Environmental Effects

Although p,p-DDT is really the only component of DDT-R potent enough to be an insecticidal ingredient (as far as environmental effects are concerned), all the DDT-related compounds are presumed to be potentially toxic. Perhaps the best example of the extreme toxicity of DDE is its effects on bird reproduction. Because DDT is slowly converted into DDE in the environment over many years, environmental samples of DDT-R today are actually mostly DDE.

Another important compound is o,p'DDT, which is known to mimic the actions of estrogen in several vertebrate biological systems. The action of o,p'-DDT can be attributed to its ability to bind to the estrogen receptor as an agonist, like estrogen itself, and to activate estrogen signals in the organism. Interestingly, p,p'-DDE acts as an antagonist to the androgen receptor in males, thereby blocking male sex hormone signaling in many vertebrate species.

Of all the effects of DDT-related compounds on wildlife, the biological damage cited most frequently is that of eggshell thinning. This phenomenon was originally reported by Ratcliffe in 1967 and verified by Anderson and Hickey in

1976 in North America. In addition to DDT, both DDE and polychlorinated biphenyls also have deleterious effects on eggshell production. Eggs affected by these chemicals crack easily and contribute to the decline of vulnerable bird species.

Eggshell thinning is not the only harmful effect for which DDT-R has been implicated. DDT-R has also been shown to contribute to the increased mortality as well as myriad reproductive problems among a broad range of wildlife including birds, fish, and other aquatic organisms. Behavioral changes are also caused by exposure to DDT-R.

A current view among scientists is to interpret many of these effects as "endocrine disruptions" caused by the hydrocarbon pollutants, with DDT-R being one of the prominent study materials. Certainly, DDT-R, particularly o,p'-DDT, acts in an estrogen-like manner, whereas p,p'-DDE acts as an anti-androgen. Deleterious effects of such endocrine disruptions by DDT-R in birds are well documented. Because disruptions of endocrine actions, including those of some vitamins, are expected to cause serious effects on reproduction, development, and nutritional balance of animals, this topic is likely attract increased attention in the scientific community.

Despite the difficulty of conducting and evaluating environmental effects studies, evidence for the harmful biological effects of DDT on wildlife and ecosystems has been overwhelming. Clearly, the decision to ban the use of DDT was sound.

See Also the Following Articles

Insecticides • Integrated Pest Management • Pollution

Further Reading

Bradley, D. J. (1998). The particular and general issue of specificity and verticality in the history of malaria control. Parasitología (Rome) 40, 5—10. Fry, D. M. (1995). Reproductive effects in birds exposed to pesticides and industrial chemicals. Environ. Health Perspect. 103 (suppl. 7), 165—171. Matsumura, F. (1985). "Toxicology of Insecticides," 2nd ed, pp. 51—55.

Plenum Press, New York. Metcalf, R. M. (1955). "Organic Insecticides," pp. 127-180. Interscience, New York.

Peakall, D. (1970). Pesticides and the reproduction of birds. Sci. Am. 222, 72-78.

Peterle, T. J. (1991). "Wildlife Toxicology," pp. 157-172. Van Nostrand

Reinhold, New York. Ratcliffe, D. A. (1967). Decrease in eggshell weight in certain birds of prey. Nature 215, 208-210.

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