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

Abstract

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.

Bioavailability: Exposure, Dose and Risk Assessment

“…Concentrations of contaminants in the soil adhering to the skin are enriched relative to the concentrations of contaminants present in the bulk soil. This may be due to fine particles, on which contaminants tend to be concentrated, preferentially adhering to the skin [50].…”

“…(c) A human doseresponse relationship is then constructed. The animal dose is scaled to a human equivalent dose by taking a single value (that is the median value, in this case the effective dose that results in the outcome of interest being realized on 50% of the study population, ED50 ) from the interspecies extrapolation distribution. (Modified from Evans, J. S.; Rhomberg, L.R.…”

Transfer factors of226Ra,210Pb and210Po from NORM-contaminated oilfield soil to someAtriplexspecies,AlfalfaandBermuda grass

“…On the other hand, natural environmental radioactivity arises mainly from primordial radionuclides, such as 40 K, and the radionuclides from the 232 Th and 238 U series and their decay products are also considered important due to their contributions to the internal radiation dose. Several studies on transfer of natural radionuclides from soil to plants have been carried out in different regions in the world (Sheppard and Evenden, 1992;Martinez-Aguirre and Perianez, 1998;Ewers et al, 2003;Staven et al, 2003;Vera Tomé et al, 2003;Pulhani et al, 2005;Blanco Rodríguez et al, 2006Al-Masri et al, 2008).…”

Determination of Sediment Profile for ²¹⁰Pb, Pb, U and Th from Sultan Abu Bakar Dam Due to Soil Erosion from Highland Agriculture Area, Cameron Highlands, Malaysia

“…Natural weathering agent such as rainfall will cause soil erosion and enrichment of these element (Sheppard and Evenden, 1992;Nziguheba and Smolders, 2008). These elements were transported by the water through river and deposited at the bottom of the lake together with the sediment (Begy et al, 2009;Swarzenski et al, 2003).…”