Studies On Effects Of Avermectin B_1a On Soil Microorganisms And The Bioaccumulation And Elimination Of Avermectin B_1a In Earthworms (Eisenia Fetida)

Content: Avermectins (AVMs) belong to a group of compounds called macrocyclic lactones, which are natural products produced by the microorgamanism streptomyces avermitilis. In recent years the AVMs are used as a potent antiparasitic animal health drug in the treatment of parasitic infections for food producing animals. The AVMs are notable pesticides used in agriculture. In this paper, several studies were conducted to evaluate the ecotoxicity of AVM BU on earthworms (Eiseniafetida) and soil microorganisms.The influence of AVM B1a on microbiological population of bacteria and fungi in the soils that came from four different places is studied in this paper. The results show that the inhibition actions of AVM BU for population of bacteria in the soil come into being only under the case that the concentration of AVM B1a is higher than 83.3 mg.g-1. Effect of AVM B1a on the respiration of microbes in the soils for 24 hours has been studied using the method of direct absorption. The results demonstrated that AVM BU had significant inhibition effect on soil respiration in its higher concentrations. The acute toxicity tests of AVM BU on earthworms were performed using the filter paper contact test and artificial soil test. And the half lethal dosage (LD50) of AVM B1a is 4.63 ug.cm-2 (48h) and 24.13 mg.kg-1 (7d) and 17.06 mg.kg-1 (14d), respectively, for the filter paper test and artificial soil test. All above results suggested that the ecotoxicity of AVM B1a in the soil should be affected by the composition of the soil.A method of determination of AVM BU in earthworms was established by high-performance liquid chromatography (HPLC) with fluorescence detector. Homogenized earthworms sample was extracted by acetonitriie, and cleaned up on alumina B and C18 solid-phase cartridges, followed by derivatization with 1-methylimidazole (1-MIZ) and trifluoroacetic anhydride (TFAA), and analyzed by HPLC with fluorescence detector set at 365 nm excitation and 475 nm emission wavelengths. The average recovery of AVM B,.in earthworms was 104.8%, 86.6% and 83.0%, at the levels of 5 ng.g-1, 50 ng.g-1, 500 ng.g-1. The relative standard deviation (RSD) ranged from 2.99% to 7.34%. The limit of the detection is 0.5 ng.g-1.The rapid uptake of AVM BU was observed and steady-state levels were reached within 9-18 days. On the 18th day, the final concentrations of AVM BU in the earthworms were 106.86 ng.g-1 and 165.17 ng.g-1, respectively, in the low dose group and high dose group. Both of the AVM B1a concentrations in the earthworms are lower than that in the artificial soil. After 19-day elimination test, the concentrations of the AVM Bt. in the earthworms were 1.03 ng.g-1 and 2.36 ng.g-1, respectively, in the low dose group and high dose group. The test of bio-enrichment and elimination of AVM B1a in the earthworms showed that there are no significant enrichment ofAVM B1a, in earthworms, but the trace amount of AVM B1a can be found for a relative long time in earthworms.