"Cocktail Effect" Of Typical Pesticides On Aquatic Organisms And Environmental Risk Assessment For Mixed Preparations

The environmental risk of pesticides those with single active ingredient has been widely evaluated,but the "cocktail" effects on aquatic organisms caused by the pesticide mixtures has been neglected and become a very common and hidden ecological problem.Focusing on the technical difficulties faced by pesticide environmental risk management in China,in this study,studies on the acute and chronic combined toxicity effects and risk assessment of typical mixed formulations on zebrafish and Daphnia magna were carried out,with the following results1.Acute half-lethal concentrations(LC50)on zebrafish of chlorpyrifos(DSP),beta-cypermethrin(GX)and the typical mixed formulation(12%emulsion)with these two active ingredients were:0.244 mg/L,0.0019 mg/L and 0.0040 mg/L,respectively,indicating that the joint effect of DSP and GX on fish maybe synergeous(the calculated model deviation rate(MDR)was 5.45);The observable effect concentrations(NOECs)of DSP and GX on zebrafish embryos and larvelfish were 0.0074 and 0.00043 mg/L(1/33 and 1/4 of their corresponding acute LC50),respectively.When the end point of acute toxic effect on fish was used to evaluate,the acute risk quotient(RQ)of DSP and GX to aquatic vertebrates was 1.06 and 17,respectively.When the synergistic effects of these two active ingredients were taken into account,RQ was 72.5,which is much higher than the RQ obtained by using the toxicity data of single active ingredients respectively2.When DSP and GX were exposed for 34 days at a lower concentration than their respective NOECs and were mixed at a ratio of 20:1,the NOEC was 0.00018 mg/L(0.00017 mg DSP/L+0.0000084 mg GX/L)for zebrafish embryos and larvel fish,also showing an obvious synergeous toxicity effect(MDR=21.6);When mixed with concentrations below or equivalent to their respective NOECs in a ratio of 3:1 to 13:1,the toxicity of mixtures on zebrafish larvae was comparable to that of each active ingredient alone;when they were mixed at ratios ranged from 3:1 to 13:1 and at concentrations lower than or equal to their respective NOECs,the mixtures showed additive combined effects;when they were mixed at concentrations higher than their NOECs,no obvious synergistic effect was found in the second high concentration group(DSP:GX=250:1),but a significant increase in the mortality rate of zebrafish juveniles(100%death)was found in the highest concentration group(DSP:GX=90:1).The predicted environmental time-weighted concentrations(PECtwa-21d)of DSP and GX was approximately 18:1 after 12%emulsion of DSP and GX be used on cotton according to GAP.If the endpoints of chronic toxic effects on fish of DSP and GX were used separately for risk assessment,RQ was 1.38 and 1.40,respectively,and if the synergistic toxic effects of the two active ingredients were taken into account,RQ was 60,which was much higher than the predicted chronic risk predicted using endpoints of single active ingredient.3.The chronic NOECs for reproductive effects of pymetrozine(PYT)and dinotefuran(FCA)on Daphnia magna after 21-day-exposure were 0.040 and 50 mg/L(1/24 and 1/5 of the acute half-effect concentrations(0.97 and 266 mg/L)),respectively.The NOECs of the mixture(PYT:FCA=4:1)on the reproduction yield of Daphnia magna was 10.04 mg/L(BYT 0.040 mg/L),showing an addition effect(MDR=0.83),consistent with the results of the acute toxicity study(MDR=0.94).It is shown that when evaluating the joint action mode between active ingredients,priority should be given to the results of studies from the same source and the same laboratory.4.Based on the above-mentioned research results,through the investigation of pesticide mixed toxicity data and relevant risk assessment methods at home and abroad,a framework and tierd method has been proposed for risk as sessment of pesticide mixtures on aquatic ecosystems in China.At the same time,the scientificity and feasibility of this framework(including pre-assessment,primary assessment and higher-tier assessment)has been verified by a case study using a wettable powder formulation of 60%pymetrozine and dinotefuran.The results showed that this tiered assessment system combining pre-assessment,primary assessment and advanced assessment allows for an efficient,rapid and targeted scientific assessment of the risks of mixing agents to aquatic ecosystemsIn this study,the acute and chronic toxic effects and risks of two groups of typical insecticide mixtures on fish and Daphnia magna were identified,and the key factors that should be considered in the risk prediction and evaluation of pesticide mixtures were revealed:the combined effecs of different components,the exposure concentration of each component,the concentration ratios and the influence with the changes of these ratios on the interactive effecs.On this basis,a framework has been proposed for risk assessment of pesticide mixtures on aquatic organisms,in order to provide technical support for the development and evaluation of "green" pesiticides and their reasonable usage in field.