The persistence, degradation, and mobility of metolachlor in soil and the fate of metolachlor and atrazine in surface water, surface water/sediment, and surface water/aquatic plant systems

摘要

Metolachlor and atrazine are two of the most widely used herbicides in the Midwest. Detection of pesticides in drinking water resources has increased interest in the environmental fate of these compounds in soil, surface water, and groundwater. The persistence of a compound and its adsorption to soil are the two most important factors related to the off-site movement of pesticides from the soil to groundwater or surface water. The aim of my research was to (1) study the environmental fate of metolachlor in soil and evaluate its potential to become a groundwater contaminant and (2) investigate the persistence of metolachlor and atrazine in surface water and evaluate the ability of aquatic plants to remediate pesticide-contaminated waters;Soil incubation experiments and undisturbed soil column studies were conducted to determine the influence of soil depth and soil moisture on the persistence of metolachlor and to study its mobility through the soil profile. Metolachlor was more persistent in subsurface soils than surface soil, regardless of soil moisture or herbicide concentration. Greater quantities of bound residues and extractable degradation products were found in the surface soils. Saturated soil favored degradation and the formation of bound residues compared to unsaturated soil. In the undisturbed soil columns, metolachlor was transformed to a number of degradation products. Metolachlor and its degradates were detected throughout the soil profile and in the leachates. These results provide evidence that metolachlor and a number of metolachlor degradation products are capable of becoming groundwater contaminants;Metolachlor- and atrazine-treated surface water, surface water/sediment, and surface water/aquatic plant incubation systems were studied to evaluate (1) the persistence of metolachlor and atrazine in surface water, (2) the influence of sediment on the persistence of metolachlor and atrazine in surface waters, and (3) the remediation of metolachlor- or atrazine-contaminated surface water with submerged aquatic plants. The addition of sediment significantly reduced the quantity of metolachlor and atrazine found in the water. Results of the surface water/aquatic plant systems clearly demonstrated Ceratophyllum demersum and Elodea canadensis can remediate atrazine- and metolachlor-contaminated water.