Hexavalent chromium quantification by isotope dilution mass spectrometry in potentially contaminated soils from south Italy

Due to carcinogenicity of hexavalent chromium [Cr(VI)], its accurate quantification in Cr-contaminated soils is of paramount importance. The aim of this work was to quantify Cr(VI) by species-specific IDMS in soil samples from two Italian case studies: A) farmland potentially contaminated by pseudototal Cr and Zn and heavy hydrocarbons due to past illegal burial of tannery wastes; B) Solofrana valley where volcanic soils are potentially contaminated by pseudo-total Cr and Cu due to tannery activities. Hexavalent Cr extraction from soils was performed by focused microwaves (5 min at 80 °C) using 50mM EDTA, followed by the separation of Cr species by IC and detection by ICP-MS. The Cr(VI) extracted from 20 soil samples of case study A ranged from 0.15 to 11.18 mg g-1, with 70% of samples exceeding the Cr(VI) screening value set by Italian Parliament for residential/urban soil to assess their potential contamination. Higher levels of Cr(VI) (22.0-107.1 mg g-1) were extracted from other 7 Cr-most-enriched soil samples, which required a pre-treatment with n-hexane to remove part of organic compounds from each sample, since these reducing agents made the quantification of Cr(VI) by IDMS more challenging because they caused an almost complete reduction of 50Cr(VI) used for IDMS quantification. Hexavalent Cr extracted from soil samples of case study B ranged from 0.70 to 5.79 mg g-1, with 42% of samples exceeding the value set by Italian legislation. In both case studies, the Cr(VI) extracted from soil was significantly correlated to the pseudo-total Cr content.