Accumulation Ability of the Native Grass Species, Cyperus rotundus for the Heavy Metals; Zinc (Zn), Cadmium (Cd), Nickel (Ni) and Lead (Pb)

Abstract

In this paper, laboratory pots experiment was conducted to assessing the absorption and accumulation potential of the native grass species, Cyperus rotundus. Viable seed of the grass were seeded into soil (2.0 kg) amended with different concentrations of the metals, Zn, Pb, Cd and Ni. Experimental soil was amended with, 150, 1000, and 3000 ppm Zn as Zn(SO4)3.6H2O; 150, 500, and 1000 ppm Pb as Pb(NO3)2; 150, 250, and 400 ppm Cd as Cd(NO3)2; 150, 500, and 1000ppm Ni as Ni(NO3)2.6H2O. plants were allowed to grow under careful supervision with adequate watering for a period of eight weeks along with the control experiment. Plants were harvested by pulling carefully to avoid damages to the roots. Separated into roots and shoots and washed with tap water. Soil, roots and shoots of the grass were analysed using atomic absorption spectroscopy (AAS) following digestion with aqua-regia for the soil and 6M HCl for the plant parts. The bioconcentration (BCF), enrichment (EF) and translocation factors (TF) of the metals were determined from their concentration in the soil, root and shoot. The results showed that, Zn had BCF values of 1.38, 6.13, 5.67, and 1.93; EF of 1.46, 1.65, 3.31, and 1.55; TF of 0.27, 0.59, and 0.80 at the control, 150, 1000, and 3000 ppm Zn in the soil respectively. Lead has BCF values of 1.31, 1.87, 0.92, and 1.66; EF of 0.62, 0.88, 0.23, and 1.18; TF of 0.47, 0.47, 0.25, and 0.71 at the control, 150, 500, and 1000 ppm Pb in the soil respectively. Cadmium has BCF values of 1.01, 1.00, 1.00, and 0.87; EF of 0.89, 0.87, 1.17, and 1.19 at the control, 150, 250, and 400 ppm Cd in the soil respectively. Nickel had the BCF values of, 14.0, 2.8, 2.3, and 1.4; EF of 18.0, 3.9, 5.4, and 3.6, TF of 1.29, 1.40, 2.30, and 2.57 at the control, 150, 500, and 1000 ppm Ni in the soil respectively. High values of one (1) and above for the BCF and EF indicates absorption, high retention and concentrating of the metals in the roots with less translocation to the shoots. The grass, Cyperus rotundus may, therefore, be best described as a metal excluder or stabiliser for Zn and Ni having greater values of BCF and EF than TF. A phenomenon is known as phytostabilisation. It could also absorb and retain the metal, Pb in the roots having BCF of 1.66, EF= 1.18 at 400 ppm Pb.