Emergent disease or compromised immunity: Pesticides as immuno-suppressants in amphibians

The popular herbicide, atrazine, is a potent endocrine disruptor that de-masculinizes and feminizes exposed amphibians, by reducing androgens and increasing estrogen production. This effect is not unique to amphibians, but has been demonstrated in fish, reptiles, and mammals (including laboratory rodents and humans cell lines) as well. In addition, several independent studies in amphibians and laboratory rodents have demonstrated now that atrazine also increases stress hormone (glucocorticoid) synthesis and secretion as well.  Furthermore, when combined with other commonly applied pesticides, the effects of atrazine are magnified. Exposed larvae suffer from retarded growth and development and immuno-suppression resulting in increased disease contraction and increased mortality. These effects have been demonstrated in both the laboratory and in the field: Tadpoles downstream of agriculture show retarded growth and development and suffer high mortality rates in response to pathogens relative to tadpoles upstream of agriculture. These effects indicate that pesticide contamination may play a critical role in amphibian declines even in localities and incidences where population declines appear to be due to other causes such as disease.