DETERMINATION OF ARSENIC CONTENT IN WASTEWATER-FED FISH POND IN HOANG MAI DISTRICT, HANOI, VIETNAM

Aquaculture in pond fed with wastewater has been practiced since the 1960s in Hoang Mai and Thanh Tri districts in Hanoi, Vietnam. Wastewater after directly discharged in to Kim Nguu and To Lich river is currently used for cultivation of vegetables and fishes. According to the previous studies, the content of some heavy metals in water and sediments from Kim Nguu and To Lich river exceeded the Vietnamese standard values. In this study, arsenic concentration in water, sediment, fish and plant collected from a wastewater fed-fish pond in Hoang Mai district, Ha Noi, Vietnam were determined by graphite furnace atomic absorption spectrometry (GF/AAS). Arsenic concentration in water collected from inlet and outlet sites of the pond were of 45.86 and 23.22 μg/L, respectively and those levels were higher than the Vietnamese standard. About 14% of arsenic entered the fish pond was in the suspended particulate mater (SPM) form. Arsenic concentration in the sediment ranged from 12.26 to 23.87 mg/kg (dry weight). The highest levels of arsenic found in the sediment near the pond outlet were probably caused by the movement of the sediment and heavy metals with the water flow. Based on the Vietnamese standards for agriculture soils, the studied pond sediment is not safe for crop application. Arsenic contents of 0.20 and 0.06 mg/kg (dry weight) were found in tissues of common carp and tilapia. The lower As contents in the outlet water in comparison to the inlet water showed that part of As was removed in the fish pond by different processes including the sedimentation and bio-adsorption. The As contents in the coarse stems/leaves of the water spinach samples were about 2.6 times higher than those in the shoot tips/younger leaves. As the findings, the water spinach and fish in this wastewater –fed fish pond were considered safe for human consumption with respect to arsenic content and Vietnamese standard.