Rare Earth Elements and Bioavailability in Northern and Southern Central Red Sea Mangroves, Saudi Arabia

Abstract

Different hypotheses have been tested about the fractionation and bioavailability of rare earth elements (REE) in mangrove ecosystems. Rare earth elements and bioavailability in the mangrove ecosystem have been of significant concern and are recognized globally as emerging pollutants. Bioavailability and fractionation of rare earth elements were assessed in Jazan and AlWajah mangrove ecosystems. Comparisons between rare earth elements, multi-elemental ratios, geo-accumulation index (Igeo), and bio-concentration factor (BCF) for the two mangroves and the influence of sediment grain size types on concentrations of rare earth elements were carried out. A substantial difference in mean concentrations (mg/kg) of REE (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) was established, except for mean concentrations of Eu, Gd, Tb, Tm, and Lu. In addition, concentrations of REEs were higher in the Jazan mangrove ecosystem. However, REE composition in the two mangroves was dominated by the lighter REE (LREE and MREE), and formed the major contribution to the total sum of REE at 10.2–78.4%, which was greater than the HREE contribution of 11.3–12.9%. The Post Archean Australian Shale (PAAS) normalized values revealed that lighter REE (LREE and MREE) were steadily enriched above heavy REE. More so, low and negative values of R(H/M) were recorded in the Al Wajah mangrove, indicating higher HREE depletion there. The values of BCF for REEs were less than 1 for all the REEs determined; the recorded BCF for Lu (0.33) and Tm (0.32) were the highest, while the lowest BCF recorded was for Nd (0.09). There is a need for periodic monitoring of REE concentrations in the mangroves to keep track of the sources of this metal contamination and develop conservation and control strategies for these important ecosystems.

Elemental Composition of Above and Belowground Mangrove Tissue and Sediment in Managed and Unmanaged Compartments of the Matang Mangrove Forest Reserve

“…The accumulation of elements in soil or subsurface soil was due to the slow decomposition of roots. Below-ground mud soil acts as a storage unit for elements [ 24 ]. For terrestrial forests, the storage of nutrients or elements is mainly concentrated on floor litter [ 25 ].…”

“…The measurements of elemental concentration in mangroves and the identification of natural and anthropogenic contributions are important in assessing the quality of the mangrove ecosystem quality and restoration practice, and for providing valuable knowledge for the assessment of environmental health risks [ 21 , 22 ]. In addition, the assessment of the distributions and concentration of elements plays a crucial role in mangrove risk assessment and enables the restoration of coastal ecosystems [ 23 , 24 ]. Several studies have demonstrated that more than 90% of elements including metals are absorbed by sediments in suspended form, thus leading to accumulation in coastal environments [ 22 ].…”

The Global Biogeochemical Cycle of the Rare Earth Elements

“…On the other hand, other studies have reported increased accumulation of REEs in mangrove‐vegetated sediments from the Zhangjiang estuary in China (R. Zhang et al., 2013), Sepetiba Bay in Brazil (Silva‐Filho et al., 2011), and Red Sea Mangroves in Saudi Arabia (Aljahdali & Alhassan, 2022). In these cases, the observed patterns were attributed to the variability of particle nature and the influence of anthropogenic inputs rather than the direct impact of plant activity.…”

“…Mandal et al (2019) demonstrated that mangrove plants exhibit higher uptake of REE in belowground parts compared to aboveground plant tissues, although the total concentration of REE in the plants is lower than in the rhizosediment. The bioaccumulation and translocation factors show species-specific variability, indicating different partitioning of REEs and varying levels of efficiency in mangrove uptake (Alhassan & Aljahdali, 2021;Aljahdali & Alhassan, 2022;Mandal et al, 2019).…”

Organophosphate Triesters and Their Transformation Products in Sediments of Mangrove Wetlands in the Beibu Gulf, South China Sea

“…Meanwhile, mangroves provide abundant organic matter, serving as nurseries for marine animals, making significant contributions to nearshore fisheries and biodiversity conservation. Nevertheless, as an important sink of various pollutants, heavy metals, polycyclic aromatic hydrocarbons (PAHs), and the persistent organic pollutants (POPs), such as organochlorine pesticides, polychlorinated biphenyls (PCBs) and polybrominated Biphenyls (PBDEs), have also been reported in mangrove sediments [26][27][28][29][30], plants and organisms (e.g., mollusks, bivalves and fish) [31,32]. Furthermore, Bayen et al [31] revealed the biomagnification of PCBs, OCPs, and PBDEs in a food web composed of twenty-four biota species, including algae, worms, crustaceans, and fish, in two mangrove sites in Singapore, and thunder crabs (Myomenippe hardwicki) and fish exhibited the highest contaminant levels [31].…”