## 1 Introduction  
The soil environment is prone to contamination by both organic and inorganic substances, which poses potential threats to the fauna and flora. Contamination of soils with petroleum hydrocarbons and heavy metals with carcinogenic, mutagenic and teratogenic properties seems particularly dangerous [1, 2]. In view of the above, there is an urgent need to rehabilitate the areas contaminated with such xenobiotics and restore them [3]. One common method of land remediation is phytoremediation, which is a green chemistry technique, which uses plants capable of removing, metabolizing, assimilating and adsorbing harmful substances. Plants used in phytoremediation are classified as so-called hyperaccumulators. Hyperaccumulators are plants characterized by their ability to accumulate large amounts of xenobiotics without the harm caused by phytotoxic effects [4; 5; 6]. For sites contaminated with petroleum hydrocarbons, plants belonging to the so-called naphtho-phytes are used in the phytoremediation process. Naphthophytes show an evolutionarily acquired ability to grow on oil lands [7; 8; 9]. Identifying potential plants, which can be used in the remediation of land contaminated with both organic and inorganic substances, is an interesting area of research into the phytoremediation process. One promising plant in this regard appears to be purple coneflower (_Echinacea purpurea_). _Echinacea purpurea_, commonly known as purple coneflower, is a plant species from the Asteraceae family, originating from North America [10]. Adaptability to different climatic conditions, resistance to environmental stress and the ability to grow in different soil conditions have made _Echinacea purpurea_ suitable for cultivation in most climate zones. In addition, _Echinacea purpurea_ is characterized by high biomass production and a well-developed root system (fibrous root). The large surface area and high activity of the root system (production of root exudates) of purple coneflower allow for the stimulation of microbial activity in the root zone, thus enhancing mineralization at the root-soil interface, which enables rhizodegradation [11]. Among other mechanisms occurring during phytoremediation are biodegradation, phytoextraction, phytovolatilization, phytostabilization and abiotic loss, which can act individually or co-occur [12]. Phytoremediation studies conducted using _Echinacea purpurea_ have shown that the plant has a high tolerance for petroleum and is suitable for remediating soils with petroleum concentrations exceeding 10,000 mg/kg [11]. In addition, purple coneflower has been proven to be effective in cleaning up soils polluted with PAHs and alkyl-PAHs [13; 14; 15; 16]. A few studies also suggest that _Echinacea purpurea_ can be used to clean up areas tainted with heavy metals [13; 14]. However, it should be noted that when planning remediation strategies for land contaminated with various types of xenobiotics, the concentration, age and type of contamination should be taken into account. It has been proven that aged soils containing a greater variety of contaminants, with higher concentrations of xenobiotics, undergo the treatment process more slowly than freshly contaminated soils with a single type of contaminant. For real soils with a wide spectrum of contaminants, the efficiency of phytoremediation alone may be too low [17]. Therefore, it is critical to find a new, efficient and economically beneficial approach to the phytoremediation process. In recent years, so-called combined methods using micro-organisms have become increasingly popular for remediating land contaminated with petroleum substances [18]. The most commonly used combination methods include phytoremediation in combination with bioaugmentation. It is based on the interaction of plants and microbes to increase the efficiency of pollutant degradation.