpyrifos, chlorpyrifos-methyl, ica has been very critical of EPA's rediazinon, dichlorvos, dicrotophos, dimethassessment of organophosphates. But its oate, disulfoton, ethoprop, fenamiphos, reaction to the cumulative assessment so fenthion, malathion, metha-midophos, far has been low key "Our main criticism methyl parathion, mevinphos, naled, oxyis that the assessment is still preliminary," demeton-methyl, phorate, phosolone, McAllister says. He also objects to the use phosmet, phostebupirin, pirimiphos of a benchmark dose that reduces cholinmethyl, profenofos, terbufos, tetrachloresterase only 10%—the BMD10. "In huvinphos, tribufos, and trichlorfon. mans, unless you exceed a 20% inhibition, there is no adverse effect. Anything lower David Miller, also a chemist in OPP's cannot be distinguished from natural variHealth Effects Division, pointed out that ability," he asserts. Furthermore, McAllister says, EPA does EPAhas not yet decided what margin of exposure is acceptable. Also, EPAhas not yet not need to apply an additional 10-fold decided on a threshold percentile for reg- safety factor because combining data in ulation, he said. For example, will the the cumulative assessment reduces unceragency try to protect all the children ages tainty and numerous conservative safety one to five below the 99th percentile of parameters have already been included in exposure from excess organophosphate the analysis. CropLife America is working residues, or will it choose a more lenient on a parallel cumulative risk assessment for comparative purposes, McAllister says. figure, such as the 95th percentile? EPA's Science Advisory Panel will evaluate FOR THE DRINKING water portion of the it in late April. The next step in the organophosphate assessment, EPA produced 12 regional assessments reflecting exposures from typ- assessment process is a review of the cuical organophosphate usage in vulnerable mulative document by the Science Adviwatersheds in each region, said Nelson sory Panel on Feb. 5-8. The public comThurman of OPP's Environmental Fate & ment period on the assessment ends March Effects Division. The agency found that 8. Under a requirement in the law, EPA "exposures from drinking water are 0.1 to must have reassessed two-thirds of the 0.01 of those from food," he said. risks of all the pesticide tolerances—the Jeff Evans of OPP's Health Effects Di- legal limits for pesticide residues in food— vision explained how EPA calculated risks by the end ofAugust. Reaching this numfrom residential sources, which include ex- ber—an additional 3,200 out of a total of posures from indoor, home garden, and 9,600 tolerances—will require use of the golfcourse uses of organophosphates. EPA cumulative assessment. will be refining its estimates after it obtains EPA, as required by FQPA, reassessed better data on organophosphate exposures 3,200 tolerances by August 1999, in many from pet products, pest strips, and home cases by removing unused tolerances from treatments, he said. the books. But the agency will have to work Adam Goldberg, policy analyst at Con- very hard to reach the two-thirds goal. It sumers Union, is concerned that EPA will will have to finalize the cumulative risk aschoose an exposure percentile lower than sessment and then apply it to the 3,200 the 99.9th in setting regulations to pro- tolerances. tect children from organophosphate risks. EPA is truly breaking new ground. It is "We want the agency to protect everyone the first government agency in the world up to the 99.9th percentile," he says. to develop a cumulative risk assessment, Goldberg also wants EPA to apply the and it will undoubtedly encounter critiadditional 10-fold safety factor when set- cism every step of the way as it makes the ting tolerances for organophosphates. policy decisions required to finalize the as"FQPA says to use a 10-fold safety factor sessment. After the assessment is comunless strong data support not using it," he plete, other countries, especially European says. Furthermore, he objects to the fact nations, are likely to emulate the process, that EPA is not including data on mea- McAllister says. •
Thirty-one Organophosphate Pesticides Are Under EPA Scrutiny hen the Environmental Protection Agency began the cumulative assessment process, there were 39 registered cholinesterase-inhibiting organophosphate pesticides. Eight of these have been excluded from the assessment because they are being phased out or have negligible, if any, exposures. The potency of one as-yet-unregistered organophosphate, fosthiazate, was evaluated because it may soon be approved as a substitute for methyl bromide.
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such as diet. The resulting values are added together to get the compound's total cumulative exposure in terms of the index chemical. Under previous regulations, EPAused a safety factor of 100 for setting acceptable tolerances ofpesticides on food. Thus, tolerances were set at a level 0.01 times the dose right below where an effect was observed in lab animals. However, under FQPA, Congress added a 10-fold safety factor, so now EPA is looking for a margin that is 0.001 times the BMD10 dose, unless there are compelling data that permit a lower margin. William O. Smith, a chemist in OPP's Health Effects Division, described how the dietary portion of the cumulative assessment was developed. EPA relied on food consumption data from the Department of Agriculture's surveys and pesticide residue datafromUSDA and the Food & Drug Administration. It assumed that the USDA consumption data reflect food choices across the year and around the country No attempt was made to estimate seasonal or regional differences in food exposures. The results of EPA's analysis show that children have the greatest exposure to organophosphates from dietary sources and that the age group with the highest exposure is children ages one to five, Smith said. Starting at the 90th percentile of exposure for this group—that is, the 10% of children with the highest estimated exposures —the margin of exposure is less than the 1,000 required by FQPA. This means that those children above the 90th percentile in the distribution maybe exposed to more organophosphates than allowed by the law. To increase the factor to more than 1,000, some tolerances would have to be lowered or some pesticide registrations revoked. 1U
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