The average daily doses (ADDs) of single trace elements are provided in Table 5. The HQ of a single trace element and the hazard index (HI) of multiple trace elements are presented in Table 6. In total, 16 trace elements were included in the health risk assessment. Cadmium was excluded because it was not detected in any river and lake water samples. Gallium and lead were excluded because their oral reference doses (RfDs) were not available at the USEPA. Calculations indicated that male and female Cambodian residents ingested less amount of trace elements in water from the Tonle Sap River and the Tonle Sap Great Lake than those in Pakistan (Iqbal et al. 2013) and China (Wu et al. 2009; Li & Zhang 2010). Moreover, risk calculation indicated that all HQs of each single trace element and the HI of the multiple trace elements were less than one, indicating male and female Cambodian residents were at minimal risk of single and multiple trace elements through consumption of the Tonle Sap Great Lake and River water. Health risk assessment of trace metals in freshwater Rawal Lake, Pakistan revealed that Co and Pb were the major pollutants during summer and Cd, Co, Cr and Pb were the major pollutants during winter, which could pose adverse health effects to the local consumers through the water drinking pathway (Iqbal et al. 2013). Recently, a health risk assessment of trace elements in the upper Han River, China indicated that As, Pb, Sb, Se and V were the largest contributor to chronic risk in the dry season while As, Co, Pb, Sb and V in the rainy season (Li & Zhang 2010). Concurrently, a health risk assessment of trace metal in surface water from the Yangtze River in Nanjing section, China suggested trace metals could pose a minimal hazard to local residents (Wu et al. 2009). It is apparent that the Tonle Sap River and the Tonle Sap Great Lake water were substantially safe in trace elements and could be used as drinking water sources, considering the treatments of microbial contaminants and organic pollutants as well as emerging environmental pharmaceuticals. However, Cambodian local residents were at relatively high potential health risks of As, Tl, Ba, Co, Mn and Cr when compared to other trace elements (Table 6). The management and control of the contamination sources should be taken into account. In fact, if industrial and municipal sewages are well managed and controlled prior to discharges to the Tonle Sap River, it might reduce the potential health risks to the consumers who rely on the Tonle Sap Great Lake resources such as water and fishery products. It might also reduce the ecological risks to the aquatic plants and animals in the Great Lake system. Nevertheless, we have not investigated seasonal changes which are believed to influence the concentrations of these trace elements and the water quality of the Great Lake and its tributary due to budget and time constraints. These limitations allowed us to assess the health risks of consumers only in the rainy season (May to November). However, the authors feel that it is substantially informative because a few people would consume lake and river water in the dry season (December to April) due to a long-distance carrier. Our previous study showed that groundwater in the Mekong River basin is the main source of drinking although many people live alongside surface water (Phan et al. 2010). Many people switched from the consumption of surface water to groundwater owing to their concerns about microbial contaminations (Phan et al. 2010). Of course, surface water is consumed during the raising stage of the Mekong River water which results in an overflow and flooding.