Quaternary Ammonium Compounds in Paired Human Urine and Feces: Relative Significance of Biliary Elimination
Zhongmin Li, Kurunthachalam Kannan
Abstract
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.