农田土壤中农药的环境行为浓度预测

Concentration Prediction of Pesticides with Different Transformation Fate in Agricultural Soil Environment

根据农药的理化参数和环境参数预测农药在田间土壤中的分布浓度是进行农药管理的重要手段。以Freundlich等式衍化出来的线性吸附曲线X=Kf×C和农药指数降解动力学C(t)=C0×exp(-kt)为基础,根据农药有机碳吸附常数(Koc)、辛醇/水比常数(Kow)、半衰期(DT50)等重要参数和土壤理化性质参数,建立了一段时间后田间土壤中农药的残留浓度、渗漏在地下水中的浓度、蒸发在空气中浓度和吸收在植物体内的浓度的预测方法,为农药管理、使用和风险评价提供了一种工具,以降低农药污染。该方法被应用于预测42种喷雾用杀菌剂和7种土壤施用杀菌剂的环境浓度。结果表明,喷雾施用丙森锌渗漏在地下水中的浓度最高,超过欧盟标准0.1μg·L-1两倍多;土壤残留浓度较大的为硫酸铜(0.039mg·kg-1)、多菌灵(0.023mg·kg-1)和甲霜灵(0.24mg·kg-1)。土壤施用90d后,噁霉灵渗漏在地下水中的浓度约为1.11μg·L-1,五氯硝基苯土壤中残留浓度更是达到1.78mg·kg-1。浓度预测结果可以与毒理学数据相结合用于农药风险评价。

Excessive or improper use of pesticides will bring pollutions into the environment. Prediction of pesticides concentration is an important instrument to manage pesticide use. In this study, based on pesticide parameters and soil parameters, a method was used to estimate the concentrations of pesticides that persist in soil, leach into groundwater, volatilize into air and enter to plant tissues. After depositing and being incorporated into the field soil, the pesticide was bound to soil solids following linear absorption kinetics X = Kf×C or dissolved in the soil water, Kf being the function of Kow （organic carbon-water partition coefficient）. Degradation by biological activities occurred to absorp- tive pesticide and followed exponential kinetics C（t） = C0 ×exp（-kt）, in which the degradation rate k was affected by reciprocal of pesticide dissipation haft-life （DT50） in the field. However, pesticide potential of leaching into groundwater relied on the soil property and soil water flux （q）, by which the leaching concentration was calculated. The volatilization of pesticide with high vapor pressure from soil into air depended on pesticide Henry＇ s law constant（HENRY）or air-water partition coefficient（Kair-water）. We estimated pesticide concentration in plant tissues uptake from soil through transpiration stream concentration factor（TSCF）, the ratio between the concentration in the transpiration stream and the concentration in soil water. According to the calibration equations developed, the environmental concentrations of 42 spray and 7 soil-applied fungicides were predicted with their scientific default parameters being used. The results showed that after spraying, propineb concentration in groundwater was two times higher than 0.1 μg·L^-1. Copper sulfate, carbendazim and metalaxyl had greater residual concentration in soil than other fungicides. If mixed with soil, hymexazol concentration in groundwater was 1.11μg· L^-1 and quintozene in soil was 1.78 mg·kg^-1 after 90 days. The prediction results could serve the management and use of pesticides and be helpful for developing pesti- cide risk assessment if combined with toxicity studies.