Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/2/2003
Publication Date: 5/1/2004
Citation: Rice, P.J., Anderson, T.A., Coats, J.R. 2004. Effect of sediment on the fate of metolachlor and atrazine in surface water. Environmental Toxicology and Chemistry. 23:1145-1155. Interpretive Summary: The present study was conducted to determine the influence of sediment on the persistence of atrazine and metolachlor in surface water. Sediment significantly reduced the concentration of these herbicides with atrazine and metolachlor persisting in the sediment-free surface water four times longer than in the surface water systems that contained sediment. Surface water concentrations of atrazine were primarily reduced by the accumulation of atrazine and/or atrazine degradation products in the sediment, while metolachlor concentrations were primarily reduced by degradation of the herbicide. This research illustrates the importance of sediment in the fate of pesticides in surface water. Pesticides and sediment may be transported to surface water with runoff from agricultural fields. Sediment and particulates in surface water can alter the availability of contaminants to organisms and will influence their toxicity and availability for degradation. These results will be of benefit/interest to farmers, extension agents and scientist to better understand the ability of sediment to accumulate contaminants or influence the degradation of contaminants. This will allow for more accurate prediction of the environmental fate of these herbicides and the potential hazard of surface water contaminants to aquatic organisms.
Technical Abstract: Experiments were conducted to determine the persistence of atrazine and metolachlor in surface water, and to evaluate the contribution of sediment to their dissipation from surface waters. Atrazine was more persistent than metolachlor in the sediment-free surface water systems. First-order 50% dissipation (DT50) values were 150 and 33 d for atrazine and metolachlor, respectively. Sediment significantly reduced the concentration of atrazine and metolachlor in the surface water. Adsorption was more important than degradation in the dissipation of atrazine from the surface water, while degradation was favored in the metolachlor-treated systems. DT50 values for metolachlor and atrazine in the surface water/sediment incubation systems were almost four times smaller than the DT50 values calculated for the sediment-free systems. The results of this research illustrate the importance of sediment in the fate of pesticides in surface water. Pesticides may be transported in the dissolved or particulate phase of runoff. In aquatic environments, pesticides can partition between the dissolved and particulate phase depending on the type of suspended sediment present, and the properties of the pesticides and water. Particulate matter and sediment can alter the bioavailability of contaminants to organisms and influence their toxicity and availability for microbial degradation. Greater comprehension of the role of sediment to sequester or influence degradation of agricultural contaminants in aquatic systems will provide a better understanding of the potential hazards of surface water contaminants.