Assessment of ecological risk of heavy metals in sediment and different tissues of Avicennia marina in the coasts of the Persian Gulf

The present study was conducted to measure the heavy metals of Cu, Ni, Pb and Zn in sediments, roots, stems and leaves of mangrove tree (Avicennia marina) from five stations in Khamir port located in the southwest of Bandar Abbas with three replications in summer 2020. In addition, some geochemical parameters of the sediments of the bed of these mangroves such as Muller index, contamination factor and ecological risk index have been evaluated. The accumulation pattern of heavy metals in the sediment was obtained as Ni> Pb>Zn>Cu. This pattern for root, stem and leaf tissues were determined as Ni>Cu>Zn>Pb, Cu>Zn>Ni>Pb and Cu>Zn>Ni>Pb, respectively. According to the bio concentration factor, plant tissues can be a suitable bio-indicator for Cu in the region. Root can also be considered a good bio indicator for Pb and Ni metals. For Zn metal, leaf and stem tissues were also identified as suitable indicators in the region.Transfer factor was significant only for Cu and Zn metals in stem and leaf tissues, which showed a direct relationship between cu and Zn concentrations in roots and then in leaves and stems. Also, examination of metal concentrations in sediments in all stations showed that only nickel metal concentration was critical. Also, the findings of the study of environmental assessment index of heavy metals showed that the sediments of Khamir port are in the category of low ecological risk (RI<150) in terms of ecological pollution index. In general, the process of accumulation of metals in sediments and mangroves tissues showed that increasing the concentration of elements in sediments, the amount of these elements in plant tissues can also increases, so, A. marina can be a bioindicator for heavy metals in the studied ecosystem. In addition, this plant reduces the mobility and bioavailability of the studied metals in the sediments of this ecosystem.