Influence of marine phytoplankton, transition metals and sunlight on the species distribution of chromium in surface seawater

Shun-Xing Li (1) , Feng-Ying Zheng (1, 2) , Hua-Sheng Hong , Nan-Sheng Deng (2) , Lu-Xiu Lin (1)

1 Department of Chemistry & Environmental Science
2 Department of Environment Science

The photo-reduction of Cr(VI) to Cr(III) by marine phytoplankton (diatoms, red and green algae),with or without the presence of transition metals (Fe(III), Cu(II) and Mn(II)) was studied. The direct influence of marine phytoplankton on the photochemical reduction of Cr(VI) was confirmed for the first time, and two kinds of mechanism were suggested to be responsible for the species transformation: (a) Cr(VI) in excited state could be reduced by the electron donor in its ground state via photo produced electrons; and (b) the solvated electrons reduce the CrO4 anions in their ground state. The conversion ratio of Cr(VI) to Cr(III) increased with increasing algae concentration and irradiation time. Different species of marine phytoplankton were found to have different photo-reducing abilities. The photochemical redox of transition metals could induce the species transformation of chromium. After photo-reduction by marine phytoplankton and transition metals, the ratio of Cr(VI) to Cr(III) was in the range of 1.45∼2.16 for five green algae (, and ), and only 0.48 for (diatom) and 0.71 for (red alga). The species distribution of chromium in the sunlit surface seawater was greatly affected by combined effects of marine phytoplankton (main contributor) and transition metals; both synergistic and antagonistic effects were observed. The results provided further insights into the species distribution and the biogeochemical cycle of chromium, and have significant implications for the risk assessment of chromium in the sunlit surface seawater.

Mots clés: Chromium; Photoreduction; Marine phytoplankton; Species transformation

Shun-Xing Li, Feng-Ying Zheng, Hua-Sheng Hong, Nan-Sheng Deng, Lu-Xiu Lin. Influence of marine phytoplankton, transition metals and sunlight on the species distribution of chromium in surface seawater. Marine Environmental Research, 2009, 67 (4-5), pp.199. ⟨10.1016/j.marenvres.2009.02.001⟩. ⟨hal-00563070⟩