Natural attenuation of chloroacetinilide herbicides in aquatic systems

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Edited by:
Andrea Leeson and Bruce C. Alleman


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Chloroacetanilide herbicides (e.g. alachlor and metolachlor) and their breakdown products are frequently found in agriculturally impacted and other natural waters. Although these compounds are usually present at low concentrations in aquatic systems, defining their fate and attenuation rate is important because they can be toxic at comparatively low exposure levels. This paper summarizes results from a four-year research program assessing factors that affect herbicide attenuation rates and breakdown product formation patterns in aquatic systems. Over 70 different field microcosms (11.3 m3 cylindrical fiberglass tanks) were selectively manipulated (in replicate) to create nine unique aquatic ecosystems for this study. Alachlor and/or metolachlor were added to these units and transformations were observed over time. Alachlor half-lives ranged from 6.0 days to more than 100 days depending upon the temperature, oxygen conditions, and the nutrient conditions in the microcosm waters. The highest rates of alachlor decay were observed in warm, nutrient-rich, anaerobic water columns, whereas the lowest alachlor decay rates were observed under cooler, aerobic, oligotrophic water conditions. Similar relationships were observed for metolachlor, although metolachlor decay rates were about 40% slower. Our data suggest that herbicides will decay rapidly in waters that are high in nutrients possibly resulting from human activities. Alternately, low nutrient or pristine waters will have the lowest rates of herbicide decay. On a policy level, all efforts should be made to prevent exposure of comparatively pristine waters to herbicide inputs.

Additional publication details

Publication type:
Conference Paper
Publication Subtype:
Conference Paper
Natural attenuation of chloroacetinilide herbicides in aquatic systems
Year Published:
Battelle Press
Publisher location:
Colombus, OH
6 p.
Larger Work Type:
Larger Work Subtype:
Conference publication
Larger Work Title:
Natural attenuation of chlorinated solvents, petroleum hydrocarbons, and other organic compounds: Volume 5(1) of Proceedings from the Battelle Memorial Institute international in situ and on-site bioreclamation symposium
First page:
Last page:
Conference Title:
5th International In Situ and On-Site Bioremediation Symposium
Conference Location:
San Diego, CA
Conference Date:
April 19-22, 1999