Georeferenced regional simulation and aquatic exposure assessment.

A simulation model system of the waste water pathways and the aquatic fate assessment is coupled to a discrete digitized river network. Temporal concentration distributions of down-the-drain chemicals are calculated from variable and uncertain input data and compared to monitoring data. The accuracy of the predictions are within a factor of three for the studied pilot catchments. Spatial distributions of the whole catchment give stochastic information on a regional basis for probabilistic risk assessments.

New PEC definitions for river basins applicable to GIS-based environmental exposure assessment.

By means of GREAT-ER (Geo-Referenced Regional Exposure Assessment Tool for European Rivers) aquatic chemical fate simulations can be performed for river basins. To apply the resulting digital maps with local (river stretch specific) predicted concentrations in regional aquatic exposure and risk assessment, the output has to be aggregated to a (single) value representative of exposure in the catchment. Two spatially aggregated PEC definitions are proposed for this purpose: PECinitial (unweighted aggregation of concentrations just downstream of wastewater emissions) and PECcatchment (weighted aggregation of all average stretch concentrations). These PECs were tested using simulations for two pilot study catchments (Calder and Went, UK). This confirmed the theoretical considerations which led to the definitions, and it illustrated the need for weighting to resolve scale-dependencies.

The identification of thresholds of acceptability and danger: the chemical presence route.

European Union chemical legislation requires the calculation of local and regional Predicted Environmental Concentrations (PEC) for the assessment of the exposure of new and existing chemicals to aquatic and terrestrial ecosystems. Current methods use local models for air, water and soil to estimate chemical concentrations close to the source and a generic multimedia 'unit world' approach to estimate regional PECs. These models assume generic environmental scenarios representing typical situations in European countries and do not account for the spatial heterogeneity and temporal variability in ecosystem characteristics, soil properties, river flow rates, chemical emissions, etc. The environmental and ecological complexity can best be represented in a Geographic Information System (GIS). By coupling a GIS with a fate simulation model the concentrations of substances in a specific environment are predicted more realistically. The GREAT-ER project (Geography-referenced Regional Exposure Assessment Tool for European Rivers) was launched to refine regional and local exposure assessments for down-the-drain chemicals by applying real, spatial-referenced datasets instead of generic or average values. A modular approach was developed consisting of a hydrological model and a waste-flow, river quality and fate model which are linked to a regional GIS-database. For the calibration and validation in two European study areas representative detergent chemicals (LAS, boron) are used. In a parallel study, high-volume intermediates discharged into the river Rhine are simulated.