The effects of fulvic acid (FA) on heavy metal bioaccumulation by algae have been extensively studied, but the quantitative description on its adsorption behavior is not elaborately illustrated. In the study, the two-step adsorption model is firstly proposed to describe the adsorption of Pb by algae in the presence of FA (R² > 0.984), which is characterized with two-plateaus in the biosorption curves. The first plateau in the curve represents a monolayer adsorption process of free Pb²⁺; while the second reveals a multilayer adsorption process of Pb-FA binding to those adsorbed Pb by algae, and the bonding material was called as ternary complex of algae-Pb-(FA-Pb). The formation of the ternary complex caused a sharp increase of the amount of adsorbed Pb by algae which was measured by an atomic absorption spectrophotometry, and a decrease of the toxicity of Pb to algae verified with SEM and TEM images. The ternary phase diagram showed FA could participate in the formation of ternary complexes at very low concentration. The study is important for a comprehensive understanding of the metal-microalgae interaction and its biogeochemical cycle in surface waters.

富里酸（FA）对藻类重金属生物富集的影响已得到广泛研究，但并未详细说明其吸附行为的定量描述。在研究中，首先提出了两步吸附模型来描述藻类在FA（R ²  > 0.984）存在下对铅的吸附，其在生物吸附曲线中具有两个平台。曲线中的第一个平台代表游离Pb ²⁺的单层吸附过程; 而第二种方法揭示了藻类吸附被铅吸附的Pb-FA的多层吸附过程，其结合材料称为藻类-Pb-（FA-Pb）三元复合物。三元复合物的形成导致藻类吸附的Pb量急剧增加（通过原子吸收分光光度法测量），Pb对藻类的毒性降低（通过SEM和TEM图像验证）。三元相图显示FA可以以非常低的浓度参与三元复合物的形成。该研究对于全面了解地表水中金属-微藻的相互作用及其生物地球化学循环具有重要意义。