COMPARATIVE STUDY ON THE GROWTH RESPONSE AND REMEDIATION POTENTIAL OF PANICUM MAXIMUM AND AXONOPUS COMPRESSUS IN LEAD CONTAMINATED SOIL

Abstract

The global problem concerning contamination of the environment as a consequence of heavy metals is on the increase. Soil contamination by heavy metals is a worldwide problem, therefore effective remediation approaches are necessary. Some plants can absorb these toxic metals and help to clean them up from the soil and sediment. This fact may be useful for developing rational forms of environmental safety management and innovative technology which more efficiently clean soils and improve their ecological condition with for agriculture. Phytoremediation is known as an eco-friendly and cost-effective way of reducing pollutants from the soil. Therefore, the present experiment was undertaken to investigate the comparative potential of two grasses, Panicum maximum and Axonopus compressus to bioremediate lead polluted soils. In addition, the impact of Pb on the antioxidant defense system of the plants was studied. Pb(NO3)2 salts were mixed with soil at various concentrations 5 mg/kg, 10 mg/kg, 20 mg/kg, 40 mg/kg and 80 mg/kg in triplicates and control experiment was also setup. After 4 months, the plants were removed and their parts (root, shoot and leaf) separated. They were analysed for morphological, biochemical parameters and Pb concentration. Soil samples were also analyzed for Pb. The root length of both P. maximum and A. compressus generally decreased as the concentration of Pb in the soil increased. The least shoot length inhibition of A. compressus was 7.13 % (5 mg/kg) while the highest shoot length inhibition was 36.29 % (40 mg/kg). The least shoot length inhibition of P. maximum was 10.51 % exposed to 5 mg/kg and the highest shoot length inhibition was 42.46 % (40 mg/kg). There was more significant reduction of the heavy metals in vegetated soils for both P. maximum and A. compressus at the end of the study compared to the to the heavy metals in the soils at the beginning of the study (p < 0.05). A. compressus is a better removal of Pb than P. maximum, however, it was not significant. Glutathione (GSH) levels varied significantly (p ≤ 0.05) with respect to concentration of heavy metals as well as different part of the plants. A. compressus has more effects on the Glutathione activities than P. maximum. Pb caused a decrease in the metallothionein level (10.11 %) in P. maximum while A. compressus metallothionein level increased by 116.10 % in 5 % treatment.