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

The fate and transport of triclosan (5-chloro-2-[2,4-dichlorophenoxy]phenol), a widely used antimicrobial agent in personal care products, in aquatic ecosystems is a growing environmental concern. At ecosystem scales, triclosan potentially interacts with co-occurring nutrient stressors to affect overall biogeochemical cycling through consumer-mediated nutrient recycling pathways. We examined N- and P-excretion rates of snails (Physella spp.) in 12 outdoor experimental stream mesocosms dosed with 3 P treatments crossed with 3 triclosan treatments and a methanol carrier control. Snail N- and P-excretion rates increased with decreasing periphyton C:N and C: P ratios across the P-enrichment gradient. N- and P-excretion rates were significantly higher in the high-triclosan than in the methanol control treatments on day 14, but only in high-P-enrichment streams. However, methanol had positive effects on N- and P-excretion rates in low- and high-P-enrichment treatments compared to nonsolvent controls, but no effect at background P concentrations. Multiple inferences can be drawn from our study. First, whereas many investigators have confirmed that using methanol as a carrier below established regulatory levels does not influence laboratory and mesocosm ecotoxicology responses, our results suggest that low-level methanol concentrations can influence measures of ecosystem function. Second, higher use of triclosan and other antimicrobial agents in commercial products coupled with predicted urbanization and surface water shortages in the future have the potential to increase triclosan concentrations and shift patterns in consumer mediated nutrient cycling in aquatic systems because of interactive effects of antimicrobial agents and nutrient enrichment.