Periphytic chlorophyll--a response to triclosan exposure: application of a passive diffusion periphytometer

In situ assessments of chemical toxicity in streams may be accomplished using natural periphytic communities when allowed to colonize an artificial substrate. The proliferation of Triclosan (TCS) in consumer products has resulted in its presence in wastewater influent, effluent, and subsequently in streams. In this study, the two objectives were: 1) assess the utility of a passive-diffusion periphytometer in toxicity tests, and 2) evaluate the growth-inhibiting effects of TCS on periphytic algae at the White River, Northwest Arkansas. The periphytometer was deployed for one week with seven replicates of nine treatments, including control (deionized H2O), methanol, low TCS (50 microgram L(-1)), medium TCS (100 microgram L(-1)), high TCS (500 microgram L(-1)), nutrients (2000 microgram PO4-P L(-1) and 20000 microgram NO3-N L(-1)), low TCS with nutrients, medium TCS with nutrients, and high TCS with nutrients. Relatively low stream nutrient concentrations were observed; maximum nitrate-nitrogen (NO3-N), total N, ammonium-nitrogen (NH4N-N), total organic carbon (TOC), and soluble reactive phosphorus (SRP) concentrations during the deployment were 230, 603, <50, 12500, and 15 microgram L(-1), respectively. The Student-Newman-Kuels test (alpha = 0.05) identified three significantly different groups within the treatments. The nutrients and low TCS with nutrients treatments had chlorophyll-a means of 10.9 and 5.8 mg m(-2), respectively, which were significantly different from each other and all other treatments. Chlorophyll-a content means of the remaining treatments ranged from 1.8 to 3.5 mg m(-2) and were not significantly different from each other. Exponential regression of chlorophyll-a contents in nutrient and TCS with nutrient treatments against TCS concentration produced a significant decreasing trend; however, no trend in chlorophyll-a content was observed in treatments without nutrients. The observed inhibition of periphytic algal growth in the treatments with additional NO3 and SRP suggests that the mechanism of TCS may be more complex than postulated. Periphytic response to TCS exposure was quantified using an innovative, in situ approach that warrants additional investigation.