Pyrene Sorption to Water-Dispersible Colloids: Effect of Solution Chemistry and Organic Matter

Abstract

Chemical sorption to mobile soil colloids is a controlling factor for colloid-facilitated chemical transport in the vadose zone and groundwater. We investigated sorption of pyrene to soil colloid suspensions originating from soils differing in organic matter content for different solution chemistries. Colloids were obtained from two soils with different organic matter contents but similar geological histories by three different methods: (i) chemical dispersion, (ii) mechanical dispersion in water, and (iii) spontaneous release in water. Batch sorption experiments were conducted at five pyrene concentrations, in either pure water or at two different concentrations of K + and Ca 2+ . Generally, K + addition enhanced pyrene sorption, whereas Ca 2+ addition decreased sorption. The chemically dispersed colloids exhibited the highest pyrene sorption capacity and had the most nonlinear sorption isotherms, whereas whole soil had the most linear isotherm. Model calculations of the potential amounts of leachable pyrene illustrated the importance of including both colloid- and dissolved organic matter (DOM)-facilitated transport in risk assessment models when dealing with pyrene transport. The leaching potential of dissolved pyrene (with no DOM- and colloid-facilitated transport) was 5% of the leaching potential when both DOM- and colloid-sorbed pyrene was included.