Quaternary Ammonium Compounds in Paired Human Urine and Feces: Relative Significance of Biliary Elimination

Quaternary ammonium compounds (QACs) are widely used as disinfectants in consumer and medicinal products that contribute to widespread human exposure. We determined 7 benzylalkyldimethylammonium (BACs), 6 dialkyldimethylammonium (DDACs), 6 alkyltrimethylammonium (ATMACs), and 8 metabolites of BACs (BACm) in paired human urine and feces. We found QACs in human feces at total concentrations (∑All) ranging from 170 to 8270 ng/g dry weight (dw) (median: 746 ng/g dw). BACs were dominant among the four classes of QACs analyzed, accounting for 49% of ∑All, followed by DDACs (40%), BACm (9%), and ATMACs (2%). In urine, only ω-carboxyl (COOH−) metabolites of BACs were frequently found, with a median concentration of ∑BACm at 0.49 ng/mL. QACs measured in human feces exhibited positive correlations, suggestive of the usage of these chemicals as a mixture. The cumulative daily intakes (CDIs) were calculated based on QAC concentrations measured in feces, through a reverse dosimetry approach. The average CDI of QACs was estimated to be 551 ng/kg body weight (BW)/day for adults, which was 3 orders of magnitude below the toxicity reference dose (RfD) suggested for BACs (0.44 mg/kg BW/day) and DDACs (0.1 mg/kg BW/day). This study provides important quantitative information about human exposure to and fecal elimination of QACs.