Combined biological effects of polystyrene microplastics and phenanthrene on Tubifex tubifex and microorganisms in wetland sediment

Microplastics, as emerging pollutants, can adsorb polycyclic aromatic hydrocarbons (PAHs) in aqueous envi-ronments. However, the coeffects of PAHs and microplastics on aquatic organisms are vague. In this study, nanoscale and micron-scale microplastics (30 mg/kg) and phenanthrene (10 mg/kg) were added to aquatic sediment to explore the effects of different particle sizes of microplastics and typical PAHs on invertebrates (Tubifex tubifex) and microbes after 28 days operation. The fluorescence signal of fluorescently labelled micron-scale and nanoscale microplastics were detected in T. tubifex, especially nanoscale microplastics. The reduced activities of CAT, GST, SOD and MDA in T. tubifex suggested that the micron-sized microplastics and PAHs exacerbated the oxidative damage to T. tubifex. Microbial analysis confirmed that microplastics and PAHs decreased the abundance of Proteobacteria, Fusobacteriota and Bacteroidetes in the gut of T. tubifex and thereby affected the degradation of phenanthrene. Microplastics also reduced the abundance of Bacteroidetes, Acid-obacteria and Proteobacteria in sediment. The abundance of salicylate hydroxylase enzyme that related to PAHs metabolism was increased with the addition of phenanthrene. The results in this study would be useful for further risk assessment of PAHs and microplastics in aquatic environments.