Acute toxicity to zebrafish of two organophosphates and four pyrethroids and their binary mixtures.

BACKGROUND: Environmental pollutants, including metals, pesticides and other organics, pose serious risks to many aquatic organisms. The acute toxicities to zebrafish (Brachydanio rerio Hamilton & Buchanan) were determined for two organophosphorus insecticides, four pyrethroid insecticides and 50:50 binary mixtures.
RESULTS: At 24, 48, 72 and 96 h after treatment, LC(50) of permethrin, tetramethrin, bifenthrin, etofenprox, dichlorvos and phoxim to zebrafish were 0.0052-0.0025, 0.0782-0.0460, 0.0065-0.0032, 0.0969-0.0791, 51.3-13.0 and 1.28-0.469 mg L(-1) respectively. LC(50) of permethrin + dichlorvos, permethrin + phoxim, tetramethrin + dichlorvos, tetramethrin + phoxim, bifenthrin + dichlorvos, bifenthrin + phoxim, etofenprox + dichlorvos and etofenprox + phoxim were 0.0082-0.0046, 0.0078-0.0042, 0.264-0.124, 0.141-0.121, 0.0251-0.0154, 0.0154-0.0087, 0.396-0.217 and 0.213-0.0391 mg L(-1).
CONCLUSION: Toxicity levels of all pyrethroid insecticides to the zebrafish were high or very high. The organophosphate dichlorvos showed low toxicity, but phoxim showed high or intermediate toxicities to zebrafish, and the toxicities of binary mixtures of permethrin and dichlorvos or phoxim, bifenthrin and dichlorvos or phoxim and etofenprox and phoxim (48, 72 and 96 h exposure) were very high. The toxicities of binary mixtures of tetramethrin and dichlorvos or phoxim, etofenprox and dichlorvos and etofenprox and phoxim (24 h exposure) were high.