Rehabilitation and Phytoremediation-of Heavy Metal Polluted Riverine Wetlands using Bamboo for Phytoextraction in Kibera, Kenya
Bosire, Geoffrey Orina
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Urban and peri urban unplanned settlements have mushroomed widely in Kenya today. Examples of settlements that are now congested with domestic wastes open draining into wetlands include Kibera (Africa's largest slum), Mathare and Dandora slums both, which drain their wastes into Nairobi River and its tributaries that pass through them. Nairobi River has through academic research, government and industrial partnerships attracted activities that seek to foster transformation from polluted to sustainable clean water. The river is a natural receptacle for possible heavy metal pollutants from domestic and industrial activities. Heavy metals are highly toxic when they fall beyond accepted standards. Their effects are evidenced as tetratogenic, mutagenic and others being carcinogenic. This is a great concern of whose subsequent research gives birth to bioremediation using plant species. Phytoremediation is a more cost-effective, more environmentally friendly, and more aesthetically pleasing method for polluted water purification and filtration. Plants also offer a permanent, in situ, no intrusive, selfsustaining method of soil and water contaminant removal. Potential danger might exist for animals and humans who live in the areas in which phytoremediators are grown, especially if they typically feed on the species of plant being used for phytoremediation. Rehabilitating the wetlands with an alternative that reinstates the purification and filtration capacity, and that is not consumed as food, is therefore urgently needed. A promising alternative is the bamboo that could serve to uptake heavy metals from polluted aquatic ecosystems. In this research, Zn Cu, Cd and Pb concentrations were investigated in soils, water and plants along Kibera riverine. Four species of bamboo and other plants investigated were grown on potted polluted soils from Motoine riverine, and the levels of Cd, Cu, Zn and Pb determined at regular intervals. Data was analysed by Genstat package for natural sciences for regression analysis and ANOVA. Soils were found to contain Pb in the range of 60.01±3.35 to 69.75±7.19 mg/kg, Cd in the range of 1.819±0.19 to 2.151±0.059 mg/kg, Zn from the range 34.76±6.27 to 38.47±9.4 mg/kg and Zn in the range of 875.84±215 to 1035.25±67.07 mg/kg. Results on soils further showed that the heavy metal levels reduced significantly after the growing plants on contaminated soils. For the vegetation comparative study herein, Bamboo plants showed trends that could serve to absorb Cd, Pb, Zn, and Cu. Bamboo absorption therefore translates to 6.66-16.65 kg of Zn, 7.29-18.225 kg of Cu, 1.08-2.7 kg of Pb, 39-97.5 g of Cd per ha/year. It will therefore be appropriate to argue that building up bamboo systems along Ngongi Motoine River in Kibera slums as a purifying model, substituting them for cultivated edible vegetation in slums currently around wetlands is highly encouraged.