I began to look too closely when three of my colleagues were working on a pesticide data base. I watched them, asked questions, and learned how the Environmental Protection Agency (EPA) regulates the amount of pesticide in our food.
For those who haven't the stomach to delve into the details, here's the main conclusion. No one really knows how much of the 1.3 million tons of pesticides used annually by U.S. farmers shows up in our food. No one knows what a safe level of pesticide ingestion might be. The EPA is working in a haze of statistical and scientific uncertainty.
Now, for you brave ones who want to look at the innards, here's how the process works.
A company wanting to market a new pesticide must test it by feeding increasing amounts of it to laboratory animals. The toxicity of the pesticide is measured by how much it takes to kill 50% of the animals outright. Other tests of internal and external exposure determine whether the chemical causes cancers or birth defects.
The test data are submitted to the EPA. They are scientific observations, fairly incontestable as long as the test lab is honest. The EPA must then convert these animal results to permissible human exposures and farm application procedures. That requires a lot of assumptions.
First the EPA determines a No Observable Effects Level (N.O.E.L.) -- the daily dose that produces no visible ill effect on test animals. Assumptions: 1) no observable effect means no actual effect; 2) there is some safe level of exposure to this chemical (except for carcinogens, where the assumption is that no exposure is safe -- an assumption hotly contested by the chemical companies.)
Then comes the problem of converting data from animals to human beings. Assumption: humans are 10 to 100 times more sensitive to pesticides than are test animals. The EPA takes the N.O.E.L., divides it by some number between 10 and 100, and calls that the Acceptable Daily Intake (A.D.I.).
The EPA determines, for example, an A.D.I. of .05 milligrams of Captan per kilogram of body weight per day. Captan is a fungicide used on apples, tomatoes, peas, sweet corn, onions, beans, squash, carrots, and oranges. How can the EPA know how much of each of those foods you eat every day, so it can set permissible residue levels for each crop that won't add up to more Captan than you should be eating?
Assumption: we all eat the average American diet. The EPA has survey data on what a sampling of Americans eat. It averages us all together, you and me and your finicky two-year-old and my vegetarian grandfather.
Given the average diet it sets tolerances for each chemical and crop -- maximum permissible amounts of Captan on apples and beans. Then it lays down field procedures specifying how much Captan can be used on each crop, and what period must elapse between application and harvest, to assure that crops will meet tolerance.
A lot more assumptions creep in here. 1) The public's only exposure to a pesticide comes through food ingestion. 2) When several pesticides are present in the diet together, they do not do more damage than they would separately. 3) Farmers obey field guidelines. 4) Obeying field guidelines results in tolerances being met.
Crop samples are taken by the Department of Agriculture to test for compliance. Some of the samples do have pesticide levels over tolerance. Many crops have residues far below tolerance, and some farmers use no pesticides at all.
My colleagues did an experiment to test just one of this long string of assumptions. They calculated the pesticide exposures of people who do not happen to eat the average national diet. They used data on the actual diets of people of different ages, sexes, and ethnic groups. Their findings were especially striking for children.
According to their calculations, children 1-6 years old receive more than the acceptable daily intake of 10 out of 18 fungicides they investigated. Some of the calculated overexposure levels were enormous -- from 5 to 200 times the acceptable daily intake. (Calculations were made for only 18 fungicides out of 600 possible pesticides.)
Does this mean our children are being poisoned? Probably not, but the EPA can't be sure of that. All anyone can say is that, assuming that foods contain pesticides at the tolerance level, and assuming the EPA's definition of safe exposure, the average child eating an average child's diet, as revealed by one nutrition survey, is overexposed to 10 of the 18 pesticides investigated.
The EPA has no choice but to operate on assumptions. No one fully understands the effects of pesticides on the human body. The EPA Office of Pesticide Programs has a finite (and shrinking) budget. The task of regulating 600 chemicals on 376 crops in the hands of 3 million farmers who feed 240 million people is far beyond what any agency, no matter how well-funded, can handle.
My personal conclusion from this exercise in looking too closely is that, if we are to go on using pesticides, much more research and monitoring needs to be done. It should be paid for by the chemical companies who are profiting from this massive experiment in which we are all the white rats. And in the meantime, I'll get as much food as I can from my own garden and from farmers whose methods I know and trust.
.jpg)
No comments: