[Photoreduction of Se (VI) by marine algae-transitional metals-light system]

Seven marine phytoplankton, including five green algae (Tetraselmis levis, Chlorella autotrophica, Dunaliella salina, Nannochloropsis sp. and Tetraselmis subcordiformis), one diatom (Phaeodactylum tricornutum), one red alga (Porphyridium purpureum), and three usual transitional metals (Fe(III), Cu(II), Mn(II)) were used to make up marine phytoplankton-light or transitional metals-light or marine phytoplankton-transitional metals-light system. In such system, Se(VI) could be transformed into Se(IV) by photoreduction. The species transformation of selenium could be photo-induced by redox reaction of transitional metals. The photochemical activity of marine phytoplankton was confirmed for the first time, because marine phytoplankton could adsorb and concentrated of selenium, transitional metals and organic substances (including the exudation of algae, as reducing agent) which redox potentials were changed. The ratios of Se(VI) to Se(IV) were dominated by the species, the concentration of marine phytoplankton and transitional metals, and it could be enhanced through increasing the concentration of marine algae or the combined effect from marine algae and transitional metals. After photoreduction by ternary system, the ratio of Se(VI) to Se(IV) ranges from 1.17 to 2.85, which is close to the actual value in euphotic layer of seawater. The photochemical process that is induced by marine algae and transitional metals dominative the leading effects on the distribution of oxidation states of selenium.