A Case Study: Chromium Concentration and its Species in a Calcareous Soil Affected by Leather Industries Effluents

Annually, a large amount of effluents is discharged from an industrial zone dedicated to leather industries into a dried seasonal waterway bed in Mashhad plain, Northeast of Iran. These soils are high in pH, CaCO contents and have no naturally occurring chromium detectable in mg/kg range. Considering high 3 concentration of chromium in the discharged leather industries effluents and their direct release into the soil with no further treatments the current research was performed to investigate the total chromium concentration and its trivalent and hexavalent species in contaminated soils. In order to obtain chromium distribution pattern among different soil fractions and evaluate its bioavailability, sequential extraction was carried out and chromium concentration was measured in exchangeable, organic, carbonated and residual fractions. As the mean of measured trivalent and hexavalent chromium in 0-45 cm depth of the contaminated soil were 193.64 mg/kg and 1.74 mg/kg, respectively, the experiment results showed that soil was polluted with chromium. Also considering high mobility and extreme toxicity of hexavalent chromium the threat of groundwater and other local water resources contamination is a major concern. Fractionation results indicated that more than 90% of the total chromium belonged to the residual fraction. However, because of its high concentration in polluted soil and specific characteristics of the contaminated area, as well as using plants growing in the vicinity of contaminated area for animal feeding, the potential risk of food chain toxicity is serious.