Occurrence and microbial remediation of polycyclic aromatic hydrocarbons and heavy metals pollution in soils

The presence of soils contaminated with polycyclic aromatic hydrocarbons and heavy metals presents a widespread environmental challenge in industrial areas. Unlike single-pollutant systems, co-pollution by polycyclic aromatic hydrocarbons and heavy metals exhibits synergistic toxicity that weakens traditional remediation technologies. This review systematically examines microbial remediation strategies for such co-polluted soils, focusing on three levels of intervention: functional microorganisms, compost-based enhancement, and engineered microbial solutions. We highlight the role of noncovalent interactions, especially cation-π bonding and hydrophobic partitioning, in decreasing pollutant bioavailability and increasing co-toxicity. Functional microbes improve pollutant removal through intracellular transformation, extracellular secretion of biosurfactants and chelators, and surface adsorption. Compost-enhanced systems incorporating biochar, vermicompost, and mycorrhizal fungi demonstrate improved pollutant breakdown and soil health. Engineered microbes offer advanced remediation capabilities but face challenges related to metabolic load, ecological safety, and regulation. Despite promising laboratory results, field implementation remains limited by low pollutant bioavailability, biosafety concerns, and uncertain cost efficiency. We propose critical future research directions to bridge this gap and enable practical remediation of soils co-contaminated with polycyclic aromatic hydrocarbons and heavy metals.