Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 225

Table 5.1 Overview of possible exposure pathways, subdivided into oral, inhalation and dermal
exposure pathways, and indoor and outdoor exposure

Indoor exposure Outdoor exposure

Contact
medium Pathway Contact medium Pathway

Oral Dust ingestion Dust Soil ingestion (Soil)

Vegetable
consumption

Vegetables

Drinking water
consumption

Groundwater/
drinking water

Meat
consumption

Meat

Milk
consumption

Milk

Egg consumption Eggs

Inhalation Air inhalation Indoor air Air inhalation Outdoor air

Airborne dust
inhalation

Indoor airborne
dust

Airborne dust
inhalation

Outdoor
airborne
dust

Water vapours
inhalation
during
showering

Drinking water

Dermal Dust contact Dust Soil contact (Soil)

Water contact
during bathing

Drinking water

total vegetable consumption', for example, 'it must be possible to consume at least
10% of total consumption from one's own garden'. Obviously, this boundary condi-
tion is based on a political decision and is very much dependent on the situation of
the contaminated site (this differs, for example, for sites in rural areas and in cities).
Since site characteristics generally are more stable over time, these can to a large
extent be related to the present situation. However, in case the pH, for instance, is
strongly influenced by gardening practices, it might be important to include a cer-
tain degree of conservatism by adopting a less favourable pH and associated higher
plant uptake rates in the Risk Assessment, as in the present situation.
In fact, changes in the contaminant concentrations due to migration and degrada-
tion also must be considered. Remarkably, this is not often done in Human Health
Risk Assessments. In many Risk Assessments the exposure calculation is based on
the present or historical concentration in soil, even when the purpose of the Risk
Assessment relates to the human health risks over longer time periods. Since the
concentrations in soil generally decrease in time due to leaching and degradation,
this can be considered as a worst-case situation. This is not always true for ground-
water, however, since leaching from soil could increase contaminant concentrations
and contaminant migration could lead to increased concentrations at a distance some
ways away from the site. Furthermore, degradation processes may actually worsen
conditions (e.g., when TCE is broken down into the more toxic vinyl chloride).