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Effects of a Chronic Lower Range of Triclosan Exposure on a Stream Mesocosm Community
Citation:
Nietch, C. T., E. L. Quinlan, J. M. Lazorchak, C. A. Impellitteri, D. Raikow, AND D. Walters. Effects of a Chronic Lower Range of Triclosan Exposure on a Stream Mesocosm Community. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 32(12):2874-2887, (2013).
Impact/Purpose:
Results of a community-level stream mesocosm study showed a significant effect of triclosan on stream bacteria, including increased resistance, at a nominal concentration of 500 ng/L. There was a tendency for change indicated at the lowest nominal dose tested of 100 ng/L and dose-response curves fit to bacterial-specific endpoints suggest effective concentrations (EC20s) even lower. Collectively, this leads us to conclude that a no effect concentration for triclosan under conditions of chronic exposure is likely below 100 ng/L. This is a concentration well within the range reported for streams currently permitted to receive treated wastewater effluents. These results have impacted the occurrence of triclosan in consumer products and will impact water quality criteria for triclosan.
Description:
Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) is an antimicrobial found in consumer soaps and toothpaste. It is in treated wastewater effluents at low part per billion concentrations, representing a potentially chronic exposure condition for biota inhabiting receiving streams. A naturally colonized stream benthos was created using continuous flow-through indoor mesocosms. Once colonized, mesocosm communities were dosed to achieve different in-stream triclosan concentrations (0, 0.1, 0.5, 1.0, 5.0, and 10 µg/L) for 56 days. Water quality parameters and 73 endpoints from bacteria to macroinvertebrates plus interacting abiotic components were quantified for a system assessment. Effects of triclosan on specific microbial endpoints were measured at doses 0.5 µg/L and higher, including a negative effect on litter decay dynamics at doses 1.0 µg/L and higher. Resistance of periphytic bacteria to triclosan increased in doses 0.5 µg/L and above. An overall stimulatory effect of the antimicrobial on periphyton was exhibited by the three lowest doses. The two highest doses significantly decreased bacteria cell densities, cyanobacteria abundance and tended to depress the bulk of the periphyton. The chronic responses observed are likely to occur at an effective concentration below 0.1 µg/L. Here they did not translate to detectable change in the colonizing macroinvertebrates, food web, or carbon and nutrient dynamics. The results shed light on the role a low, chronic exposure to triclosan may play in effluent dominated streams.
