Temporal Variability of Urinary Organophosphate Flame Retardant Metabolites Among E-Waste Workers in France: A Pilot Study to Inform Occupational Biomonitoring Sampling Design.

Workers in the e-waste industry are exposed to chemical hazards, including organophosphate esters (OPEs) used as flame retardants (FRs). Assessing exposure through spot urine metabolite analysis is challenging due to limited knowledge of the toxicokinetics and urinary excretion patterns of OPEs. This pilot study investigates the temporal variability of seven organophosphate flame retardants (OPFRs) in urine samples from e-waste workers over five workdays to identify the most representative spot urine sample for accurately assessing occupational exposure. Six exposed workers provided urine samples from the first shift of the working week to the morning after the last workday. Seven metabolites, (bis(2-chloroethyl) phosphate (BCEP), diphenyl phosphate (DPHP), di-o-cresyl phosphate (DoCP), di-m-cresyl phosphate (DmCP), di-p-cresyl phosphate (DpCP), bis(1,3-dichloro-2-propyl) phosphate (BDCPP) and bis-(1-chloro-2-propyl) phosphate (BCPP)), were analyzed using liquid chromatography-mass spectrometry. DmCP + DpCP showed weekly increases and fair to good intraclass correlation coefficient (ICC), indicating moderate temporal variability across days. Conversely, DPHP and BCEP showed rapid decreases and lower ICC, suggesting higher intra-day variability. A grouping approach based on collection time and workday showed that the suitable spot urine is 2-5 h delayed post-shift for BCEP and DPHP, whereas the end of the workweek is the most appropriate time for DmCP + DpCP. This pilot study provides preliminary information on temporal variability to inform sampling design. This approach could be extended to a broader range of FRs, thereby enhancing the efficiency and accuracy of occupational biomonitoring.