Determination of extractable chromium(vi) in soils using a photometric method

For determination of soluble Cr(VI) beside Cr(III) in soil a method was developed based on the photometric standard protocol used for determination of Cr(VI) in waters. For Cr(VI) extraction, the soil is shaken with a mixture of aluminium sulfate solution and phosphate buffer. To prevent interfering redox reactions, oxidizing compounds are reduced by adding sulfite, and afterwards reducing compounds are oxidized by hypochlorite. After reaction of Cr(VI) with 1,5-diphenylcarbazide, the photometric determination is performed. Using this approach, Cr(VI) concentrations of 0.2 – 25 mg/kg in soils are detectable. Analyses of a number of soils revealed that anthropogenically chromium-contaminated soils showed relatively high amounts of soluble Cr(VI), while only traces of Cr(VI) were extractable from soils with high geogenic chromium contents.