How does DDT affect the Earth?
DDT is a persistent organic pollutant with a half life of between 2-15 years, and is immobile in most soils. Its half life is 56 days in lake water and approximately 28 days in river water. Routes of loss and degradation include runoff, volatilization, photolysis and biodegradation (aerobic and anaerobic). These processes generally occur slowly. Breakdown products in the soil environment are DDE (1,1-dichloro-2,2-bis(p-dichlorodiphenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane), which are also highly persistent and have similar chemical and physical properties. These products together are known as total DDT. DDT and its metabolic products DDE and DDD magnify through the food chain, with apex predators such as raptors having a higher concentration of the chemicals (stored mainly in body fat) than other animals sharing the same environment. In the United States, human blood and fat tissue samples collected in the early 1970s showed detectable levels in all samples. A later study of blood samples collected in the later half of the 1970s (after the U.S. DDT ban) showed that blood levels were declining further, but DDT or metabolites were still seen in a very high proportion of the samples. Biomonitoring conducted by the CDC as recently as 2002 shows that more than half of subjects tested had detectable levels of DDT or metabolites in their blood, and of the 700+ milk samples tested by the USDA in 2005, 85% had detectable levels of DDE. DDT is a toxicant across a certain range of phyla. In particular, DDT has been cited as a major reason for the decline of the bald eagle in the 1950s and 1960s as well as the peregrine falcon. DDT and its breakdown products are toxic to embryos and can disrupt calcium absorption thereby impairing egg-shell quality. Studies in the 1960s and 1970s failed to find a mechanism for the hypothesized thinning,however more recent studies in the 1990s and 2000s have laid the blame at the feet of DDE, but not all experts accept those claims. Some studies have shown that although DDE levels have fallen dramatically that eggshell thinness remains 10-12 percent thinner than pre-DDT thicknesses.In general, however, DDT in small quantities has very little effect on birds; its primary metabolite, DDE, has a much greater effect. DDT is also highly toxic to aquatic life, including crayfish, daphnids, sea shrimp and many species of fish. DDT may be moderately toxic to some amphibian species, especially in the larval stages. In addition to acute toxic effects, DDT may bioaccumulate significantly in fish and other aquatic species, leading to long-term exposure to high concentrations. http://www.answers.com/topic/ddt?cat=health