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This article in JEQ

  1. Vol. 35 No. 5, p. 1884-1893
    Received: Apr 10, 2005

    * Corresponding author(s): monique.dube@usask.ca
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Contrasting Pathways of Assimilation

  1. Monique G. Dubé *a,
  2. Glenn A. Benoyb and
  3. Leonard I. Wassenaarc
  1. a Univ. of Saskatchewan, Toxicology Centre, 44 Campus Dr., Saskatoon, SK S7N 5B3, Canada
    b National Water Research Institute, Environment Canada, Potato Research Centre, 850 Lincoln Rd., Fredericton, NB E3B 4Z7, Canada
    c National Water Research Institute, Environment Canada, 11 Innovation Blvd., Saskatoon, SK S7N 3H5, Canada


Fish are commonly used for monitoring the quality of waters receiving pulp mill effluents (PMEs). Isotopic assays of fish tissues have the potential to provide empirical evidence to link an effluent source to exposure. We show in a 45-d factorial laboratory experiment that different exposure pathways lead to isotopic signatures in fish tissue. Rainbow trout (Oncorhynchus mykiss) were exposed to 10% PME in three ways; direct exposure through addition of PME to aquaria, indirect exposure through invertebrate food consumption (Chironomus tentans cultured in 10% PME), and a combination of both exposure pathways. Of the four stable isotopes measured (δ13C, δ15N, δ34S, δ37Cl), δ13C, δ34S, and δ37Cl showed significant differences in exposed animal tissues. δ37Cl of fish muscle tissue showed consistent differences across trophic levels and revealed contrasting pathways of PME exposure. Contrasting δ 37Cl values in C. tentans due to the presence or absence of 10% PME did not translate into δ37Cl differences in fish. Rather, δ37Cl ratios of fish muscle tissue were specifically related to 10% PME exposure in the aquaria (waterborne exposure pathway). Feasible distributions of 37Cl source contributions for observed mixture ratios confirmed that PME accounted for observed differences in δ37Cl among treatments. Direct uptake of chloride ions across gill surfaces is the most likely pathway for assimilation of PME into fish tissues. Considering the variability of PMEs and receiving environments, use of a multi-isotope approach is recommended for tracing exposure of fish. Use of 37Cl should also be considered in light of its alternative assimilation pathway.

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