Heavy metal pollution and Phytoremediation potential of Avicennia officinalis L. in the southern coast of the Hoogly estuarine system

Mangroves in Sunderbans are being increasingly subjected to heavy metal pollution mostly due to their unique location as they receive pollutants both from upstream area of the Hoogly estuary and the sea. In the present study absorption, accumulation and partitioning of Zn, Cu, Pb, Cr and Cd in Avicennia officinalis L. in Jharkhali was studied to ascertain the phytoremediation capacity of the mangrove species. Sediment, root, bark and leaves were analysed by Atomic absorption spectrometer to know the concentration of these metals and their variability in post-monsoon, pre-monsoon and monsoon periods. Concentration (mg kg ) of Zn was 40.39±4.62, 33.38±3.19 and 49.46±5.94 in root; 23.63±1.67, 20.35±3.56 and 31.25±3.69 in bark; 21.55±4.40, 18.54±2.62 and 28.23±2.31 in leaves; that of Cu was 17.38±1.53, 14.92±4.79 and 20.77±3.43 in root; 10.31±1.59, 8.51±2.79 and 13.77±2.1in bark; 8.88±2.76, 6.76±2.23 and 11.88±1.67 in leaves; that of Pb was 9.52±1.98,7.40±1.42and 11.96±2.65 in root; 5.75±2.51, 4.52±2.56 and 6.22±0.49 in bark; 4.04±2.0, 3.26±2.46 and 4.57±1.24 in leaves; that of Cr was 6.51±3.05, 3.34±1.73 and 8.44±2.36 in root; 3.82±2.34, 2.27±1.22 and 4.69±1.89 in bark and 2.33±1.12, 1.25±0.83 and 3.63±1.17 in leaves in postmonsoon, pre-monsoon and monsoon respectively. It was found that though the sediments exhibited the highest concentration of the metals, yet they were below the general critical soil concentration. Metal accumulation in roots was comparable to those in adjacent sediments with root bio-concentration factor of <1.Metal concentration was lower in bark and the lowest in the leaves with essential metals like Zn and Cu exhibiting leaf translocation factor of >0.5 while non essential metals like Pb and Cr had translocation factor < 0.5. This shows that Avicennia officinalis L. tend to exclude non-essential metals and regulate the uptake of essential metals. Thus, in conjunction with its environmental settings, the mangrove species plays a vital part in reducing transport of heavy metals to adjacent estuarine and marine ecosystems.