The antimicrobial triclosan was analyzed in unfiltered samples from influent, effluent, and receiving stream and before and after a pilot-scale constructed wetland at a North Texas municipal wastewater treatment plant. Triclosan concentrations were reduced by 97 to 99% by the activated sludge treatment plant. Effluent concentrations were further reduced by passage through the constructed wetland, but receiving stream concentrations were not statistically significantly different from effluent concentrations. Effluent concentrations of triclosan were seasonal with highest concentrations occurring during the summer months. The effluent-dominated receiving stream maximum concentrations during summer months were below reported algal no-observed-effect concentrations based on biomass and growth rate but exceeded concentrations reported to cause shifts in algal community structure.
Robust canonical correlation and classification methods were used to evaluate relationships between ambient toxicity and instream biological response. Ten studies of freshwater aquatic systems were used in the analysis. These studies included eight site studies conducted by the U.S. Environmental Protection Agency's Complex Effluent Toxicity Testing Program, one study by the University of Kentucky and one study by the University of North Texas.
Results from ambient toxicity tests, including Ceriodaphnia neonate production and Pimephales promelas dry weight and survival, were used to predict impact at sampling stations. Instream biological response variables, including fish and benthic richness, were used to classify whether or not a station was impacted. The strength of the relationship between ambient toxicity and instream impact was determined by statistically evaluating agreement between the predicted and observed impacts. Results of the analysis showed that statistically significant relationships between ambient toxicity and instream impact were found in each of the studies.
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