Mineralogical and physicochemical methods to differentiate between naturaland anthropogenic sources of chromium in soils

This study evaluates pollution from a former tannery by examining soils con taining high concentrations of chromium (between 138 and 720 mg/kg dry matt er according to the sample). This study presents an original methodology fo r characterizing chromium according to its two possible origins in soils: n atural or anthropogenic. Conducting both a mineralogical study and a physic ochemical study made it possible to clearly understand these origins. Natur al chromium is particularly linked to pyroxenes, a primary mineral of the M assif Central, France, and found in large quantities in the samples studied . Anthropogenic chromium is adsorbed by vermiculites on their interfoliary sites. These clays possess a high capacity of cationic exchange and can thu s attract chromium easily. In all of the samples studied, the naturally chr omiferous mineral contribution was high (97 to 519 mg/kg dry matter), where as that of the clays was low (41 to 201 mg/kg dry matter), indicating a sma ller proportion of chromium introduced by humans. Natural chromium values a re approximately 70 to 80%, whereas those for anthropogenic chromium are ap proximately 20 to 30%. This approach makes it possible to set realistic obj ectives for the cleanup of chromium-contaminated soils.