Fate of Triclocarban and Triclosan in Soils Receiving Biosolids Applications

Triclocarban (N-(4-chlorophenyl)-N'-(3,4-dichlorophenyl)urea) (TCC) and Triclosan (5-chloro- 2-[2,4-dichloro-phenoxy]-phenol (TCS) are bactericidal compounds that are added to a wide range of household and personal care products such as hand soap, dish-washing products, laundry detergents, cleaning wipes, toothpaste, deodorants and plastics. There is a growing concern about the discharge of these compounds from wastewater treatment plants into the environment. It has been postulated that land application of biosolids could be a possible source since it has been estimated that about 90% of these compounds get removed from the water stream and are accumulated onto the sludge. Once released into the environment, these compounds may undergo degradation, and can be transformed into methyl triclosan (MeTCS), and other chlorinated compounds. While it has been established that TCC and TCS are present in the biosolids, to date, little information is available on their distribution in biosolids and their fate upon land application.In the first phase of this study, the concentrations of TCC and TCS in biosolids collected from a WWTP periodically for over two years. In the second phase, we analyzed their presence in soil samples collected from commercial farms in the Mid-Atlantic region that have received boiosolids. In biosolids leaving the plant, TCC and TCS concentrations were measured at mg/Kg dry weight (d.w.), with TCC concentrations running a little higher than TCS concentrations. Our results suggest very little temporal and seasonal variability over a 2 year time period. Concentrations of these compounds in soils receiving biosolids were much lower, i.e., levels in the ng/g d.w. range. Fields receiving biosolids applications always resulted in higher levels of the compounds than in non-treated fields with the TCC concentrations typically higher than TCS in all soils. In an effort to assess build up of these compounds upon multiple applications, we evaluated the compounds' soil half lives. Our results suggest that levels of TCC were elevated even two years after application, while levels of TCS went to background levels and no buildup was observed with multiple applications. While build-up was observed for TCC, our results also illustrated that soil dissipation of this compound occurred. Our results also illustrated the presence of MeTCS at levels higher than in the biosolids, suggesting that TCS is being biodegraded in the soil.