Lethal and sublethal effects of atrazine, carbaryl, endosulfan, and octylphenol on the streamside salamander (Ambystoma barbouri)

Agricultural contaminants may be contributing to worldwide amphibian declines, but little is known about which agrichemicals pose the greatest threat to particular species. One reason for this is that tests of multiple contaminants under ecologically relevant conditions are rarely conducted concurrently. In this study, we examined the effects of 37-d exposure to the agrichemicals atrazine (4, 40, and 400 μg/L), carbaryl (0.5, 5, and 50 μg/L), endosulfan (0.1, 1, and 10 μg/L for 31 d and 0.1, 10, and 100 μg/ L for the last 6 d), and octylphenol (5, 50, and 500 μg/L) and to a solvent control on streamside salamanders (Ambystoma barbouri) in the presence and absence of food. We found that none of the agrichemicals significantly affected embryo survival, but that hatching was delayed by the highest concentration of octylphenol. In contrast to embryos, larval survival was reduced by the highest concentrations of carbaryl, endosulfan, and octylphenol. Growth rates were lower in the highest concentrations of endosulfan and octylphenol than in all other treatments, and the highest concentration of endosulfan caused respiratory distress. Significantly more carbaryl, endosulfan, and octylphenol tanks had larvae with limb deformities than did control tanks. Refuge use was independent of chemical exposure, but 10 μg/L of endosulfan and 500 μg/L of octylphenol decreased larval activity. Systematically tapping tanks caused a greater activity increase in larvae exposed to 400 μg/L of atrazine and 10 μg/L of endosulfan relative to solvent controls, suggesting underlying nervous system malfunction. Hunger stimulated a decrease in refuge use and an increase in activity, but this response was least pronounced in larvae exposed to the highest concentration of any of the four agrichemicals, possibly because these larvae were the most lethargic. More studies are needed that concurrently examine the effect of multiple contaminants on amphibians so we can better identify effective mitigating measures.