Predictors of coarse particulate matter and associated endotoxin concentrations in residential environments

Exposure to coarse particulate matter (PM), i.e., particles with an aerodynamic diameter between 2.5 and 10 μm (PM10–2.5), is of increasing interest due to the potential for health effects including asthma, allergy and respiratory symptoms. Limited information is available on indoor and outdoor coarse PM and associated endotoxin exposures. Seven consecutive 24-h samples of indoor and outdoor coarse PM were collected during winter and summer 2010 using Harvard Coarse Impactors in a total of 74 Edmonton homes where no reported smoking took place. Coarse PM filters were subsequently analyzed for endotoxin content. Data were also collected on indoor and outdoor temperature, relative humidity, air exchange rate, housing characteristics and occupants' activities. During winter, outdoor concentrations of coarse PM (median = 6.7 μg/m3, interquartile range, IQR = 3.4–12 μg/m3) were found to be higher than indoor concentrations (median 3.4 μg/m3, IQR = 1.6–5.7 μg/m3); while summer levels of indoor and outdoor concentrations were similar (median 4.5 μg/m3, IQR = 2.3–6.8 μg/m3, and median 4.7 μg/m3, IQR = 2.1–7.9 μg/m3, respectively). Similar predictors were identified for indoor coarse PM in both seasons and included corresponding outdoor coarse PM concentrations, whether vacuuming, sweeping or dusting was performed during the sampling period, and number of occupants in the home. Winter indoor coarse PM predictors also included the number of dogs and indoor endotoxin concentrations. Summer median endotoxin concentrations (indoor: 0.41 EU/m3, outdoor: 0.64 EU/m3) were 4-fold higher than winter concentrations (indoor: 0.12 EU/m3, outdoor: 0.16 EU/m3). Other than outdoor endotoxin concentrations, indoor endotoxin concentration predictors for both seasons were different. Winter endotoxin predictors also included presence of furry pets and whether the vacuum had a high efficiency particulate air (HEPA) filter. Summer endotoxin predictors were problems with mice in the previous 12 months and mean indoor relative humidity levels