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The development of the ERA methodology was an important step forward with
the inclusion of such models for pollutant fate calculations. Figure 4.2 shows a
general overview of the exposure assessment by multimedia modeling for human
health. This figure shows the influence of human activities on the environment and
illustrates the connections of the different important impact pathways within the
total exposure. Thus, this figure describes the main goal of multimedia modeling:
to identify the different pathways of a pollutant fate and to calculate the total
exposure due to the different sources. Starting with emission from the plant, the
distribution of the pollutants goes over the air, soil, ground water and surface water
in the other bordering compartments. Through these paths the pollutants can enter
the food chain of human beings and animals. With the direct consumption of
agricultural products, i.e., plants or animals, humans stand under the direct and
indirect pollutant influence (see Figure 4.2).
Numerous model classification systems with different complexities exist in prac-
tice; these are broadly categorized as analytical or numerical models, depending on
the degree of mathematical sophistication involved in their formulation. Analytical
models are models with simplifying underlying assumptions, often sufficient and
appropriate for well-defined systems for which extensive data are available and/or
for which the limiting assumptions are valid. Whereas analytical models may be
enough for some situations, numerical models (with more stringent underlying
assumptions) may be required for more complex configurations and systems.
The procedure of deriving an exposure level by applying model calculations
must be transparent and the input data or default values used for the calculations
should be documented. Nowadays a large number of different models are available
to describe an exposure situation, so the choice of the most appropriate model for
the specific substances and scenario should be made and explained. The choice of
which model will be used for specific applications depends on numerous factors;

Emissions ATMOSPHERE
to Air

Emissions HUMAN Animals
to Soil BEING and
HUMAN Vegetables
ACTIVITY
Emissions
to Water* TERR. EC.
AQ. EC.

TERRESTRIAL AQUATIC
ECOSYSTEM ECOSYSTEM

*Emissions to superficial and underground water.
FIGURE 4.2 Cause–effect chain for ecosystem and human health as basis for exposure
assessment by multimedia modeling.

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