Research On The Effect Of Carbonous Materials On The Bioavailability Of Sediment-associated Pyrethroids

Pyrethroids in sediment of aquaculture zone have attracted more and more attention due to their threat to the quality of aquatic products and human health,which is caused by long-term usage in large dose.Organic carbon(OC),especially black carbon(BC)dominates the sorption and desorption of hydrophobic organic contaminants(HOCs)in sediments and affects the bioavailability of HOCs to some extent.In the present study,the effect of carbonous materials(peat soils,biochar,charcoal and activated carbon)on the bioavailability of pyrethroids has been investigated via two chemical techniques: solid phase micro-extraction with polydimethylsiloxane(PDMS)and desorption kinetics using Tenax.The correlation between chemical techniques and organisms was calibrated on the basis of the economic benthic animal Venerupis philippinarum.The results showed that:(1)Based the previous experimental work of our laboratory,the determined methods were improved for lamba-cyhalothrin,bifenthrin,permethrin and fenpropathrin in sediments and organisms.The method was described for measuring pyrethroids in sediments as follows.The four pyrethroids of sediment samples were extracted used microwave extraction,solvent extraction were 15 m L acetone /exane(V/ V=1:1)mixture,temperature is 80?,time is 40 min,and power is 1600 W.The cleanup of extracts was performed using dual-layer GCB/PSA SPE cartridges and the elution of hexane/ dichloromethane(V/V=7:3)mixture with 7mL.The method was described for measuring pyrethroids in organisms as follows.The four pyrethroids of organisms samples were extracted as described above.The methods of dislodging fat,cleaning up and analyzing was identify with the previous experimental work.The percent recoveries was over 70%,and the relative standard deviation was under 15% in sediment and biological sample,which were used for detecting pyrethroid pesticides in real sediment and biological sample.(2)The bioaccumulation results demonstrated that carbonaceous materials amendment can greatly reduce the residues of pyrethroids in Venerupis philippinarum.There were significant negative correlations between the residues of pyrethroids and the carbon level in sediments and four materials displayed a similar sequestration capacity except peat soils.Because charcoal,biochar and activated carbon represent combustion/pyrolysis products(BC)while peat soils would be classified as humic substances and the sorption of HOCs to humic substances is weaker than to combustion/pyrolysis products.However,because of the large molecular sizes and the nonplanar structure of pyrethroids,three BC materials had similar inhibitory effect on the pyrethroids uptake in spite of different microporosity.Bio-sediment accumulation factor(BSAFobs)of four pyrethroid pesticides in venerupis philippinaram was 0.03~0.14.The bioaccumulation model OMEGA was introduced to simply predict the accumulation of pyrethroids in the different sediments.BSAFpre without BC correction of pyrethroids are between 0.056 and 0.17.BSAFpre corrected with OC and BC sorption of pyrethroids are between 0.03 and 0.12.The predicted BSAF values only based on OC fraction were always higher than our experimental values and estimations with BC modification(3)The freely dissolved concentrations of the four pyrethroid pesticides in carbonous materials amended sediment pore water were measured in this study based on negligible depletion solid-phase microextraction using the polymer of polydimethylsiloxane(PDMS).The results showed that the effect of carbonous materials on the freely dissolved concentrations(Cfree)had similar tendency with which on the residues in the organisms.However,the BSAFobs are reduced by one order of magnitude compared to the PDMS-Solids Accumulation Factors(PSAF)of the four pyrethroids in the sediments,which might be related to the strong biotransformational ability of pyrethroids in V.philippinaram.In spite of this,PDMS still have the potential for directly quantifying the bioaccumulation of sediments contaminants,it can link chemical burdens in sediment to the residues in benthic organisms.The theoretically uniform Klip-PDMS value is 0.03 for the pyrethroids.The predicted equilibrium concentration Cb,lip was compared with real concentration Cb,lip to demonstrate the feasibility and accuracy of this method.Except for which was impacted by the sediments with 5% biochar amendment,the measured Cb,lip deviated by less than a factor of 4 from the predicted data.The results demonstrated that PDMS-based passive sampling basically provides a satisfactory quantitative estimation of contaminants toxicity in sediments with varying compositions but a large amendment of BC might make the method instability.(4)Tenax desorption kinetics of four pyrethroids were analyzed,meanwhile results based on Tenax extraction were applied to predict the bioaccumulation of pyrethroids in V.philippinaram.The results showed that the carbonous materials can reduce the fraction of rapid desorption(Frap)and improve the fraction of very slow desorption(Fvs)of pyrethroids in sediment,which indicated the bioavailability of sediment-associated pyrethroids was reduced.Significant correlations were observed between Tenax 6h and 24 h and the Frap of pyrethroids(P<0.0001)in sediment,which indicated that the single time-point Tenax 6h or 24 h instead of the whole desorption kinetics can be used to evaluate the bioavailability of sediment-associated pyrethroids.Siginificant correlation existed between Frap and the body residual of pyrethroids in V.philippinarum(R2=0.38,P<0.0001),which indicated that Tenax extraction also can predict the concentrations of prethroids in benthic organisms in complex matrix.In conclusion,the bioavailability of pyrethroids was significantly reduced when the sediment was amended with carbonous materials.Bioaccumulation model OMEGA,PDMS and Tenax could all evaluate the bioavailability of pyrethroids in the sediments with different physicochemical properties.Therefore,this study not only simplifies the evaluation process of the breeding sediment pollution and bioaccumulation but also contributes to the migration,transformation and bioavailability of HOCs in sediment.In parallel,to provide the theoretical basis for the environmental management,optimization,quality standards and restoration in contaminated sediment,as well as provide an early warning for the quality and safety risks associated with consumption of aquatic products.