Li Shun-Xing, Zheng Feng-Ying, Hong Hua-Sheng, Deng Nan-sheng, Lin Lu-Xiu
Department of Chemistry and Environmental Science, Zhangzhou Teachers College, Zhangzhou, Fujian 363000, PR China.
Mar Environ Res. 2009 May-Jun;67(4-5):199-206. doi: 10.1016/j.marenvres.2009.02.001. Epub 2009 Feb 28.
The photoreduction 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 mechanisms 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 CrO(4)(2-) 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 photoreduction 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 (Tetraselmis levis, Chlorella autotrophica, Dunaliella salina, Nannochloropsis sp., and Tetraselmis subcordiformis), and only 0.48 for Phaeodactylum tricornutum (diatom) and 0.71 for Porphyridium purpureum (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.
研究了海洋浮游植物（硅藻、红藻和绿藻）在有或没有过渡金属（Fe(III)、Cu(II)和Mn(II)）存在的情况下将Cr(VI)光还原为Cr(III)的过程。首次证实了海洋浮游植物对Cr(VI)光化学还原的直接影响，并提出了两种负责物种转化的机制：(a) 激发态的Cr(VI)可通过光生电子被基态的电子供体还原；(b) 溶剂化电子还原基态的CrO(4)(2-)阴离子。Cr(VI)向Cr(III)的转化率随藻类浓度和照射时间的增加而增加。发现不同种类的海洋浮游植物具有不同的光还原能力。过渡金属的光化学氧化还原可诱导铬的物种转化。经海洋浮游植物和过渡金属光还原后，五种绿藻（纤细四爿藻、自养小球藻、盐生杜氏藻、微拟球藻和亚心形四爿藻）的Cr(VI)与Cr(III)之比在1.45 - 2.16范围内，而三角褐指藻（硅藻）仅为0.48，紫球藻（红藻）为0.71。海洋浮游植物（主要贡献者）和过渡金属的综合作用极大地影响了阳光照射的表层海水中铬的物种分布；观察到了协同和拮抗作用。这些结果为铬的物种分布和生物地球化学循环提供了进一步的见解，对阳光照射的表层海水中铬的风险评估具有重要意义。
