Abstract The accumulation of heavy metals by freshwater algae becomes more complex in the presence of dissolved organic matter but it is unclear how and to what extent. In this study, we comparatively assessed the effects of malic acid and citric acid on the bioaccumulation of Pb by Chlorella pyrenoidosa. A 6 h exposure experiment showed that adding organic acid (OA) to an algae–Pb binary system prolonged the adsorption equilibrium time and that the extended time was related to the concentration and number of carboxyl groups of the OA. A pseudo-second-order model fit the kinetic data well in the presence of OAs. The normality of carboxyl groups was negatively correlated with the bioaccumulation rate, k2, but positively correlated with the maximum bioaccumulation capacity, qmax, of Pb following a linear equation, Y = 121.3x + 52.2, R2 = 0.9877. Neither the Freundlich model nor the Langmuir model could fit the isotherm data in the presence of OA, suggesting that a new mechanism might exist. The quantitative relationship between bioaccumulated Pb and carboxyl group of OA indicated a stoichiometric relationship, which seemed to support the theory of a ternary complex of Pb, OA, and algal surface. Our results have added clarity to the current understanding of the accumulation of heavy metals by algae in freshwater ecosystems.

中文翻译：

---

有机酸存在下淡水藻对铅的生物富集机制

摘要 在溶解有机物存在的情况下，淡水藻类对重金属的积累变得更加复杂，但尚不清楚如何以及在多大程度上。在本研究中，我们比较评估了苹果酸和柠檬酸对蛋白核小球藻 Pb 生物积累的影响。6 小时的暴露实验表明，向藻类-铅二元体系中加入有机酸 (OA) 延长了吸附平衡时间，延长的时间与 OA 的羧基浓度和数量有关。在存在 OA 的情况下，伪二阶模型很好地拟合了动力学数据。羧基的正态性与生物积累率 k2 呈负相关，但与 Pb 的最大生物积累能力 qmax 呈正相关，遵循线性方程 Y = 121.3x + 52.2，R2 = 0.9877。Freundlich 模型和 Langmuir 模型都不能拟合 OA 存在下的等温线数据，这表明可能存在一种新机制。生物积累的Pb与OA的羧基之间的定量关系表明了化学计量关系，这似乎支持了Pb、OA和藻类表面三元复合物的理论。我们的结果使目前对淡水生态系统中藻类积累重金属的理解更加清晰。