PERIPHYTIC CHLOROPHYLL-A RESPONSE TO TRICLOSAN EXPOSURE

Abstract

Triclosan (TCS) usage in consumer products has resulted in its entry into wastewater influent and subsequently into streams. Triclosan aquatic toxicity to periphyton was assessed using an instream passive-diffusion periphytometer (or Matlock Periphytometer) at the White River, Northwest Arkansas. The periphytometer was deployed for one week with seven replicates of nine treatments, including: control, methanol, low (0.05 mg/L) TCS, medium (0.1 mg/L) TCS, high (0.5 mg/L) TCS, nutrients (2 mg PO4-P/L and 20 mg NO3-N/L), low TCS with nutrients, medium TCS with nutrients, and high TCS with nutrients. The Student-Newman-Kuels test (a=0.05) identified three significantly different groups within the treatments. Nutrients and low TCS with nutrients had chlorophyll-a means of 10.9 and 5.8 mg/m2, respectively, which were significantly different from each other and all other treatments. The remaining chlorophyll-a treatment means ranged from 1.8 to 3.5 mg/m2 and were significantly different from nutrients and low TCS with nutrients, but not from each other. Exponential regression of chlorophyll-a content on nutrient treatments against TCS concentration provided a decreasing trend with p<0.0001; however, exponential regression on treatments without nutrients did not exhibit a significant trend. Low background nutrient concentrations were observed; maximum NO3-N, total N-N, NH4N-N, TOC, and SRP concentrations were 0.23, 0.603, <0.05, 12.5 and 0.015 mg/L, respectively. Nutrient, particularly P, limitations may explain the minimal periphyton chlorophyll-a content found in non-nutrient enriched treatments. Periphytic response to TCS exposure was quantified using an innovative approach, which warrants additional investigation.