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Title: LABORATORY ASSESSMENT OF ATRAZINE AND FLUOMETURON DEGRADATION IN SOILS FROM A CONSTRUCTED WETLAND

Author
item Weaver, Mark
item Zablotowicz, Robert
item LOCKE, MARTIN - USDA, ARS, WQERU

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2004
Publication Date: 10/10/2004
Citation: Weaver, M.A., Zablotowicz, R.M., Locke, M.A. 2004. Laboratory assessment of atrazine and fluometuron degradation in soils from a constructed wetland. Chemosphere 57:853-862.

Interpretive Summary: Constructed wetlands offer promise for removal of non-point source contaminants such as herbicides from agricultural runoff. Laboratory studies assessed the potential of soils to degrade and bind two common agricultural herbicides, atrazine and fluometuron, within a recently constructed Mississippi Delta wetland. Surface soil from two cells of the constructed wetland (excavated and natural) were treated with atrazine and fluometuron, and incubated under either saturated or flooded conditions. Fluometuron degraded rapidly under saturated conditions but was very persistent under flooded conditions. Atrazine dissipated rapidly in saturated and flooded soil with a half-life of approximately 23 days. There was little effect of wetland excavation on overall dissipation of either herbicide. The major fate of atrazine dissipation was incorporation into soil-bound components, while metabolites of fluometuron accumulated under saturated conditions. Atrazine had a greater binding potential to wetland soil compared to fluometuron and bound atrazine was released less rapidly than to fluometuron. Constructed wetlands may be a useful management practice to mitigating atrazine contamination in runoff water.

Technical Abstract: Constructed wetlands offer promise for removal of non-point source contaminants such as herbicides from agricultural runoff. Laboratory studies assessed the potential of soils to degrade and sorb atrazine and fluometuron within a recently constructed wetland. The surface 3 cm of soil was sampled from two cells of a Mississippi Delta constructed wetland; one shallow area disturbed only hydrologically, and the second excavated to provide greater water-holding capacity. The excavated area was more acidic on average (pH 4.85 vs. 5.21), but otherwise the physical properties and general microbial enzyme activities in the two areas were similar. Soils were treated with 84 and 68 ug kg**-1 soil atrazine and fluometuron, respectively, and incubated under either saturated (88% moisture, w:w) or flooded (1 cm standing water) conditions. Soil were sampled over 32 d and extracted for herbicide and metabolite analysis. Under saturated conditions, fluometuron metabolized to desmethylfluometuron with a half-life equal 25 to 27 d. However, under flooded conditions, the half-life of fluometuron was more than 175 d. Atrazine dissipated rapidly in saturated and flooded soil with a half-life of approximately 23 d, but only 10% of atrazine was mineralized CO2. The overall atrazine and fluometuron dissipation rates were similar between the two cells, but each area had a different pattern of metabolite accumulation. The major route of atrazine dissipation was incorporation of atrazine residues into methanol-nonextractable (soil-bound) components, with minimal extractable metabolite accumulation. A mixed-mode extractant (potassium phosphate:acetontrile) recovered greater amounts of 14**C-residues from atrazine-treated soils, suggesting that hydrolysis of atrazine to hydroxylated metabolites was a major component of the bound residues. These studies indicate the potential for herbicide dissipation in wetland soils and a differential effect of flooding on the fate of these herbicides.