Assessment of heavy metal pollution in an urbanized waterway of the Pearl River Delta, China

To combat environmental pollution, a viable option is to adjust industrial structures to reduce the emissions of pollutants. One means to gauge the effects of such change is assessing the potential ecological risk of the pollutants of anthropogenic origin. The present study examines an urbanized waterway in the Pearl River Delta (PRD) of China as the study region. This study aims to gauge the effects of such an industrial adjustment by assessing the state of pollution as well as related ecological risk in surface water and sediment caused by certain largely anthropogenically derived heavy metals (Cr, Ni, Cu, Zn, As, Cd, and Pb, which are the key heavy metal pollutants that need to be prevented and controlled as per the list in the 13th Five Year Plan for Comprehensive Prevention and Control of Heavy Metal Pollution in Guangdong Province). The average concentrations of heavy metals in sediments were present in the order Zn > Cr > Cu > Pb > Ni > As > Cd and were all higher than baseline values. These concentrations increased in the period from 2008 to 2011, but declined from 2011 to 2018, which is consistent with the shift in local industrial structures from high pollutant-emitting industries to low ones. The results revealed that there was an overwhelming occurrence of Cr in the residual fraction, as it can strongly bound to crystalline structures. Nickel and As also mainly occurred in the residual fraction. Zinc was chiefly bound to the reducible and residual fractions. Cadmium was primarily affiliated with the acid-soluble fraction, whereas Cu and Pb were mainly affiliated with the reducible fraction. These results suggest that the presence of Cu, Zn, Cd, and Pb was impacted more by human activities as compared to that of Cr, Ni, and As. Further, nickel was the most dominant contributor to ecological pollution in water, while Cd contributed the most to sediment pollution. Despite the tremendous efforts in adjusting industrial structures in the study region, potential ecological risks due to anthropogenic activities has remained a threat to the aquatic environment and should be further reduced.