Enhanced ecological risks of pollutant-adsorbed engineered environmental particles to soil microorganisms

Engineered environmental particles are introduced, generated, or released during engineering activities, significantly accumulating after entering the soil ecosystem. When these particles adsorb pollutants, they inevitably interact with soil microorganisms, potentially altering soil microbial ecosystem function. This study evaluated the variation of ecological risks before and after pollutant (organic tetracycline and inorganic Cd) adsorption of three commonly detected engineered environmental particles and one natural soil particle on soil microorganisms. Absorbance measurements of soil bacterial suspensions indicated that pollutant-adsorbed particles significantly inhibited soil bacterial growth compared to raw particles. These composite particles triggered bacterial stress responses and activated bacterial self-protective mechanisms through enhanced extracellular polymeric substance (EPS) production, with protein and polysaccharide concentration ranges increased from 163.12-243.10 mg/L and 75.25–87.23 mg/L to 232.84–294.10 mg/L and 74.29–93.96 mg/L, respectively. Soil bacteria exhibited consistent biofilm formation and robust stress responses when exposed to nanoparticles (either alone or pollutant-complexed). These responses created extracellular barriers that mitigated harmful substance penetration while maintaining cellular integrity and viability, reducing LDH concentration range from 173.55 to 300.92 U/CFU to 88.26–154.45 U/CFU. 16S rRNA sequencing exposed phylum-level community shifts under particle stress: Firmicutes abundance decreased 11–13 %, inversely correlating with Proteobacteria increases. The pollutant adsorption significantly increased the selective enrichment of ARGs and virulence factor genes (VFGs), suggesting an enhanced survival advantage for pathogenic microbes and accelerated dissemination of resistance determinants. This study reveals the mechanisms determining the ecological risk of engineered environmental particles during the pollutant adsorption and benefits the development of new environmental risk assessment frameworks.