Fate of atrazine and metolachlor in a phytoremediation system: mass balance and plant uptake

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2004-01-01
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Henderson, Keri
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Atrazine and metolachlor have been implicated in point-source pollution at agrochemical dealerships in the Midwest, as well as in nonpoint-source contamination of surface waters caused by runoff. Prairie grasses have been used in filter strips and are also useful for phytoremediation; however, little is known about the fate of contaminants and their metabolites within a grassed system. Effects of plant uptake on formation and fate of degradation products are not known. In this thesis, atrazine and metolachlor were evaluated individually. Each 14C-labeled herbicide was added to enclosed systems to determine the fate of the parent compound and its metabolites in soil, plant, and air. Soil was treated with 25 mg/kg 14C-labeled herbicide and allowed to age for a short period to simulate conditions that could be found at an agrochemical dealership site. Four systems were then amended with a mixture of prairie grasses, and the remaining four chambers were unvegetated controls. Dissipation of each herbicide and distribution of parent compound and metabolites were recorded for 21 days for 14C-atrazine and 90 days for 14C-metolachlor. 14C-CO2 and volatile 14C-organic metabolites were collected throughout the study. After the testing period, soil and plant materials were evaluated for radioactivity, and identity of metabolites was determined. Mass balance of atrazine for both vegetated and control systems was >76%, with 40% of the applied radioactivity remaining bound to soil particles after a sequential extraction technique. Parent atrazine was the dominant compound detected, with major metabolites in soil being deethylatrazine and didealkylatrazine. Less than 0.5% of applied 14C-residue was taken up by the grasses. Approximately 2% of total applied 14C-atrazine was mineralized to 14C-CO2, with no differences between vegetated and unvegetated systems. Mass balance for metolachlor was >92% for both vegetated and control systems. Vegetation decreased the amount of metolachlor in soil, with significantly higher concentrations of the metabolites metolachlor ethane sulfonic acid and the morpholinone metabolite present in vegetated soil compared to unvegetated soil. Over 7% of applied radioactivity was taken up into plant tissue during the 97-day study, thus indicating that plant uptake plays a major role in the phytoremediation of metolachlor.

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Thu Jan 01 00:00:00 UTC 2004