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Objective Organophosphate esters (OPEs) are a group of chemicals used in many industries due to their dual flame retardant and plasticizing properties. OPEs have been associated with some cancers in humans and other adverse effects. Firefighters are potentially exposed to OPEs in protective equipment and paramedics may be exposed to OPEs in vehicle components to meet flammability standards. This study aims to characterize external and internal OPE exposure among firefighters, paramedics and office-workers in Ontario, Canada.Methods Participants wore a wristband for 24-hours and provided two urine samples (0h and 24h). Twelve urinary metabolites (mOPEs) and 13 OPEs from wristbands were quantified; those detected in >50% of wristbands and urine (0h and 24h) are reported here. Urinary mOPEs and wristband OPEs were described and between-group differences examined using ANOVA.Results In total 40 firefighters, 12 paramedics and 13 office-workers participated (78% male; mean age=41years). Eight wristband OPEs and six urinary mOPEs had >50% detection. Wristband triphenylphosphate (TPhP) (GM=258.6 ng/wristband [GSD=2.72]) and urinary diphenyl phosphate (GM-0h=1.09 µg/g-creatinine [GSD=2.4]; GM-24h=1.20 µg/g-creatinine [GSD=2.2]) had the highest levels. TPhP levels were significantly higher among firefighters (GM=395.6 ng/wristband [GSD=2.43]) and paramedics (GM=230.1 ng/wristband [GSD=2.2]) than office-workers. OPE concentrations tended to be higher among paramedics, while mOPE levels tended to be higher among firefighters, though differences were not always significant. Office-workers had significantly higher tris(2-chloroethyl) phosphate levels (GM=141.1 ng/wristband [GSD=2.13]) than firefighters (GM=61.3 ng/wristband [GSD=2.3]).Conclusion OPE exposure is widespread among the studied occupations. Firefighters tended to have higher urinary mOPE levels than other groups, but this was not consistent with their external (wristband) exposure, suggesting multiple exposure routes. Research is needed to identify exposure pathways driving these differences. Subsequent analysis will explore how work-related activities contribute to exposure. Future research will examine a broader Canadian workforce to identify additional high-exposure groups.