Risk Assessment of Triclocarban in Land-Applied Biosolids

Triclocarban (TCC) is an active ingredient in antimicrobial bar soaps, a High Production Volume (HPV) chemical, and a common constituent of domestic wastewater. Activated sludge treatment readily removes TCC from the liquid waste stream and concentrates the antimicrobial in the solid fraction (i.e. sludge). The sludge is often processed to produce biosolids intended for land-application. In a collaborative project funded by USEPA, the Soil and Water Science Department at the University of Florida and the Procter & Gamble Company (P&G) are working to characterize the fate and transport of TCC in land-applied biosolids. We first quantified TCC concentrations (5-43 ppm) in 22 biosolids representing various treatment processes, and measured TCC solubility (0.045 mg L^-1) and log K_ow (3.5 ± .06) by HPLC/MS. In 2007, we initiated a biosolids-amended soil biodegradation study using ¹⁴C-TCC. During the eight-month study, 2-4% of the spiked ¹⁴C-TCC was mineralized and RAD-TLC detected no intermediate degradation products. In 2008, we initiated the first of two earthworm TCC toxicity studies, assessed indigenous biosolids-borne TCC partitioning in 14 biosolids (log Kd: 3.1-3.9; log Koc: 3.6-4.6), and analyzed biosolids-amended soil column leachates (0-3.3 ng TCC mL^-1). Biosolids of known initial TCC content leached ≤0.18% of applied TCC. We are currently utilizing HPLC/MS/MS to analyze TCC concentrations in plant tissue collected from biosolids-amended soil columns. Study data will ultimately contribute to a biosolids-borne TCC environmental and human health risk assessment.