A comparison of spatially explicit and box models for the fate of chemicals in water, air and soil in Europe

This paper compares the results of a box model for the environmental fate of chemicals with spatially explicit models for water, air and soil. The spatially explicit models are based on the same model formulations as the box model, but use maps of emission patterns and environmental properties instead of average values. Results are expressed as a spatial distribution on a 25×25 km scale over Europe. For water and soil, the calculated maximum values are a factor 100–1000 higher than the box model results, for the air compartment, the maximum difference is approximately a factor 10. The consequences of the present results for the use of box models in risk assessment are discussed. It is concluded that for the air and soil compartments the box model gives a fair estimate of the calculated spatial average, given emission and chemical property data. The use of a local-scale model in addition to the overall model would give sufficient information to make application of spatially explicit models unnecessary in risk assessment. For the water model the box model underestimates the spatial average and the spatial maximum may be a factor 100–1000 above this average. For this compartment, an assessment of spatial variability would give important additional information. The present paper shows that a simple model may not be able to provide good local predictions of concentrations, but is able to provide the required spatial distribution in concentrations.