First assessment of metal contamination and ecological risks in aquaculture ponds in Hanoi city, Vietnam

Freshwater aquaculture strongly contributes to the socio-economic development of many countries in Southeast Asia. Water and sediment quality, including ten metals and some other variables (pH, total organic carbon (TOC), and nutrients) were investigated in five aquaculture ponds in Hanoi city in 2023. The average concentrations of ten metals in surface waters and sediments (in mu g.L-1 and mg.kg-1, respectively) measured by Inductively coupled plasma mass spectroscopy, were: Fe (263.6; 7,686); Mn (171.6; 516.0); Cr (5.7; 57.2); Cu (4.8; 50.2); Ni (3.6; 37.8); Zn (3.4; 204.3); As (1.6; 23.0); Pb (0.8; 39.9); Cd (0.3; 0.08); and Hg (0.1; 0.16). The mean concentrations of Mn, TOC, total nitrogen, and total phosphorus in water and As in sediments exceeded the permissible values of the Vietnam national regulations. The potential ecological risk assessment revealed that within 10 metals, Mn in water was at slight pollution level whereas As may have a toxic effect on organisms in sediments. Untreated wastewater from households and craft production villages and agricultural runoff were probably the anthropogenic sources of pollution to these ponds. The results of this 'snap-shot' study underline the need of filling the gaps in national regulations, higher frequency monitoring and reveal the importance of identifying and treating pollution sources to aquaculture ponds in order to improve environmental and human health. This work also demonstrated the need for synergistic efforts from scientists, policy makers, government managers, and communities to manage and protect environment of aquaculture ponds in Hanoi as well as in Vietnam.