Photoreduction of manganese dioxide in seawater by organic substances under ultraviolet or sunlight

The reduction of particulate Mn(IV) in the presence of phytoplankton culture solution or hydroxycarboxylic acids, which might be derived from photodecomposition of phytoplankton cells, under ultraviolet (u.v.) or sunlight irradiation was investigated. The measurement of the oxidation number of the dissolved Mn during these experiments showed 2.1, indicating the reduction of particulate Mn(IV) to dissolved Mn(II). The reduction proportion of Mn(IV) to Mn(II) was 65, 30 and 30% for glucaric, gluconic and tartaric acids, respectively, The present study suggests that the reduction of particulate Mn(IV) to dissolved Mn(II) in seawater occurs under natural condition.