Transformation of Triclosan and Triclocarban in Soils and Biosolids‐applied Soils

Triclosan (TCS) and triclocarban (TCC), widely used as antibacterial agents, have been frequently detected in biosolids. Biosolids land application may introduce pharmaceuticals and personal care products (PPCPs) such as TCS and TCC into the environment. Microcosm studies were conducted to investigate TCS and TCC transformation in Marietta fine loam and McLaurin coarse loam. Both compounds were spiked into the soils with and without biosolids amendment under non‐sterilized and sterilized conditions and incubated aerobically at 30°C for up to 100 d. In both soils, transformation of TCS followed second‐order reaction kinetics, with estimated reaction rate constants of (5.27 ± 0.920) × 10 −1 and (9.13 ± 1.58) × 10 −2 (mg kg −1 ) −1 d −1 for Marietta fine loam and McLaurin coarse loam, respectively. Transformation of TCC in both soils was slower than that for TCS. After 100 d, 53 ± 1% and 71 ± 2% of the initially added TCC and only 2.8 ± 0.35% and 6.2 ± 0.80% of initially added TCS remained in Marietta fine loam and McLaurin coarse loam, respectively. The transformation of both compounds were faster in the Marietta fine loam (pH 7.8; 1.8% organic matter) than in the McLaurin coarse loam (pH 4.7; 0.65% organic matter). Our result suggests that biotic processes are more of a controlling factor affecting TCS transformation, whereas abiotic processes may affect TCC transformation more significantly. Addition of biosolids to the two soils slowed the transformation of both compounds, indicating interactions between both compounds and biosolids may adversely affect their transformation in soils, an important factor that must be included in models predicting environmental fate of biosolids‐associated PPCPs.