Indoor exposure pathways

High levels of indoor air pollutants result from the use of either open fires or poorly functioning stoves to bum biomass or coal (Ezzati Kammen, 2001). Women, especially those responsible for cooking, are the ones most heavily exposed. Young children who spend their time close to their mothers also have high exposures (Bruce et al., 2000). Many of the substances in smoke from either biomass or coal burning can be hazardous to humans. The most important are suspended particulate matter, carbon monoxide, nitrous oxide, sulfur oxides (coal), formaldehyde, and PAHs (Bruce et al., 2000 Smith et al., 2000). 

Several studies have identified house dust as an important route of exposure for many chemical contaminants (Butte Heinzow, 2002 USEPA, 2004b). House dust is a sink for semivolatile organic compounds and particle-bound matter (Butte Heinzow, 2002). House dust and compounds adsorbed to it may enter the body by inhalation of suspended and resuspended particles, through non- 

Indoor concentrations of pesticides in proximity to pesticide-treated farmland have been measured (Fenske et al., 2002). For example, it has been shown that pesticide exposure in children could potentially be increased if they live in homes in close proximity (60 m) to pesticide-treated farmland (Fenske et al., 2002). Clothing and cars of farm workers can also be a source of pesticide exposures for children. Usually, applications of insecticides and herbicides in and around the home are a more likely source for children s exposures. 

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Indoor exposure pathways are very important. First, in many regions of the world, children spend more than 90% of their time indoors. Second, the indoor concentrations of many contaminants are much higher than those found outdoors. It is estimated that 70% of the poorest people in developing countries live in rural areas (World Bank, 2005). The indoor exposure pathway is especially important for these individuals (Figure 16). Approximately 50% of the world s population and up to 90% of rural households in developing countries still rely on coal or unprocessed biomass material in the form of wood, dung, and crop residues for fuel (Bruce et al.,... 

McKone TE. 1987. Human exposure to volatile organic compounds in household tap water The indoor inhalation pathway. Environmental Science and Technology 21 1194-1201. 

For each category of land or water body use, one may envision a simplified scenario. In each scenario, only those activities most likely to lead to toxic exposures are considered. For example, In the Industrial scenario, Indoor workers would not be exposed to levels of dust bearing high concentrations of soli contaminants outdoor workers who stir up dry soli with heavy machinery, however, could expect to Inhale contaminant-laden dust. A scenario could Involve more than one exposure pathway. Thus, the Industrial worker might drink water from a contaminated well, In addition to breathing contaminated dust these exposures might represent not only different pathways but different sources. 

Harrad S, de Wit CA, Abdallah MAE, Bergh C, Bjorklund JA, Covad A, Damerud PO, de Boer J, Diamond M, Huber S, Leonards P, Mandalakis M, Oestman C, Haug LS, Thomsen C, Webster TF (2010) Indoor contamination with hexabromocyclododecanes, polybrominated diphenyl ethers, and perfluoroalkyl compounds an important exposure pathway for people Environ Sci Technol 44 3221-3231... 

McKone, T. E., Human Exposure to Volatile Organic Compounds in Household Tap Water The Indoor Inhalation Pathway, Environ. Sci. Technol., 21, 1194-1201 (1987). 

The exposure pathway and physicochemical characteristics of a particular environmental chemical can provide useful information on the likelihood of childhood exposure (chapter 5). Age-specific exposure pathways of particular relevance include those during the prenatal and early developmental years postnatally (e.g. placental transfer, breast milk, toys, soil, indoor air/dust, child-care centres). Exposures to persistent environmental chemicals are of special concern, since the internal exposure may continue and result in a level sufficient to cause effects during critical developmental stages, even after the external exposure has ceased or been removed. 

For example, depending on which exposure pathway is dominant, it may be important to measure either plant concentrations or indoor air concentrations since model calculations on such aspects can be uncertain. 

Currado, G. M., Harrad, S. (1998) A comparison of polychlorinated biphenyl concentrations in indoor and outdoor air and the potential significance of inhalation as a human exposure pathway. Environ. Sci. TechnoL, 32 3043-3047. 

There are also a number of approaches taken to sampling indoor dust. It is important to emphasise that the matrix under study is settled dust for which the exposure pathway is ingestion (usually accidental, but for a small number of individuals, particularly young... 

Exposure to indoor hydrocarbon vapors can occur as a consequence of changes of land use from commercial or industrial to residential. Residual hydrocarbons in soils or groundwater may result in a chronic vapor exposure pathway. Analysis of risk associated with exposure to hydrocarbons typically is undertaken in a multi-step approach known as risk assessment. A thorough discussion of the use of risk assessment at contaminated sites is provided in Chapter 9.01. Assessing risks posed by hydrocarbon spills or wastes is complex and involves estimates of chemical concentrations at each potential exposure point, identification of the potential populations that may be exposed, and assessment of exposure pathways, intake rates, and the toxicity of the chemicals of concern. 

Contradictory results for associations between pesticide levels indoors (air, dust) and results form human biomonitoring may be due to different volatilities of the pesticides and may be determined by the magnitude in contamination levels. For semivolatile pesticides it may be easier to detect an association, as indoor air and house dust may serve for exposure in contrast to particle-bound pesticides with house dust as the only exposure path. Furthermore high contamination levels make it easier to detect an association, as with low indoor contamination levels associations may be hidden by the ubiquitous presence of pesticides in indoor environments and by nonindoor exposure pathways like dietary intake. 

In Fig. 1, we present a diagram of om understanding of the human exposure pathways and potential factors that affect human asthma susceptibility between mban and rmal areas. In this model, different environmental mban-based exposures (e.g., particulate or gaseous air pollutants from vehicular traffic, and indusfiy), and similar ones in rmal areas (e.g., indoor pollution from biomass fuel combustion, and keeping or herding animals) are known to potentially affect susceptible adult hosts. Such exposmes may produce airway inflammation and obstruction. However, there... 

Considering the migration possibilities of such chemicals from their original products, complex studies were performed for classical plasticizers such as DEHP or DBP to evaluate the relevance of each pathway to human exposure assessments. Therefore, the total exposure of adults of such plasticizers was evaluated by quantifying the target substances in duplicate diet portions (collected daily over 7 consecutive days), and also by measuring indoor air and dust concentrations [129]. The results indicate that dietary exposure is the dominant... 

Human exposure to PAEs may occur via ingestion, inhalation, and dermal pathways. Dermal exposition is usually very low, being via ingestion (food) and inhalation (indoor/outdoor ambient) the most important ones. An estimation study... 

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