Abstract:
Nairobi River has high quantities of heavy metals emanating mainly from industrial and domestic wastes.
Phytoremediation is a promising alternative to conventional clean-up methods; however, not enough
information is available on plant species suitable for this application. Plant screening on contaminated sites
can lead to the identification of more species. A phytoremediation study was carried out along Nairobi River in
six sites; Kikuyu, Kawangware, Chiromo, Gikomba, Njiru, and Fourteen falls. The objective of this study was to
ascertain the extent of heavy metal pollution and the potential of Amaranthushybridus (A. hybridus) as a
phytoremediant. The heavy metals studied were Copper (Cu), Cadmium (Cd) and Zinc (Zn). The heavy metals
present in A. hybridus (biotic indicator), water and soil (abiotic indicators) were detected using the atomic
absorption spectrophotometer (AAS). The observed values of heavy metals in water, soil and A. hybridus did
not vary significantly (p>0.05) among the sampling sites. The concentration of these metals in soil (42.88 ± 0.03
mg/Kg) was higher than the values recorded in water (37.61 ± 0.65 mg/L). Based on the concentration
observed in A. hybridus; Cd - 4.19 ±0.15 mg/Kg, Cu –8.73 ±0.5 mg/Kg and Zn - 17.42 ± 2.4 mg/Kg, Zn > Cu > Cd.
Zn showed the highest accumulation and can be considered as one of the major pollutants in Nairobi River.
Bio-concentration factor obtained was 8.44 ± 0.06. This study showed that A. hybridus can accumulate heavy
metals even when the concentration of the metals in the abiotic components is low; suggesting that it can be
used in phytoremediation of heavy metal polluted aquatic ecosystems.
