## 2 Materials and Methods  
### Soil, Microbial Consortia, \(\gamma\)-PGA and Plant Description  
Two types of soil contaminated with petroleum hydrocarbons were used in the study. Soils were taken from two locations, which were the G-70 pit area--which was used in the 1970s to store drilling waste mixed with soil (Soil DW)--and an oil spill site (Soil OS). Forty soil samples weighing 2 kg were collected from each site. Samples were taken from the surface layer (0-0.25 m below ground level) and the deep layer (0.25-1.5 m below ground level). Each type of soil taken was mixed and homogenized for averaging, followed by physical and chemical analyses. The composition of the soils used in the bioaugmentation-assisted phytoremediation study is shown in Table 1.  
\begin{table}
\begin{tabular}{l c c} \hline
**Parameter** & **Soil DW** & **Soil OS** \\ \hline pH\({}_{\text{H2O}}\) & 7.06 & 6.99 \\ Initial water moisture (\%) & 21.9 & 23.01 \\ BTEX (benzene, toluene, p-, m-ksylen) & 0.59 & 0.97 \\ TPH & 5176.03 & 4025.65 \\ WWA & 17.71 & 10.30 \\ Cl\({}^{-}\)a & 168.5 & 258.6 \\ S\(-\)SO\({}_{4}^{\text{2--a}}\) & 781.5 & 826.3 \\ N\(-\)NH\({}_{4}^{+}\)a & 70.1 & 79.4 \\ N\(-\)NO\({}_{3}\)\({}^{-}\)a & 241.2 & 230.4 \\ P\(-\)PO\({}_{4}^{-}\)\({}^{-}\)a & 272.26 & 32.1 \\ Al\({}_{2}\)O\({}_{3}\)b & 688.5 & 426.9 \\ SiO\({}_{2}\)b & 236.5 & 315.6 \\ Fe\({}_{2}\)O\({}_{3}\)b & 5.3 & 6.2 \\ MgO\({}^{\text{b}}\) & 3.9 & 3.0 \\ CaO\({}^{\text{b}}\) & 6.9 & 6.5 \\ Sand (\%) & 54.01 & 75.21 \\ Silt (\%) & 10.37 & 6.92 \\ Clay (\%) & 35.62 & 17.87 \\ As & 0.9 & 0.7 \\ Ba & 28.9 & 23.5 \\ Cd & 1.0 & 0.7 \\ Cr & 11.1 & 9.1 \\ Co & 3.1 & 3.0 \\ Cu & 22.2 & 24.5 \\ Heavy metal content a & Hg & 0.5 & 0.2 \\ Pb & 22.9 & 15.4 \\ Mo & 1.8 & 2.1 \\ Sn & 5.4 & 6.7 \\ Zn & 20.6 & 17.1 \\ Ni & 11.8 & 9.3 \\ \hline \end{tabular}
\end{table}
Table 1: Results of physical and chemical analyses of soils used in studies of bioaugmentation-assisted phytoremediation process.  
Two microbial consortia developed from indigenous micro-organisms isolated from contaminated sites were used to carry out the bioaugmentation procedure. Microbial consortium B1 contained the bacterial strains _Dietzia_ sp. IN118, _Gordonia_ sp. IN101, _Mycolic bacterium frederiksbergeuse_ IN53, _Rhodococcus erythropolis_ IN119, _Rhodococcus glopherulus_ IN113 and _Raoultella_ sp. IN109. Microbial consortium B2 consisted of bacteria present in microbial consortium B1 and was additionally enriched with fungal strains _Aspergillus sydowii_, _Aspergillus versicolor_, _Candida_ sp., _Cladosporium haltolerans_, _Penicillium chrysogenum_. The density of cells in both consortia was in the range of \(5\times 10^{8}\)-\(1\times 10^{9}\) CFU/mL. The bacterial and fungal strains used in the microbial consortia had proven abilities to metabolize petroleum hydrocarbons and did not exhibit pathogenic properties. A detailed description of the design of microbial consortia B1 and B2, along with the method of identification of the strains of bacteria and fungi present in them, is provided in a previous article [17]. More information about the microbial consortia used in the research is available in Supplementary Materials. A commercially available formulation of Ambiogel(r) (Ambioteco, Staszow, Poland) containing 5% pure poly-\(\gamma\)-glutamic acid [64], whose impact on the efficiency of bioremediation has been confirmed in earlier studies, was used as an additive for microbial consortia. The phytoremediation process was carried out using seeds of _Echinacea purpurea_ (Legutko, Poland), which were sown in each of the tested systems.