Comparative determination of heavy metals bioaccumulation in bamboo as a phytoremediative process to polluted riverine wetlands

Abstract

Nairobi's unplanned settlements have resulted into open drained domestic and industrial waste into tributaries that join the larger Nairobi River at different stages of its development. Polluted water, to is either directly taken up by planted riverine crops or used through irrigation by the residents. Crop production acts as an important commercial venture for the communities living around the basin. Bioaccumulation of heavy metals such as Zn, Cu, Cd and Pb is evident in these crops causing a health risk to urban consumers. Rehabilitating these wetlands with alternative plant species that reinstate purification, not consumed as food with significant commercial value is therefore urgently needed. Bamboo, due to its growth characteristics and heavy metal accumulation tendencies could serve to uptake heavy metals from polluted aquatic ecosystems and also provide an income generating alternative. four species of bamboo; water bamboo, giant bamboo (Dendrocalamus gingateus), yellow and green bamboo (Bambusa spp) and other plants were grown on potted polluted soils from Motoine riverine, and the accumulated levels of Zn, Cu, Pb and Cd were determined at regular intervals. The results showed that bamboo averagely absorbs 243 mg/kg of Zn, 1.3 mg of Cd, 222 mg/kg of Cu and 36 mg/kg of Pb annually in its initial years. Significant correlations were observed between heavy metal concentrations in the soils after the harvests and the bioaccumulations in the bamboo species (P>0.05, DF12, t-test). Very high correlations between reducing soil heavy metal contents and increasing bamboo heavy metal accumulation (r = -0.788).therefore due to the first growth rate and large biomass index, bamboo forms a good plant for bio filtration of these heavy metals. Bamboo production per year is estimated to be between 30-75 tons/ha per year. The total absorption therefore translates to 6.66-16.65 kg of Zn, 7.29- 18.23 kg of Cu, 1.08-2.7kg of Pb, 39-97.5g of Cd per ha/ year. The study recommends building up of bamboo systems along Motoine River in Kibera as a purifying model and substituting them for commercial edible vegetation in slums around wetlands a viable option.