Development and evaluation of a dynamic multimedia model (ECORAME) for local scale assessment of aquatic ecological exposure to chemicals originating from sources in environmental media

Use of multimedia models (MMMs) has been limited in exposure assessment for aquatic ecosystems at local scale typically due to their coarse spatial resolution and inability to predict the individual concentrations of multiple streams within a watershed cell. An MMM named ECORAME is presented which overcomes the limitations by treating each water segment as an independent cell rather than a compartment within a watershed cell. This offers two advantages for exposure assessment, i.e., i) the spatial resolution for water is readily adjustable and ii) multiple water streams within one watershed cell could be handled individually. Model evaluation with respect to polycyclic aromatic hydrocarbons (PAHs) demonstrated that ECORAME's prediction of relative concentration agreed with measured values within a factor of five or less. A case study of PAHs using ECORAME shows that the concentration can change by more than 10 fold over the 40 km main stream stretch of the Han River in Seoul, Korea. The concentration difference among multiple streams in the same watershed cell could be substantial (greater than 100 fold). Besides a need of finer spatial resolutons than those typically used in MMMs, the results strongly suggest that exposure prediction capability for individual streams in the same watershed is necessary for local scale assessment. As demostrated with ECORAME, the need can be effectively met by handling the water segments as individual cells in future MMMs.