Indoor Air and Public Health

Abstract This chapter lays out and critically assesses the current evidence on combined exposure to health hazards in specific indoor built environments to identify the most frequent exposure combinations and to estimate the impact of combined exposure on risk ratios for reported health outcomes. Actual exposure within the indoor built environment may vary significantly depending on the proximity to traffic sources (particulate matter [PM], NO 2 ), the presence of strong indoor emissions from combustion sources such as biomass for space heating (PM, polycyclic aromatic hydrocarbons [PAHs]), smoking (PM, PAHs, volatile organic compounds [VOCs], carbonyls), building materials (VOCs), furnishings (carbonyls and phthalates), and consumer products (phthalates, flame retardants, polychlorinated biphenyls, and pesticides). Assessment of cumulative risks was done following a tiered level of complexity, according to the prototype connectivity approach developed by the authors. Occupants are continuously exposed to a cocktail of carcinogens, endocrine disruptors, and allergens. Based on the concentration levels identified and clustered by indoor setting and country, cumulative cancer risks are in the 10 −4 range. A significant attributable fraction to allergies and asthma is the result of coexposure to PM, VOCs, and biological allergens. Public buildings such as schools/kindergartens and daycare centers are mostly affected by the proximity to traffic sources rather than to contributions from indoor sources. The combined effects of these chemicals are still not sufficiently elucidated, since their physicochemical and biochemical properties would favor multiple ways of interaction upon human uptake; there might be synergies in effect (e.g., PAHs and nitrosamines causing lung cancer), or they might inhibit each other's metabolism (the case of benzene, toluene, ethylbenzene, and xylene mixture).