Phytoremediation of Lead Polluted Soils with Grass Species

Abstract

Heavy metals pollution, especially the lead (Pb), is caused by mining, industrial dumping and other anthropogenic activities which are corroding the environment. Efforts being made to control these pollutants include physical, chemical, biological and immunological methods. The failure of the aforementioned methods, are largely due to the fact that they are cumbersome, expensive and not eco-friendly. Some plant species however can be used for remediation in reclaiming the polluted environment. The objective of this work therefore is to evaluate the abilities of two native grass species to remediate two lead polluted soils: Battery dumpsite and naturally occurring lead mine. Soil samples were taken from two dominant sites of lead: Kumapayi in Ibadan, a
battery dumpsite and Zamfara, a natural lead mine. A screen house factorial experiment laid out in a completely randomized design (CRD) replicated three times was carried out at the International Institute for Tropical Agriculture (IITA), Ibadan. Unpolluted soils were collected from the experimental site of the Department of Agronomy, University of Ibadan in Ibadan, Nigeria and polluted with varying Pb soil concentrations from Kumapayi and Zamfara at 0, 0.1, 0.2, and 0.5%. A thorough mixing of the two lead soils with unpolluted soil was done, respectively, and the seedlings of Gomphrena celuosoides and Sporobolus
pyramidalis were planted directly after harvesting on the polluted soils. Plant growth parameters such as plant height, number of leaves, and dry matter were monitored for twelve weeks, after which the grass species were harvested. Dry weights were taken, while the uptake of Pb by the plant species was determined. Analysis of data was carried out using ANOVA (p<0.05) and descriptive statistics. Relative concentration of Pb in the stem and leaf, and root parts of Gomphrena celuosoides revealed that a higher amount of Pb was taken up in the root compared to the shoots at different concentrations of Pb pollution. The Pb uptake was in this ordering 0.5% > 0.2% > 0.1% > Control. Phytoremediation ability of G. celuosoides was highest at 0.5% Pb polluted soil and its retention was greater in the root than the shoot. In S. pyramidalis, soil retention ranged from 0.1% > 0.5% > 0.2% > control, while the Pb uptake was highest at 0.5% > 0.1% > 0.2% in shoot. Uptake of Pb heavy metal in leaves was highest at 0.2% concentration but none in the 0.5% pollution. This probably implies that rooting systems affect the amount and way different plant species absorb Pb (Gomphrena spp. rooting system is tap root, while that of S .pyramidalis is fibrous).