Development and field validation of a multimedia exposure assessment model for waste load allocation in aquatic ecosystems: Application to 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,3,7,8-tetrachlorodibenzofuran in the Fraser River watershed

Knowledge of the relationship between contaminant, emissions and ambient concentrations is crucial in achieving environmental quality objectives. This paper reports the development and field validation of EcoFate, a time dependent multimedia mass balance simulation mod;el of the environmental distribution and food-chain accumulation of organic contaminants in aquatic ecosystems. The purpose of the model is to present a methodology for deriving maximum daily-loading estimates in accordance with environmental quality objectives for a variety of aquatic ecosystems impacted by emissions from one or several point or nonpoint sources. The application of the model to multiple, time-varying pulp and paper mill discharges of 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,3,7,9-tetrachlorodibenzofuran in the Fraser-Thompson River system from 1988 to 1995 is demonstrated. The ability of the model to predict chemical. concentrations in various environmental media and organisms resulting from chemical emissions is tested against field data collected over a 7 year period. The results include (i) a comparison of observed and predicted concentrations,(ii) an assessment of uncertainty; and (iii) a test of the model's temporal response to changes in contaminant loadings. The application of the model for the derivation of maximum daily loadings for multiple point sources in watersheds is illustrated.