Adsorption of BPA, EE2, and 4-NP By Alluvial Soils in Iowa.

Bisphenol-A (BPA), 17α-ethinylestradiol (EE2), and 4-nonylphenol (4-NP) are endocrine disrupting chemicals that may interfere with the reproductive systems of aquatic species. To better understand the potential for movement of these compounds from soil to aquatic systems, in the present study, we determined the degree of their adsorption by two Iowa alluvial soils with varying organic matter and clay concentrations [Zook (clay) and Hanlon (sandy loam)]. The soil samples were equilibrated against a range of solution concentrations, and the difference in the initial and the equilibrium concentrations was assumed to represent that adsorbed by the soil.

The data were fit by the combined Langmuir-Freundlich model, also referred to as Sip’s isotherm, to generate the adsorption parameters Q_max (adsorption capacity), K (affinity constant), and n (index of heterogeneity). In general, over the wide range of equilibrium concentrations, the model fit was good, with R² = 0.99. The n values were typically less than 1 or greater than 1, suggesting considerable heterogeneity of the sorption sites, although in BPA-Hanlon system, n=0.96 indicated relatively homogenous sorption sites. Among the three compounds, 4-NP is the least polar and BPA is the most polar. The value of the affinity index, K, for 4-NP was the largest in both the Hanlon and Zook soils, and it was also many times larger than that of in EE2 and BPA. Between the two soils, the Zook soil had much greater adsorption affinity and capacity for EE2 and 4-NP than the Hanlon soil, although with BPA the differences in affinity and capacity were not significant. While organic matter and clay concentration play a big role in adsorption, the chemical properties of the compounds, such as water solubility and octanol-water partition coefficient, are also useful predictors of sorption behavior.