Interaction between metal(loid)s and soil mineral-organic matter associations

Mineral-organic matter (OM) associations sequester metal(loid)s in the environment, controlling their mobility and bioavailability in soils. This review describes processes and mechanisms operating at the interfaces between OM and mineral phases in mineral-metal(loid)-OM and metal(loid)-OM-mineral associations. It will demonstrate the assumption that metal(loid)s interact with "pure" mineral and OM matrixes in soils is overly simplistic as numerous interactions such as adsorption, precipitation and incorporation of metal(loid)s on the surfaces, interfaces or within minerals and OM can occur. For example, multi-layer organic compounds can control the incorporation of minerals and regulate the carbon and metal(loid)s mobility and sequestration. To simplify complex metal(loid)-mineral-OM interactions, we propose five nanometric mechanisms for the sequestration of metal(loid)s by mineral-OM associations: I. heterogeneous nucleation of metal(loid)s-bearing nanomaterials (NMs) within the organic matrix, II. nucleation of NMs via reduction of metal(loid) species on OM/mineral surfaces, III. nucleation of NMs via transformation of preexisting NMs, IV. heterogeneous nucleation of NMs on mineral inclusions and V. diffusion and homogeneous distribution of metals in mineral inclusions and organic matrix. This review helps to develop potential materials for (a) remediation techniques that allow the effective removal of metal pollutants from water and soil and (b) biomass carbon removal and storage techniques that can sequestrate and stabilize carbon in terrestrial systems and thus help fight the current climate change. Future studies need to identify the spatial and functional complexity and the heterogeneous structure and composition of metal(loid)-mineral-OM associations, in which matrixes and adsorbed or incorporated metal(loid)s can transform during multi-dynamic processes.