Concentration enrichment of sparingly soluble contaminants (U,Th and Pb) by erosion and by soil adhesion to plants and skin

Sparingly soluble contaminants are less likely to affect human health through food chain transfers, such as plant uptake or passage through animal-based foods, because mobility in these pathways is limited by solubility. Direct ingestion or inhalation of contaminated soil becomes the dominant pathway. However, both of these can be selective processes. Clay-sized particles carry the bulk of the sparingly soluble contaminants, and mechanisms that selectively remove and accumulate clay from the bulk soil also concentrate the contaminants. Erosion is another process that selectively removes clays. This project examined the degree of clay and contaminant-concentration enrichment that could occur by these processes, using U, Th and Pb as representative contaminants and using a clay and a loam soil. Erosion by water in natural rainfall events caused concentration enrichments up to 7 fold, and enrichments varied with characteristics of the erosion events. Enrichments were higher for the coarser, loam soil. Adhesion to skin gave modest enrichments of 1.3 fold in these soils, but up to 10 fold in sandy soils studied subsequently. Adhesion to plant leaves, where there was no root contact with contaminated soil, gave leaf concentrations comparable to situations where the roots contacted the contaminated soil. Clearly, adhesion to leaves is an important component of plant accumulation of sparingly soluble contaminants.