Saturday, 15 July 2006

Fate and Transport of Biosolids-Borne Triclocarban.

Elizabeth A. Hodges and George A. O'Connor. Soil and Water Science Dept, Univ of Florida, 408 Newell Hall, PO Box 110510, Gainesville, FL 32611

Triclocarban (TCC) is an antimicrobial compound routinely added to bar soaps in the United States (HPV, 2002). Approximately 80% of antimicrobial bar soaps on the US market contain TCC (Perencevich et al, 2001), accounting for much of the 227,000 454,000 total kilograms of the compound used each year in the US (HPV, 2002). Following use, much of the TCC becomes a component of wastewater and is subsequently removed during activated sludge treatment. The sludge is later processed to produce biosolids, which may then be land applied. Despite the masses of TCC used annually in the United States, extensive partitioning of TCC into activated sludge (Halden and Paull, 2005), and chemical properties that suggest a tendency for TCC to persist, few studies have been conducted on the environmental fate of TCC following land application of biosolids. Multiple components of a comprehensive TCC risk assessment for land applied biosolids are incomplete, including development of conclusive solubility data, quantification of retention/release, movement, persistence, and impacts on soil microbes. Also missing is characterization of important exposure routes associated with biosolids-amended soils and identification of potentially susceptible human populations. With funding from the United States Environmental Protection Agency (USEPA) the Soil and Water Science Department at the University of Florida and the Procter & Gamble Company are working together to fill the TCC data gaps. The first year of a four year collaboration has delivered crucial preliminary data that is now shaping the direction of subsequent research. Most importantly, extraction methods previously developed by Procter & Gamble for the antimicrobial Triclosan (TCS) were adapted and validated for TCC removal from contaminated biosolids. The extraction technique was applied to various select biosolids to evaluate TCC content and identify effects of biosolids preparation processes (e.g. anaerobic and aerobic digestion, heat-drying, alkaline stabilization, and composting) on TCC concentrations. Fundamental TCC chemical qualities and behaviors were characterized using the USEPA Office of Prevention, Pesticides, and Toxic Substances (OPPTS) Harmonized Test Guidelines. Developed for testing pesticides and other toxic substances, the guidelines are designed to minimize variation across testing procedures. Discrepancies in reported TCC solubilities were resolved and TCC hydrolysis rate constants were quantified to make a preliminary assessment of TCC movement, bioavailability, and persistence potential. TCC thermal stability in biosolids was also characterized and used to assess the effects of elevated temperatures on TCC concentration during biosolids preparation and following land-application. Remaining research will address retention/release of TCC in biosolids-amended soils as a function of soil type, TCC concentration, biosolids application rate, and environmental conditions; and persistence as a function of time, TCC concentration, and various environmental factors. If retention/release studies indicate the potential for TCC movement by soil leaching or as a component of surface runoff, column mobility or runoff studies will be conducted to assess ground and surface water quality impacts. If TCC is determined to be labile and persistent in the soil, the toxicity and bioconcentration potential of TCC in select soil microbes and the effect of TCC on soil microbial community function will be assessed. References: (1) High Production Volume (HPV) Chemical Challenge Program Data Availability and Screening Level Assessment for Triclocarban. 2002. The TCC Consortium. CAS#: 101-20-2, 2002; Report No. 201-14186. (2) Perencevich, E., Wong, M. and Harris, A. 2001. National and regional assessment of the antibacterial soap market: A step toward determining the impact of prevalent antibacterial soaps. American Journal of Infection Control. 29:281-283. (3) Halden, R. and Paull, D. 2005. Co-occurrence of triclocarban and triclosan in US water resources. Environmental Science and Technology. 39:1420-1426.

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