Study on mangrove species as phytoindicator for inorganic contaminants and assessment of Zn, Fe and Cu bioaccumulation rate through in vivo model system using lemna minor and salvinia natans

Abstract

Heavy metals or inorganic contaminants exhibit in aquatic ecosystems including freshwater, mangrove as well as marine ecosystems due to anthropogenic activities that discharge directly without filtration or treatment system. This study proposes an landscape ecological indicator for specific inorganic contaminants using true mangrove species (Sonneratia alba, Rhizophora apiculata and Avicennia alba) and an experimental model to assess the capability of selected aquatic plant species (Lemna minor and Salvinia natans) to act as biosequester agents. Three types of true mangrove species were evaluated as potential landscape ecological indicators or bio-monitoring agents for five types of heavy metal contaminants (copper, iron, lead, manganese and zinc) and the level of toxicity in the mangrove ecosystem, especially in intertidal zones (shoreline) through plant leaf and root tissues as well as sediment collected from three different localities. Factors controlling heavy metal contaminant resistance and tolerance levels differ greatly with respect to types of plant species, biotic and abiotic components, source of pollution, localities, accumulation of heavy metals in plant tissues and plant interaction mechanisms. The analysis of variance established a significant to highly significant differences (P <0.001) between the three mangrove species, the three locations, the leaves, and roots and sediment samples and their interaction for all the five heavy metals content. From the findings, Zn and Pb concentration were found at toxic levels in mangrove tissues and sediment and was highly accumulated in S. alba, R. apiculata and A. alba at selected locations followed by Cu > Fe >Mn. The three mangrove species studied, namely S. alba, R. apiculata and A. alba were found to have great potential for landscape ecological indicator species to indicate specific heavy metals contaminants in mangrove ecosystems. Meanwhile, through the experimental model system, the sequestration rate of L. minor and S. natans showed that approximately 90% efficiency of copper, iron and zinc were sequestrated in different concentration ranges at different incubation periods except for iron by L. minor and dead at certain concentrations of copper. Interestingly, S. natans’ ability and resistance over three types of heavy metals toxicity were much greater and stable compared to L. minor. In this study, L. minor and S. natans served as good potential biosequester agents to clean-up heavy metals pollutants in aquatic ecosystem due to the fact that they have been able to sequester all heavy metals in a linear relationship within the incubation period. The result revealed that the metal removal efficacies were increased initially through the increasing of time and concentration. Thus, both plants are good potential biosequester agents to clean-up heavy metals pollutants in aquatic ecosystems. In order for this finding to be applied on a large scale, certain factors need to be determined such as plant capabilities and tolerance towards toxicity level, aquatic plant species sequestration rate as well as type of contaminants that will determine the effectiveness of the plant sequestration rate.