Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
Air dermal contact inhalation
Tap water dermal contact ingestion
Food and beverages ingestion
Surface soil dermal contact ingestion
Surface water dermal contact ingestion
6.5.1 Inter-media transfer factors
Transfer of contaminants between media is commonly modelled as
partitioning of a chemical between two or more media. Thus,
multiple-pathway models require the measurement or estimation of
partition coefficients of contaminants between several pairs of
environmental media. There are two general classes of partitioning
coefficients. The first class relies on basic physicochemical
properties of the compounds of interest such as aqueous solubility,
vapour pressure and dipole moment; they describe partitioning due to
diffusive processes. Coefficients in the second class describe
partitioning resulting from what may be considered advective
processes, but also implicitly include diffusive partitioning.
6.5.1.1 Diffusive partition coefficients
The class of diffusive partition coefficients includes those
between soil and water in soil (e.g., groundwater), air and plants,
soil and plants, animal intake and food, surface water and fish,
mother's uptake and breast milk, residential water and indoor air,
soil-gas and indoor air, human skin and soil, and human skin and
water. In many cases, partition coefficients developed from
laboratory-scale experiments are the basis for modelling partitioning
of a compound between environmental media (Lyman et al., 1990). For
example, the octanol-water partition coefficient is often used as a
proxy for partitioning non-polar organic compounds (e.g.,
organochlorine substances) between water and fish lipids. In this
case, n-octanol is considered a good model for fish lipids.
Similarly, the organic carbon-water partition coefficient is used to
characterize partitioning of non-polar substances between organic
matter in soil and water. Finally, Henry's constant describes
partitioning of volatile and non-volatile compounds between air and
water. Connell et al. (1997) provide a comprehensive introduction to
the use of this type of partition coefficient in environmental science
and exposure assessment.
6.5.1.2 Advective partition coefficients
The second class of partitioning coefficients jointly describe
bulk transfer of compounds from one medium to another and diffusive
partitioning. They are often used to model active uptake of
contaminants by animals, principally livestock and game such as fish
or fowl. Factors of this type are used to model transfer of
semi-volatile compounds (SVOCs) such as dioxins from air to soil, soil
to beef and soil to cow's milk (e.g., Nessel et al., 1991; Fries,
1995). Bioaccumulation of lipophilic compounds and some forms of heavy
metals (e.g., methylmercury) in fish from ingestion of contaminated
prey and diffusive uptake through respiration is also modelled using
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