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