PBET-based bio-accessible trace metal content in mangrove patches of Danshuei River, Taipei

Glomalin-related soil protein (GRSP) has received extensive attention due to its ability to immobilize metals in the environment. However, whether it can enter the food chain through digestion is still unclear. Mangroves occupy the transition zone between the sea and land, have important ecological functions. Mangroves suffer from fragmentation due to human activities and urbanization. A variety of waterfowls inhabit near the mangroves and ingest sediment settled on their food inadvertently or for grit; therefore, they are ideal for revealing GRSP’s role in metal enrichment. Herein, we investigated the release of metals from mangrove surface sediments and GRSP through a physiologically based extraction test. The investigated metals (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in sediments and those bound to GRSP were mainly released in the gizzard phase. GRSP was an efficient carrier of Cu, Zn, Pb, and As from sediments to the waterfowls via direct sediment ingestion. For instance, 3.21% and 3.34% of sediment Cu were released in the gizzard and intestinal phase, respectively, meanwhile GRSP-bound Cu contributed 5.04% and 5.42% to this flux. Fertile factors (i.e., SOC, P) were more strongly related to the metal release during the gizzard phase. Overall, this study provides new insights into the potential risk of GRSP acting as a metal delivery vehicle in the food chain.