Scenario analysis of a level III multimedia model using generic and regional data

In order to realise EU legislation, the environmental risk of new and existing chemical substances has to be assessed. The methods for risk assessment are laid down in the Technical Guidance Documents TGD (EC 1996A). Basically, risk assessment consists of a comparison of predicted environmental concentrations (exposure assessment) and concentrations which may cause adverse effects (effect assessment). With the European Union System for the Evaluation of Substances EUSES (EC 1996B) a decision support system is available which integrates the models presented in the TGD into a Windows 95/NT-based software product. Meanwhile, EUSES has attained a far reaching and extensive use in governments, industry, and research institutes. For exposure assessment, various exposure models (regression equations, simple generic models, multimedia compartment models) are used. One of the objectives is to investigate the validity of model calculations and evaluate uncertainty in models and data arising in model application. Scientific justification of underlying equations, limitations, and respective software are tested and checked for possible errors. The project consists of several work packages: comprehensive data collection and evaluation, conceptual validation, model simulations, sensitivity and uncertainty analyses, comparison of model results with measured values (numerical validation), appropriateness of models (operational validation), comparison with alternative models, and software evaluation. It is determined for which substances and for which environmental segments the models deliver realistic values. Within this project, exposure assessments are carried out for different substances which represent a wide variety of physical-chemical properties. Substances of interest are those which are used in many products or chemical processes and which are frequently found in the environment. Due to their relatively good data availability, typical and well-known pollutants such as dioxins and PCBs are also investigated. For validation studies, in particular to compare measured concentrations with predicted ones, spatially and temporally coherent data sets must be available. Thus, before starting the project, an environmental segment of regional scale had to be chosen. The German state of North Rhine-Westphalia (approximately 34 000 km(2)) was selected as an environmental segment of regional scale.