Investigation of the photolysis of the common UV filter chemical octyl dimethyl para-amino benzoic acid and its photoproducts

Organic ultraviolet filter chemicals (UVFCs) are often contained in products that include some level of sun protection factor (SPF). As UVFCs are exposed to UV radiation, they can generate photochemical transformation products. UVFCs are deemed safe enough to be approved by the FDA; however, the toxicity of their photoproducts is unknown. Both UVFCs and their photoproducts have the potential to pollute water sources and harm the environment. To address this issue, the goals of this project include determining the kinetics of photoproduct generation and isolating the photoproducts to investigate their toxicity. This study is focused on octyl dimethyl para-amino benzoic acid (OD-PABA, also known as padimate O). Photoproducts are generated using a solar simulator, and analytical-scale high performance liquid chromatography (HPLC) is used to determine the kinetics of transformation. Photoproducts are isolated and purified using preparative-scale HPLC and are identified using liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy. Studying the kinetics of photoproduct formation guides their isolation and characterization. Two OD-PABA photoproducts have been isolated and characterized by mass spectrometry and NMR. The cellular toxicities of OD-PABA and its photoproducts are tested using the neutral red assay with NIH 3T3 cells. The whole OD-PABA photolysate is more toxic to cells than OD-PABA itself, and one isolated photoproduct appears to contribute to this, exhibiting cellular toxicity at concentrations at and above 0.25 mM. Ongoing work is focused on isolating, characterizing and testing the toxicity of other photoproducts.