Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 222

Exposure Through Indoor Air Inhalation
Exposure through indoor air inhalation is the most important pathway for volatile
contaminants. This exposure is dependent on the representative concentration in
indoor air and on human characteristics, such as inhalation rate. The representative
concentration in indoor air is dependent on advective and diffusive transport of con-
taminants in pore water and soil air, from the groundwater or the soil into a building
and, hence, on the soil properties. It also depends on the building characteristics,
such as the possibility for intrusion of contaminated air through holes and cracks, the
dimensions of the building and the ventilation characteristics of the building. As in
the case of the representative vegetable concentration for the calculation of exposure
through vegetable consumption, it is important to focus on the most relevant indoor
air concentration for the calculation of exposure through indoor air inhalation.
Indoor air concentrations often are characterised by a large variation in time and
space (height). Therefore, the calculation of indoor air concentrations typically has a
relatively limited reliability. Analogous to the calculation of the relevant concentra-
tion in vegetables, for the calculation of the relevant concentration in indoor air, only
those contaminants that originate from the soil are of importance. Contaminants that
originate from indoor sources (e.g., formaldehyde from furniture, benzene from a
garage), however, could contribute to the background exposure (see Section 5.5.4 ).
Several models exist to estimate the human health risk due to vapour intrusion, for
example, in Australia for the derivation of the Australian Health-based investigation
levels (HILs) (Turczynowicz and Robinson 2007 ). The inhalation exposure through
indoor air inhalation, including the parameter identification, is described in detail in
McAlary et al. ( Chapter 10 of this topic).
Insight into Major Exposure Pathways
For the purpose of better understanding the variation in calculated human exposures
due to soil contamination, Swartjes ( 2009 ) compared the variation in calculated
exposures with the variation in calculated concentrations in contact media and in
the soil compartments, along with the variation in the input parameters. Serving as
the basis for this study were calculations using seven European exposure models for
20 different exposure scenarios. This led to the conclusion that most of the variation
in Exposure through soil ingestion could be explained by differences in the input
parameter average daily soil intake . When model-specific input parameters were
used, the variation in Exposure through crop consumption could be explained by
differences in the product of total consumption rate and fraction of total consump-
tion rate that is home-grown . When standardized input parameters were used, this
variation was comparable to the variation in Concentration in root vegetables and
in Concentration in leafy vegetables. The variation in Exposure through indoor air
inhalation was comparable to the variation in Concentration in indoor air . This sug-
gests that the parameters that control the variation in Concentration in the indoor
air , that is, surface and volume of the building and, to a lesser extent, ventilation
frequency of the building, also control the variation in Exposure through indoor air
inhalation.