Health effects related to indoor ultrafine particles

Health effects of outdoor particulate matter are well described. Toxicology and some epidemiological evidence particularly point to strong effects of combustion-related ultrafine particles (UFP) explained by high alveolar deposition, poor clearance, insoluble carbon core, large surface area, adherence of toxic compounds, such as metals and PAH and potential translocation. Outdoor UFP penetrate indoor, where multiple sources generate UFP as well. However, little is known with respect to the possible specific health effects associated with indoor UFP. A few home or personal monitoring studies have found associations between outdoor and indoor UFP numbers and biomarkers related to health effects, including oxidative stress-induced DNA damage in leukocytes, inflammation and vascular activation. Indoor intervention with HEPA air filtration is a direct way to assess the effects of indoor UFP, although particles with larger size are also reduced. Using this design we found improved microvascular function, indicative of the risk of cardiovascular disease, after 48 hours filtration reducing UFP numbers from 10,000 to 3,200/cm3 among 41 healthy elderly subjects in a double-blind randomized controlled study. Similar results have been obtained using this design in a wood-smoke impacted community, although indoor UFP levels were not reported. Recently, we repeated the intervention design but extended to 2 weeks air filtration and 2 weeks of placebo filtration with health marker measurements at baseline and day 2, 7 and 14 of each scenario among 48 elderly subjects. However, we found no effect on microvascular function, lung function or biomarkers of inflammation, vascular activation or lung cell damage associated with UFP reduction from median 7,600 to 5400/cm3. In conclusion, indoor UFP are likely to have important adverse cardiopulmonary effects. However, well characterised and probably substantial exposure gradients in well-designed studies are required for documentation.