The potential ecological risks and bioavailability of heavy metals in the sediments of Lake Baiyangdian

Being the primary sink for heavy metals in lakes, the sediment is the hotspot for the research and remediation of heavy metals in lakes. In the current study, the horizontal and vertical distributions of 16 kinds of heavy metals in the sediment of multiple areas in Lake Baiyangdian were analyzed and based on the concentrations of several typical harmful heavy metals in the sediment, the potential ecological risk was assessed. The bioavailability of heavy metals was further analyzed according to the acid volatile sulfide (AVS), simultaneously extracted metals (SEM), dissolved metals in the pore water, and fractionation of mobile metals. The results showed that the concentrations of heavy metals in the sediment followed the descending order of:Fe (29630.50 mg/kg)>Ti (3213.07 mg/kg)>Mn (539.44 mg/kg)>Zn (104.01 mg/kg)>V (76.63 mg/kg)>Cr (52.60 mg/kg)>Cu (43.49 mg/kg)>Ni (35.83 mg/kg)>Pb (26.75 mg/kg)>Co (10.32 mg/kg)>As (8.96 mg/kg)>Mo (2.06 mg/kg)>Sb (1.57 mg/kg) >Tl (0.43 mg/kg)>Cd (0.31 mg/kg)>Hg (0.16 mg/kg). Among all the heavy metals studied, 10 kinds of the metals in the sediment of the studied areas showed a gradually decreasing trend from north to south of the lake. The variations in the horizontal distribution of metals between different areas were most likely caused by the external pollution input from the north part of the lake. The potential ecological risks of heavy metals in most parts of the lake were generally at low levels except for the Shaochedian area in the north. The inflowing rivers around this area were the main sources of heavy metal pollution. While the pollution input and the accumulation of heavy metals in the sediment have generally stabilized and gradually decreased during the past 10 years, the pollution input not only increased the total amount of heavy metals in the sediment of this area but also led to the high proportion of mobile heavy metals (mostly between 30% and 90%), which increased the bioavailable potential of metals. The massive enrichment of endogenous organic matter from the wither of aquatic plants led to the strong reductive status of the sediment, which thereby resulted in high concentrations of AVS. The average concentrations of AVS and ΣSEM in the sediment of the whole lake were (10.59±6.37) μmol/g(dw) and (2.23±1.53) μmol/g(dw), respectively. Due to the immobilization with a high concentration of sulfides, the bioavailability of Cd, Cu, Ni, Pb, and Zn were generally low. However, As and Hg are much easier to dissolve and release from the sediment under such high organic matter content and strong reducing environment. These two metals had relatively high potential bioavailability with the concentration in the pore water reaching (17.07±0.23)μg/L and (2.39±0.94)μg/L, respectively, which should be given more attention during future research and remediation works. © 2022 Science Press. All rights reserved.