Risk assessment of potential toxic metal pollution in water-sediment-submerged macrophyte systems: a case study of urban shallow lakes in Central China

Six potential toxic metals (PTMs) in water-sediment-submerged macrophyte systems were investigated in six shallow lakes in Changsha City, Central China. The mean metal concentrations in the surface and interstitial water were in the order of Cu>As>Zn>Cr>Pb>Cd and As>Cu>Zn>Cr>Pb>Cd, respectively. Both surface and interstitial water were not polluted, except the interstitial water of Yue Lake with slight pollution ( P N =1.93). The mean metal concentration was in the order of Zn>Cr>As>Cu>Pb>Cd in the sediments. The concentration of As in all urban shallow lakes exceeded 25 mg kg ‒1 , and Cd in Meixi Lake and Xianjia Lake also exceeded 0.3 mg kg ‒1 . The sediments were slight to severe pollution in the studied urban shallow lakes. Among the submerged macrophytes, the concentrations of PTMs were decreased in the order of Vallisneria natans (Lour.) Hara > Myriophyllum verticillatum L. > Centella asiatica (L.) Urban > Potamogeton crispus L. Zn was the most accumulated in all the submerged macrophytes, and the highest bioaccumulation factor (BAF) of Zn was 43.0 in V. natans . V. natans also exhibited relatively high BAFs of 4.6, 2.4, and 4.7 for Cu, As, and Pb, compared with other submerged macrophytes. The translocation factor (TF) of As was no more than 0.3 in all submerged macrophytes. The TFs of the other metals were dependent on the plant species. For most studied metals (As, Pb, Zn, and Cd), significant positive correlations were identified between submerged macrophytes and their surrounding water/sediments ( P <0.05). These results indicated that the potential use of native submerged macrophytes, especially for V. natans , for PTM removal from urban shallow lakes is worth further exploration.