Consumer-mediated nutrient recycling is influenced by interactions between nutrient enrichment and the anti-microbial agent triclosan

Authors: Taylor, Jason; BACK, JEFF - Baylor University; BROOKS, BRYAN - Baylor University; KING, RYAN - Baylor University

Submitted to: Freshwater Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2016
Publication Date: 6/30/2016
Publication URL: https://handle.nal.usda.gov/10113/62917
Citation: Taylor, J.M., Back, J.A., Brooks, B.W., King, R.S. 2016. Consumer-mediated nutrient recycling is influenced by interactions between nutrient enrichment and the anti-microbial agent triclosan. Freshwater Science. 2016. 35(3):856-872. DOI: 10.1086/687838.

Interpretive Summary: Many anti-bacterial agents found in personal care products (soaps) such as triclosan persists through the water treatment process and are released into aquatic environments with wastewater effluent. There is concern that long-term chronic exposure may have subtle effects on aquatic organisms that could culminate in larger scale environmental impacts. Researchers need more tools for evaluating chronic effects of antibiotics and other chemical stressors in aquatic environments. An ARS scientist in Oxford, MS collaborated with researchers from Baylor University to conduct an experiment that evaluated how different combinations of triclosan and nutrient enrichment influenced recycling of nutrients by snails. Recycling of nutrients by aquatic organisms is potentially a useful ecotoxicology tool because it represents an integrative measure of organism health that can also influence larger scale ecosystem processes. Results indicated that triclosan only influenced snail nutrient recycling at concentrations higher that currently observed in aquatic environments and when phosphorus concentrations were also high. However, results also indicated that methanol, a solvent currently used in many ecotoxicolgy studies to dissolve contaminants in water, influenced nutrient recycling results at concentrations much lower than internationally recognized standards. These findings will not only help ecotoxicologists develop new integrative measures for assessing impacts of multiple chemical stressors on aquatic ecosystems, but also require ecotoxicologists to reconsider current methods regarding acceptable solvent concentrations when conducting ecotoxicology studies that involve more subtle measures of ecosystem function.

Technical Abstract: Triclosan (5-chloro-2-(2, 4-dichlorophenoxy)phenol) is a widely used antimicrobial agent in personal care products whose fate and transport in aquatic ecosystems is a growing environmental concern. Evidence for chronic ecological effects of triclosan in aquatic organisms is increasing. At larger scales, triclosan potentially interacts with co-occurring nutrient stressors to affect overall biogeochemical cycling in aquatic ecosystems through alteration of structural and functional properties of food resources and lower consumers. We examined nitrogen (N) and phosphorus (P) excretion rates of physid snails from 12 outdoor experimental stream mesocosms with 3 P treatments (7 [background], 20, 100 µg L-1 PO4-P) crossed with 3 triclosan treatments (0, 2, and 20 µg L-1) and a methanol carrier control. Snail N and P excretion rates increased with P enrichment. Methanol had positive effects on N and P excretion rates in low and high P enrichment treatments, but had no effect at background P concentrations. Additionally, N and P excretion rates were significantly higher than methanol control treatments in the high triclosan treatments on day 14, but only in high P enrichment streams. Although interactive effects were only observed at triclosan concentrations above environmentally relevant levels for effluent dominated or dependent streams in developed countries, multiple implications can be drawn from this study. First, while many studies have confirmed that using methanol as a carrier below established levels does not influence laboratory and mesocosm ecotoxicology responses, our results suggest that even at currently acceptable levels for regulatory studies methanol can influence measures of ecosystem function and mesocosm studies need to account for carrier effects to make valid interpretations. Second, increasing use of triclosan in commercial products coupled with predicted future surface water shortages, has the potential to increase triclosan concentrations and shift patterns in consumer-mediated nutrient cycling in aquatic systems due to interactive effects of antimicrobial agents and nutrient enrichment.