Study On Disstribution,Release Of OCPs And Environmental Risk Assessment Of Mixtures In Qingshitan Reservoir

As the largest reservoir in northern Guangxi,Qingshitan reservoir is drawing people's attention to the OCPs residues,which influence the irrigation,aquaculture,Lijiang River tourism recharge and drinking water sources in Guilin.In order to investigate distribution,release characteristics of OCPs in surface water and sediment/paddy soils,and the risks of OCPs mixtures to aquatic ecological environment,surface water samples,sediment samples,and paddy soil samples were collected.This research systematically studied the temporal and spatial distribution characteristics of OCPs in Qingshitan Reservoir,demonstrated the OCPs released to surface water from different types of substrate in Qingshitan Reservoir area,and made an aquatic ecological risk assessment of OCPs mixture to surface water of Qingshitan Reservoir.Results illustrated as follows:?1?15 kinds of OCPs in surface water of Qingshitan Reaervoir area with the detection rates of 30%¹00%.The residues of OCPs in the reservoir water,pond water,and stream water ranged 21.83¹48.89 ng/L,52.34²04.42 ng/L,and12.30⁸0.88 ng/L,respectively.Residual levels of OCPs in the surface water from Qingshitan Reservoir were present at moderate levels,compared with respective data,and lower than the limit specified in the Standards for Drinking Water Quality.The residual concentrations of OCPs in the surface water of Qingshitan Reservoir area have obvious seasonal fluctuations,showing the dry season is higher than the wet season.The concentration of OCPs in surface water of East Lake was significantly lower than that in West Lake,and the content of OCPs in the lake center was lower than that in the lakeside.The total OCPs residual concentration in reservoir,pond,stream sediments,and paddy soils ranged 19.42¹17.24 ng/g,40.55¹39.56 ng/g,23.49⁸8.65 ng/g,and 47.66¹18.09 ng/g respectively.Residual levels of OCPs in the sediments and paddy soils from Qingshitan Reservoir were present at moderate levels,compared with respective data,and lower than the limits specified of secondary standards in the Environmental Quality Standard for Soils.The OCPs residues in sediments and paddy soils showed obvious surface enrichment in summer,autumn and winter.A majority of the OCPs detected were HCHs,followed by heptachlor?heptachlor and heptachlor epoxide?and DDTs.The HCHs pollution in the reservoir area mainly comes from the application of lindane,and most of them belong to historical application residues;some DDTs are recently entered.?2?Many factors influence the OCPs that accumulated in sediment and paddy soils released to the overlying water,such as the physical and chemical properties of OCPs,the composition of the substrates,the disturbance of the substrate by external forces,etc.There is a clear difference between the rate and the detected concentration of different experimental device.High water solubility,low octanol-water partition coefficient,low content of clay and organic matter,and disturbance are more conducive to the migration of OCPs from substrates to the overlying water.Surfactants?SDS?have a significant solubilization effect on OCPs remaining in sediments and paddy soils,which increased the concentration of OCPs in overlying water of sediment and paddy soil by 134.44%and 118.41%respectively in stationary and disturbance groups.?3?Based on the acute toxicity data of single spacies to algae,crustaceans and fish,a risk quotient?RQ?of 15 organochlorine pesticide mixtures was predicted using the CA model.The sanples with RQ_STU>1 accounting for 43.98%of the total of 166samples at 22 sampling points,indicating OCPs mixtures pose a potential risk to the aquatic environment.The three trophic levels were sensitive to OCPs mixture in surface water as fish>crustaceans>algae.Methoxychlor and?-HCH are the most toxic compounds of the organochlorine pesticide mixture,and contribute at least 50%of the mixture toxicity in samples that RQ>1.