Concentration of 22,23-dihydroavermectin B1a detected in the sediments at an Atlantic salmon farm using orally administered ivermectin to control sea-lice infestation.

摘要

An HPLC analytical method based on a methanol extraction, C8 clean-up, derivatization using trifluoroacetic acid anhydride and reverse-phase HPLC was developed for the detection of 22,23-dihydroavermectin B1a (H2B1a) in marine sediment. The limit ofquantitation was determined 0.93 ng H2B1a per gram of sediment. This method was used to determine the concentrations of H2B1a in sediments from a fish farm where ivermectin had been administered orally at 0.05 mg/kg twice weekly, to control sea-lice infestation in 350thin000 post-smolt Atlantic salmon. Before sampling, 23 g of ivermectin were administered during the current production cycle. The mean concentration of H2B1a detected in the 6 sediment cores taken directly under the cage block was 5.0 ng/g in the top 3 cm, 3.1 ng/g in the 3-6 cm fraction and 0.7 ng/g in the 6-9 cm fraction. Concentrations were under the limit of quantitation at depths below 9 cm in all cores taken from directly under the cage block. H2B1a was not detected in any samplestaken further than 22.5 m from the cage block in the eastern, western and southern directions. To the north of the cage block, H2B1a was detected in samples taken 31 m from the cage block and the limit of distribution in this direction was not established.