Metal Pollution and Bioaccumulation in the Nhue-Day River Basin, Vietnam: Potential Ecological and Human Health Risks

(1) Background: Metal pollution in the Nhue-Day River basin has impacted approximately 12 million people. However, none of the previous studies considered the entire basin’s environmental and health risks. Thus, this research aims to fill knowledge gaps and reduce risks. (2) Methods: Sediment and fish samples from the basin were analyzed to determine the levels of Zn, Cu, Pb, and Cd pollution and their potential ecological (EF, modified Pollution Index—mPI, and expanded, modified potential ecological risk index—emRI) and human health risks (THQ, HI, and TR indices). (3) Results: Metal levels in sediment exceeded Canadian aquatic life protection guidelines, indicating moderate to severe contamination (EFs: 1.3–58.5 and mPIs: 4–39). Compared to the new proposed ecological risk threshold, all river sites and Site 1 for ponds had elevated metal levels; and these posed a very high ecological risk in spring (emRI > 4.5), with Cd being the most hazardous. Lead levels in all fish tissues surpassed Vietnamese and EU food regulations. In agreement with THQ, EWI (Zn, Cu) and EMI (Cd) were both less than 2.5% of the PTWI and PTMI, respectively. However, HI values of 0.67–1.26 suggested a moderate health risk. Carcinogenic risk (TR > 10(−6); estimated for Pb) was detected in several localities for Common carp and Tilapia during the warm season. (4) Conclusions: Metals had a negative impact on the basin’s ecosystem, with Cd being the most dangerous. Because of lead, consumption of Common carp and Tilapia from the basin may pose both non-carcinogenic and carcinogenic health concerns.