Lead availability in soils from Portugal's Centre Region with special reference to bioaccessibility

Abstract

Previous environmental biomonitoring studies indicated higher environmental lead (Pb) pollution levels at the districts of Aveiro and Leiria (Portugal). In evaluating the risk for human health, which is associated with contaminated soils after oral uptake, total soil concentrations have generally been held against criteria established from toxicological studies based upon the assumption that the uptake of the contaminant is similar in the toxicological studies and from the soils assessed. This assumption is not always valid, as most toxicological studies are carried out with soluble forms of the contaminants, whereas many soil contaminants are or become embedded in the soil matrix and thus exhibit limited availability. This study intends to estimate the soluble fraction of Pb in the soils from central Portugal, and to assess the bioaccessibility of Pb and, hence, infer exposure and risk for human health. Yet, as the physical-chemical properties of the soil exert some control over the solubility of Pb in the surface environment, the relation between such soil properties and the estimated soluble and/or bioaccessible fractions of Pb is also investigated. Other objective, with a more practical nature, was to give some contribution to find a suitable in vitro mimetic of the gastrointestinal tract environment. The results indicate relatively low total metal concentrations in the soils, even if differences between regions were observed. The Aveiro district has the higher total Pb concentration and the metal is in more soluble forms, that is, geoavailable. Soils with higher concentrations of soluble Pb show higher estimates of bioaccessible Pb. Soil pH seems to influence human bioaccessibility of Pb.