Combination of DGT and fluorescence spectroscopy for improved understanding of metal behaviour in mangrove wetland

Understanding bioavailable metal behaviour in situ is critical for pollution evaluation and contaminant management in mangrove wetland. Here, the diffusive gradients in thin films technique (DGT)was used for characterizing the (bio)available portions of Cr, Zn, Pb, Cu, Fe and Mn in two mangrove wetlands affected by industrial waste discharges (Jiulong Estuary)and domestic discharges (Zhangjiang Estuary), in Fujian Province, China. In addition, fluorescence excitation emission matrices-parallel factor analysis (EEM-PARAFAC)was applied for characterizing the occurrence and behaviour of dissolved organic matter (DOM)in soil solution, as well as their feasibility for assessing behaviours of metals. The results demonstrated that the combination of DGT and EEM, which are well suitable for studying DOM impacted metal behaviors in mangrove sediments. Discharge of difference wastewater into the mangrove wetlands of Jiulong and Zhangjiang Estuaries, gave rise to the DGT-labile metal concentration of Zn > Cu > Cr > Pb and Zn > Cr > Pb > Cu, respectively. A variety of humic-like fluorescent components was characterized here, providing valuable insights into the chemical composition of DOM in rhizosphere and bulk sediment. Terrestrial humic-like compounds indicated a different binding affinity for heavy metals in mangrove sediments. These findings are useful for the future understanding of the metal speciation and molecular binding mechanisms in such mangrove wetlands.