Environmental risk of ivermectin to sediment dwelling organisms

Ivermectin (22,23-dihydroavermectin B1) has been proposed as a feed additive to alleviate sea lice infestation of farmed salmon. The present study investigated the acute toxicity of ivermectin in sediment to two sediment-dwelling organisms, the amphipod, Corophium volutator and the starfish, Asterias rubens. The degradation of ivermectin in sediment was studied over a three-month period, by chemical measurements and observation of changes in toxicity of the contaminated sediment with time to C. volutator in whole sediment bioassays. The 10 day LC50s of ivermectin to C. volutator and A, rubens were 0.18 mg kg(-1) and 23.6 mg kg(-1), respectively. The estimated NOECs of ivermectin for mortality to C. volutator and A. rubens were 0.05 mg kg(-1) and 5 mg kg(-1), respectively. The lowest observed concentration which had a sublethal effect (LOEC) on the ability of A. rubens to turn themselves over after the 10-day test was 20 mg kg(-1). Measured concentrations of ivermectin in the sediment, and the decrease in toxicity, indicated that the half-life of ivermectin in marine sediments is greater than 100 days. An initial assessment of the potential risk to the marine environment from sediment-associated ivermectin indicated that there may be significant risk to infaunal polychaetes in sediment immediately below and around the fish cages. Crown Copyright (C) 1998 Elsevier Science B.V. All rights reserved.