Assessment of As, Cd, Zn, Cu and Pb Pollution and Toxicity in River Wetland Sediments and Artificial Wetland Soils Affected by Urbanization in a Chinese Delta

The concentrations of As, Cd, Zn, Cu and Pb were analyzed to assess their pollution levels and toxic risks in different wetlands affected by urbanization. The results showed that As and heavy metals (especially Cd) showed higher concentrations in urban and rural river wetland sediments compared with artificial wetland soils. Comparatively, urban river wetland sediments contained higher Cu, Pb and Zn and lower As and Cd levels than rural river wetland sediments and artificial wetland soils. Cu, Pb, Zn, soil/sediment organic matter (SOM) and total phosphorous (TP) were all positively correlated with each other. The highest geoaccumulation indexes and pollution levels were observed in urban river wetlands, followed by rural river wetlands, while artificial wetlands showed the lowest values. In urban and rural river wetlands, the enrichment factor (EF) values for As and heavy metals exceeded 1.5, implying that they might be mostly from anthropogenic sources. In artificial wetlands, the EF values suggested that only Cd was mainly from anthropogenic sources. The sum of toxic units (ΣTUs) values showed that As and heavy metals in both river wetland sediments had moderate toxic risks with ΣTUs values exceeding 4, while a low toxicity risk was observed in artificial wetland soils.