In lightly polluted water containing heavy metals, organic matter, and green microalgae, the molecular weight of organic matter may influence both the growth of green microalgae and the concentration of heavy metals. This study elucidates the effects and mechanisms by which different molecular weight fractions of fulvic acid (FA), a model dissolved organic matter component, facilitate the bioaccumulation of hexavalent chromium (Cr(VI)) in a typical green alga, Findings show that the addition of FA fractions with molecular weights greater than 10 kDa significantly enhances the enrichment of total chromium and Cr(VI) in algal cells, reaching 21.58%−31.09 % and 16.17 %−22.63 %, respectively. Conversely, the efficiency of chromium enrichment in algal cells was found to decrease with decreasing molecular weight of FA. FA molecular weight within the range of 0.22 µm-30 kDa facilitated chromium enrichment primarily through the algal organic matter (AOM) pathway, with minor contributions from the algal cell proliferation and extracellular polymeric substances (EPS) pathways. However, with decreasing FA molecular weight, the AOM and EPS pathways become less prominent, whereas the algal cell proliferation pathway becomes dominant. These findings provide new insights into the mechanism of chromium enrichment in green algae enhanced by medium molecular weight FA.

中文翻译：

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有机质分子量对绿色微藻富集六价铬的影响

在含有重金属、有机物和绿色微藻的轻度污染水中，有机物的分子量可能会影响绿色微藻的生长和重金属​​的浓度。本研究阐明了黄腐酸 (FA)（一种模型溶解有机物成分）的不同分子量分数促进典型绿藻中六价铬 (Cr(VI)) 生物积累的作用和机制。研究结果表明，添加分子量大于10 kDa的FA组分显着增强了藻细胞中总铬和Cr(VI)的富集，分别达到21.58%−31.09 %和16.17 %−22.63 %。相反，发现藻细胞中铬富集的效率随着 FA 分子量的降低而降低。 FA 分子量在 0.22 µm-30 kDa 范围内主要通过藻类有机物 (AOM) 途径促进铬富集，藻类细胞增殖和胞外聚合物 (EPS) 途径的贡献较小。然而，随着 FA 分子量的降低，AOM 和 EPS 途径变得不那么突出，而藻细胞增殖途径变得占主导地位。这些发现为中等分子量 FA 增强绿藻中铬富集的机制提供了新的见解。