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.
