A new generic approach for estimating the concentrations of down-the-drain chemicals at catchment and national scale

A new generic approach for estimating chemical concentrations in rivers at catchment and national scales is presented. Domestic chemical loads in waste water are estimated using gridded population data. River flows are estimated by combining predicted runoff with topographically derived flow direction. Regional scale exposure is characterised by two summary statistics: PECworks, the average concentration immediately downstream of emission points, and, PECarea, the catchment-average chemical concentration. The method was applied to boron at national (England and Wales) and catchment (Aire–Calder) scales. Predicted concentrations were within 50% of measured mean values in the Aire–Calder catchment and in agreement with results from the GREAT-ER model. The concentration grids generated provide a picture of the spatial distribution of expected chemical concentrations at various scales, and can be used to identify areas of potentially high risk.