Subsurface Transport of As, Se, Cu, and Pb Contaminants in Association with Soil and Biosolid Nano- and Macro- Colloid Fractions

This study investigated the potential of nanocolloid and macrocolloid fractions separated from selected soils and biosolids to co-transport two anionic (Se, As) and two cationic (Cu, Pb) contaminants through intact soil monoliths. The soil colloids represented smectitic, kaolinitic, and mixed mineralogical compositions while the biosolid colloids were derived from an aerobically digested municipal sewage sludge. Selected characterizations of the colloids included particle size (DLS, TEM, SEM), SA, settling stability, EC, pH, CEC, OC, zeta potential, Kf, and mineralogy. Leaching experiments involved the elution of nano- and macrocolloid suspensions mixed with 2 mg L-1 contaminants through soil monoliths during a four pore volume leaching cycle. In spite of similar contaminant sorption affinities and notable nanocluster formation during the transport, nanocolloids were eluted in greater quantities than macrocolloids and co-transported higher metal contaminant loads for both anionic and cationic contaminants. Significantly higher contaminant loads were mobilized in association with the colloids over the control contaminant solution, with soluble forms dominating the anionic and colloid-bound forms the cationic contaminants. The enhanced elution of both soluble and sorbed contaminant loads in the presence of nanocolloids is attributed to preferential flow, size exclusion and ion exclusion mechanisms. The findings of this study emphasize the importance of considering multiple physicochemical and mineralogical parameters in contaminant transport models in order to accurately assess environmental pollution risks and develop efficient remediation strategies.