The role of submerged macrophytes in phytoremediation of arsenic from contaminated water: A case study on Vallisneria natans (Lour.) Hara.

Arsenic contamination of water is a global concern due to its heavy threat to human health. In this study, the submerged macrophyte Vallisneria natans (Lour.) Hara was used to remove environmentally relevant concentrations of arsenic in the binary As(III)/As(V) system. The concentrations of total arsenic (tAs) and As(III) in water dropped rapidly within 3 days, while As(V) first increased slightly within 3 days and then gradually decreased. About 1.2% dimethylarsinate (DMA) was detected at the 14th day of treatment. These findings indicated that As(III) could be oxidized to As(V) and methylated to DMA in water with V. natans. In relation to V. natans, both tAs and As(V) were much higher in roots compared to leaves. Arsenate was the predominant species (≥ 95.65 ± 0.10%) in roots, and As(III) was only found at the 14th day (3.45-6.96 mg kg-1). In leaves, As(III) significantly increased (P < 0.05) as the treatment duration increased. The proportions of As(V) (27.99-40.03%) were lower than those of As(III) and arsenobetaine (AsB) was detected (0.52-1.87 mg kg-1) after 7 d. The results of arsenic speciation demonstrated that the transformation of arsenic species in V. natans included As(V) reduction and As(III) methylation to AsB. There were a decrease in chlorophyll content, and an increase in MDA level and antioxidant enzymes (SOD, CAT, and POD) activities. The MDA level was much higher in leaves than roots, whereas the activities of SOD, CAT, and POD were the opposite, suggesting their possible role in arsenic resistance and detoxification. Our results indicate the potential of V. natans in phytoremediation of arsenic-contaminated water.