What evidence is there that environmental contaminants are causing endocrine disruption in humans or wildlife?
Recent studies of wildlife, including alligators, birds, and fish, have investigated the relationship between chemical exposure and reproductive problems. Many of these studies have shown that exposure to high doses can result in malformed reproductive organs, consistent with sex hormone imbalance at a critical stage of fetal development. Studies where very high doses of dioxin were fed directly to pregnant rats show effects on sexual development, sperm production, and sexual behavior in male pups. Directly feeding very high doses of DDT to rats has also shown adverse effects on sexual development. The dramatic results of these high dose studies has lead to speculation by toxicologists that the risk to reproductive success, associated with exposure to much lower levels of some chemicals in the environment, may be unacceptable. In humans, a recent epidemiology study suggesting that sperm counts have declined by almost 50% over the past 50 years, and that this decline is associated with
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