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

Abstract

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.

Differential Uptake of Endosulfan in the South American Toad Under Sublethal Exposure

“…Bionda et al (2013) reported that amphibians in altered Argentinean agroecosystems had lower egg and larval survival compared with organisms from noncultivated area with population projections less favorable leading to extinction in crop-dominated areas. Several laboratory studies reported adverse effects of endosulfan on amphibian embryo-larval development, i.e., lethality in various species at environmentally relevant concentrations (Jones et al 2009;De Jong Westman et al 2010), delay to complete metamorphosis (Brunelli et al 2009), malformations of gills (Bernabó et al 2008), failures in the endocrine system (Goulet and Hontela 2003), and neurotoxic effects (Agostini et al 2009;Denoël et al 2013;Svartz et al 2014). However, most toxicity studies evaluate adverse effects under acute exposure condition only during certain periods of the life cycle.…”