A mass balance model of contaminant fate-transport was applied to 11 organic compounds in the Bay of Quinte and its foodweb. Total loadings were back-calculated from measured concentrations in sediment and/or fish for most chemicals due to limited measured concentrations in the contributing tributaries and point sources such as STPs. Total loadings decreased between 1988 and 2000 from 1–2 orders of magnitude for TCDD/F to 30% B[a]P and 80% for ΣPCBs. Total loadings in 2000 ranged from 10 mg day−1 for TCDD/TCDF to ∼0.01–0.5 kg year−1 for mirex, p,p′-DDT and BDE-47, to ∼1 kg year−1 for dieldrin and HCB, ∼10–50 kg year−1 for ΣPCB and B[a]P, and 2000 kg year−1 for atrazine. Despite concentration reductions, sport fish exceeded the lowest Ontario fish consumption guidelines for ΣPCB, TCDD and TCDF. Model results suggested that atmospheric deposition was the main source of lower molecular weight PCBs, TCDD/F and DDT, tributaries for higher molecular weight PCBs, and Lake Ontario for mirex, atrazine and dieldrin loadings. The main source of B[a]P was thought to be urban runoff, unknown for long-banned HCB and sewage treatment plants for 17β-estradiol. Results for BDE-47 were illustrative due to the lack of data. Industrial sources did not contribute to overall sediment or fish concentrations (not including “hot spots”). Organic compounds in the Bay were estimated to have a short residence time of days in the water column due to rapid export to Lake Ontario, except for HCB and 17β-estradiol which were estimated to be lost by volatilization and transformation, respectively. The response time of organic compounds in sediment varied from <1 year (atrazine) to ∼50 years (ΣPCB).

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