Chromium Species and Fractions in Agricultural and Urban Mediterranean Soils: Effects of Aging and Soil Properties on Soil Cr (III) and Cr (VI) Availability

In this study, both trivalent and hexavalent forms of chromium were examined in urban and agricultural Mediterranean soils. Chromium partitioning in different soil fractions was studied. Pot experiments included contamination of soil samples using Cr solutions, as well as a further study regarding Cr distribution in naturally contaminated soils. The soils were subjected to quantitative determination of both the available and total Cr concentration, as well as Cu and Zn, which were naturally present in the soil samples. Metal concentrations in the soil fractions were quantified after the application of the BCR fractional extraction method. The numbers of both trivalent and hexavalent Cr ions in each extract were determined. Considerable discrepancies were noticed regarding the Cr content of each soil fraction in both municipal and cultivated soils, indicating the possible origin of the pollution. The increasing impact of pollution is a significant parameter for the availability of chromium ions in both agricultural and urban soils. Increased pollution durations resulted in a significant increase in the non-available fraction of toxic Cr (VI), mainly in urban soil. Variations were also observed in the chromium species, as changes in soil parameters and in the conditions of the experiment seem to affect the conversion of the less harmful trivalent chromium to the toxic hexavalent chromium. In urban soils, the amount of toxic Cr (VI) bound to iron and manganese oxides exceeds 37.8%, while in agricultural soils, the amount of Cr (VI) associated with soil organic matter reaches 35%. Knowing the mechanisms and variables influencing Cr availability in agricultural and urban Mediterranean soils is desirable, as safe living in ecologically acceptable fields and producing safe goods in healthy soil systems are paramount goals.