Oxide weathering and trace metal release by bacterial reduction in a New Caledonia Ferralsol

Bacterial reduction of Fe- and Mn-oxides was studied in a surface horizon o f a New-Caledonian Ferralsol in batch experiments. Two treatments were impo sed containing different sources of organic matter (soil organic matter wit h or without glucose addition) to link organic matter biodegradation with r eduction process. The concomitant solubilization of Ni and Co was also stud ied. Results showed that anaerobic Fe- and Mn-reducing bacterial activity w as responsible for Fe- and Mn-oxide solubilization by anaerobic respiration or fermentation. When C was more available, oxide reduction was enhanced. Mn-oxide appeared as the major reducible phase and metal source rather than goethite. Co and Ni were solubilized with Fe and Mn but their amounts in s olution decreased at the end of experiment. The bioavailability of heavy me tals in this soil was increased by biological reduction but was limited by adsorption or precipitation phenomena.