Assessment of the phytoremediation potential of Panicum maximum (guinea grass) for selected heavy metal removal from contaminated soils

Abstract

Non-vascular plants have potential for rapid uptake of metals, but are rarely used for phytoremediation because of their short life cycle. This property can however be advantageously used in a number of metal removal cycles within a short time. The selection of promising plants is critical to success of phytoremediation. The potential for heavy metal uptake by Panicum maximum a non-vascular plant was investigated using pot plant experiments. Seventy-two (72) pots of 7 L capacity were each filled with 5 kg of mixed soil collected from the Fadama (fertile soil) and College of Animal Sciences and Livestock Production farms (less fertile) of the University of Agriculture Abeokuta, Ogun State Nigeria. The pots were divided into six groups of twelve pots each. Each of the group of 12 pots was further divided into three groups of four pots each, in which P. maximum were planted. Five of the six groups were treated with 20, 50, 75, 100 and 120 ppm each of Pb²⁺, Cr³⁺ and Cd²⁺ and the sixth served as control. Levels of Pb²⁺ decreased from 1.40 to 1.05 µg/g and 1.57 to 1.30 µg/g in soils treated with 20 and 120 ppm of Pb²⁺, respectively. Generally there was increase in Pb²⁺ uptake by the different tissues of P. maximum ranging between 0.21 to 0.38 µg/g, 0.18 to 0.30 µg/g, and 0.09 to 0.18 µg/g in root, stem and foliage, respectively. Corresponding bioaccumulation factors (BAF) ranged between 0.21 to 0.45, 0.17 to 0.35 and 0.08 to 0.21. Metal uptake followed similar trends for Cr³⁺ and Cd²⁺ in plant tissues. The BAF values for Cr³⁺ ranged between 0.31 to 0.69 in root, 0.17 to 0.52 in stem and 0.07 to 0.34 in foliage. Similar values for Cd²⁺ were 0.14 to 0.53, 0.10 to 0.44 and 0.05 to 0.37. Accumulation of heavy metals in P. maximum ranged from 13 to 45%, Pb²⁺; 13 to 65%, Cr³⁺ and 11 to 52%, Cd²⁺ of the soil concentration level with tissue abundance decreasing in the order Cr³⁺ > Pb²⁺ > Cd²⁺. Furthermore, the concentration of metals in P. maximum tissues decreased in the order root > stem > foliage. The phytoremediation of Pb²⁺, Cr³⁺ and Cd²⁺contaminated soils with P. maximum seems to be promising under the conditions of the experiment. Obvious signs of phyto-toxicity however appeared in plants exposed to 120 ppm Pb²⁺ and Cd²⁺ at day twenty-three, suggesting that P. maximum may be a moderate metal accumulator.

Keywords: phytoremediation, heavy metals, uptake, tissues, accumulator

African Journal of Biotechnology, Vol 13(19), 1979-1984