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 (KOC) apply to all solid matrices and that the partitioning process is completely reversible. Partition coefficients (Kd) (from which the KOC 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 [14C]TCC or [14C]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 Kd values determined in biosolids (log Kd 3.34 ± 0.13 for TCC and 3.76 ± 0.39 for TCS) were greater than those determined in soils (log Kd 1.71 ± 0.09 for TCC and 2.25 ± 0.26 for TCS) and biosolids-amended soils (log Kd1.90 ± 0.16 for TCC and 2.31 ± 0.19 for TCS), however, the KOC values of all three solid matrices were similar (log KOC 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 KOC 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