The evidence for endocrine disruption in wildlife
During the 1970s and 1980s, biologists found alligators in Florida with reduced penis size and low fertility. About the same time Western gulls in the USA were found with abnormal mating behaviour and reproductive organs. These anomalies were linked to high levels of PCBs (polychlorinated biphenyls), DDT and dioxin in the local environment. Around the same time, reproductive abnormalities were found in fish living in British rivers close to sewage outfalls. Such findings stimulated ecotoxicologists to start looking closely at a range of xenobiotic chemicals and their possible endocrine-disrupting effects.
For example, atrazine is the most widely used herbicide in the world; 30 000 tons of it are sprayed onto farmland in the USA each year. It can be detected at quite high levels in streams and rivers that collect run-off from farmland and has been detected at high levels in rain. In a laboratory study, tadpoles of the African clawed frog (Xenopus laevis) were reared in water containing atrazine at concentrations similar to those found in natural water bodies in the USA. The tadpoles grew, developed and metamorphosed into frogs, at which point they were examined in detail. Many of them were hermaphrodites, meaning that their gonads (testes and ovaries) contained both egg- and sperm-producing tissues. Many of those that were unequivocally male had a poorly developed larynx, the means by which males produce mating calls. Males that were allowed to develop to adult age showed a ten-fold decrease in testosterone level compared with untreated males (Hayes et al., 2002a, b).