Competitive sorption of bisphenol A and phenol in soils and the contribution of black carbon

Abstract

The sorption of contaminants such as bisphenol A (BPA), an endocrine disrupting chemical associated with various health problems, plays an important role in their transport and bioavailability in soils. This study investigates the sorption of BPA and phenol in two soils, Lu-Kung soil (LK) and Chen-Chu-Llu soil (CCL), as well as in straw-derived black carbon (BC). The sorption of both phenolic compounds in LK is much higher than that in CCL because of the higher organic content in LK (3.5%) as compared to CCL (1.3%). In addition, a higher BC fraction is observed in LK than in CCL. Furthermore, the sorption of BPA is greater than that of phenol because BPA exhibits higher hydrophobicity. For BPA, Freundlich affinity constants, Kf, are 2.62 (Freundlich exponent constant, n=0.91) in LK and 1.54 (n=0.92) in CCL. For phenol, Kf is 0.695 (n=1.0) in LK and 0.0014 (n=2.3) in CCL. For competitive sorption experiments, phenol sorption in LK could be suppressed by BPA, but the reverse is not possible. Chemical hydrophobicity strongly affects their competition. Similar competitive adsorption behaviour is observed on BC. Phenolic compounds’ sorption on carbonaceous materials occurs through a bilayer formation. Thus, surface adsorption on carbonaceous materials largely determines the sorption of organic compounds in soils.