Widespread occurrence of volatile methyl siloxanes in settled dust from three regions in Vietnam: Geographical variations, indoor-outdoor differences, and human exposure assessment.

This study investigated 4 cyclic and 10 linear volatile methylsiloxanes (VMSs) in 155 dust samples collected across three regions in Vietnam. Despite their widespread use, research on the temporal trends of VMSs in dust within developing countries in Southeast Asia remains limited. The total concentrations of VMSs ranged from 55.1 to 20,300 ng/g (mean: 2,960 ng/g; median: 1,430 ng/g). Volatile methylsiloxane concentrations measured in indoor dust samples were significantly higher than in outdoor dust samples. Regionally, the highest concentrations were found in indoor dust collected from the north, followed by the south and central regions. Cyclic VMSs (mean: 1,850 ng/g) were more prevalent than linear VMSs (mean: 1,110 ng/g), with decamethylcyclopentasiloxane and octadecamethyloctasiloxane being the dominant compounds in their respective groups. A moderate correlation was observed between cVMS and lVMS concentrations, except in indoor dust from southern Vietnam. However, correlations between individual VMSs in indoor and outdoor samples were negligible. The positive matrix factorization analysis reveals a clear functional separation, yet active exchange between indoor and outdoor siloxane reservoirs. Indoor dust is dominated by emissions from consumer products and silicone materials, whereas outdoor siloxane profiles are primarily shaped by atmospheric aging, surface storage, and dust resuspension, favoring particle-bound linear homologues. The estimated exposure doses through dust ingestion were 2.47 ng/kg-body weight/day for adults and 3.94 ng/kg-body weight/day for children, suggesting a relatively low health risk.