Oxidative stress and chemical characteristics of indoor PM2.5: a case study in an underground (-3rd) floor

Many studies have examined the associations between exposure to indoor and outdoor atmospheric particulate matter and health outcomes in humans. There is increasing evidence that the oxidative characteristics of such particulate matter have a role in determining the adverse health effects of fine particulates. Moreover, since people spend more time in indoors (office and home), indoor air quality and its impact on human health have increased in importance. However, to date, studies examining the oxidative characteristics of indoor particulates are few, and there has been a limited examination of the impact on physiological conditions of indoor fine particulates exposure on microorganisms. Therefore, this study aimed to investigate the oxidative characteristics of fine particulates in an indoor environment on the -3rd floor. The chemical characteristics of indoor PM2.5 samples were determined through their elemental composition, particle oxidation state, and organic and inorganic functional groups using EDX and FTIR spectrometry. Oxidative characteristics were also examined in terms of the cellular response of opportunistic bacteria ( Staphylococcus aureus and Escherichia coli ) by oxidative stress indicators (e.g., antioxidant, catalase, superoxide dismutase, glutathione (reduced), lipid peroxidation, and hydrogen peroxide), applied to artificial lung fluid and TRIS soluble fractions of aerosol that was extracted from the fine mode (PM2.5) of 120-h filter samples. Bacterial activity and protein content of S. aureus and E. coli were also studied in order to understand the main biochemical response of opportunistic bacteria. The chemical analysis results showed that elements in the indoor PM2.5 filters were both crustal origin (e.g., Al, Si, K, and Ca) and anthropogenic (e.g., Ba, Zn, and Ce). The identified functional groups were S = O, N–H, N = O, C = O, C-H, and O–H, which can cause oxidative stress. Bacteria-based oxidative indicators showed that both PM2.5 and physicological fluids induced the oxidative stress. However, oxidative responses were changed by the type of bacteria and physicological fluid, and PM2.5 was disturbed by the natural protection of physicological fluids.