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The Deadly Dust: The Unhappy History Of DDT
February 1971 | Volume 22, Issue 2
In other studies the magnification rate in specific food chains was measured. In the bottom of Lake Michigan’s Green Bay, for example, live billions of tiny crustaceans. The mud was found to contain 0.014 p.p.m. of DDT; the crustaceans, absorbing DDT from the mud, concentrated it in their bodies to 0.41 p.p.m.; fish, feeding on the crustaceans, concentrated DDT in their bodies to from 3 to 6 p.p.m.; herring gulls feeding on the fish accumulated DDT to the level of 99 p.p.m. This concentration, though not immediately fatal to individual gulls, reduces normal reproduction. The eggs of these herring gulls contained 227 p.p.m. of DDT, and their shells were abnormally thin.
By the late 1950’s it was clear to Miss Carson, and other knowledgeable observers, that DDT’s increasingly massive invasion of the food chain was largely responsible for the fact that bald eagles were ceasing to breed on the East Coast between Florida and Maine (large concentrations of DDT residues were found in the brains of prematurely dead eagles) ; that eagles in the Great Lakes region faced extinction because their egg shells were growing too thin (the physiological mechanism by which DDT inhibits calcium production would soon be discovered); that peregrine falcons were disappearing as breeding birds in the whole eastern half of the U.S.; that ospreys would disappear from Connecticut by the early 1970's if present rates of decline continued. Nor was DDT’s invasion of the food chain limited to land or to offshore waters. Oceanic food chains were being similarly contaminated, and ocean currents were spreading DDT residues to the most remote corners of the earth.
Predictable in a general way by the pattern of events was the sad case of the Bermuda petrel, a carnivorous bird that feeds solely on oceanic life far from any area where DDT is used. The bird comes to Bermuda for only a few hours, at night, to lay its eggs. It eats nothing there. Yet its eggs in the late 1960’s contained 6.44 p.p.m. of DDT on the average, and its reproduction was declining at a rate which, if continued, must end in complete reproductive failure by 1978. Even Antarctica’s Adélie penguins, Weddell seals, and skua gulls, carnivores all, were soon found to carry trace amounts of DDT in their fat, though they live thousands of miles from the nearest area of DDT use. Undoubtedly they ingest DDT residues in their food.
But DDT was also found, in the 1960’s, in Antarctic snow,∗ indicating that the food chain is not the only means by which the poison spreads. Studies conducted in Maine and New Brunswick, Canada, in the 1950's showed that approximately half the DDT sprayed over forests at treetop level hung suspended in the atmosphere to be spread worldwide on the wind. DDT attached to erosion debris also travels in irrigation water, rivers, and ocean currents.
∗Some 2,400 tons of it have been estimated to have accumulated by now in Antarctica’s snows.
The realization that the oceans’ organisms are becoming depositories for DDT has led some ecologists to premonitions of an apocalypse, based on the assumption that much of the oxygen in the atmosphere is produced through photosynthesis by marine phytoplankton (vegetable life). Hence, anything that might inhibit oceanic photosynthesis on a large scale is a threat to life on earth.
Scientists of this persuasion took little comfort in the 1968 report by Charles F. Wurster, Jr., of the State University of New York at Stony Brook; in the laboratory very low concentrations of DDT had measurably reduced photosynthesis in cultures of four species of coastal and oceanic phytoplankton representing four major classes of algae. Furthermore, the same had been found true of a natural phytoplankton community (as distinct from a laboratory culture) at Woods Hole. “I’ll tell you what we worry about most,” said David M. Gates, director of the Missouri Botanical Garden in St. Louis, to a reporter in 1969, "—an irreversible catastrophe. A number of pesticide spills, for example, in those areas of the ocean where … much of the world’s oxygen [is produced]. If you plot the frequency of this kind of event, they’re getting closer and closer.” Much of this kind of fear has been allayed by recent scientific findings that suggest that no significant interchange of oxygen occurs between ocean and atmosphere, and, in addition, that some phytoplankton are considerably less sensitive to pesticides than others. Such findings, of course, do not alter the fact that any large-scale interference with ocean life would have serious repercussions.
Whatever its ultimate effects may be, the frightening fact is that most of the hundreds of millions of pounds of DDT sprayed over the world during the last quarter century remain in circulation- only a fraction has decayed into harmless substances—and no one can say what fatal damage it alone (apart from the DDT being constantly added) may yet do.