Mobility of water-soluble aerosol organic matters (WSAOMs) and their effects on soil colloid-mediated transport of heavy metal ions in saturated porous media

Abstract

Water-soluble aerosol organic matters (WSAOMs) produced by biomass pyrolysis/burning can penetrate subsurface environment, and are anticipated to have a profound effect on the fate of contaminants in aquatic ecosystems. Herein, WSAOMs derived from corn straw (CS-WSAOMs) and pinewood sawdust (PW-WSAOMs) pyrolysis at 300–900 °C were utilized to investigate their mobility characteristics and impacts on the transport of heavy metal ions (i.e., Cd2+) in saturated quartz sand with or without soil colloids. This study clearly demonstrated that WSAOMs in subsurface systems exhibited high mobility, which increased as WSAOMs molecular sizes decreased and hydrogen-bond interactions between WSAOMs and sand grains declined. WSAOMs significantly improved heavy metal (i.e., Cd2+) and soil colloid-mediated Cd2+ mobility in the porous media, which stemmed from the increased binding affinities of colloids toward metal ions and the high mobility of WSAOMs. Interestingly, in terms of the mobility and colloid-facilitated transport of Cd2+, WSAOMs from higher pyrolysis temperatures exhibited enhanced effects; meanwhile, the PW-WSAOMs demonstrated stronger effects than the CS-WSAOMs. The trends were mainly attributed to the differences in the metal-binding affinities (e.g., cation-π interactions) and transport abilities of WSAOMs, as well as diverse Cd2+ adsorption capacities of colloids induced by various WSAOMs.