Retention‐release characteristics of triclocarban and triclosan in biosolids, soils, and biosolids‐amended soils

Transport models that incorporate retention/release characteristics of organic compounds in soils and sediments typically assume that organic‐carbon normalized partition coefficients ( K OC ) apply to all solid matrices and that the partitioning process is completely reversible. Partition coefficients ( K d ) (from which the K OC was calculated), and retention/release characteristics of triclocarban (TCC) and triclosan (TCS) in biosolids, soils, and biosolids‐amended soils were determined. Four soils of different physicochemical properties amended with biosolids at 10 g/kg, together with unamended soils, and several biosolids were separately spiked with either [ 14 C]TCC or [ 14 C]TCS for the various determinations. The hysteresis coefficient values of the two compounds were consistently <1 in all three solid matrices, suggesting strong hysteresis. Multiple desorption steps (24 h each) over several days revealed incomplete desorption of the two compounds from all three solid matrices. The K d values determined in biosolids (log  K d 3.34 ± 0.13 for TCC and 3.76 ± 0.39 for TCS) were greater than those determined in soils (log  K d 1.71 ± 0.09 for TCC and 2.25 ± 0.26 for TCS) and biosolids‐amended soils (log  K d 1.90 ± 0.16 for TCC and 2.31 ± 0.19 for TCS), however, the K OC values of all three solid matrices were similar (log  K OC of 3.82 ± 0.16 for TCC and 4.26 ± 0.31 for TCS). Thus, it was concluded that a single or a narrow range of K OC values for TCC and TCS may be appropriate to describe retention of the compounds in soils and sediments. However, models that assume complete reversibility of the retention/release processes of the compounds in soils and sediments may not adequately describe the retention/release characteristics of the compounds in soils and sediments, especially when the chemicals are biosolids borne. Environ. Toxicol. Chem. 2010;29:1925–1933. © 2010 SETAC