Quaternary ammonium compounds in paired indoor dust and human urine: suspect screening and exposure associations

The occurrence of quaternary ammonium compounds (QACs) in the environment has received increasing attention due to their widespread applications. Indoor dust is an important medium for human exposure, yet knowledge regarding the influence of dust exposure and human metabolism on the composition profiles of QACs in excretions remains limited. In this study, an integrated workflow combining targeted analysis and suspect screening was developed to comprehensively identify QACs in paired indoor dust and urine samples collected across China. A total of 69 compounds were detected in indoor dust, including 23 target analytes and 46 emerging analogues spanning both traditional hydrocarbon-based structures and subclasses bearing additional functional groups, such as choline, betaine, ester, amide, aryl, and pyridine. In urine, both traditional (n = 12) and emerging (n = 15) analogues were also detected, along with four hydroxyl or carboxyl metabolites of benzalkonium chlorides (BAC). Several influencing factors derived from the questionnaire survey (e.g., household income and frequency of personal care product use) were positively associated with QAC concentrations in indoor dust. After controlling for these covariates, the total concentration of BACs in dust remained positively correlated with that of the carboxyl metabolites in urine, suggesting these metabolites could serve as exposure biomarkers. By exploring the chemical space of QACs in paired samples, this study provides the first evidence linking indoor dust exposure to human urinary excretion. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.