Co-occurrence of polypropylene microplastics and silver sulfide nanoparticles with organic emerging contaminants in surface water: comprehensive assessment of photolysis considering climate change impacts

Emerging contaminants (ECs) coexist in natural water sources due to contamination from both point and diffuse sources. Photolysis is one of the primary processes contributing to the assimilation capacity of surface water. However, the characterization of pollutant photolysis needs to be updated to account for recently introduced co-contaminants, such as microplastics (MPs) and nanoparticles (NPs). MPs and NPs have unique physicochemical properties that influence the fate and toxicity of ECs. In addition to co-contaminants, extreme environmental conditions, including temperature variations and organic matter concentrations, should be considered to account for climate change. In this study, the photolysis of diclofenac (DCF), diuron (DIU), terbutryn (TER), ciprofloxacin (CIP), and 17α-ethinylestradiol (EE2) (as a mixture) was investigated in the presence of polypropylene microplastics (PP-MPs) and silver sulfide nanoparticles (Ag₂S-NPs) at different temperatures and organic matter concentrations. The presence of PP-MPs and Ag₂S-NPs inhibited the photolysis rates of diuron, EE2, and ciprofloxacin by 3-5-fold while doubling the photodegradation of diclofenac. The effects of organic matter and temperature in the presence of PP-MPs and Ag₂S-NPs varied widely. For example, higher organic matter concentrations enhanced the photodegradation of EE2 and ciprofloxacin (which were otherwise inhibited by these particles), while they suppressed the photodegradation of diclofenac, which was promoted in their presence. The inhibition of photodegradation for EE2, ciprofloxacin, and diuron due to the presence of PP-MPs and Ag₂S-NPs suggests that these pollutants will persist longer in surface water. The findings of this study can support the development of characterization factors for EC photolysis, considering the presence of MPs, NPs, and climate change impacts. These characterization factors could be key parameters in environmental risk assessment and life cycle analysis.