DEVELOPMENT AND FIELD VALIDATION OF A MULTIMEDIA EXPOSURE ASSESSMENT MODEL FOR WASTE LOAD ALLOCATION IN AQUATIC ECOSYSTEMS - APPLICATION TO2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN AND 2,3,7,8-TETRACHLORODIBENZOFURAN IN THE FRASER-RIVER WATERSHED

Knowledge of the relationship between contaminant, emissions and ambie nt concentrations is crucial in achieving environmental quality object ives. This paper reports the development and field validation of EcoFa te, a time dependent multimedia mass balance simulation mod;el of the environmental distribution and food-chain accumulation of organic cont aminants in aquatic ecosystems. The purpose of the model is to present a methodology for deriving maximum daily-loading estimates in accorda nce with environmental quality objectives for a variety of aquatic eco systems impacted by emissions from one or several point or nonpoint so urces. 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 1 988 to 1995 is demonstrated. The ability of the model to predict chemi cal. concentrations in various environmental media and organisms resul ting from chemical emissions is tested against field data collected ov er a 7 year period. The results include (i) a comparison of observed a nd predicted concentrations,(ii) an assessment of uncertainty; and (ii i) a test of the model's temporal response to changes in contaminant l oadings. The application of the model for the derivation of maximum da ily loadings for multiple point sources in watersheds is illustrated.