PARENT SESSION
MP2 - Aquatic Toxicology
Chair: Spehar, Bob¹, ¹ U.S. EPA, Duluth, MN
Co-chair: Henry, Mary², ² U.S. Fish and Wildlife Service, Arlington, VA
2:10 PM to 5:30 PM - Monday, 18 November 2002
Room Ballroom J

(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