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 of a New-Caledonian Ferralsol in batch experiments. Two treatments were imposed containing different sources of organic matter (soil organic matter with or without glucose addition) to link organic matter biodegradation with reduction process. The concomitant solubilization of Ni and Co was also studied. Results showed that anaerobic Fe- and Mn-reducing bacterial activity was 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 solution decreased at the end of experiment. The bioavailability of heavy metals in this soil was increased by biological reduction but was limited by adsorption or precipitation phenomena.