The urbanization impacts on potentially toxic metals: the distribution, sources and contamination risks in river situated in typical megacity, China

Abstract

The excessive presence of potentially toxic metals (PTMs) in urban river ecosystem deteriorates water quality and presents high potential health issues on both aquatic and urban residents’ life. River water was thus collected around Beijing and Tianjin megalopolis to evaluate urban water pollution. Inverse distance weighted (IDW) method was adopted to reveal PTMs distributions, principle component analysis (PCA) was applied to identify metal origins, and metal pollution indices were applied to evaluate potential contamination threat. PTMs contents displayed in the sequence of Zn > Ni > V > As > Cu > Sb > Fe > Mn > Cr > Co, and Mn concentrations of the most downstream site (321.12 μg/L) far exceeded standard limitation, indicating intense input of urban pollutants near estuary. The distribution of Ni, Co, Cr, V and Sb exhibited a similar variation trend which decreased in middle reach of the Yongding River. As for the Chaobai River, all PTMs concentration in mainstream generally displayed an emerging trend from upper to lower reach without a specific variation pattern. PCA results indicated that Cr, Ni, V, Sb, Co and As mainly originated from mixing sources directly impacted by industrial (thermal) pollution and natural reactions, whereas sources from cultivation (agriculture) and weathering process were associated with Fe and Zn presence. Mn and Cu were mainly responsible for urban activities. The water quality level of the Yongding-Chaobai River varied between “good” and “undrinkable”, and water quality near the river estuary was much lower than other area. Heavy metal pollution index calculation revealed low risks of metal contamination in river water. The electrochemical remediation is more appropriate for PTMs pollution control in megacity river. These findings support the development of effective assessments and monitoring strategies to control urban river pollution and maintain sustainable environment.