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(259) Use of stable isotopes to "fingerprint" pulp mill effluents and trace biotic exposure .
Dube, Monique*,1, Wassenaar, Len1, 1 National Water Research Institute, Saskatoon, SK, Canada
ABSTRACT- Stable isotopes of carbon (13C) and nitrogen (15N) have been used to describe food web relationships amongst organisms and food sources. Stable isotopes of sulfur (34S) and chloride (37Cl) have illustrated exposure of aquatic biota to pulp mill effluent (PME) and chlorinated solvents, respectively. Our objective was to use a multi- isotope approach (13C, 15N,34S, 37Cl) to: 1) characterize the isotopic signatures of Canadian PMEs; and 2) assess fish tissue assimilation of isotopes in a laboratory exposure. PMEs were collected and represented a cross section of mill process types and effluent treatment strategies. Analyses of the effluents revealed signature ranges of -25.5 to -14.7 for 13C, -4.0 to -2.6 for 15N, -3.7 to 16.5 for 34S, and -1.7 to 0.8 for 37Cl. Principal components analyses showed each PME had a distinct isotopic "fingerprint". To assess tissue assimilation of isotopic signatures, hatchery-reared juvenile rainbow trout (Onchorhynchus mykiss) were raised for 45 d in the laboratory under control and 10% PME treatments. Fish within each treatment were fed chironomids (Chironomus tentans) cultured under either control or effluent exposed conditions (10%). There were no significant differences among treatments with respect to 13C,15N, or 34S. The PME was significantly depleted in 37Cl (-1.690) compared to the laboratory dilution water (0.612). Chironomids exposed to 10% PME were significantly depleted in 37Cl (-2.34) compared to controls (-0.792). Rainbow trout increased in wet weight (g) by 50% in both treatments over the exposure period. Fish exposed to 10% PME were significantly depleted in 37Cl relative to controls and the depletion resulted from waterborne exposure rather than through their food source. These results are highly significant because they suggest that 37Cl may be a tracer of biotic exposure to PME. In addition, we have identified a potentially different mechanism for incorporation of 37Cl into fish and chironomid tissues that suggests "you are not always what you eat".
Key words: Stable isotopes, Pulp mill effluent, Tracer, Rainbow trout
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