Assessing Heavy Metals Accumulation in the Leaves and Sediments of Urban Mangroves ( Avicennia marina (Forsk.) Vierh.) in Bahrain

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.