A mesocosm study on the use of clay minerals to improve heavy metal phytoremediation capacity of vetiver grass (Chrysopogon zizanioides L. Roberty)

Abstract

Fast-paced global industrialisation due to population growth poses negative environmental implications, such as pollution by heavy metals. We assessed the application of vetiver grass assisted by clay minerals for the remediation of soil and water contaminated by multiple metals in a mesocosm study. The technique was tested previously in a greenhouse study that confirmed the effectiveness of 2.5% (w/w) attapulgite and 2.5% (w/v) bentonite to improve vetiver grass remediation of soil and water contaminated by multiple metals. At the end of the experiment, the total accumulation of Co, Cr, Cu, Ni and Zn by vetiver grass from the soil was 1.8, 38.1, 19.0, 7.2 and 55.4 mg/kg, respectively, while in water, the total metal accumulation of Al and Mn by vetiver grass was 4534.5 and 104.5 mg/kg, respectively. The results confirm the effectiveness of attapulgite and bentonite as amendments to improve the remediation potential of vetiver in soil and water under natural conditions. Metal accumulation was generally higher in the roots than in shoots. We found the removal efficiency in the soil to be in the order Zn > Cr > Cu > Ni > Co and Al > Mn in water. Results also demonstrated that heavy metal accumulation was even better under natural conditions than in the greenhouse study. For example, Zn accumulation increased from 0.4 mg/kg in the greenhouse study to 55.4 mg/kg in the outdoor study. This study validates the application of bentonite and attapulgite-assisted phytoremediation for heavy metal contaminated soil and water. Significance: Heavy metal pollution of soil and water is very common in industrialised and mining areas. It is important to find cost-effective, eco-friendly and easy-to-apply methods of removing these heavy metals from soil and water, so as to provide a clean and safe environment for living organisms. Phytoremediation is the use of plants to remove pollutants from the environment and is a cost-effective, aesthetically pleasing and eco-friendly method. Attapulgite and bentonite (clay minerals) are effective in improving the phytoremediation capacity of a phytoremediation plant known as vetiver grass.