Probabilistic emissions model for organic UV filters released to recreational waters during swimming/bathing events

A critical element for understanding measured concentrations and predicting exposure levels of UV filters (UVFs) in recreational waters relates to mass released from sunscreen products applied to skin during swimming and bathing. A probabilistic mass transfer kinetic model was developed to estimate distributions of the mass of five organic UVFs released during individual swim events with sunscreen. The model incorporates the ratios of different demographics and distributions of their total skin areas, adjusted to account for body areas to which sunscreens are not typically applied or do not contact water. The resulting distribution of skin areas is combined with distributions of sunscreen application rates and UVF levels in sunscreen products to generate a distribution of UVF masses on skin that are exposed to water with the fraction released to water calculated using a first-order equation describing the kinetics of release. The predicted median mass released during a swim event was 112 mg for oxybenzone, 32.6 mg for avobenzone, 23.5 mg for octocrylene, 47.7 mg for homosalate, and 7.59 mg for octisalate. As proof of principle, the model was used to repeat previous modeling at Prophète Beach, which resulted in predicted median values for oxybenzone and avobenzone within a factor of three of the reported measured environmental concentrations.