Phytotoxic indicators of soils after pollution by oil by treatment of biochar and sodium humate

Petroleum hydrocarbons are highly toxic and carcinogenic substances that adversely affect ecosystems and human health. This study aimed to evaluate the impact of biochar and sodium humate treatments on phytotoxic indicators of soils contaminated with oil. The results show that Haplic Chernozem is more sensitive to remediation than Haplic Cambisol, as evidenced by a significantly greater reduction in the integral phytotoxicity index (IPT). Oil pollution in both Haplic Chernozem and Haplic Cambisol led to a decrease in radish root growth compared to the control group. Application of biochar at all tested dosages promoted increased root growth in both soil types. The study identified the most effective doses of ameliorants for oil-polluted soils: biochar (10 and 20%); sodium humate (1% water solution). Notably, the integral phytotoxicity index of Haplic Cambisol proved more resistant to oil pollution following the application of ameliorants. Among the assessed parameters, the length of radish roots emerged as the most informative and sensitive phytotoxic indicator for monitoring the remediation of oil-contaminated soils. These findings confirm the effectiveness and reliability of the proposed approach for biodiagnosis of oil-contaminated soils, providing a solid foundation for monitoring soil health and quality. Future research should focus on: (1) Expanding the use of phytotoxicity assessment as a quick, simple, and cost-effective method for evaluating the condition of oil-contaminated soils after remediation; (2) studying the biochemical parameters of plants used in phytotesting of remediated oil-contaminated soils; (3) investigating the phytotoxicity and efficacy of microbiological preparations in the remediation of oil-contaminated soils.