Desorption Rates of Antimicrobial Chemicals from Biosolids and Soils Amended with Biosolids at Different Aging Points

The high use antimicrobial chemicals Triclocarban (TCC) and Triclosan (TCS) are hydrophobic, weak acidic organic compounds that are found in personal care products such as soaps, toothpastes, and deodorants. After the use of products that contain TCC and TCS, the majority of the waste is diverted to wastewater treatment plants (WWTPs). Several surveys have shown that sludge and biosolids (i.e. treated sludge) from different WWTPs contains TCC and TCS at a high frequency and relatively high concentrations (> 10 mg/kg is typical). Currently 55% of biosolids that are produced are land applied in the United States. Once added to soils the chemicals can be released by desorption from or breakdown of biosolid particles and be released to soil pore water. Following desorption or degradation of organic matter, TCC and TCS can travel through the vadose zone and then enter groundwater. Because TCC and TCS have antimicrobial properties, there is concern that these chemicals may cause damage to the soil microbial ecosystem, disrupting key elemental cycles in soils. The rate and extent of release of TCC and TCS from biosolids has not been well researched. This research quantifies the rate at which TCC and TCS are released to the aqueous system from biosolids following different chemical-biosolid contact times, because previous research has shown that desorption rates in soil organic matter can be aging time dependent. Desorption rate experiments with aged biosolid amendments were conducted to determine whether such an aging effect occurs for TCC and TCS. Aerobically and anaerobically digested biosolids and two well characterized surface soils were used for these experiments. The data were fit to a dual exponential release model and the first order rate constants for the fast and slow desorption domains were on the order of 10−1/h and 10−3/h, respectively, for the majority of the experiments. The rate of desorption was faster for both chemicals for anaerobic than aerobic biosolid. Forbes soil, which had a higher percentage of organic carbon, that was amended with the biosolids overall had a slower desorption rates for TCC and TCS at each aging point. Finally, desorption rates in general were much faster for TCS than TCC.