Polanyi-Based Models for the Competitive Sorption of Low-Polarity Organic Contaminants on a Natural Sorbent

The development of appropriate equilibrium sorption relationships for anthropogenic organic contaminants with soils and sediments is essential to predicting the extents and rates of solid−water interactions in the environment. In this context, we previously reported results that showed how nonlinear sorption isotherms with nine low-polarity organic chemicals on a silty aquitard material could be modeled as a combined adsorption-partitioning process. The adsorption component was ascribed to presumed traces of a carbonaceous adsorbent, for which adsorption was well described by a Polanyi-based isotherm. In this work, we report competitive sorption behavior on the same material, as observed from batch experiments in binary solute systems that contain combinations of the previously studied sorbates (chorinated benzenes and polyaromatic hydrocarbons) over wide ranges of concentra tion. The results confirmed our expectation that partitioning is an increasingly dominating contribution to overall sorption when cosorbates are present. Moreover, the competitive effects could be very well predicted on the basis of Polanyi-Manes adsorption theory and the prior single solute results. Overall, the results further validate the applicability of a Polanyi-based modeling approach and lend additional support to the hypothesis that this sorbent contains trace quantities of high surface area carbonaceous material.