Risk Assessment and Binding Mechanisms of Copper in Sediments of Typical Coastal Wetlands around Bohai Bay

  Objective  The pollution status of copper (Cu) and its microscale combination information with various components in sediments around the Bohai Bay, the behavior mechanism of Cu in sediments at various water levels and depths was studied in coastal wetlands around the Bohai Bay.

  Method  Chemical extraction and synchrotron-radiation (SR)-based Fourier transform infrared (FTIR) spectro-microscopy combined with micro X-ray fluorescence (μ-XRF) were used to investigate the characteristics of Cu in wetland sediments. The distribution and combination characteristics of Cu, mineral components, and different functional groups were also explored in situ at micro-scale.

  Result  The concentrations of total carbon, total nitrogen, and organic carbon in the sediments of Beidagang wetland decreased with depth of sediment. The enrichment factor (EF) and potential ecological risk index (RI) of Cu at different sampling sites were less than 2 and less than 40, respectively, indicating that Cu is slightly enriched and has low ecological risk. In surface sediments, the distribution of Cu was familiar with that of iron-bearing components, clay minerals/carbonates, and mineral (Si/Al) functional groups, while mineral compounds had obvious binding characteristics to Cu in the bottom sediments.

  Conclusion  Cu in surface and bottom sediments of coastal wetlands at different water levels is in a state of slight enrichment and low ecological risk. The spatial distribution and micro-scale binding characteristics of Cu in surface and bottom sediments are different. Mineral components and organic matter in surface sediments show obvious binding characteristics with Cu, while mineral components play a leading role in Cu binding in bottom sediments. These results can provide valuable technical and theoretical guidance for restoring current polluted wetlands and ensuring their healthy and sustainable utilization.