Fractionation, transfer, and ecological risks of heavy metals in riparian and ditch wetlands across a 100-year chronosequence of reclamation in an estuary of China

• Published in: The Science of the total environment Vol. 517; pp. 66 - 75
• Main Authors: Xiao, Rong, Bai, Junhong, Lu, Qiongqiong, Zhao, Qingqing, Gao, Zhaoqin, Wen, Xiaojun, Liu, Xinhui
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.06.2015
• Subjects: Bioconcentration factor; Brackish; China; Copper; Ditches; Environmental Monitoring; Estuaries; Fractionation; Freshwater; Geologic Sediments - chemistry; Heavy metals; Lead (metal); Metals, Heavy - analysis; Plant biomass; Reclamation; Risk; Risk assessment code; Rivers; Soil (material); Soil Pollutants - analysis; Translocation factor; Water Pollutants, Chemical - analysis; Wetlands; China; China, People's Rep., Zhu R; China, People's Rep; Fractionation; Risk assessment code; Bioconcentration factor; Translocation factor; Heavy metals; Plant biomass
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2015.02.052

The effect of reclamation on heavy metal concentrations and the ecological risks in ditch wetlands (DWs) and riparian wetlands (RWs) across a 100-year chronosequence in the Pearl River Estuary of China was investigated. Concentrations of 4 heavy metals (Cd, Cu, Pb, and Zn) in soil and plant samples, and sequential extracts of soil samples were determined, using inductively coupled plasma atomic absorption spectrometry. Results showed that heavy metal concentrations were higher in older DW soils than in the younger ones, and that the younger RW soils contained higher heavy metal concentrations compared to the older ones. Although the increasing tendency of heavy metal concentrations in soil was obvious after wetland reclamation, the metals Cu, Pb, and Zn exhibited low or no risks to the environment based on the risk assessment code (RAC). Cd, on the other hand, posed a medium or high risk. Cd, Pb, and Zn were mainly bound to Fe–Mn oxide, whereas most of Cu remained in the residual phase in both ditch and riparian wetland soils, and the residual proportions generally increased with depth. Bioconcentration and translocation factors for most of these four heavy metals significantly decreased in the DWs with older age (p<0.05), whereas they increased in the RWs with younger age (p<0.05). The DW soils contained higher concentrations of heavy metals in the organic fractions, whereas there were more carbonate and residual fractions in the RW soils. The non-bioavailable fractions of Cu and Zn, and the organic-bound Cd and Pb significantly inhibited plant growth. [Display omitted] •Heavy metals in ditch wetland accumulated with increasing reclamation history.•Heavy metals exist in the Fe–Mn oxides and residual fractions in both wetlands.•Cd posed a medium to high environmental risk while low risk for other metals.•Long reclamation history caused lower BCFs and TFs in DWs and higher levels in RWs.•RW soils contained more heavy metals in the carbonate and residual fractions.