Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 229

However, it is a misstatement to say that measured concentrations are per def-
inition better than calculated concentrations. The reason for this is that the actual
concentration is not always a synonym for representative concentration. Since con-
centrations in contact media are fluctuating in time and space, in many cases
an average concentration in time and space (or a statistically appropriate con-
centration, e.g., a 90 percentile) is relevant for Human Health Risk Assessment
purposes, while a measurement only relates to a specific place and moment in time.
Calculations, although less reliable in estimating actual concentrations in contact
media at a specific place, generally focus on an average concentration in time and
space.
Moreover, including the variation of the measured concentration in contact media
in time and space in Risk Assessment requires special skills of the Risk assessor.
Relevant issues include:

• The type and number of vegetables that must be sampled in a vegetable garden.

In many small vegetable gardens, however, see Fig. 5.3 as an example, the choice
of type and number of vegetables is limited. In this specific case the fast growing
crops such as spinach and endive that have a relatively high uptake are not grown
on the site.

• The frequency and seasonal planning of indoor air measurements.

By analogy with the position of measurements in body fluids or body tissue, a
'smart' combination of calculating and measuring is the most optimal procedure in

Fig. 5.3 A small vegetable garden in IJmuiden, the Netherlands, as an example of a site which
offers the possibility for measuring the concentration in contact media (this is, the edible parts
of vegetables), but offers a limited choice of type and number of vegetables for sampling (photo:
F. Swartjes)