Retention-Release Characteristics of Triclocarban and Triclosan in Biosolids, Soils, and Biosolids-Amended Soils.

Current models used to describe retention/release characteristics of organic compounds usually consider only organic compounds’ interactions with soils or biosolids alone, and assume that organic carbon partition coefficient apply to all solid matrices. Concern about biosolids-borne organics applied to soils requires a more complete understanding of organic compounds retention/release characteristics in biosolids amended soils. We determined partition coefficient (K_d), and retention/release characteristics of triclocarban (TCC) and triclosan (TCS) in biosolids, soils, and biosolids-amended soils. Four soils of different physicochemical properties amended with biosolids at 10 g kg^-1, together with soils alone and biosolids alone were utilized for the study. Triclocarban and TCS adsorption was rapid initially, followed by a slower stage. At equilibrium, > 98% of the spiked TCC and TCS was adsorbed by biosolids, whereas 50-70 % of spiked TCC and 65-78 % of spiked TCS was adsorbed by soils and by biosolids amended soils. The K_d values determined in biosolids (log K_d of 3.12-3.55 for TCC and 3.61-3.97 for TCS) were greater than those determined in soils and biosolids amended soils (log K_d of 1.2-2.4 for TCC and 1.7-2.9 for TCS). Only 1-3% and 2-5% of the previously adsorbed TCS and TCC desorbed from the biosolids in 24 h. Multiple desorption steps (24-h each) over several days revealed incomplete desorption from all three solid matrices.  We conclude that TCC and TCS should be minimally mobile in the soil environment and that the common biosolids application rates will have no significant impact on TCC and TCS retention/release characteristics.