Potentially toxic elements (PTEs) in the soils of a densely populated active volcanic area: the Campi Flegrei case study in Italy.

The line of research on potentially toxic elements (PTEs) is of growing interest to the scientific community for protecting society against adverse health issues. The Campi Flegrei caldera in southern Italy is an active volcanic area where above two million people live, making it an ideal study area for investigating PTEs of natural and anthropogenic origin through the latest advances in geochemical data analysis. Therefore, a total of 394 topsoil samples (0 to 15 cm) were collected for determining the “pseudo-total” concentrations of elements in the <2 mm fraction using a combination of inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS), following aqua regia digestion.

The median values show that concentrations of Zn, Cu, Pb, V and As are greater (>10 mg/kg) than Cr, Co, Ni, Tl, Sb, Se, Cd and Hg. The geochemical maps generated by the Empirical Bayesian Kriging interpolation technique indicate that the higher concentrations of Pb, Zn, Cd, Cr, Hg, Ni and Sb are related to the greater population density (>6500 persons per Km²) in the urban area, but the elevated levels of As, Tl, Co, Cu, Se and V are observed in the other parts. In the context of compositional data analysis, the correlation diagram and robust principal component analysis detected: (1) the Pb–Zn–Hg–Cd–Sb–Cr–Ni association that likely shows anthropogenic activities such as heavy traffic load and fossil fuel combustion in the urban area; (2) the Al–Fe–Mn–Ti–Tl–V–Co–As–U–Th association that mostly represents the contribution of pyroclastic deposits; and (3) the Na–K–B association that probably reveals the weathering degree.

To choose the PTEs with potential health risks for the local inhabitants, the PTE quantities in soil are compared with the corresponding contamination thresholds established by the Italian legislation for residential land use. The Tl, Pb and Zn contents exceed the threshold in more than 15% of the collected samples, but Tl which derives from a natural source (e.g., leucite) is culled before evaluation. Then, children (0-6 years old) are considered for health risk assessment because: (1) Pb has significant adverse health effects in children; and (2) the more frequent hand-to-mouth behavior in children under 6 years old is linked to the higher chance of exposure. The probabilistic health risk modeling for the children <6 years old highlights negligible (hazard quotient below 1) Pb and Zn non-carcinogenic risk and unexpected (cancer risk ≤1E-06) Pb carcinogenic risk for exposure through soil ingestion. However, for the inhalation pathway, the children aged <1 year old have the highest chance (90%) of acceptable (i.e. from 1E-6 to 1E-4) Pb carcinogenic health risk. This should not be overlooked because Naples is under high environmental pressure and previous studies reported increased Pb and Zn quantities in soil between 1974 and 1999. Overall, the results of geostatistical interpolation, compositional data analysis and probabilistic health risk modeling potentially uncover the link between soil geochemistry and human health in densely populated active volcanic areas.