Mangrove species selection for phytoremediation of heavy metals from the Sundarbans, Northeast coast of India

Abstract

In the Sundarbans mangrove forest, heavy metals like Zn, Cu, Ni, Co, Pb, and Cr were assessed in soil, leaf, stem and root tissue of various mangrove species. Except for Zn and Cu, the levels of other metals in plant organs were lower than the metal concentration in sediments. Cu and Cr accumulations were to some extent higher in tissues of all mangrove species in comparison to the permissible limit in plants. Physicochemical properties of sediments might greatly influence the availability of metals to mangroves. The mangroves, Nypa fruiticans, Ceriops decandra and Phoenix paludosa are classified as excluders of Cu with more accumulation of metals mainly occurring in roots, with a resultant Translocation Factor (TF) < 1 and a Bioconcentration Factor (BCF) > 1. Both Heritiera fomes and Aegialitis rotundifolia are classified as accumulators, extractors and translocators of Cu and extractors and translocators of Zn. Accumulators could be considered as tolerant as well as indicator plants for controlling the movement of metals from root to shoot that becomes proportional to the metals in the sediment. All of these characteristics of mangrove species in terms of heavy metal accumulation could be considered as phytoremediation potentiality of mangrove plants and associates. More investigation in these aspects needs to be carried out not only to identify other species suitable for phytoremediation but also to ensure safe food chains in the coastal ecosystems.