This is the fourth article in the series on USES, the Uniform System f
or the Evaluation of Substances. This article describes the modelling
approach used to predict concentrations in the environmental media (ai
r, surface water, agricultural soil and groundwater) and the intake me
dia for humans (fish, drinking water, root crops, leaf crops, meat and
milk) and for predatory birds and mammals (fish and earthworms). Dist
ribution and intake are estimated on two spatial scales: locally near
a point source, and regionally over a larger area. This article focuse
s on the local distribution and the general intake models. Local distr
ibution is modelled in a hypothetical standard environment, using typi
cal environmental characteristics. Humans and predators are assumed to
be exposed to food products from the contaminated system. The choice
of models in a system like USES, is limited by the small data sets leg
ally required for risk assessment purposes. Therefore, USES focuses on
relatively simple models, and is able to work with the limited input
data.