Identification Of High-Risk Pesticides In Water Of Liangzi Lake And Their Ecological Risks

Freshwater ecosystem is seriously threatened in terms of losses in ecosystem services and species extinctions during recent years.Previous studies reported that the contamination of pesticides was recognized as a major stressor in fresh water ecosystems.In freshwater ecocsystems,the effective methods for identifying regional high-risk pesticides are still lacking,and the reports illustrate the adverse effects of pesticides on aquatic biota under natural condition are rare.Previous field survey by our laboratory found that the contamination of pesticides in Liangzi Lake might induce a population decline of zooplankton.Therefore,a target and suspect screening method for the identification of high-risk pesicides in the water of Liangzi Lake was established based on the toxic effects of zooplankton（Daphnia magna）combined with instrumental analysis.The list of high-risk pesticides in water of Liangzi Lake was constructed.On the basis,the key toxic pesticides that led to the decline of zooplankton density in Liangzi Lake were identified,and we further explored pollution status of high-risk pesticides in surface sediments and aquatic organisms of Liangzi Lake,revealed the aquatic ecological and health risks of pesticide pollution in Liangzi Lake.This study will give a valuable theoretical and methodological support for identification of high-risk pestcides in freshwater ecosystems,and provide scientific basis for standardized use and management of pesticides in Liangzi Lake.The main conclusion are as follows:1.Three toxic water extracts were identified according to the 48 h acute toxicity test of D.magna using the water extracts from 14 sampling sites in Liangzi Lake.The list of 29 high-risk pesticides was established by screening the 2119 suspect pesticides and target analysis of 64 pesticides.The sum of toxic units of high-risk pesticides in three toxic water extracts was higher than that of other extracts and was exceeded the risk threshold,indicating that the contamination of the pesticides in three toxic water extracts had sufficient toxicity potency to cause the acute toxicity of D.magna.Finally,the results of acute toxicity validation for toxic pesticides in D.magna showed that the high-risk pesticides（such as chlorpyrifos,cypermethrin）caused significantly survival inhibition in D.magna,high-risk pesticides in toxic water extracts explained about 70%of the toxicity potency,and confirming the reliability of high-risk pesticides screening in current study.2.Based on the established list of high-risk pesticides above,quantitative analysis for lake water of Liangzi Lake in summer and autumn was performed,and the chronic toxicity potency of high-risk pesticides in lake water was calculated.The results indicated that the∑TUs_-chronic of 7 sampling sites were exceeded the risk threshold among the 14 sampling sites of Liangzi Lake in summer,and the significantly negative correlation between the∑TUs_-chronic of pesticides and the density of zooplankton in 14sampling sites was confirmed.As well as the combination of 5 pesticides（chlorpyrifos,permethrin and cypermethrin and abamectin and dichlorvos）provided with 99.4%toxicity potency in 7 high-risks area of Liangzi lake.Among them,chlorpyrifos and cypermethrin might be the high-risk pesticides that induced the decline of zooplankton communities.Afterwards,the toxicity potency of pesticides was reduced to a safe range during the trough period of pesticide application,which was consistent with the results of the field survey.Furthermore,in order to confirm the key toxic pesticides in water of Liangzi Lake in summer,the 21 d chronic toxicity test of high-risk pesticides to D.magna was carried out,and the effects of pesticides on survival,growth,reproduction and behavior of D.magna at different life stage were evaluated.The results showed that chlorpyrifos and cypermethrin were two key toxic pesticides in Liangzi Lake in summer,which drove the decline of zooplankton abundance in Liangzi Lake by affecting the swimming behavior and reproductive ability.3.To investigate the ecological risks of high-risk pesticides to aquatic organisms in Liangzi Lake,we carried out the ecological risk assessment of pesticide pollution in the surface sediments of Liangzi Lake firstly.The results showed that the surface sediments of 14 sampling sites in Liangzi Lake were all in the medium-risk or above of pesticide pollution.Among them,five sites were at high risks which were distributed in the eastern and central region of Liangzi Lake.Furthermore,the pesticide pollution of aquatic organisms in the two lake areas was analyzed.The aquatic plants had relatively stronger capacity of enrichment for high-risk pesticides,and the average concentration of the pesticide enrichment in aquatic plant was 2.5 times to aquatic animal.The aquatic ecological risk of pesticide pollution was seriously in the middle of Liangzi Lake,and over 80%of aquatic animals were in the middle ecological risks or above of pesticide pollution,and the Bellamya aeruginosa,Macrobrachium nipponense and Culter alburnus were at the high-risk status of pesticide pollution.Moreover,two organophosphorus pesticides,dichlorvos and chlorpyrifos,were the major contributors that caused ecological risks in aquatic organisms and surface sediments.In addition,the health risk assessment results of aquatic organisms in Liangzi Lake showed that the contamination of pesticides in B.aeruginosa and M.nipponense in Liangzi Lake were confirmed to be a non-carcinogenic risk.