Abstract
Accumulation of 8 heavy metals (HM), Cr, Cu, Fe, Mn, Mo, Ni, Pb, and Zn, was assessed in the leaves and sediments of gray mangrove (Avicennia marina (Forsk.) Vierh.) at three sites along Tubli Bay using Inductive Coupled Plasma Analyzer. The results showed no significant differences in HM contents in the leaves of mangroves between the sites except for Mo and Zn. HM concentrations (mg L−1) in leaves were in the following order: Fe > Zn > Mn > Mo > Cu > Ni > Cr. Significant differences existed between sediment content of Tubli site and the other two sites with regard to Cr, Cu, Pb, and Zn due to direct exposure of the site to wastewater outfalls. A general trend of decline in HM concentrations was noticeable from the top towards deeper sediment layers in all the sites of the study area. Concentration of HM in sediment was in the following order: Fe > Mn > Zn > Cu > Cr > Pb > Ni. HM concentration in sediments far exceeded the amount present in the leaves of the mangrove except for Ni. The amounts of HM in mangrove sediments were comparable to regional findings and fell within known sediment quality guidelines.
Highlights
Accumulation of heavy metals (HMs) in natural ecosystems poses threats to human health and biodiversity due to their persistence and toxicity [1,2,3,4]
The results showed no significant differences in HM content in the leaves of mangroves between the study sites, except for Mo which was significantly higher (P ≤ 0.05) in Sitra (1) compared to Tubli and Sitra (2)
HM concentration in leaves of mangrove does not reflect the complete picture of HM status in mangrove or its temporal sequestration of these metals
Summary
Accumulation of heavy metals (HMs) in natural ecosystems poses threats to human health and biodiversity due to their persistence and toxicity [1,2,3,4]. Coastal vegetation plays a major role in trapping and storing these pollutants [11,12,13]. In this context, mangrove (Avicennia marina (Forsk.) Vierh.) grows in the intertidal zones along the eastern coastlines of the Arabian Peninsula, forming discrete communities in several locations [14]. In Bahrain, the species grows naturally in only four localities along the coastlines of Tubli Bay measuring 0.5 Km2 in the total area [15, 16]. The species was classified as critically endangered in Bahrain as its area dwindled by more than 60% in the last three decades [18]
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