Photodegradation of Plastic Leachate: Revealing the Key Role of Halogen in Reduced Cytotoxicity in Marine Systems

Understanding the cytotoxicity of plastic leachate from
photodegraded
sunscreen-derived microplastics (SDMPs) in various aquatic environments
remains a challenge. This study reveals the crucial role of halogens
in reducing leachate toxicity by examining the photodegradation of
SDMPs in freshwater and seawater settings. Microplastics (MPs) extracted
from three different commercial sunscreens, predominantly composed
of methacrylate-based polymers, exhibited reduced photodegradation,
leachate release, and leachate transformation in seawater. The diminished
degradation in seawater can be attributed to halogens, especially
bromide (Br–), which hinder photocatalytic oxidation
by suppressing the activity of hydroxyl radicals (•OH). Consequently, leachates from SDMPs photoaged in seawater exhibited
notably reduced cytotoxicity, as evidenced by minimal mitochondrial
dysfunction involving mitochondrial dehydrogenases and membrane potential,
fragmented mitochondria, and regulated metabolic processes. This included
the alleviation of amino acid catabolism inhibition, coenzyme A (CoA)
biosynthesis inhibition, glycolysis activation, and the enhancement
of the compensatory antioxidant system. In the absence of halogen
protection, photodegradation is predicted to produce oxidative byproducts
such as hydroperoxides as toxic agents that induce cytotoxicity in
the freshwater leachate. These findings underscore the critical influence
of water chemistry on shaping the photodegradation and toxicity of
SDMP leachates, emphasizing the necessity of conducting region-specific
risk assessments for MPs in personal care products.