## 1 Introduction
Therefore, seeking environmentally friendly and economically viable technological solutions to mitigate the harmful effects of oil pollution on soils is fully justified and in line with the EU's climate and economic initiatives. In terms of protecting the soil environment, a preventive approach would be to replace conventional fossil fuels with biofuels wherever possible. Studies suggest that biodiesel is significantly more biodegradable than conventional diesel oil [29] and less toxic [30], thanks to its hydrocarbon-free composition and low particulate emissions [31]. This alternative fuel can be used by various indigenous soil microorganisms as a source of carbon and energy [32]. However, its higher density and viscosity compared to conventional diesel oil [33] result in reduced mobility in the soil profile, which may limit its dispersion in the environment. Despite its superior environmental properties, biodiesel can still cause soil contamination [34], especially in the event of a large spill [30], negatively affecting soil pH, the number of microorganisms and their relative composition, as well as the quantitative indicators of microbial processes [29; 35]. The ecotoxicity profile of biodiesel depends largely on the dose, the type of feedstock used and the type of alcohol used during the production and further processing of the biofuel [31]. Methods for remediating contaminated soils can be categorised as physical methods (including storage, thermal desorption, vitrification and electrokinetics), chemical methods (including washing, solidification, redox transformation and stabilisation) and biological methods (including bioremediation, phytoextraction, phytovoltaatisation and rhizfiltration) [36; 37]. Undoubtedly, chemical methods have many advantages, including in situ stabilisation. These include low economic cost, simple implementation, the absence of secondary waste, applicability even to heavily contaminated sites and rapid results [37]. In situ chemical stabilisation technology uses a combination of inorganic (e.g., calcium- and phosphate-based compounds, fly ash and clay minerals) and organic (e.g., sewage sludge, compost and biochar) materials to treat contaminated soils. These materials immobilise contaminants by increasing soil pH and improving soil structure, water capacity and nutrient status [38; 39], and increasing sorption capacity and/or improving soil microbial activity [40]. The mechanism by which contaminants are immobilised following the application of these soil additives involves a combination of adsorption, complexation and precipitation processes [41]. This reduces the mobility and availability of contaminants, as well as their vertical migration and surface runoff with rainwater [42]. Trace elements are primarily immobilised by precipitation when calcium compounds are applied due to the resulting elevated pH levels [43]. Concurrently, the availability of trace elements is diminished by the formation of insoluble organometallic complexes when compost is applied [42]. Additionally, [PERSON] et al. [44] reported that introducing alkaline materials into contaminated soil significantly improves microbial diversity in the soil and encourages the growth of beneficial bacterial communities. This also increases catalase and urease activity, indicating its role in improving soil health and biochemical properties. The application of clay materials such as bentonite reduces the amount of trace elements available to plants in the soil due to their adsorption to the material's surface and edges, as well as intercalation (i.e., the replacement of a cation in the interlayer space) [45]. It also increases the soil's sorption capacity [46] and microbial and enzymatic activity [47]. The main component of bentonite is the clay mineral montmorillonite, which belongs to the smectite group of layered silicates and has very small particle sizes [48]. Consequently, it has a large specific surface area, a high permanent negative charge and a high cation exchange capacity (CEC) [49].