Study On Enantioselective Bioaccumulation, Degradation And Toxicity Effects Of Chiral Pesticides On Tubifex Tubifex

Pesticides play very important role in increasing crop production, however, tons of pesticides enter into the environment as contaminants and affect the ecosystem greatly. In the process of production or use, pesticides can entery into aquatic ecological system via direct spraying, rain wash and surface runoff, causing toxic effect on aquatic organisms. As we kown that almost25%current used pesticides were chiral, they have two or more enantiomers. Previous studies have shown that the enantiomers of a chiral pesticide have identical physical and chemical properties but they may perform different behavior in the processes of absorption, accumulation and degradation when confront with chrial environment. This makes it necessary to study the behavior of the enantiomers of chiral pesticides individually to understand the effects more comprehensively on the environmental safety and public health. As a typical aquatic benthic organism, Tubifex tubifex always be found in ecosystems contaminated by organic matter with a low level of oxygenation. These worms are very widely distributed and frequently dominant in freshwater benthic communities. They have an intimate contraction with the solid phase and the pore water of the sediment, burrowing the anterior part in the sediment and undulating the posterior part in the overlying water. Because of the endobenthic lifestyle and stress resistance, tubifex has been designated as a representative freshwater benthic infauna for aquatic system bioassays. In the present work, we study the differences in bioaccumulation and degradation behaviors of individual enantiomers of four chiral pesticides in tubifex. We also evaluated the effects of the tubifex on diffusion and degradation of pesticides. This is the first report about enantioselective behaviorof chiral pesticides in tubifex.Four chiral pesticides were studied in this work and the enantiomers of pesticides were separated on high-performance liquid chromatography (HPLC) or gas chromatography (GC) based on chiral stationary phases (CSP).The enantiomers concentrations of the selected chiral pesticides in tubifex, soil and water samples were analysed by solvent extraction and SPE clean-up. Tubifex worm were cultivated in two different contamination systems, including spiked water and spiked soil, to compare the influence of different uptake routes on bioaccumulations and excretions. In bioaccumulation experiments, the results indicated that tubifex can accumulate fipronil, isocarbophos (ICP), triadimefon (TF) and triadimenol (TN). However, diclofop-methyl (DM) was not detected in worm during the whole accumulation process. Furhter studies showed that DM can be rapidly hydrolysis to diclofop acid (DC), resulting only the metabolite DC was detected in tubifex. The bioaccumulations of fipronil, ICP, TF, TN and DC were enantioselective in tubifex tissue in spiked water treatments, with the concentration orders R-(-)-fipronil>S-(+)-fipronil,(-)-ICP>(+)-ICP,S-TF>R-TF,(1R,2S)-TN>(1S,2R)-TN>(1R,2R)-TN>(1S,2S)-TN, R-(-)-DC> S-(+)-DC. However, in the spiked soil treatments, enantioselective accumulations were not detected except for fipronil and TN. It was speculated that, there were different chiral selective factor in different uptake routes. The excretions of TF and TN in tubifex were also studied, the results showed that the excretion rate of TF was higher than that of TN, what’s more the excretion of the two fungicides were also enantioselective in spiked water treatment.Studies about the the effects of the tubifex on diffusion and degradation of pesticides showed that, with the presence of tubifex worms, higher concentrations of pesticides in overlying water and lower concentrations in soil were detected than that in the absence of tubifex treatment during the whole exposure period. This means that tubifex has positive functions in pesticides’ diffusion from bottom solid substrate to overlying water and in the degradation of the soil-associated pesticides. We also found that, the present of tubifex can accelerated the hydrolysis of DM and make the hydrolytic process have enantioselectivity. Further studies showed that DC enantiomers were configuration?lly stable in water, however the DM enantiomers experienced inversion of configuration in hydrolytic process.Crude enzyme was prepared using tubifex homogenates, and methods that determining the content of protein and MDA, the enzyme activities of CAT, GST and GR were developed. Changes in CAT and GR activities were tested by exposing tubifex to solutions rac-fipronil and its enantiomers, respectively. The results showed there’s no significant effect on the enzyme activities. Studies on the ICP and its enantiomers showed that, there’s no obvious dose-response relationship, but at the same concentration, there’s significant effect of ICP on the activities of CAT and GR and the toxic effects were enantioselective, following the order (+)-ICP> Rac-ICP≥(-)-ICP. ICP has no significant influence on the content of MDA. For TF experiment, the changes of CAT and GR activities showed a significant dose-response relationship with TF. Meanwhile, there’s a significant increase for the content of MDA, but TF performed no effect on the content of protein and activity of GST. For TN experiment, there’s a significant dose-response relationship between the fungicide and activities of CAT, GST and GR. There’s also a significant increase for the content of MDA, but the level was lower than that of TF. Changes on GR activity were not sifnifincant.