Assessment of Pb and Cd contaminations in the urban waterway sediments of the Nen River (Qiqihar section), Northeastern China, and transfer along the food chain.

The increasing anthropogenic inputs of Pb and Cd into China's Nen River (Qiqihar section) owing to rapid urbanization in the past 50 years may pose ecological risks to the river's aquatic system. To confirm this hypothesis, we determined the Pb and Cd concentrations in the sediments of the Nen River flowing across Qiqihar City by comparing the control group (samplings in the Nen River branch bypassing the city) and bioaccumulation along the food chain. We found significantly higher Pb concentrations in the sediments than in the control group (39.21 mg kg dry weight [dw] vs. 22.44 mg kg dw; p < 0.05). However, the difference between the Cd contents of the two groups was nonsignificant (0.33 mg kg dw vs. 0.30 mg kg dw) (p = 0.07). Accumulated Pb and Cd in the sediments pose a medium risk to the system of Nen River according to the result of risk assessment code analysis. The increased Pb and Cd levels along the food chain had adverse health effects in the species at the top level of the food chain. For example, the feathers of Corvus frugilegus and Sterna hirundo contained 0.28-2.25 mg kg dw of Cd. These values are considered potentially toxic to common avian species. The bone Pb level of C. frugilegus ranged from 4.82 to 7.41 mg kg dw within the increasing Pb range (2-15 mg kg dw) of common water birds. The inputs of Pb and Cd into the local environment should be reduced for the preservation of aquatic system health.