Heavy metal accumulation and chemical composition of the essential oils of yarrow (Achillea millefolium L.) cultivated on heavy metal-contaminated soils

Comparative research has been conducted to determine the content of heavy metals and the chemical composition of yarrow oils, as well as to identify the possibility of yarrow growth on soils contaminated by heavy metals. The experimental plots were situated at different distances of 0.5 km and 15 km, respectively, from the source of pollution, the Non-Ferrous-Metal Works (MFMW) near Plovdiv, Bulgaria. On reaching the flowering stage, the yarrow plants were gathered. The content of heavy metals in flowers was determined by microwave mineralization and analyzed by ICP. The oils were obtained from the flowers of the plant by hydro distillation and analyzed by gas chromatography-mass spectrometry (GC-MS) technique. Heavy metals do not affect the development of yarrow and the quality and quantity of oil obtained from it. The heavy metal content of yarrow essential oil is very low and is not affected by the degree of heavy metal contamination of the soil. Twenty components were identified in oils. In yarrow oil, the highest content was oxygenated sesquiterpenes (36-38%), followed by sesquiterpene hydrocarbons (24-25%), oxygenated monoterpenes (20-21%) and monoterpene hydrocarbons (17-19%). For the first time, it is reported yarrow oil with mixed α-bisabolol oxide B, α-bisabolol, and β-caryophyllene chemotype. The essential oil of yarrow can be a valuable product for the farmers from polluted regions.