Combined effects of P25 TiO2 nanoparticles and disposable face mask leachate on microalgae Scenedesmus obliquus: analysing the effects of heavy metals†

Disposable surgical face masks extensively used during the COVID-19 outbreak would release microplastics into the aquatic environment. The increasing usage of titanium dioxide nanoparticles (nTiO₂) in various consumer items has led to its ubiquitous presence in freshwater systems. This study determined the quantity and kind of microplastics discharged from disposable surgical face masks. The mask-leached microplastics were identified to be polypropylene of varying shapes and sizes, spanning from 1 μm to 15 μm. In addition, heavy metals like Cd, Cr, and Hg leached from the face masks were quantified. Four concentrations of nTiO₂, 0.5, 1, 2, and 4 mg L⁻¹, were mixed with leached solution from the face masks to perform the combined toxicity test on freshwater algae, Scenedesmus obliquus. A dose-dependent decrease in algal cell viability was observed upon treatment with various concentrations of nTiO₂ individually. The mixtures of nTiO₂ and the leached solution from the face masks exhibited significantly more toxicity in the algal cells than in their pristine forms. nTiO₂ promoted increased production of oxidative stress and antioxidant enzyme activities resulting in cellular damage and decreased photosynthesis. These impacts were elevated when the algal cells were treated with the binary mixture. Furthermore, the heavy metal ions leached from face masks also contributed to the toxic effects. Our study shows that the leachates from disposable surgical face masks, combined with nTiO_2, may pose a severe environmental threat.