## 4 Discussion  
Phytoremediation is now a widely used method for remediating land contaminated with petroleum hydrocarbons, but for aged drilling waste or soils heavily contaminated with various types of xenobiotics, its effectiveness is usually too low. Therefore, so-called combined methods using micro-organisms are increasingly being used [18]. The study showed that the effectiveness of phytoremediation using _Echinacea purpurea_ as a test plant largely depends on the concentration, type and age of the contaminant, as well as the conditions under which the treatment process is carried out [17]. The chromatographic analyses performed proved that the use of phytoremediation supported by inoculation with microbial consortia produced on the basis of indigenous micro-organisms allows for a significant reduction in the amount of TPHs and PAHs in the studied soils. This is probably due to the fact that the effectiveness of the soil remediation process using plants is affected by the number of bacteria, fungi and yeasts in the surrounding root zone [77]. Thus, the introduction of micro-organisms isolated from contaminated sites (biopreparation) into the soil makes it possible to improve the efficiency of contaminant elimination while avoiding antagonistic interactions of the soil's indigenous microflora with foreign microbial cultures [9; 78; 79]. Moreover, inoculating the soil with the microbial consortia makes it possible to increase the concentration of micro-organisms near the roots, which influences their better growth [80]. The penetration of roots into the deeper layers of the rhizosphere causes the soil to expand, resulting in improved ventilation and permeability of the test soil, as well as increased interaction between micro-organisms and contamination. On the other hand, the plant's roots secrete organic compounds, such as organic acids, sugars, amino acids, etc., which provide a source of carbon and energy for the growth of rhizosphere micro-organisms. It should also be remembered that dead root cells are treated by soil micro-organisms as an excellent source of nutrients, which further increases their metabolic activity [9; 81; 82; 83]. Therefore, the synergistic interactions occurring among the micro-organisms present in the _Echinacea purpurea_ root inoculant allow for an improvement in bioavailability to pollutants, thereby increasing their degradation efficiency. Based on the chromatographic analyses of the soils, roots and shoots, it can be concluded that during phytoremediation studies using _Echinacea purpurea_, the petroleum-based contaminants underwent mechanisms of degradation, extraction, inhibition or a combination thereof [12; 18]. Chromatographic analyses of the soils showed a slight reduction in the concentration of TPHs and PAHs in non-inoculated systems, while inoculation with microbial consortia and microbial consortia with \(\gamma\)-PGA allowed for a significant increase in the treatment efficiency of the studied soils. This proves the validity of the phytoremediation method assisted by microbial consortium inoculation. It should also be noted that among the inoculants tested, the B2 microbial consortium with \(\gamma\)-PGA was the most effective. This confirms the hypothesis that the use of an inoculant, which contains in its composition micro-organisms from different species (bacteria, fungi) and additives promoting the degradation of xenobiotics (\(\gamma\)-PGA), allows for an improvement in the efficiency of phytoremediation of soils, as well as biodegradation of oil pollutants by micro-organisms. Purification of the soils from toxic substances occurs due to the ability of the micro-organisms present in microbial consortia, natural soil microflora and _Echinacea purpurea_ to produce enzymes and other chemicals, which break down or convert organic pollutants into simpler compounds with lower toxicity and better assimilation by plants [81; 82]. Enzymes such as nitroreductase, dehalogenase, lactase, peroxidase and others are responsible for the degradation of petroleum hydrocarbons [84].