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Abstract Glomalin-related soil protein (GRSP) is a widespread glycoprotein found to have strong ability of sequestering heavy metals in soils. However, the underlying mechanism for metal and metalloid removal as well as water quality improvement and the ecological role played by GRSP are still not well documented. This study was initiated to investigate the interconnection of metal loading in GRSP between sediments and suspended solids, focusing on the mobilization mechanisms of GRSP in the coastal mangrove wetland. Combined indicators of nine heavy metals were significantly positively correlated with GRSP concentration by Principal Component Analysis, indicating that GRSP could act as an indicator of contamination level in the mangrove wetlands. Large distribution of GRSP in sediments and suspended solids elevated sequestration potential of heavy metals (Fe, Mn, Cr, Cu, Zn, Ni, Cd, Pb) and metalloid arsenic in the mangrove aquatic ecosystem. GRSP mobilized and sequestered heavy metals in sediment profiles, which reduced the bioavailability of heavy metals. GRSP was also a significant contributor for suspended solids to adsorb heavy metals, enhancing suspended solids deposition and burial process in sediments. This new finding provided insights into the ecological functions of GRSP and the heavy metal cycling in wetland environments. Graphical abstract Image 1 Highlights • Metals were sequestered by GRSP in mangrove wetlands. • GRSP-bound arsenic was found to be only associated with elevated Fe in GRSP. • GRSP-bound metals were buried in sediments and their mobility was reduced. • GRSP in suspended solids has higher metal sequestration potential than in sediment. • GRSP in suspended solids contributed to heavy metal transport and deposition. [ABSTRACT FROM AUTHOR]

• HBCD inherent in PS MPs greatly promotes the metals' adsorption. • log K MeOH can be used as an indicator parameter for the adsorption affinity. • The –O and –Br groups of HBCD/PS MPs are involved in the metals' adsorption. • HBCD enhances the long-range transfer of the metals via MPs. Microplastics (MPs) are known to act as carriers of heavy metals; however, little is known about the intrinsic chemical additives of MPs, such as hexabromocyclododecane (HBCD), in terms of the adsorption behaviors and migration risks of heavy metals on MPs. Here, we reported the potential mechanisms and risks of HBCD inherent in polystyrene (PS) MPs with Cu(II), Ni(II), and Zn(II) adsorption/desorption. A comparison of the adsorption capacity of the metals onto HBCD/PS composites (HBCD/PS) MPs (10.31–20.76 μmol/g), pure MPs (0–3.60 μmol/g), and natural minerals (0.11–13.88 μmol/g) showed that the addition of HBCD significantly promoted the metals adsorption onto the HBCD/PS MPs, and even exceeded that of natural particles. Isotherms and thermodynamic data suggested that the adsorption process of the metals onto the HBCD/PS MPs was spontaneous and endothermic, and that the adsorption was a mainly multi-ion process with an inclined direction. Furthermore, the results of SEM-EDS, FTIR, and XPS analyses, as well as density functional theory well explained that the metals were mainly adsorbed on the –O and –Br groups of the HBCD/PS MPs via electrostatic interactions and surface complexation. More importantly, by comparing the desorption activity with natural river water and seawater, HBCD inherent in MPs can enhance the long-range transfer of metals carried by the HBCD/PS MPs from contamination sources to potential sink like oceans. Thus, the HBCD/PS MPs with high loading of Cu(II), Ni(II), and Zn(II) could be potential secondary sources of these metals in seawater. Overall, these findings revealed the potential risks of flame retardant in MPs associated with metal migration, and advocated that flame retardant-related waste MPs should be included in coastal sustainable development. [Display omitted] [ABSTRACT FROM AUTHOR]