Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2000
Publication Date: N/A
Interpretive Summary: Atrazine is the most commonly used herbicide for weed control in corn production. Because of its extensive use, atrazine is also the most frequently detected herbicide in streams across the US, and its levels are regulated in drinking water because of human toxicity concerns. Wetlands offer one possible management strategy to reduce atrazine in stream water. Wetlands have long been known to reduce sediment and nutrient levels of input water, but little is known about their ability to reduce herbicide levels from agricultural runoff. In this study, we used sediments from a wetland site to create small wetlands, referred to as wetland mesocosms. The wetland mesocosms were constructed with 15 to 20 in. deep sediment layers, maintained under saturated conditions, and planted with cattails. Atrazine was added to the water of each wetland mesocosm, and the water was sampled periodically over the next 8 wks and analyzed for levels of atrazine and its metabolites (i.e., breakdown products). After 8 wks, sediment samples were also collected and analyzed for levels of atrazine and its metabolites. Three sets of these studies were conducted during 1998 and 1999. After 8 wks, only 1-12% of the added atrazine remained in the water. Another 29-67% of the applied atrazine was bound to sediments, either as the parent compound or as one of its metabolites. In addition, up to 40% of the applied atrazine was taken up by the cattails. Thus, wetlands showed a very strong potential for atrazine remediation of agricultural runoff water by the processes of degradation, plant uptake, and sediment binding of atrazine and its metabolites. This work will benefit farmers and land management agencies by providing needed information on effective strategies to reduce atrazine levels in stream water.
Technical Abstract: Laboratory wetland mesocosms were studied for their potential to reduce atrazine in runoff. The wetland mesocosms were constructed with 38- to 51- cm deep sediment layers, maintained under saturated conditions, and planted with cattails. Sediments were collected from a constructed wetland site. Three experiments, in which one ppm atrazine was added to the water column of three wetland, one soil control, and one water control mesocosm, were conducted. Atrazine dissipation from the water column and metabolite formation (deethylatrazine (DEA), deisopropylatrazine (DIA), hydroxy- atrazine (HA)) were monitored over a 56-day period. Atrazine dissipation from the water column of wetland mesocosms was biphasic. Less than 12% of the atrazine applied to wetland mesocosms remained in the water column on day 56. DEA and DIA were the predominant atrazine metabolites in water, accounting for 0.34-3.2% of the applied atrazine. Analysis of day 56 sediment samples indicated that 29-67% of the applied atrazine was bound t sediments, either as parent or one of its metabolites. HA was the predominant sediment-bound metabolite, accounting for 12-24% of the applied atrazine. Mass balance calculations indicate that up to 40% of the applied atrazine was taken up by the cattails. Most probable number (MPN) assays demonstrated that atrazine degrader populations were small in wetland sediment. This observation combined with the predominance of HA, compared to DEA and DIA, in the wetland sediments indicated that the primary atrazine degradation pathway in these sediments was abiotic hydrolysis. Wetlands showed a very strong potential for atrazine remediation of agricultural runoff water by the processes of degradation, plant uptake, and sediment binding of atrazine and HA.