A Probabilistic Approach for Estimating Human Health Risk from Lead-Contaminated Soils

This study proposes a method for estimating the risk associated with the ingestion of soil contaminated with lead (Pb), considering the nature of the source and the parameters that influence its bioavailability. Statistical variables related to the solubility and bioavailability of Pb are used, including pH, electrical conductivity (EC), particle size distribution, mineralogical composition, and bioaccessibility/bioassimilability. These parameters allow indicators to be generated and an algorithm based on probability distributions to be constructed, which requires in-depth knowledge of the source materials in order to assess the health risk derived from the concentration of the metal.

To this end, 186 samples from areas affected by mining activities in the Region of Murcia (southeast Spain) and nearby soils were analysed. The samples were screened, homogenised and characterised by determining pH, EC, particle size, total and extractable Pb content, oral bioaccessibility tests and mineralogical analysis by X-ray diffraction.

The main objective was to develop a flexible and applicable procedure to estimate whether a soil poses a risk to human health in residential settings. The methodology is based on variables with a significant correlation with total Pb content and on parameters related to its solubility and bioavailability. The expected result is a global risk indicator, useful for taking corrective measures at contaminated sites that may be used for residential purposes. This approach allows for the incorporation of new indicators or the modification of existing ones, provided they are based on knowledge of the source of contamination.

Statistical analysis makes it possible to explain the uncertainty associated with parameters such as mineralogy, bioaccessibility and granulometry, offering valid results. Mineralogy is confirmed as a key factor in estimating risk, although it requires prior classification of the components present. The results show a significant correlation between the non-carcinogenic risk calculated using accessible Pb content and the risk estimated by the proposed indicator, with no false negatives. In some cases, risk overestimation (false positives) was detected, attributable to particular characteristics of the site, with values above the permissible limit but with a hazard index (HI) below unity.

This procedure is an effective tool for assessing risks in critical mining areas and planning preventive measures, contributing to the safe management of lead-contaminated soils.