Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 224

• meat, milk and eggs;

• outdoor air;

• airborne dust particles indoors;

• airborne dust particles outdoors.

Oral exposure through deposited house dust, as well as input parameter identifi-
cation, is described in detail in Bierkens et al. ( Chapter 6 of this topic). The other
exposure pathways and intercompartimental relationships mentioned in this section,
as well as the input parameter identification, are described in detail in Elert et al.
( Chapter 11 of this topic).
In general, dermal uptake of contaminants from soil contributes little to total
exposure. Contaminants with a relatively high potential for dermal transfer (several
PAHs, DDT) can result, however, in significant contributions to exposure through
dermal uptake via contact of the skin with water during bathing or showering. In
absolute terms, inhalation of dust particles is of minor importance. This route should
not be neglected, however, as toxicity by the inhalation route can be significantly
different from toxicity by the oral route.

5.3.3.6 Overview Exposure Pathways

In Table 5.1 an overview is given of possible exposure pathways for contaminated
sites, including the relevant contact media for each pathway. The pathways are sub-
divided into oral, inhalation and dermal exposure pathways, and indoor and outdoor
exposures.

5.3.3.7 Exposure Scenarios

Any exposure calculation must be based on an exposure scenario . Such a scenario
describes the site, the soil and, last but not least, human behaviour at the site. With
the purpose of promoting understanding of exposure, an exposure scenario could be
visually presented by a Conceptual Model.
Two types of exposure scenarios are recognised, that is, actual exposure
scenarios for site-specific Risk Assessment and potential exposure scenarios for
generic Risk Assessment (mostly the derivation of Soil Quality Standards).
The basic idea behind actual exposure scenarios is simple: mimic the characteris-
tics of the site, the soil under investigation and human behaviour on that site, as well
as possible. However, since the outcomes of the Risk Assessment usually need to
represent the risks over longer time periods, assumptions must be made for factors
that change over time, mainly in regard to the layout of the site and human behaviour
characteristics. An example of a transitory factor that relates to human behaviour is
the fraction of home-grown vegetables to total vegetable consumption on the site.
It is not appropriate to focus on a present situation where no vegetables are grown,
since a subsequent resident might be a fanatical gardener, who supplies a substan-
tial part of the total vegetable consumption from the same garden. In this example,
it makes sense to define a 'representative contribution of home-grown vegetables to