Ecological Risk Assessment Of Organochlorine Pesticides In Daling River Basin

Organochlorine Pesticides(OCPs),such as Dichlorodiphenyltrichloroethanes(DDTs)and Hexachlorocyclohexanes(HCHs),have been widely used in China since the 1980s.Because OCPs are of easy accumulation,difficult degradation and high toxicity,they will still have sustained and long-lasting effects on the ecosystem although they have been banned for use.Therefore,the ecological risk assessment of OCPs is of great significance in the field of environmental contamination control.In addition,microorganisms have an important role in maintaining the balance of ecological systems.Moreover,the microbial community structure,as a sensitive bioindicators,can be used to reflect the change of environmental factors,such as pollutions,etc.,in some extent.In this paper,the ecological risk of OCPs in water and sediment of Daling River was studied,and the association between microbial diversity and microbial community structure was analyzed to investigate the relationship between microbial community structure and pesticide pollution.Firstly,the ecological risk of representative OCPs in the Daling River Basin,HCHs and DDTs,were evaluated.The species sensitivity curves of HCHs and DDTs were constructed by the method of species sensitivity distribution(SSD),their corresponding Hazard Concentration of 5%(HCs)and predicted no-effect concentration(PNEC)in water were calculated,and then the PNEC in sediments were deduced by TGD formulated by EU.The results showed that the contents of HCHs and DDTs in surface sediments were in accordance with environmental standards.The risk quotient of HCHs in surface sediment samples was higher than that of DDTs,suggesting that HCHs were the major pollutants in the surface sediments.Secondly,the relationship between microbial community structure and ecological risk of OCPs was analyzed to explore whether microbial diversity could reflect ecological risk.The Shannon Index and Simpson Index were used to characterize the microbial community diversity of the sediment samples.The ecological risk of OCPs in the sediment samples was calculated by using the constructed SSD curve.The results showed that ?-HCH(P<0.01)and HCH(P<0.05)were significantly correlated with microbial diversity in surface sediments,indicating that the main OCPs affecting the microbial community structure in surface sediments are y-HCH and HCH,which is consistent with the previous studies;In sediment samples,OCPs is significantly correlated with DDT(P<0.05),suggesting that DDT was the most important factor influencing the microbial community structure in sediments at different ages.It can be seen that the OCPs risk can be reflected by the changes of microbial diversity.Finally,the specific ecological effects of OCPs on microbial community change were studied to find the key microorganisms.Based on the high-throughput sequencing data,the Analysis of Variance(ANOVA)method was used to calculate the differential microorganisms among the samples at the genus level.It was found that in the surface sediment samples,the microbes that were significantly associated with the risk of pesticides were Clostridium,Flavobacterium,Proteobacteria and Bacillus.In the sedimentary column samples,the microbes associated with pesticide risk were Clostridium,Flavobacterium,and Proteobacteria.These microbes may be potential indicator of ecological risk of pesticide contamination.In summary,the ecological risks of OCPs can cause the changes of microbial diversity,while some key microbial changes can also reflect the ecological risk of OCPs to some extent,and further,these microbes can be regarded as the potential indicators of pesticide contamination.