Biomonitoring of trace elements in Vietnamese freshwater mussels

The objective of the present study was to conduct a preliminary investigation of the pollution situation in the northern part of Vietnam with focus on trace elements including heavy metals. A freshwater bivalve species of the Unionidae family (Pletholophus swinhoei), abundant in this part of the country and frequently used for human consumption, was chosen as biomonitor. Ten specimens each were collected at two rural sites, Duy Minh, approximately 40 km south of the capital Hanoi, and An Thin, situated approximately 11 km south of the Pha Lai power plant. The concentrations of 20 elements were measured using total reflection X-ray fluorescence and graphite furnace atomic absorption spectroscopy. Significant site-specific differences were found for the elements As, Ba, Be, Br, Cr, Fe, Mn, Ni, P and Sr. A comparison with other in situ biomonitoring studies using Unionidae bivalves showed that the concentrations of most elements were within the same order of magnitude, whereas heavy metal concentrations were distinctively low, suggesting the absence of major anthropogenic pollution sources in this area. The concentrations of Cd, Cr, Cu, Pb, Se and Zn were below the levels regarded as harmful according to the international standards for metals in mollusks compiled by the Food and Agricultural Organization of the United Nations.