Comprehensive Ecotoxicity of the Complex System of Polycyclic Aromatic Hydrocarbon-Contaminated Sites to Wheat (Triticum aestivum L.) During Microbial Remediation

Microbial remediation is an eco-friendly and cost-effective method for treating organic-contaminated soil, essential for sustainable land use due to its minimal secondary pollution and operational simplicity. However, during the degradation of polycyclic aromatic hydrocarbons (PAHs), the formation of polar or toxic intermediate metabolites can lead to unpredictable ecotoxicological impacts. In this study, we investigated the effects of the microbial remediation of organic-contaminated soils on wheat seedling growth and physiology, and evaluated soil ecotoxicity throughout the remediation process. The results showed that the concentrations of benzo[a]anthracene (BaA) and benzo[a]pyrene (BaP) decreased by 70.4% and 49.9%, respectively, following microbial degradation, with the degradation process following a second-order kinetic model. Despite the reduction in pollutants, soil toxicity increased from days 10 to 20, peaked on day 20, and then gradually decreased, but it remained elevated throughout the remediation process. Increased ecotoxicity inhibited wheat seed germination, seedling growth, and chlorophyll content, induced oxidative stress, and suppressed soil enzyme activity. Gas chromatography–mass spectrometry (GC-MS) analysis identified toxic intermediate metabolites as the primary contributors to enhanced ecotoxicity. Wheat seed germination potential, plant height, root length, and superoxide dismutase (SOD) and catalase (CAT) activity in roots can effectively indicate soil ecotoxicity throughout the microbial remediation process. These parameters facilitate the optimization of remediation strategies to ensure restored soil functionality and long-term ecological sustainability.