Effects of Heavy Metals on the Yield of Essential Oil From Vetiver Grass Cultivated in Mine Tailings Amended With EDTA and Arbuscular Mycorrhizal Fungi

Background/Objective: Vetiver grass (Vetiveria zizanioides (L.) Nash. Syn. Chrysopogon zizanioides (L.) Roberty; family Poaceae) is well-known for producing essential oil that is commonly used in premier perfumery, food, and pharmaceutical industries. The quality of essential oil produced should be assessed before application in production of various products. Methods/Results: In this study, the yield of essential oil extracted from vetiver grass found in Botswana was assessed after cultivation in mine tailings. The respective influence of chelating agents and microbes such as ethylene diamine tetra-acetic acid (EDTA) and arbuscular mycorrhizal fungi (AMF) on the yield of essential oils was also evaluated. Results obtained showed that vetiver grass grown in mine tailings produced more essential oils compared to unpolluted soils. Vetiver grass grown on sterilized soils yielded only 0.26% of essential oils compared to 0.86% of that cultivated in mine tailings. Furthermore, essential oil yield was increased in soil amended with EDTA (0.95%) and after inoculation with AMF (0.89%). Addition of EDTA and AMF enhanced the uptake of heavy metals by vetiver grass and increased heavy metal stress and thereby making vetiver grass release secondary metabolites in the form of essential oils. It is important to note that even though the mine tailings accumulated high concentrations of heavy metals (As: 47.31 +/- 1.40, Cu: 1632.24 +/- 38.20, Mn: 402.68 +/- 18.21, Ni: 728.26 +/- 46.20, Pb: 41.26 +/- 5.38, and Zn: 103.97 +/- 5.34), very low concentrations of metals were detected in essential oils extracts. Conclusion: This study indicates the ability of vetiver grass to produce more essential oil under heavy metal stress making it useful for both essential oil production and important candidate for phytoremediation.