Biological Assessment of Soils Following Waste Tyre Fires and Potential Remediation—A Case Study

Waste tyre fires are a significant environmental issue that leads to the release of toxic substances into the soil, particularly polycyclic aromatic hydrocarbons and heavy metals. These contaminants can adversely affect the physicochemical properties of the soil, its microbial activity, and plant growth. The aim of this study is to assess the degree of phytotoxicity in soils affected by tyre waste fires using acute and biological tests, while simultaneously measuring microbial respiration as an indicator of soil biological activity. Furthermore, the effectiveness of the application of a 5% dose of biochar as a remediation measure was evaluated. The results showed that leachates from contaminated soils exhibited phytotoxic effects, with growth inhibition of 26.94–28.12% and reduced seed germination of 55.6–55.9%. The application of biochar to the soil under study significantly reduced phytotoxicity-induced growth inhibition (20–23.11%) and improved seed germination rates (79.76–83.71%). Microbial respiration gradually increased following the application of biochar; after 28 days it was over 30% higher compared to soils without biochar amendment. This study confirms that biochar can be an effective amendment that improves the biological quality of soils impacted by tyre waste fires.