# Ingestion of Surface Residues Dominates Quaternary Ammonium Compounds (QACs) Exposure in Chinese Urban Homes: Evidence from Silicone Wristband Passive Sampling and Urinary Biomonitoring

## TL;DR

This study finds that ingesting surface residues is the main way people are exposed to QACs in urban homes in China.

## Contribution

The study introduces urinary biomarkers and silicone wristbands for assessing QAC exposure routes.

## Key findings

- Silicone wristbands and dust showed strong correlations in QAC concentrations.
- Urinary biomarkers confirmed ingestion of surface residues as a major exposure route for C10- and C12-BACs.
- C12-BACs accounted for nearly half of total exposure via ingestion.

## Abstract

The quantitative characterization of multiple exposure
routes to
quaternary ammonium compounds (QACs) remains underexplored. In this
study, paired samples of indoor dust, bulk air, hand wipes, silicone
wristbands, and urine were collected from 109 adults residing in urban
homes from South China in 2023. First, seven urinary biomarkers, including
hydroxylated and carboxylated metabolites of C10–C14 benzylalkyldimethylammonium
compounds (BACs), were identified using a combined in silico and in vitro workflow. Then, 23 QACs, including
6 C8–C18 BACs, 6 dialkyldimethylammonium compounds (C8–C18
DADMACs), 6 alkyltrimethylammonium compounds (C8–C18 ATMACs),
and 5 emerging QACs, were ubiquitously detected in various environmental
matrices, including dust (median ∑QAC concentrations of 39.6
μg/g), bulk air (130 pg/m3), hand wipes (1420 ng
for two hands), and silicone wristbands (225 ng/g), respectively.
A significantly positive correlation was observed between the logarithmically
transformed masses of QACs detected in silicone wristbands and those
from dust, bulk air, and hand wipes (r: 0.564, p < 0.01). Moreover, urinary hydroxylated and carboxylated
C10- and C12-BACs were significantly correlated with corresponding
parent compounds in wristbands (r: 0.481–0.607, p < 0.01). Finally, back calculation from urinary exposure
biomarkers revealed that ingestion of surface residues was the dominant
exposure route for C10-, C12-, and C14-BACs, accounting for 3.7%,
49.6%, and 18% of total exposure, respectively. The findings from
this study propose suitable urinary exposure biomarkers and silicone
wristbands as useful indicators for accurate internal and external
exposure assessment, respectively, and highlight the importance of
ingestion of surface residues as a major exposure route.