Photodegradation Controls of Potential Toxicity of Secondary Sunscreen-Derived Microplastics and Associated Leachates.

Summary

Using combined mechanical and photodegradation, the study shows that photodegradation of sunscreen-derived microplastics drives chemical transformations that increase intracellular sequestration and leachate toxicity, with mitochondrial fragmentation as a key biomarker. Non-targeted HRMS identified 46 plastic-associated leachate compounds, implicating additive dissociation and oxidative conversion in cytotoxicity.

Key Findings

• Photodegradation, beyond mechanical fragmentation, introduced oxidation, bond scission, and cross-linking in secondary sunscreen-derived microplastics.
• Both physical fragmentation and photooxidation increased intracellular sequestration of microplastics; leachate toxicity was primarily driven by photochemical transformations.
• Non-targeted HRMS identified 46 plastic-associated compounds in leachates; photodegradation facilitated dissociation of hydrophobic additives and oxidative conversion.
• Mitochondrial fragmentation was the primary subcellular biomarker indicating leachate-induced cytotoxicity.

Clinical Implications

Dermatology and primary care can counsel on reef-safe, microplastic-minimizing sunscreens and support policies to limit harmful additives; industry can prioritize formulations less prone to toxic leachates post-UV exposure.

Limitations

• Findings are based on in vitro cellular models and may not fully capture in vivo ecological or human exposure contexts.
• Specific sunscreen polymers/additives tested may limit generalizability across all cosmetic formulations and environmental conditions.

Future Directions

Test broader polymer/additive chemistries under realistic UV and environmental conditions, quantify human/environmental exposure, and develop safer-by-design cosmetic carriers.