Lanthanoid geochemistry in rainwater from rural, urban, industrial, and volcanic areas of Sicily, Italy

Despite only a few studies on the concentration of the lanthanoid elements (from La to Lu) in rainwater are available in the literature, their significant environmental impact has been recognized. Shale-normalized lanthanoid patterns are used to determine the source of these elements in rainwater. Lanthanoid concentrations were measured in 74 rainwater samples collected, from March 2021 to November 2021, at 15 sites in Sicily, located in different contexts: rural (Nebrodi), urban (Palermo and Catania), industrial (Milazzo and Priolo Gargallo) and volcanic (Etna). Rainwater samples were collected using bulk collectors and underwent a pre-concentration procedure, according to Arslan et al., 2018, before analytical determination by ICP-MS (Agilent 7800ce). The concentrations in rainwater samples were variable, with the total dissolved lanthanoids (TDLs = Σ of lanthanoids) and the TDLs increased with decreasing pH values (r = 0.611, p <0.0001). Median concentrations of 29 ng/L, 42 ng/L, 51 ng/L, 66 ng/L, 67 ng/L, and 74 ng/L were measured for Milazzo, Nebrodi, Palermo, Catania, Priolo Gargallo, and Etna, respectively. Lanthanum concentrations were elevated in all the sampling sites, reaching median La/Ce ratios up to 3.80 for the Priolo Gargallo industrial area. The source of the La enrichments in urban areas may be due to the vehicular traffic (automobile catalysts), while for both industrial areas, the sources may be related to the traffic emissions and, given the emissions from the combustion of fuel oils from the power plants (low La/V ratios: 0.06 for Priolo Gargallo and 0.02 for Milazzo). Small La enrichments, sometimes accompanied by Eu enrichments, had also been observed at Nebrodi and Etna, and possible sources were the crustal source and the volcanic emissions, respectively. This study confirmed that lanthanoids in rainwater can be a valuable tool to discriminate the various sources of anthropogenic pollution.