Heavy metals pollution in soil profiles from seasonal-flooding riparian wetlands in a Chinese delta: Levels, distributions and toxic risks

Soil profile samples were collected in seasonal-flooding riparian wetlands in the Yellow River Delta (YRD) of China in autumn and spring to investigate the levels, distributions and toxic risks of heavy metals in soil profiles. Total elemental contents of Al, As, Cd, Cr, Cu, Ni, Pb and Zn were determined using inductively coupled plasma atomic absorption spectrometry (ICP-AAS). Results indicated that the contents of determined heavy metals showed non-negligible depth variations (coefficient of variation > 10%), and their distribution patterns were irregular. Compared with other heavy metals, both As and Cd presented higher enrichment factors (EF) based on the classification of EF values (moderate enrichment for As while significant enrichment for Cd). Cluster analysis (CA) and principal components analysis (PCA) revealed that Cr, Cu, Ni, Pb and Zn might derive from the common source, while As and Cd shared another similar source. The toxic unit (TU) values of these heavy metals did not exceed probable effect levels (PEL) except for Ni. Both As and Ni showed higher contributions to the sum of TU (∑TUs), which indicated they were the primary concerns of heavy metals pollution. Generally, As, Cd and Ni should be paid more attention for wetlands managers and policy makers to avoid potential ecotoxicity in the study area. The findings of this study could contribute to the prevention and control of heavy metals pollution in estuarine wetlands.