Urinary metabolites of the UV filter octocrylene in humans as biomarkers of exposure

Octocrylene (OC) is a UV filter used in sun screens and other personal care products, but also in polymers and food contact materials for stabilization. In this study, we investigate human OC metabolism and urinary excretion after oral dosage of approx. 5 mg OC [≙ 61.8-89.5 µg/(kg body weight)] in three male volunteers. In a screening approach, we tentatively identified six urinary OC metabolites. For three, renal elimination kinetics was quantitatively investigated using authentic standards: the sidechain oxidation product 2-ethyl-5-hydroxyhexyl 2-cyano-3,3-diphenyl acrylate (5OH-OC), the beta-oxidation product 2-(carboxymethyl)butyl 2-cyano-3,3-diphenyl acrylate (dinor OC carboxylic acid; DOCCA), and the ester hydrolysis product 2-cyano-3,3-diphenylacrylic acid (CPAA). CPAA was the major urinary metabolite, representing 45% (range 40-50%) of the OC dose. 5OH-OC and DOCCA were only minor metabolites with low, but highly consistent renal conversion factors of 0.008% (0.005-0.011%) and 0.13% (0.11-0.16%), respectively. Peak urinary metabolite concentrations were observed between 3.2 h and 4.2 h postdose. All three metabolites were excreted with biphasic elimination kinetics, with considerably longer elimination half-lives for DOCCA (1st phase: 3.0 h; 2nd phase: 16 h) and CPAA (5.7 h and 16 h) compared to 5OH-OC (1.3 h and 6.4 h). 99% of all 5OH-OC was excreted within 24 h compared to 82% of DOCCA and 77% of CPAA. After dermal exposure, we detected the same metabolites with similar ratios in urine, however, at much lower concentrations and with considerably delayed elimination.