Sediment Metal Contamination, Bioavailability, and Oxidative Stress Response in Mangrove Avicennia marina in Central Red Sea

Abstract

Anthropogenic activities have been on the increase in the urban environment and have led to contamination of the environment with toxic metals. However, mangrove plants’ response to heavy metal stress due to anthropogenic activities explains the metal bioavailability and its potential ecotoxicological effect. We carried out a multi-approach study to investigate i) if the concentrations of metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Pb, Sr, and V) in mangroves at the central Red Sea are due to the anthropogenic influence and are above the sediment quality guidelines and ii) if an increase in metal concentration influences height and antioxidant enzyme (catalase, CAT; glutathione S-transferase, GST; and superoxide dismutase, SOD) activities in Avicennia marina. There were significant variations (p < 0.05) in metal concentrations and antioxidants across the six mangrove ecosystems with higher concentrations at Al Lith (LT) and south Jeddah (SJ). Even though the concentrations of metals in mangrove leaves are slightly higher in LT than SJ, principal component analysis showed that higher concentrations of Cr, Co, Zn, Cd, and Pb in mangrove leaves from SJ influence higher antioxidant enzyme activities and the lowest average mangrove height (2.01 m). This suggests that higher metal concentrations be factors for the biggest stress in these mangrove ecosystems. However, among the 13 metals, Cr (82.07 mg/kg), Cu (41.29 mg/kg), and As (10.30 mg/kg) in sediments have values within the ERL range of probable effect, while Ni (53.09 mg/kg) was above the ERM threshold. Hence, there is need to focus on monitoring these metals in mangrove sediments and their anthropogenic sources.

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

“…Aquatic ecosystems encompass a combination of diverse products of physicochemical processes functioning in various aspects of drainage basins [ 18 ]. This could be linked to or support the influence of grain size types on elements concentrations and distribution, which has also been reported previously to partly reflect the impacts of the hydrodynamic environment [ 19 ]. It is important to note that transportation, resuspension, and deposition of allochthonous sediments into an aquatic environment such as the mangrove ecosystem could be influenced by hydrodynamics [ 19 , 20 ].…”

“…This could be linked to or support the influence of grain size types on elements concentrations and distribution, which has also been reported previously to partly reflect the impacts of the hydrodynamic environment [19]. It is important to note that transportation, resuspension, and deposition of allochthonous sediments into an aquatic environment such as the mangrove ecosystem could be influenced by hydrodynamics [19,20]. However, the fractionation of REEs is largely due to mineralogical controls and the diversity of sediment detrital minerals composed of different grain size types triggered by the complex nature of patterns for drainage weathering and hydrodynamic sorting [21,22].…”

“…Elsewhere, in islands of Indian Sundarban and some mangroves stands in the central Red Sea, results of BCFs reported from these mangroves were in line with our findings with BCFs for REEs less than 1 (BCFs < 1). However, the highest BCF (0.33) determined in this present study was almost three-fold that of the highest value of BCF (0.10) established in Indian Sundarban [12], and 0.01 times greater than the highest BCFs previously determined in six mangroves from the central Red Sea [19].…”

“…Notably, ∑REE in Jazan mangrove sediment was almost two-fold that of the ∑REE determined in Al Wajah mangrove sediment, which is a natural reserve area with rare or few anthropogenic activities. Elsewhere, in the assessment of REEs in six mangrove ecosystems in the central Red Sea [19], the average of ∑REE (42.56 mg/kg) was lower than (about 1/3 of) the value reported from Jazan mangrove (112.54 mg/kg) in this study was established. In another study on the Egyptian coast of the Red Sea [30], the ∑REE (47.55 mg/kg) reported was about 1/2 of the ∑REE (112.54 mg/kg) in the Jazan mangrove ecosystem.…”

“…HREE depletion in benthic sediment could be as a result of their greater tendency towards the formation of soluble carbonates in a stable state and complexes of organic forms with ligands than the lighter REEs (LREE and MREE) [ 32 ]. HREEs have a high tendency towards being less reactive than LREEs and MREEs, and are well adapted or linked with phases in solid states because they have more pronounced complexation together with ligands located on surfaces of colloids and particles [ 19 , 33 ]. The removal and/or preference of LREEs could also be based on this phenomenon [ 11 ].…”