The effects of tebuthiuron on aquatic productivity



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Texas Tech University


Tebuthiuron (N-[5-(1, 1-dimethylethyl)-1,3,4-thladiazol-2-y1] =N, N'-dimethylurea) appears to control the riparian shrub saltcedar (Tamarlx spp.); however, its use is restricted since the fate and effects of this herbicide in aquatic systems are unknown. Possible tebuthiuron Impacts on aquatic production were examined in ten 2846-L microcosms. Each microcosm contained sediment, water, algae, micro- and macroinvertebrates, and fish. The following doses of tebuthiuron were used: 0 (control), 10, 70, 200, 500, and 1000 μg/L. The control and the 200 μg/L treatment level were replicated (n=3) to allow for specific statistical comparisons of treatment effects. Data generated from all treatment levels was used in tebuthiuron fate analysis and in correlation analysis between the microcosm variables. The adsorption of tebuthiuron to sediments contained in ten microcosms was described by the Freundlich equation, x/m = 3.24c^0.68. Of the system variables investigated (phytoplankton primary production, chironomid density and biomass, and fish biomass), only chironomid larvae density exhibited reductions at the 200 μg/L treatment level. The pathway by which density depressions occurred is unknown. Possible explanations include a direct toxic effect on the chironomids and/or a species shift in the algal community resulting in a greater percentage of "unpalatable" biomass. The changes in chironomid density suggest that system effects may occur at the 200 μg/L treatment level.



Tebuthiuron, Aquatic ecology