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.

球囊霉素相关土壤蛋白（Glomalin-related soil protein, GRSP）因能够固定环境中的金属元素而受到广泛关注。然而，其是否可通过消化过程进入食物链仍不明确。红树林作为海陆过渡带生态系统，具备重要的生态功能，但受人类活动与城市化影响正面临生境破碎化问题。多种水禽栖息于红树林周边，它们会无意间摄食附着在食物上的沉积物，或是为了磨碎食物而摄取砂砾，因此是揭示GRSP在金属富集过程中作用的理想研究对象。本研究通过基于生理学的提取试验，探究了红树林表层沉积物以及结合于GRSP的金属元素释放行为。本次研究涉及的金属元素包括砷（As）、镉（Cd）、钴（Co）、铬（Cr）、铜（Cu）、铁（Fe）、锰（Mn）、镍（Ni）、铅（Pb）与锌（Zn），上述元素在沉积物中以及结合于GRSP的形态下，主要在肌胃阶段被释放。GRSP可作为高效载体，通过水禽直接摄食沉积物的途径，将沉积物中的Cu、Zn、Pb与As转移至其体内。例如，沉积物中3.21%与3.34%的Cu分别在肌胃与肠道阶段被释放，与此同时，结合于GRSP的Cu分别为该释放通量贡献了5.04%与5.42%。土壤有机碳（Soil Organic Carbon, SOC）、磷（Phosphorus, P）等肥力因子与肌胃阶段的金属释放过程相关性更强。总体而言，本研究为GRSP作为金属传递载体在食物链中潜藏的潜在风险提供了全新的认知视角。