Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 214

also as concentration, expressed as mass per unit of air volume (mg/L). Both expo-
sure metrics can be used for comparison with the Toxicological Reference Values,
either as a rate or a concentration, in the Risk Characterisation step. In this chap-
ter often the terms Estimated Exposure and Critical Exposure are used. Estimated
Exposure is the best possible estimate of human exposure, either through modelling
and/or measuring. Critical Exposure enables a distinction in situations that do or do
not need further attention with regard to human health risks, either based on science
and/or political decisions.
Ideally, the relevant measure of human exposure is the amount of contaminants
that is actually absorbed into the body, i.e., the internal exposure (aka: 'dose' or
'uptake'). More precisely, human exposure relates to the contaminants that are
adsorbed into specific target organs, that is, the organs in which adverse effects
are revealed. Therefore, instead of dose-response relationships, it is more accu-
rate to refer to exposure-dose-response relationships (or external exposure-internal
exposure-effect relationships).
Exposure Assessment provides a (quantitative) evaluation of exposure, including
intensity, frequency and duration of exposure, route of exposure (oral, inhalation,
dermal), rates (intake or uptake rates), the amount that may cross the body bound-
ary (external exposure) and the amount absorbed (internal dose) (International
Programme on Chemical Safety 1999 ). However, since the fate of contaminants
in the human body is difficult to assess, certainly on the basis of calculations,
exposure often refers to the amount of contaminants that cross the outside borders
of the human body, that is, the external exposure (aka: 'intake'). Since external
exposure represents the maximum dose, that is, the dose when 100% of all con-
taminants have been absorbed into the body, this can be regarded as a worst-case
approach.

5.3.2 Biomonitoring

The most direct way to assess human exposure from soil contaminants is to mea-
sure the actual body burden through Biomonitoring . In practice this means sampling
and measuring body fluids or body tissue. For several reasons, however, these mea-
surements often offer limited possibilities and are only used in higher tier Risk
Assessments. First of all, sampling of the tissue of living humans is difficult, or
impossible, for ethical and technical reasons. For clear reasons it is next to impossi-
ble to sample organ tissue of living humans. The best options offer the sampling of
the following materials:

• blood, for example, Kim et al. ( 2005 ), who measured persistent contaminants

such as polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls
(PCBs) in human blood, in Seoul, Korea;