Ecological Knowledge and Environmental Problem-Solving Concepts and Case Studies (1986) / Chapter Skim
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24. Environmental Effects of DDT
24. Environmental Effects of DDT
Pages 358-374
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From page 358... ...
Animals in the oceans, lakes, and rivers, on land, and in the air had detectable amounts of DDT in their tissues. The resulting concern led to detailed monitoring, to increased understanding of how chemicals are transported through the environment and how quickly resistance to pesticides can evolve, and to a new awareness of how even the most careful scoping of a problem does not guarantee freedom from unpleasant surprises.
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From page 359... ...
By the early 1940s, the United States was producing large amounts of DDT for control of vectorborne diseases, and its use is credited with saving millions of lives from diseases with insect vectors, such as typhus and malaria. Its use in the United States for agricultural purposes expanded rapidly after World War II, reached a peak of 80 million pounds in 1959, and decreased thereafter until it was terminated by cancellation of its registration in 1972.
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From page 360... ...
DDT was the first pesticide to which rapid and extensive resistance evolved. The earliest field studies were of DDT applied at 5 lb/acre for spruce budworm control.
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From page 361... ...
In the mid-19SOs, massive spraying programs were undertaken to save the American elm by killing the elm bark beetle, which spread the imported Dutch elm disease fungus from tree to tree. Robin mortality was widespread, and robins dying with tremors characteristic of DDT poisoning were commonly seen in treated areas.
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From page 362... ...
DDT is not equally toxic to all species of animals. Control programs for arthropods have sometimes resulted in increased pest damage, because predators of a pest were eliminated by DDT.
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From page 363... ...
During the 1960s, more subtle effects of DDT and its metabolites were discovered. The striking eggshell thinning in some predatory birds such as bald eagles, ospreys, peregrine falcons, and pelicans was clearly the cause of decreases in their populations.
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From page 364... ...
The general belief among toxicologists had been that metabolism of toxic substances invariably decreased their toxicity, but it was discovered that some metabolites of DDT, especially DDE, were more persistent and in some cases more active biologically than the original compound. This discovery laid the groundwork for research that eventually explained the decline of a number of bird species through eggshell thinning.
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From page 365... ...
Among these effects were the decrease in songbird populations caused by massive control programs, such as those for spruce budworms in forests and Dutch elm disease in suburban areas; the declines in sport fish, such as lake trout in Lake George, caused by blackfly control programs; the contamination of fish and game desired as human food to a point greater than that permitted in domestic animals used for food; and the decline of avian predators at the top of food chains, particularly aquatic ones. Importance of the Impacts Probably of greatest importance were the drastic population decreases over large regions or continents of bird species at the top of their food chains.
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From page 366... ...
For several years, unfortunately, the manufacturer was less adept at controlling wastes from the manufacturing process than at maintaining purity of the product, so considerable waste DDT and related products continued to be emptied into the Pacific Ocean, with detrimental effects on the brown pelican and other species. Study Strategy Because of the nature of the problem, there was no formal study strategy.
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From page 367... ...
The captive birds studied eventually included bald eagles, kestrels, cowbirds, mallards, pigeons, and others. Similarly, trout and goldfish were exposed, and LCsoS for 24-48 hours were determined.
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From page 368... ...
It was hypothesized that only a small fraction of bird carcasses present were found and that, at least in areas of a few to hundreds of acres in relatively homogeneous habitat during the early nesting season, repopulation would take place very rapidly. Studies carried out at Patuxent Wildlife Research Center in Laurel, Maryland, confirmed both hypotheses.
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From page 369... ...
The importance of the eggshell thinning and consequent reduced reproductive success was understandable only in terms of population dynamics. The observations of distribution of DDT in field studies and monitoring led Metcalf (1972)
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From page 370... ...
. Hickey suggested that pesticide residues were probably responsible for reduced reproduction, primarily through egg destruction and egg-eating, but there was no mention of shell thinning.
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From page 371... ...
1973. DDE-induced eggshell thinning: Structural and physiological effects in three species.
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From page 372... ...
Persistence of organic chemicals in their original form, or as toxic metabolites, is now routinely measured as an indicator of likelihood of ecological effects. Bioaccumulation of lipid-soluble chemicals to 104 or 1Os times the concentrations present in the physical environment is now expected as a normal part of food-chain
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From page 373... ...
Nonetheless, the major lesson of the DDT story would be lost if it did not heighten our awareness of the current state of ignorance about important processes that affect the responses of individual organisms, populations, and ecological communities to toxic materials introduced into the environment. The real basis for banning of DDT was its ecological effects, rather than its effects on human health.
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From page 374... ...
374 of the interplay between laboratory analyses, field tests, and conceptual developments in both ecology and toxicology. The constraints imposed by the state of both sciences are clear in retrospect.
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