Aging enhancement and synergistic effect on toxicity to soil fauna by polystyrene microplastics-tetrabromobisphenol A toxicity exposure

Rapid development of electronic industry leads to co-contamination of soil by microplastics and brominated flame retardants, resulting in combined toxic effects on soil fauna. Nevertheless, limited information is available, especially for the aged microplastics. Therefore, the toxicity and molecular mechanisms of composite exposure of aged polystyrene (PS) microplastics and tetrabromobisphenol A (TBBPA) on earthworms were explored via histopathological, oxidative stress, gut microbiological and metabolomics assays. After 28 d of exposure, PS microplastics and TBBPA showed significant synergistic effects on earthworm growth inhibition. Notably, aging of microplastics exacerbated the combined toxicity to earthworms. Aged microplastics with rougher surfaces inflicted more severe physical damage to earthworm intestinal tissues. This physical disruption, combined with their higher TBBPA adsorption capacity, significantly enhanced the accumulation and absorption of TBBPA within earthworms. Consequently, earthworms exhibited intensified oxidative stress, severe gut microbiota disorders, and marked metabolic dysbiosis. Overall, aged microplastics synergistically amplify the toxicity of TBBPA through physical damage and carrier effect. These findings provide crucial insights for risk assessment of soil ecosystems from co-contamination with microplastics and brominated flame retardants.