The distribution of precious metals (Au, Ag, Pt, and Pd) in the soils of the Campania Region (Italy)

This study assesses the distribution of Au, Ag, Pt, and Pd in the topsoils from the Campania Region (Southern Italy). The 13,600 km2 study area was divided using a 16 km2 grid in the suburban and agricultural areas, and a 4 km2 grid in urban areas and 2120 topsoil samples were analyzed by ICP-MS after an aqua regia digestion. The maximum concentrations of Pt and Pd were 278.1 and 431.9 ppb, respectively, however, >50% of samples analyzed during this study had concentrations of Pt and Pd below the instrumental detection limit. Gold and Ag concentrations ranged from 0.2 to 1278.6 ppb, and 2 to 8132 ppb, respectively. The geochemical data was first elaborated into dot maps to assess the relationship between the real concentrations across the region. Point data were subsequently classified using their statistical percentile thresholds (25th, 50th, 75th, 95th and 98th). A C-A fractal model was then applied to the data to assess their spatial distribution and determine thresholds representing changes in concentrations highlighting background/baseline and anomalous components. Major results indicate that: (1) application of C-A fractal model on multifractal gridded data allows the discrimination of geochemical anomalies from background concentrations; (2) Au, Ag, Pt, and Pd in Campania topsoils clearly reflect both natural and anthropogenic influences on their occurrence and distribution; (3) a clear relationship exists between the abrasion of automobile catalytic converters, the occurrence of PM10 aerosol particles, and elevated concentrations of Pt and Pd in soil; (4) the concentration of Ag and Au in the soils of the study area reflect differences in the origin of their source material in the volcanic products of northern (Roccamonfina) and central Campania (Campi Flegrei, Vesuvius); and (5) clear enrichment in Au and Ag are located corresponding to the main urban areas.