Abstract: Comparative research has been conducted to allow us to determine the accumulation of heavy metals, micro and macroelements in the vegetative and reproductive organs of milk thistle, the quality of milk thistle oil, as well as the possibilities to use the plant for phytoremediation of heavy metal contaminated soils. The experiment was performed on an agricultural field contaminated by the Non-Ferrous-Metal Works (NFMW) near Plovdiv, Bulgaria. The experimental plots were situated at different distances (0.5, and 15 km) from the source of pollution. The contents of heavy metals in plant materials (roots, stems, leaves, seeds and head seeds) were determined. The quality of milk thistle oils (heavy metals and fatty acid composition) was also determined. The quantitative measurements were carried out with inductively-coupled plasma (ICP). Mllk thistle is a plant that is tolerant to heavy metals and can be referred to the hyperaccumulators of lead and the accumulators of cadmium and zinc. The plant can be successfully used in the phytoremediation of heavy metal contaminated soils. Heavy metal soil contamination has no significant effect on the oil content of the milk thistle seeds and the fatty acid composition of the oil. Oil of milk thistle grown in contaminated soils is characterized by a lower content of saturated acids (with the exception of arachidonic acid) and polyunsaturated acids, and a higher monounsaturated acid content compared to the oil from the uncontaminated area. The processing of milk thistle seeds into oil and the use of the obtained oil will greatly reduce the cost of phytoremediation.
Keywords: heavy metals, milk thistle, phytoremediation, polluted soils