Longitudinal Internal Exposure to Methylsiloxanes among Healthy Elderly from the China BAPE Study: Plasma Levels, Intake Estimation, and Risk Assessment

Methylsiloxanes (MSs) are persistent and widely distributed environmental contaminants of global concern because of their stability and multiple exposure routes. Older adults are particularly vulnerable to their effects, yet systematic research in this population remains limited. This study quantified plasma MSs and evaluated health risks among elderly residents (60–69 years) in Jinan, Shandong Province, China. A repeated-measures panel design with five monthly follow-ups was conducted on 76 healthy participants from September 2018 to January 2019. Seven MSs in plasma were measured using gas chromatography coupled with Orbitrap high-resolution mass spectrometry, and reverse dosimetry was applied to estimate daily intakes and margins of exposure. Decamethylcyclopentasiloxane (D5) showed the highest detection frequency (56.45–74.19%), followed by octamethylcyclotetrasiloxane (D4, 38.71–59.09%) and dodecamethylcyclohexasiloxane (D6, 15.69–66.67%). The median (P25–P75) estimated daily intakes for D4 and D5 were 83.43 (83.43–860.49) and 228.53 (36.05–606.66) ng/kg body weight/day, respectively. The margins of exposure values of D4 and D5 exceeded 1000, indicating large safety margins for this sensitive population. These findings demonstrate that under current exposure conditions, MSs concentrations in elderly residents are unlikely to pose appreciable health risks, although continued monitoring is warranted. These data also provide baseline evidence to support environmental risk management and public health policy development.