W8 AM Agrochemicals and Pesticides
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in 337-338

(HAY-1117-858545) Atrazine and Pesticide Mixtures: Sum of the Parts or Some of the Parts?

Hayes, T¹, ¹ LISAB, Dept. Integrative Biology, University of California, Berkeley, CA, USA

ABSTRACT- Atrazine (used in corn production) is a potent endocrine disruptor that chemically castrates and feminizes exposed male amphibians. Despite laboratory evidence, however, the impact of atrazine in wild populations remains to be firmly demonstrated. We used a combination of laboratory and field-based studies to address this question. Leopard frogs (Rana pipiens) in contaminated areas in the US that show high frequencies of feminized males (e.g. males that produce testicular oocytes), do not develop oocytes in a clean laboratory environment. This finding suggests that feminization is not "normal", but rather environmentally induced. In almost all study cites, however, atrazine is not the only pesticide present (although it is the most prevalent and most frequently detected). We examined the effects of other pesticides detected by analyes and/or reportedly used, however, and showed that only atrazine produced effects on the gonads. Furthermore, in an ongoing study, we examined a site in Wyoming where 92% of the male population displayed testicular oocytes and only atrazine was detected (year, 2001). In subsequent years, atrazine was not detectable and the percent of males producing testicular oocytes was reduced to 8%. Thus, experimental, spacial, and temporal data suggest that atrazine is an important cause of testicular oogenesis in amphibians. The overall importance of atrazine as an impairment of amphibian health is more difficult to assess otherwise, because most environs are contaminated with multiple pesticides. Furthermore, laboratory amphibians exposed to pesticide mixtures typical for corn production show a variety of adverse effects in addition to abnormal sex development. Effects include growth inhibition, retarded development and delayed metamorphosis, neurotoxicity, and immuno-suppression (leading to death by invasion of otherwise non-virulent organisms). Ongoing studies demonstrate that some of these effects are caused by single "actor" pesticides in the mixture (e.g. pyrethroids cause neurotoxicity, some fungicides are immuno-suppressive, and atrazine is a chemical castrant) that are enhanced by the accompanying "effectors". Other effects (e.g. immuno-suppression via elevation of corticoids) appear to be caused by the contributing effects of the total mixture of compounds.

Key words: atrazine, endocrine, disruptor, amphibian