ENVIRONMENTAL RISK FROM DISSOLVED IVERMECTIN TO MARINE ORGANISMS

Ivermectin (22,23-dihydroavermectin B1) has been proposed as a chemoth erapeutant for the treatment of farmed salmon infected with sea lice. The present study investigated the acute toxicity of dissolved ivermec tin to the mysid shrimp Neomysis integer, a non-target crustacean foun d in Scottish coastal waters, and also the ability of the mussel, Myti lus edulis, to bioaccumulate ivermectin from solution, and the subsequ ent depuration rate. The 96 h LC50 of ivermectin to N. integer was 70 ng l(-1), with 95% confidence Limits of 44 ng l(-1) and 96 ng l(-1). T he mussels bioconcentrated ivermectin from water at 6900 ng(-1) for 6 days by a factor of 750 (confidence limits 720-790), and showed estima ted depuration half-times of 22 days, or 235 degree days. An initial a ssessment of the potential risk to the marine environment from dissolv ed ivermectin from use on fish farms indicates that ratios of the Pred icted Environmental Concentrations to the Predicted No Effect Concentr ations (PEC/PNEC) are small (0.02-5.10(-6)) and acute direct toxic eff ects are unlikely. Mussels in the vicinity of fish farms are unlikely to accumulate detectable concentrations of ivermectin. (C) 1997 Publis hed by Elsevier Science Ltd.