The Dieldrin Dilemma

Nearly 10% of the U.S. corn crop is treated with aldrin, a highly effective pesticide. Both the manufacturer, Shell Chemical, and the Department of Agriculture consider the substance essential to control insect damage in the Midwest corn belt. Recently, after a year of still-unfinished hearings, the Environmental Protection Agency announced that it plans to order a halt in the production of aldrin and a related Shell pesticide, dieldrin. Reason: the chemicals present "extremely high cancer risk."

After it is applied, aldrin gradually breaks down into dieldrin, a durable chlorinated hydrocarbon; the pesticide is long-lasting and requires only one application per year. That makes it more popular with farmers than shorter-lived, less potent pesticides that must be used more often and only at specific stages of the corn plants' growth. Dieldrin's impressive durability, says the EPA, is the very quality that makes it an increasingly serious threat.

From cornstalks and from soybeans raised in fields previously treated with the chemical, dieldrin finds its way into animal feed. Then, because it is readily retained in fatty tissues, it accumulates and becomes concentrated in farm animals. Millions of chickens had to be destroyed last March in Mississippi because their feed had been contaminated with dieldrin. The chemical also washes into rivers and lakes and is ingested by fish. In fact, dieldrin is now found in nearly every edible product in the supermarket. A 1973 market-basket sampling by the Food and Drug Administration shows 96% of meat, fish and poultry was contaminated, and tests by the EPA have found that 99.5% of the population have some dieldrin in their body fat with an average residue level of 0.3 parts per mil lion. Levels build up faster among infants, because the chemical is concentrated in milk.

No one disputes the fact that by now most Americans have a significant amount of dieldrin in their bodies, but there is still debate about whether the levels are sufficient to cause cancer. Mice given food with levels of dieldrin similar to those in human foods have developed cancer, especially of the liver. Shell says that there is no evidence that those results apply to humans; the EPA insists that dieldrin has "unreasonable and adverse effects on man." In addition to the cancer risk, says EPA Administrator Russell Train, dieldrin has been found to hamper reproduction in birds and to cause birth defects and mental impairment in monkeys.

With its 1975 production of aldrin scheduled to begin on Sept. 1, Shell has been granted a hearing on the ban order and hopes for a quick final decision by the EPA. But at week's end, it seemed all but certain that next year corn growers will no longer have aldrin/dieldrin to kill their bugs.

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At the same time, another agricultural chemical was under attack before a Senate commerce subcommittee. It is Dow Chemical's herbicide 2,4,5-T, which was labeled "Agent Orange" and used as a defoliant in Viet Nam. Though the weed killer can cause "extensive ecological damage," the National Academy of Sciences has reported, there is "no conclusive evidence" that it triggers birth defects in humans.

The Environmental Protection Agency, however, is more concerned about a contaminant that often appears as an impurity in manufactured 2,4,5-T --dioxin, which one EPA scientist has called "by far the most toxic product known to mankind." Small animals have been killed and birth defects caused in rats by dioxin concentrations of less than one part per billion--lethal levels so minute that researchers have trouble measuring them. Because of this experimental difficulty, the EPA says it still lacks sufficient evidence to press for a ban on 2,4,5-T. But, using a newly developed method of analysis, the agency plans to continue its investigation.

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