Effects of environmentally relevant concentrations of endosulfan, azinphosmethyl, and diazinon on Great Basin spadefoot ( Spea intermontana ) and Pacific treefrog ( Pseudacris regilla )

We conducted dose–response exposures to compare the lethality of endosulfan, diazinon, and azinphosmethyl in the early‐life stages of the Great Basin spadefoot ( Spea intermontana ) and the Pacific treefrog ( Pseudacris regilla ). Our experiment occurred in two 8‐d phases: one, with developing embryos, and two, with Gosner Stage 27 tadpoles. Pesticide concentrations were representative of field‐measured concentrations (60 ng/L of endosulfan, 50 ng/L of azinphosmethyl, and 350 ng/L of diazinon), in the same geographic areas where these species occur in British Columbia. Although the concentrations met the requirements for federal water quality guidelines, we observed mortalities, deformities, and other sublethal effects. Phase 1 consisted of exposing Gosner Stage 10 embryos in the pesticide solutions for a total of 8 d. Significant mortality of S. intermontana began posthatch in the highest lethal concentrations of the commercial formulations of endosulfan (Thiodan; LC20 8d  = 2,672.7 ng/L) and diazinon (LC20 8d >175,000 ng/L). Phase 2 compared behavior, morphology, and survival of captive‐reared tadpoles exposed to the same 8‐d experimental regime as the embryo experiment. Endosulfan induced significant effects on behavior and morphology of P. regilla and significantly reduced survivorship of S. intermontana (LC20 8d  = 77.1 ng/L). Abnormal behavior and excitability was observed in both species, with P. regilla tadpoles being more sensitive. At 60,000 ng/L endosulfan, P. regilla also lost pigmentation and exhibited abnormal tail morphology. Environ. Toxicol. Chem. 2010;29:1604–1612. © 2010 SETAC