Transformation and Extractability of Antibacterial Agents Triclosan and Triclocarban in Soils and Biosolids-Amended Soils

Farmland application of biosolids is the most sensible and cost-effective option for many municipalities and it provides tremendous savings in fertilizer costs to the farmers. However, environmentalists continue to raise concerns about the safety of this practice because biosolids may contain traces of organic compounds, such as pharmaceuticals and personal care products (PPCPs). A laboratory study was conducted to investigate aerobic transformation and extractability of triclosan (TCS) and triclocarban (TCC) in two soils with and without biosolids amendment. Both compounds are widely used antibacterial agents in a variety of PPCPs. TCS and TCC were spiked in sterilized and non-sterilized soils and biosolids-applied soils under aerobic condition at 20oC and incubated for up to 100 days. TCS transformed faster than TCC in all soils. At 100 day, 97% and 94% of added TCS were transformed in non-sterilized Marietta fine sandy loam and McLaurin sandy loam, respectively, while only 48% and 30% of added TCC were transformed, in the same two soils, respectively. Sterilization of soils significantly retarded TCS and TCC transformation in both soils, indicating that biological process is important for the transformation of those compounds. Addition of biosolids to the soil also significantly retarded the transformation of both compounds, suggesting that soil microorganisms might prefer biosolids rather than TCS or TCC as carbon source. In addition, sorption of both compounds to biosolids may also prevent them from fast transformation. Our water extractability study showed higher potential for TCS than for TCC to be leached out of soil. The water extractability of both compounds decreased with incubation time in non-sterilized soils, while the opposite trend was observed for sterilized soils. Addition of biosolids to soils significantly reduced the water extractability of both compounds.