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Deposited sediments contain toxic metals which can pollute surface water as well as aquatic eco-systems. Accumulation of heavy metals in sediment was assessed based on the geoaccumulation index (Igeo), the degree of contamination (Cd value) and potential ecological risk was also proposed based on ecological risk index (RI). The surface sediments collected at Han river estuary, Da Nang city were digested with a mixture of HNO3 nd H2O2, and analyzed for five heavy metals Cd, Cr, Cu, Pb and Zn sing inductively coupled plasma-atomic emission spectroscopy (ICP-AES), separately using the AAS method for AS .  Results showed that all of metals were detected in sediment samples with mean concentration of As, Cd, Cr, Cu, Pb and Zn were 9.16; 0.083; 52.5; 45.4; 23.2 and 41.1 mg/kg dw, in respective. Cd values were smaller than 8 suggested that surface sediments of Han river estuary were moderately polluted by this metal.  Besides, the results of potential ecological risk factor show that the risks of heavy metals are in the decreasing order of Cu>Pb>As>Cr>Cd>Zn.

The Red River is the largest river in northern Vietnam, and it serves as the main water source for production and human activities in the Red River Delta region. Cities and provinces located in the Red River Delta, for example, Hanoi, Nam Dinh, and Ha Nam, have experienced rapid economic growth with various large urban, industrial zones, and agricultural areas. As a result of urbanization and industrialization, surface water in this region has been contaminated by multiple anthropogenic sources. In this study, in addition to water quality assessment using WQI, we used the reflectance values of visible and near-infrared bands and in situ data to build a regression model for several water quality parameters. Among ten parameters examined, two parameters, including total suspended solids (TSS) and turbidity, were used to construct regression correlation models using the Sentinel-2 multispectral images. Our results can contribute useful information for comprehensive monitoring, evaluation, and management scheme of water quality in the Red River Delta. The application of this method can overcome the limitation of actual observation results that only reflect local contamination status and require a lot of sampling and laboratory efforts.