Indoor and outdoor particulate matter and endotoxin concentrations in an intensely agricultural county

The objectives of this study were to characterize rural populations' indoor and outdoor exposure to particulate matter (PM)(10), PM(2.5), and endotoxin and identify factors that influence these concentrations. Samples were collected at 197 rural households over five continuous days between 2007 and 2011. Geometric mean (GM) indoor PM(10) (21.2 microg/m(3)) and PM(2.5) (12.2 microg/m(3)) concentrations tended to be larger than outdoor PM(10) (19.6 microg/m(3)) and PM(2.5) (8.2 microg/m(3)) concentrations (PM(10) P=0.086; PM(2.5) P<0.001). Conversely, GM outdoor endotoxin concentrations (1.93 EU/m(-3)) were significantly larger than indoor (0.32 EU/m(3); P<0.001). Compared with measurements from previous urban studies, indoor and outdoor concentrations of PM(10) and PM(2.5) in the study area tended to be smaller, whereas ambient endotoxin concentrations measured outside rural households were 3-10 times larger. Contrary to our initial hypothesis, seasonality did not have a significant effect on mean ambient PM(10) concentrations; however, endotoxin concentrations in the autumn were almost seven times larger than winter. Excluding home cleanliness, the majority of agricultural and housing characteristics evaluated were found to be poorly associated with indoor and outdoor particulate and endotoxin concentrations.