Chromium and Nitrogen Behavior in High-Mn Soils Fertilized with by-Products of the Intermediate Processes of Tanning.

Chromium occurs in various oxidation states in nature, although only Cr (III) and Cr (VI) are known to occur naturally in soils. The presence of Cr (III) in the diet of humans and animals is important because of its essentiality to mammals. However, Cr (VI) is toxic, mutagenic, and carcinogenic to humans and animals. Because of its high toxicity, Cr (VI) is becoming increasingly regulated and very restrictive limits concerning concentrations of Cr (VI) in the environment are being established. The objective of this work was to study changes in the forms of Cr (III) and Cr (VI), as well as ammonium and nitrate in A and B horizons of two soils containing high contents of manganese oxides (up to 75,000 mg kg-1) and/or Cr (up to 18.000 mg kg-1), which were incubated with a by-product of the tannery industry, used as a nitrogen fertilizer (total N ~ 12%, total Cr ~ 2.5%). Overall, the incubated soils had higher levels of total nitrogen, ammonium, and nitrate, especially in A horizons. Changes in the contents of Cr (III) and Cr (VI) following the application of the by-product in the soils were not directly related to their content of Mn oxides. Sponsored by CNPq, FAPEMIG and CAPES.