T9 AM Bioaccumulation and Biomagnification
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in 339-340

(GAN-1117-900730) Development of a multi-chemical food chain model: Application to study debromination and bioformation of PBDEs.

Gandhi, N^{1, 3}, Bhavsar, S¹, Gewurtz , S¹, Diamond, M¹, Evenset , A², Christensen , G², Gregor , D³, ¹ University of Toronto, Toronto, ON, Canada³ Current address: Gartner Lee Ltd., Markham, ON, Canada² Akvaplan-niva, Tromso, Norway

ABSTRACT- Mass balance models are useful tools for evaluating the mechanisms responsible for contaminant levels and trends in biota. For compounds, such as PBDEs, which are susceptible to degradation, it is important to simultaneously track both the parent chemical and its degradation products in order to fully assess risk. In this study, we present an extension of the food web model of Campfens and Mackay (1997) to simultaneously account for multiple, related chemicals by solving mass balance equations of chemicals of concern simultaneously using a matrix approach. We illustrate the model using four PBDE congeners in the food web of Lake Ellasjoen, a high arctic lake located on Bear Island, Norway. In the absence of measured degradation half-lives of the PBDE congeners, we used the model to back-calculate these values for each congener specific to each taxonomic group. The results illustrate how the model can account for bioformation of lower brominated congeners (e.g., BDE-47) and its effect on estimated concentrations. The model calibrated half-lives for BDE-99, -100, and -153 tend to be more sensitive than for the predictions for BDE-47. This occurs because concentrations of the more brominated congeners are much less than the concentrations of BDE-47 and therefore they can only contribute a limited amount to BDE-47 through bioformation, regardless of their degradation half-life. The results suggest that bioformation supplies about 8 and 6% of total BDE-47 input to small and large arctic char, respectively. Predicted metabolic degradation ranges from 20% (BDE-100) to 65% (BDE-153) of total loss rate in arctic char species. For congeners with a high potential for debromination, e.g. BDE-153 and BDE-99, degradation could become a major process of elimination within the aquatic food chain.

Key words: multi-chemical, PBDE, food web, arctic