Assessment of In-Situ Natural Dendroremediation Capability of Rhizophora racemosa in a Heavy Metal Polluted Mangrove Forest, Rivers State, Nigeria

Abstract

Environmental pollution is assuming frightening dimensions in many parts of the world. This is not excluding Niger-Delta region of Nigeria where most of the countryfs oil and gas are sourced with attendant production of noxious substances as byproducts/residues/waste. Many of these noxious substances have been noted to be removable from polluted environment through proper application of phytoremediation techniques, particularly using native plant species. Consequently, this research was conceived to evaluate potentials for phytomediation by native red mangrove tree (Rhizophora racemosa G.F.W. Meyer). This was carried out by evaluating the presence of heavy metals ions and their bioconcentration levels in the samples of root and wood tissues axially along the stem of this tree. The sorrounding soil and water were also sampled and evaluated for presence and concentration of these metal ions in comparison with those for the sampled plant tissues. All the samples were sourced from a mangrove forest in Okrika, Rivers State, Nigeria. The samples from the root, butt, 50% and 90% bole length were oven-dried at 60}5oC to constant weight, pulverised and heated with trioxonitrate (v) acid to achieve total dissolution before subjecting them to atomic absorption spectroscopy (AAS). Similarly, samples from sorrouding soil were dried at 35}2oC to constant weight, crushed and sieved using a . 2mm mesh before performing metal  extraction and detection using AAS while water samples were also subjected to AAS for heavy metal analyses, in line with appropriate standard  methods. The data obtained were statistically analysed using basic descriptive tools, Analyses of Variance and Fishersf Least Significant Difference (P < 0.05). Outcomes of these statistical analyses showed that, in terms of bio-concentration values, the evaluated metal ions that
include Fe, Cu, Mn, Cd, Pb, Ni and Cr were more in the root than the surrounding soil and water. The bio-concentration trends, for the metal ions, also progressively declined from the root towards the crown of the trees. The bio-concentration distribution in all the tree sections showed an inconsistent pattern with Fe ions having higher bio-concentration. In addition, Cr, Ni, Pd and Cu also inconsistently followed Fe in terms of bio-concentration level. c JASEM