Chemical substances—pesticides and herbicides—that are used as weed and insect control on crops and animal feed always leave some kind of residue either on the surface or within the crop itself after treatment. The amounts of residue vary, but they do remain on the crop when ready for harvest and consumption.
While these chemicals are generally registered for use on food crops, it does not necessarily mean they are "safe." As part of its program to regulate the use of pesticides, Environmental Protection Agency (EPA) sets "tolerances" which are the maximum amount of pesticides that may remain in or on food and animal feed. Tolerances are set at levels that are supposed to ensure that the public (including infants and children) is protected from unreasonable health risks posed by eating foods that have been treated.
Tolerances are initially calculated by measuring the amount of pesticide that remains in or on a crop after it is treated with the pesticide at the proposed maximum allowable level. The EPA then calculates the possible risk posed by that proposed tolerance to determine if it is acceptable.
In calculating risk, the EPA estimates exposure based on the "theoretical maximum residue concentration" (TMRC) normally assuming three factors: that all of the crop is treated, that residues on the crop are all at the maximum level, and that all consumers eat a certain fixed percent of the commodity in their diet. This exposure calculation is then compared to an "allowable daily intake" (ADI) and calculated on the basis of the pesticide's inherent toxicity.
The ADI represents the level of exposure in animal tests at which there appears to be no significant toxicological effects. If the residue level for that crop—the TMRC—exceeds the allowable daily intake, then the tolerance will not be granted as the residue level of the pesticide on that crop is presumed unsafe. On the other hand, if the residue level is lower than the ADI, then the tolerance would normally be approved. Exposure rates are based on assumptions regarding the amount of treated commodities that an "average" adult person, weighing 132 lb (60 kg), eating an "average" diet would consume.
To set tolerances that are protective of human health, the needs information about the anticipated amount of pesticide residues found on food, the toxic effects of these residues, and estimates of the types and amounts of foods that make up our diet. The burden of proof is on the manufacturer who has a vested interest in getting EPA approval. A pesticide manufacturer begins the tolerance-setting process by proposing a tolerance level , which is based on field trials reflecting the maximum residue that may occur as a result of the proposed use of the pesticide. The petitioner must provide food residue and toxicity studies to show that the proposed tolerance would not pose an unreasonable health risk.
The Federal Food, Drug, and Cosmetic Act (FFDCA) requires that the manufacturer of any substances apply to the EPA for a tolerance or maximum residue level to be allowed in or on food. Because of the way pesticide residues are defined and incorporated into the food additive provisions of the FFDCA, there are actually several kinds of tolerances, each subject to different decisional criteria. A given pesticide can thus have many tolerances, both for use on different crops and for any one crop. For example, for each crop for which it is registered, a pesticide may need a raw tolerance, a food additive tolerance, and an animal feed tolerance, each of which will be subject to particular decisional criteria.
The EPA sets tolerances on the basis of data the manufacturer is required to submit on the nature, level, and toxicity of a substance's residue. According to the EPA, one requirement is for the product chemistry data, which is information about the content of the pesticide products, including the concentration of the ingredients and any impurities. The EPA also requires information about how plants and animals metabolize (break down) pesticides to which they are exposed and whether residues of the metabolized pesticides are detectable in food or feed. Any products of pesticide metabolism , or "metabolites," that may be significantly toxic are considered along with the pesticide itself in setting tolerances.
The EPA also requires field experiments for pesticides and their metabolites for each crop or crop group for which a tolerance is requested. This includes each type of raw food derived from the crop. Manufacturers must also provide information on residues found in many processed foods (such as raisins), and in animal products if animals are exposed to pesticides directly through their feed.
A pesticide's potential for causing adverse health effects, such as cancer , birth defects , and other reproductive disorders, and adverse effects on the nervous system or other organs, is identified through a battery of tests. Tests are conducted for both short-term or "acute" toxicity and long-term or "chronic" toxicity. In several series of tests, laboratory animals are exposed to different doses of a pesticide and EPA scientists evaluate the tests to find the highest level of exposure that did not cause any effect. This level is called the "No Observed Effect Level" or NOEL.
Then, according to the EPA, the next step in the process is to estimate the amount of the pesticide to which the public may be exposed through the food supply. The EPA uses the Dietary Risk Evaluation System (DRES) to estimate the amount of the pesticide in the daily diet, which is based upon a national food consumption survey conducted by the U.S. Department of Agriculture . The USDA survey provides information about the diets of the overall American population and any number of subgroups, including several different ethnic groups, regional populations, and age groups such as infants and children.
Finally, for non-cancer risks, the EPA compares the estimated amount of pesticide in the daily diet to the Reference Dose. If the DRES analysis indicates that the dose consumed in the diet by the general public or key subgroups exceeds the Reference Dose, then generally the EPA will not approve the tolerance. For potential carcinogens, the EPA ordinarily will not approve the tolerance if the dietary analysis indicates that exposure will cause more than a negligible risk of cancer.
There have been serious problems in carrying out the law. Although the law requires a thorough tolerance review for chemical pesticides prior to registration for health and environmental impacts, the majority of pesticides currently on the market and in use today were registered before modern testing requirements were established. "Thus," according to a 1987 report published by the National Research Council Board on Agriculture, "many older pesticides do not have an adequate data base, as judged by current standards, particularly data about potential chronic health effects."
The 1972 amendments to the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) required a review—or registration—of all then-registered products according to contemporary standards. Originally, the EPA was to complete the review of all registered products within three years, but this process broke down completely. In 1978, amendments were added to FIFRA that authorized the EPA to group together individual substances by active ingredients for an initial "generic" review of similar chemicals in order to identify data gaps and assessment needs. The amendments mandate that after this generic review, the EPA is to establish as "registration standard" for the active ingredient basis. Then, the EPA must wait for additional data in order to establish specific requirements for each substance's specific use on differing crops. (The EPA does not specifically address inert ingredients, although inert ingredients have been found to be just as potentially toxic as the active ingredients.)
The 1988 amendments extended the deadline for reregistration until 1997. To date, however, the EPA only has complete residue data on less than 25% of pesticides used on foods, and less than ten products, as yet, have been registered. Thus, the backlog of substances awaiting re-registration is on the order of some 16,000 to 20,000 compounds, including, according to the General Accounting Office, over 650 active ingredients. As a consequence, most of these untested chemicals temporarily retain their registration status under the former testing requirements.
Once tested in accordance with contemporary standards, many of the older pesticides are likely to be identified as carcinogenic. In fact, the National Academy of Sciences estimates that 25–33% of the pesticides to undergo re-registration procedures are likely to be found to be oncogenic. An oncogen causes tumors in laboratory animals and is considered potentially cancerous to humans. In general, such older pesticides, registered prior to 1972, have not been tested adequately for oncogenicity. For a substance to be used on a new crop, however, current data must be submitted in order to obtain a tolerance.
One way pesticide companies are able to completely skirt EPA regulations is to send pesticides that are suspended or banned in the United States to Third World countries. At least 25% of American pesticide exports are products that are banned, heavily restricted or have never been registered for use in the United States. Hazardous pesticide exports are a major source of pollution in Third World countries where lack of regulation, illiteracy, and repressive working conditions can turn even a "safe" pesticide into a deadly weapon for the field workers. These pesticides are returned to the United States, unexamined, as residues in the imported food American consumers eat.
[Liane Clorfene Casten ]
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Raloff, J., and D. Pendick. "Pesticides in Produce May Threaten Kids." Science News 144 (July 3, 1993): 4–5.