| Content : Avermectins are a class of drugs which have been found wide usage against a board spectrum of nematodes and arthropods, many of which are important endoparasites and ectoparasites of animals. Avermectin BI is a common agriculture pesticide produced by the actinomycete Streptomyces avermitilis and registered for worldwide use. It is effective in controlling different phytophagous pests of field crop, ornamentals, vegetables, fruits and in controlling fire ants. To assess the potential impact of avermectins on the environment, the bioaccumulation potential of avermectin B1a, its major component, in sturgeon (A.schrenckif) was examined.The method for determining avermectin BU (AVM) in freshwater by high-performance liquid chromatography with fluorescence detector was established. After an initial extraction with ethyl acetate, the upper organic phase was drained through a column of anhydrous sodium sulfate. The extracts and the column rinses were then evaporated to dryness. The cleaned-up samples by adding interior standard were derivatized with 1-methylimidazole (1-MIZ) and trifluoroacetic anhydride (TFAA), then 100 uL samples were analysed by HPLC with fluorescence detector. The excitation and emission wavelength were set at 365 and 475 nm and mobile phase was methanol and water (98:2, v/v).The limit of detection is 0.01 ng-mL'1.Recoveries of AVM in freshwater fortified at 1 ng-mL"1, 4 ng-mL"'> 7 ng-mL"' ranged from 80.5% to 89.1%, Relative standard deviation ranged from 4.0 % to 5.1%.The method for determining avermectin (AVM) in muscle of sturgeon (A.schrenckif) by high performance liquid chromatography with fluorescence detector was established. The homogenized muscle sample was extracted by acetonitrile, following centrifugation at 3000 g for 15 min. The supernatant was applied to an alumina B cartridge which had previously been activated by irrigation with acetonitrile (10 mL). The column rinses by adding interior standard were evaporated and were derivatived with 1-methylimidazole (1-MIZ) and trifluoroacetic anhydride (TFAA), then 100 uL sample was analysed by HPLC with fluorescence detector. The excitation and emission wavelength were set at 365 and 475 nm and mobile phase was methanol and water (97:3, v/v). The limit of detection is 0.2 ng-g-1.Recoveries of AVM in muscle of sturgeon fortified at 5 ng-g-1, 20 ng-g-1, 100 ng-g-1 ranged from 87.4 % to 93.9 %, Relative standard deviation ranged from 3.5 % to 5.3 %?A rapid uptake of avermectin B1a was observed and steady-state levels were reached within 14 to 18 days. Depuration of avermectin BIa residues in muscle of sturgeon was relatively rapid with more than 50% clearance occurring after about 4-6 days in control water. Greater than 95% of the tissue residues were eliminated from the exposed fishes after the 14 and 18 day depuration period. Bioconcentration factors and kinetic parameters for uptake and elimination are 42, 4.95 days, 5.91 days-1 and 0.14 days-1 for low level group; Bioconcentration factors and kinetic parameters for uptake and elimination are 41, 4.33 days-1, 6.53 days-1 and 0.16 days-1 for high level group.The low BCF of avermectin B1a is probably related to its molecular weight (872), with the large size acting as a steric barrier and preventing it from being a truly lipophilic molecule and inhibitingmembrane permeation and hence bioaccumulation. Compounds with BCF values < 100 are considered to be of little environmental concern and not expected to bioconcentrate into tissues. In this in vivo test, the low uptake of avermectin B1a and its low persistence in sturgeon muscle demonstrate that it will neither bioaccumulate in individual organisms nor biomagnify in the food chain .
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