A pilot investigation of the relative toxicity of indoor and outdoor fine particles: In vitro effects of endotoxin and other particulate properties

dIn this study we assessed the in vitro toxicity of 14 paired indoor and ou tdoor PM2.5 Samples (particulate matter less than or equal to 2.5 mum in ae rodynamic diameter) collected in 9 Boston-area homes. Samples were collecte d as part of a large indoor particle characterization study that included t he simultaneous measurement of indoor and outdoor PM2.5, particle size dist ributions, and compositional data (e.g., elemental/organic carbon, endotoxi n, etc.). Bioassays were conducted using rat alveolar macrophages (AMs), an d tumor necrosis factor (TNF) was measured to assess particle-induced proin flammatory responses. Additional experiments were also conducted in which A ms were primed with lipopolysaccharides (LPS) to simulate preexisting pulmo nary inflammation such as that which might exist in sick and elderly indivi duals. Significant TNF production above that of negative controls was obser ved for AMs exposed to either indoor or outdoor PM2.5. TNF releases were fu rther amplified for primed AMs, suggesting that preexisting inflammation ca n potentially exacerbate the toxicity of not only outdoor PM2.5 (as shown b y previous studies) but also indoor PM2.5. In addition, indoor particle TNF production was found to be significantly higher than outdoor particle TNF production in unprimed AMs, both before and after normalization for endotox in concentrations. Our results suggest that indoor-generated particles may be more bioactive than ambient particles. Endotoxin was demonstrated to med iate proinflammatory responses for both indoor and outdoor PM2.5, but study findings suggest the presence of other proinflammatory components of fine particles, particularly for indoor-generated particles. Given these study f indings and the fact that people spend 85-90% of their time indoors, future studies are needed to address the toxicity of indoor particles.