Assessment of selected plants growing along Nairobi River for uptake of copper, zinc and cadmium, Nairobi County, Kenya

Abstract

Nairobi River is polluted with heavy metals emanating mainly from discharge of waste and waste wastewaters from industrial and domestic activities from the drainage basin. Plants have tremendous potential for removal and remediation of heavy metals from polluted waters. Phytoremediation is the use of plants and plant processes to remove, degrade or render harmless hazardous materials present in the soil or water. The objective of this study was to investigate the potential of selected plants to uptake copper (Cu), zinc (Zn) and cadmium (Cd). The plants selected were Polygonum senegalensis (P. senegalensis), Amaranthus hybridus (A. hybridus) and Eichhornia crassipes (E. crassipes). The study was conducted along Nairobi River in six sites; Kikuyu, Kawangware, Chiromo, Gikomba, Njiru, and Fourteen falls. The concentrations of the heavy metals in water, soil and plants were determined using Shimadzu AA7000 atomic absorption spectrometer available at the Kenya Bureau of Standards laboratory. The values obtained were used to evaluate the bio-concentration factors (BCF) of P. senegalensis, A. hybridus and E. crassipes. The concentration of Cu (26.6±0.5µg/Kg), Zn (64.7±0.8µg/Kg) and Cd (37.7±0.3µg/Kg) in soil was higher than the values recorded in water (Cu-23.1±0.5µg/L, Zn-57.9±0.8µg/L and Cd-37.7±0.3µg/L). This difference may be attributed to dilution effect of the water due to flow and pre-concentration of the metals in soil. The concentration of the heavy metals in the plants were Cu 8.73±0.08, 7.27±0.05, 7.23±0.05 µg/Kg, Zn 21.79±0.04, 17.42±0.2, 16.32±0.1µg/Kg and Cd 2.91±0.01, 4.11±0.03, 2.15±0.01 µg/Kg in P. senegalensis, A. hybridus and E. crassipes respectively. The BCF values for P. senegalensis, A. hybridus and E. crassipes ranged from 0.27-0.29, 0.24-0.26 and 0.21-0.23 respectively which indicated that the plants have a potential to uptake Cu, Zn and Cd. The study, thus, demonstrates the potential of P. senegalensis, A. hybridus and E. crassipes in phytoremediation of Cu, Zn and Cd polluted waters.