Influence of sunscreen formulation on the transfer of mineral and organic ultraviolet filters from skin to seawater in simulated ocean bathing tests

Abstract

AbstractObjectiveSignificant research and regulatory attention have been focussed on the potential for some ultraviolet filters (UVFs) to rinse off from beachgoers' skin into seawater leading to exposure to sea life, especially coral reefs. The amount of UVFs potentially rinsed from skin during recreational beach activities has not been well studied, leading to uncertainty about the potential magnitude of aquatic UVF exposure due to changes in sunscreen use patterns. This study quantifies rinse‐off of UVFs in sunscreen from skin into synthetic seawater and identifies differences in rinse‐off quantity due to formulation type with a goal of informing future modelling efforts aimed at estimating UVF exposure to sea life associated with recreational activities at the beach.MethodsUVF rinse‐off from skin during recreation in seawater was simulated by applying eight different sunscreen products to porcine skin samples followed by three periods of shaking in synthetic seawater totalling 40 min. The rinsed mass of six UVFs – zinc oxide, titanium dioxide, avobenzone, homosalate, octisalate, and octocrylene – was determined analytically in synthetic seawater and in extractant rinsate from glassware for organic UVFs and compared among formulas.ResultsAmong the 22 UVF‐formulation combinations tested, 19 resulted in less than 10% of the applied UVF rinsed from skin. All formulation‐UVF combinations where the formula types were water‐in‐oil (reverse phase) emulsions or anhydrous resulted in 5% or less of the applied UVF rinsed to synthetic seawater. Sunscreens formulated as oil‐in‐water emulsions yielded higher rinse‐off percentages for all UVFs tested, with a maximum of 20% rinse‐off of avobenzone in one lotion.ConclusionThe potential for sunscreen UVF rinse‐off is significantly influenced by formulation and is generally well below the prior assumed rinse‐off levels used to estimate risk. Formulation consideration is therefore essential for accurate exposure models used in environmental risk assessment. Anhydrous and reverse phase (water‐in‐oil) sunscreen formulations tested resulted in lower UVF transfer from skin to synthetic seawater in simulated ocean bathing tests and as a result, are expected to yield lower UVF exposures to sea life. This approach can be used in predictive environmental exposure models to support ecologically safe sunscreen formulation design.