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Lookup NU author(s): Dr Charles Knapp,
Professor David Graham
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Much work has suggested that the rate of attenuation of water-soluble organic contaminants in aerobic aquatic systems is dependent on the level of secondary nutrients in the water column. For example, the decay rate of alachlor, the common herbicide, was over 10 times higher under hypereutrophic compared with oligotrophic water conditions. It has been presumed that higher water column nutrient levels produce larger microbial communities resulting in higher rates of alachlor co-metabolism. However, most earlier field studies only assessed alachlor fate in systems with full light exposure (FLE). Therefore, new experiments were performed to assess how variations in light level affect alachlor co-metabolism in such systems. Twelve tank mesocosms were maintained using identical nitrogen (N) and phosphorus (P) supply conditions: four units with full light exposure (100% FLE), four with partial shading (19.3% FLE), and four with near complete shading (0.5% FLE). Alachlor half-lives were found to vary broadly, from 50-60 days in higher light units to >180 days in the 0.5% FLE units. Nutrient analysis indicated that the low light units were severely carbon (C)-limited for microbial decomposition, whereas the other units had excess C relative to N and P. Apparently, reduced light levels cause a decreased production of bioavailable-C for decomposition, which significantly reduces alachlor co-metabolism. The data suggest that water column nutrient levels only correlate with alachlor decay rate when light levels are high, and that the biodegradable carbon supply must be considered when assessing the fate of water-soluble contaminants in aerobic aquatic systems.
Author(s): Ensz A, Knapp CW, Graham DW
Publication type: Article
Publication status: Published
Journal: Environmental Science & Technology
ISSN (print): 0013-936X
ISSN (electronic): 1520-5851
Publisher: American Chemical Society
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