The Migration Of Chlorpyrifos In The Purple Soil By Soil Column Experiments

Chlorpyrifos has been widely used and recognized as a highly efficient insecticide; however, its toxicity may pose threats to human health, soil and water quality and ecologic safety and therefore attracts increasing attention. Chlorpyrifos is moderately toxic to human and is very toxic for aquaculture (e.g., fish). In 2000, the US EPA banned the use of chlorpyrifos for use in homes and home gardens. Chloripyrifos is one of the pesticides that are most frequently detected in surface waters. In china, chlorpyrifos is a widely used pesticide for agriculture. There is clearly an urgent need to elucidate the migration behavior of chlorpyrifos in soil. To the best of our knowledge, there have been no reports about transport of chlorpyrifos in the purple soil. The present study covers the following three aspects:1. Establishing the method for detecting chlorpyrifos in water samples using the ultrasound-assisted solvent extraction combined with GC.2. Exploring the feasibility of using the flow equilibration soil column experimental set for investigating the migration of chlorpyrifos, with emphasis on the impact of sterilization.3. Revealing the migration characteristics of chlorpyrifos in different purple soils by soil column experiments.The major conclusions are as follows:1. An improved method based on ultrasound-assisted solvent extraction and gas chromatography-mass spectrometry has been established in this study for detecting chlorpyrifos in water samples. Several factors that potentially affect the extraction efficiency, including the ultrasonic time, ultrasonic power, volume of petroleum ether, extraction times and the sample volume, were investigated. The extraction procedure and GC/MS conditions/settings were optimized. Experimental results using the optimized method showed that the linear range was 0.1～50μg·L-1 with the detection limit (S/N=3) being 0.019μg·L-1, and the relative standard deviation (RSD) at three spiked levels of chlopyrifos was 1.85%～4.67%. The recovery of chlorpyrifos added to three types of water samples ranged from 85.6% to 103.7%.2. This experiment focuses on the impact of sterilization on migration of different concentrations of chlorpyrifos in soil column. It was observed that sterilization treatment using a autoclave led to remarkable increases in concentration of chlorpyrifos in the outflow of soil column. The microbial degradation rate of chlorpyrifos in the soil exhibited a dynamic trend over time and the sterilization effect on the experimental results was greater at low concentrations. The results showed that the pseudo-partition-coefficient Kd was 18.84 L·kg-1 for the unsterilized soil, as compared to the sterilized soil (10.93 L·kg-1). This indicates that microbial degradation of chlorpyrifos in soil cannot be ignored, whose effects could be eliminated by sterilization treatment.3. On the basis of the report 1 and 2, the migration of chlorpyrifos in three kinds of purple soils column were studied using flow equilibration soil column experimental set. By excluding microbial degradation effects and neglecting hydrolysis and photolysis processes, the adsorption is considered to play the dominant role in migration of chlorpyrifos in soil. The adsorption kinetics and sorption isotherms of chlorpyrifos were examined and the final concentration of chlorpyrifos retained in soil column after completing the column transport experiment was analyzed according to the USEPA standard method. The results showed that the adsorption kinetics is inconsistent at different concentrations of chlorpyrifos. Neither the Pseudo-first-order kinetic model nor the Pseudo-second-order kinetic model can fit well to describe the adsorption behavior of chlorpyrifos at low concentrations, while the adsorption kinetics was fitted satisfactorily using the Pseudo-second-order kinetic model at high concentrations. Moreover, Freundlich and Linear isotherm were found capable of well describing the adsorption process. And the Kd value of soil I (10.93 L·kg-1) was found to be the lower than soilⅠ(15.01 L·kg-1) and soilⅡ(15.83 L·kg-1), which can be explained by the lower organic matter concentration in soilⅠcompared to soilⅡandⅢ. This is in accordance with the previous studies which reveal that soil organic matter is a major factor governing sorption of chlorpyrifos in soil.