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Photochemical Degradation of Sunscreen Chemicals in Sea Spray Aerosols

By: Jenna Ditto, Washington University in St. Louis

Xueqi Ma, Kun Li, Xiaowen Chen, and Lin Du, Environmental Science & Technology, 02/2026

DOI: https://doi.org/10.1021/acs.est.5c12704

Sunscreens contain UV filters designed to protect us from harmful UV radiation. Certain UV filters can have negative environmental impacts. For example some, like benzophenone-3, are banned in certain regions due to the threat they pose to aquatic ecosystems.

In a recent study published in Environmental Science & Technology, Ma et al. investigated the atmospheric chemistry of three common sunscreen-related ingredients: propylparaben (PrPB, a preservative), 4-methylbenzylidene camphor (4-MBC, a UV filter) and benzophenone-4 (BP-4, another UV filter). The authors motivated their study by noting that tens of thousands of tons of sunscreen may be released into the marine environment annually. Then, the sunscreen’s constituent chemicals, which tend to reside in the sea surface microlayer, may eventually be emitted to the atmosphere within sea spray aerosol. While some sunscreen ingredients have been better characterized than others, very little is known about the chemistry, fate, and impacts of these chemicals when aerosolized. Ma et al. therefore set out to determine the decay rates of the three target chemicals in sea spray aerosol, identify the products formed during their atmospheric oxidation, and assess the lifetime and fate of these ingredients under typical atmospheric conditions.

The team prepared artificial seawater containing each of the three target chemicals and then aerosolized each mixture. They measured aerosol concentration, size distribution, chemical composition, and oxidative potential.

By tracking the decay rate of each chemical with increasing hydroxyl radical exposure, the authors estimated the e-folding lifetime against oxidation for these organic chemicals within sea spray aerosol. They reported PrPB to have a lifetime of 44.52 hours, 4-MBC to have a lifetime of 89.41 hours, and BP-4 to have a lifetime of 40.99 hours under typical tropospheric hydroxyl radical levels. The authors emphasized that these sunscreen chemicals within sea spray aerosol may undergo several generations of oxidation – dramatically changing their chemical composition and properties – between the time the aerosol particle is emitted and the time it is removed from the atmosphere roughly one week later via physical processes like deposition.

Using the dithiothreitol (DTT) assay, the authors looked at the oxidative potential of these sea spray aerosol-sunscreen ingredient mixtures. Oxidative potential increased upon initial oxidation, then decreased as oxidation progressed. The team found relatively low DTT consumption rates for these mixtures, ranging from 0.1-10 pmol/min/µg. They concluded that although the oxidative stress that may be caused by these mixtures is likely low, these chemicals may still have other harmful health effects, such as endocrine disruption.

Finally, the authors estimated sea-to-air fluxes for each chemical: 1-1450 µg/m²h for PrPB, 1-1.4×10⁵ µg/m²h for 4-MBC, and 1-1850 µg/m²h for BP-4. They assessed the fraction of each chemical then removed from the atmosphere due to hydroxyl radical oxidation vs. dry deposition at different transport distances. Within 1 km of the emission location, dry deposition removed 83-92% of each target chemical, with the balance removed by hydroxyl radical oxidation. In contrast, at 50 km from the emission location, hydroxyl radical oxidation accounted for 46-63% of atmospheric removal.

Overall, Ma et al.’s work is important because it characterizes the decay times, transformation products, potential health effects, and ultimate fate of novel sea-spray aerosol-sunscreen ingredient mixtures that have been understudied in the atmosphere. It paves the way for follow-up studies on the atmospheric chemistry of additional emerging pollutants, and further health effect assessments on these novel emitted species and their chemically aged products.