Phytoremediation of lead-contaminated soil using vetiver grass (Vetiveria zizaniodes L.), cogon grass (Imperata cylindrica L.), and carabao grass (Paspalum conjugatum L.)

This study was conducted to determine the vegetative characteristics of three grass species grown in different lead levels in soil; survival rate of vetiver grass (Vetiveria zizaniodes L.), cogon grass (Imperata cylindrica L.), and carabao grass (Paspalum conjugatum L.); and ability of the three grass species in terms of lead accumulation by root and shoot organ by comparing their lead uptake. The three test plants were grown in individual plastic bags containing soil with 75 ppm lead (Pb) and 150 ppm lead (Pb) and were exposed for 6 weeks. The lead content of the test plants and the soil were analyzed before and after trials using Atomic Absorption Spectrophotometer. On the vegetative characteristics of the test plants, carabao grass got the highest percent increase in plant height and the most number of leaves. Survival rate of vetiver registered the highest percent plant survival which meant it best tolerated the Pb contamination in soil although it was comparable with carabao grass. also, vetiver grass registered the highest root, shoot and whole plant dry weight (g). Highly significant ability was shown by the test plants to absorb lead in soil at 5% level 6 weeks after exposure. Vetiver grass registered the highest rate of absorption in terms of roots (3.52 ppm), shoots (6.64 ppm) and as a whole plant (10.16 ppm). This was followed by cogon grass with 0.51 ppm in roots, 1.83 ppm in shoots and 2.34 ppm as a whole plant. Root absorption of carabao grass was comparable with root absorption of cogon grass. A statistically lower Pb absorption of carabao grass was recorded in its shoots and as a whole plant with 0.30 ppm and 0.49 ppm, respectively. Furthermore, a significant difference was observed in the amount of Pb retained in soil planted to the test plants 6 weeks after exposure at 5 % level. Lead content of soil was reduced from 76.55 ppm initial Pb content of soil to 4.52 ppm and from 151.55 ppm initial Pb content to 7.86 ppm. These results revealed that vetiver had the highest uptake of lead in soil. Among the grasses, vetiver grass was the best phytomediator of Pb contaminated soil. However, cogon and carabao grass which were statistically different in their phytoremediation potential of lead also showed remarkable absorption capabilities.