M9 PM Multiple Stressors in Amphibian and Reptile Ecotoxicology
Monday, 14 November 2005: 1:50 PM - 5:30 PM in 339-340

(SPA-1117-745051) Effects of ultra low concentrations of endosulfan on California amphibians.

Hunt, J.¹, Sparling, D.¹, ¹ Southern Illinois University, Carbondale, IL, USA

ABSTRACT- Several species of amphibians are declining in the Sierra Nevada Mountains of California. To date the most important factors resulting in these declines are pesticides that are aerially deposited from the Central Valley and introduced predators including trout and bullfrogs. The pesticides that are used in the greatest quantities in the Central Valley include chlorpyrifos, endosulfan, diazinon, and malathion. Of these, endosulfan is the most toxic. In a previous laboratory study we showed that concentrations in water as low as 0.8 ppb killed over 80% of foothills yellow-legged frog (Rana boylii) larvae before they could metamorphose. The more abundant Pacific treefrog (Pseudacris regilla) were more tolerant to endosulfan and both species were more tolerant to chlorpyrifos than they were to endosulfan. This study continues the low concentration exposure of endosulfan to R. boylii, and P. regilla. In a laboratory study from early stage larvae through metamorphosis both species were exposed to endosulfan concentrations ranging from 0.005 ppb to 15 ppb. At the time of this abstract, mortality in both R. boylii and P. regilla was similar to the previous study at concentrations > 0.8 ppb. At lower concentrations mortality is reduced but present and tadpoles appear hyperexcitable. Early results suggest a hometic effect evidenced by rapid development and metamorphosis at low endosulfan concentrations compared to controls. However, tadpoles that metamorphose early may be at a disadvantage because they are significantly smaller than those metamorphosing later.

Key words: endosulfan, Rana boylii , Pseudacris regilla, California amphibians