Adsorption of Biosolids-Derived Dissolved Organic Matter and Selected Endocrine Chemicals to Two Iowa Soils.

The heterogeneity of the soil-water system makes the fate of endocrine-disrupting chemicals (EDCs) such as bisphenol-A (BPA), 17α-ethinylestradiol (EE2), and 4-nonylphenol (4-NP) difficult to predict. In agricultural systems where biosolids are land applied, the input of exogenous dissolved organic matter contributes to the complexity of the system. In this study, we explored the adsorption of biosolids-derived dissolved organic matter (BDOM) to two soils as well as the interactions of BPA, EE2, and 4-NP with the two soils and with BDOM by a batch equilibrium method. The two soils were Zook (a fine, smectitic, mesic Cumulic Vertic Endoaquoll with 61% clay and 2.8% organic carbon) and Hanlon (a coarse-loamy, mixed, superactive, mesic Cumulic Hapludoll with 14% clay and 1.6% organic carbon).

The BDOM showed low adsorption intensity (Langmuir coefficient, K_L = 0.015 L kg^-1) to both Hanlon and Zook soil materials, suggesting that the BDOM may be relatively mobile under saturated flow conditions in soil. In general, all three EDCs showed greater adsorption affinity (as indexed by the Freundlich coefficient, K_LF) to the Zook soil materials than to the Hanlon soil materials, but 4-NP exhibited greater adsorption affinity than EE2 or BPA. The hysteresis index (HI) (using a single adsorption-desorption cycle and determined separately at concentrations of 0.2, 0.5, 1, and 2 mg L^-1), however, indicated that BPA was least readily desorbed from the soil, with HI values ranging from 0.73 to 0.93. In contrast, 4-NP was the most readily desorbed, with HI range from 0.31 to 0.62.

The interaction of the EDCs to BDOM was determined by a pore size-exclusion method using solid-phase extraction (SPE) cartridges. The Freundlich indices of adsorption heterogeneity, n, for BPA, EE2, and 4-NP were 0.89, 0.21, and 0.69, respectively. Although we cannot directly compare the K_F coefficients because of the varying n values of BPA, EE2, and 4-NP, the K_F values for adsorption to BDOM were 25,047, 3673, and 3639 mg^1-nLⁿ kg^-1, respectively. Our study suggests that BPA is most likely to interact strongly with and to be carried by the BDOM and 4-NP will be adsorbed strongly to the soil. There was no clear trend with EE2.