Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 253

complex, time-consuming and often more expensive. The philosophy behind this is:
'simple when possible (only the first tier) and more complex when necessary (higher
tiers)'. A tiered approach represents an efficient way of Risk assessing without
compromising scientific integrity.
The use of a tiered approach for Human Health Risk Assessment is often applied.
Today, the application of generic Soil Quality Standards often is the first step in this
tiered approach. Further tier assessments can be undertaken to enhance the Exposure
Assessment by making use of site-specific measurements (e.g., concentrations in
vegetables, indoor air, or dust), Biomonitoring, running more complex models (e.g.,
site-specific vapour intrusion models) or refining exposure calculations. The latter
is possible, for example, by including site-specific exposure information (e.g., time-
activity data, local food consumption, oral bioavailability in the human body), or by
applying Physiologically-Based PharmacoKinetic models. Furthermore, exposure
metrics can be tuned to the toxicological properties of the contaminants (critical
time-frame, effects by exposure route).
One example of a tiered approach in Human Health Risk Assessment is shown
in Swartjes et al. ( 2007 ), for the determination of human health risks due to the
consumption of vegetables grown on contaminated sites (Fig. 5.7 ). In this procedure
four steps have been distinguished, that is:

Contaminant
uptake
possible / likely?

STOP
(risk
“acceptable”)

TIER 0

No

Yes

Generic assessment
(e.g. generic BCF
or generic SQS)
- worst case -

STOP
(risk
“acceptable”)

TIER 1

< LV

≥ LV

Site-specific assessment
(e.g. site-sp. BCF
or soil-specific SQS)
- realistic worst case -

STOP
(risk
“acceptable”)

TIER 2

< LV

Fig. 5.7 The four step
(tiered) procedure for the
determination of human
health risk due to the
consumption of vegetables
grown on contaminated sites
used in the Netherlands, as an
example of a tiered approach
in Human Health Risk
Assessment (Swartjes et al.
2007 )

≥ LV

Measurement
in the field
according to protocol
- realistic case -

STOP
(risk
“acceptable”)

TIER 3

< LV

≥ LV

“Unacceptable”
risk

LEGENDA:
LV = Limit Value