Page 969 - The Toxicology of Fishes

Case Study: Pulp and Paper Mill Impacts 949

at all sites for collection of adequate numbers of samples; (4) there are no other effluent discharges or
anthropogenic influences (i.e., municipal sewage) that are confounding interpretation of mill-related
effects; and (5) the organisms are exposed (i.e., fish do not move between reference and exposed areas).
Most of these assumptions are easier to meet for benthic invertebrates. For fish, field designs often
involve a compromise between optimizing the study design in an effort to meet these assumptions while
striving to obtain the most relevant and interpretable data.
An example of how ecological field assessments can be optimized to meet assumptions with respect
to effluent exposure is selecting sampling sites upstream and downstream of pulp and paper mills that
are also upstream and downstream of dams (Munkittrick et al., 2000b). This design ensures that fish do
not move between reference and exposed areas. In this example, however, damming of waters presents
another set of potentially confounding factors, such as the creation of reservoir areas that act as nutrient
or contaminant sinks that can interfere with understanding cause and effect linkages between changes
in fish and PMEs. Sample sites can also be located upstream and downstream of other confounding
effluent discharges in an attempt to isolate PME-specific effects (Dubé, 2003).
Exposure of fish to PMEs can be assessed by conducting plume delineation studies and measuring
tracers of effluent exposure in fish tissues (Environment Canada, 1998). Tracers in fish bile (e.g., resin
and fatty acids) or fish tissues (e.g., chlorinated organic compounds, MFO induction, stable isotopes of
carbon, nitrogen, and sulfur) are commonly used (Dubé, 2004). In systems that lack natural or manmade
barriers to movement, the tendency in Canada has been to move toward the collection of small-bodied
species of fish that have a more localized home range compared to larger, migratory species (Gibbons
et al., 1998a,b). These studies have demonstrated the effectiveness of forage fish for measuring responses
to PME and have also improved our fundamental understanding of species biology and life history.
Despite the use of these strategies to optimize study designs for field assessments with fish, it may
not always be possible to clearly differentiate the relative contributions of specific effluents to field
responses. In many field studies, the concentration and duration of exposure to effluent are difficult to
quantify because of complex effluent dispersion in the water column, mobility of fish in and out of the
effluent plume, and the unavoidable presence of other effluent discharges (Langlois et al., 2003; Larsson
et al., 2003). In other cases, field sampling might be too dangerous, logistically demanding, or excessively
expensive to implement. In these situations, caging studies and artificial stream approaches have been
developed to isolate the potential impacts of effluents while simulating receiving environment conditions.

Laboratory Toxicity Tests
Laboratory tests of acute and chronic toxicity are a common approach used to evaluate the effects of
PMEs on aquatic organisms (Adams, 1990). In many countries, tests are required under legislation to
characterize effluent quality (Folke, 1996). Toxicity tests are used to determine if there is the potential
for effects to exist, to provide quick answers to potential benefits during mill process changes, or to
track toxicity during toxicity identification evaluation (TIE) procedures. Sublethal toxicity testing can
also play a key role in evaluating whether potential receiving environment concerns are not being
expressed under current environmental conditions.

Acute and Chronic Toxicity Tests
Acute or lethal toxicity tests involve short-term exposure of an organism to a serial dilution of effluent
to determine the concentration at which the tolerance of the organism is exceeded (mortality) (Rodier
and Zeeman, 1994). The most commonly employed acute toxicity test used to assess PME is the 96-hour
rainbow trout (Oncorhynchus mykiss) test. This test is a static acute test conducted on serial dilutions
of final effluent (e.g., 6.25%, 12.5%, 25%, 50%, 100%). After 96 hours of exposure, the median lethal
concentration that produces 50% mortality in the test organism (LC ) is determined based on compar-
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isons with a control. Specific details of test conditions, reference toxicants, and endpoint calculations
can be found in Environment Canada (1990). Chronic or sublethal toxicity tests also involve exposure
of an organism to a series of effluent concentrations, but the exposure duration is longer and response
endpoints are subtler (e.g., changes in growth and reproduction) (Rodier and Zeeman, 1994). Chronic
toxicity testing is practiced for prevention; that is, before a species is adversely affected by effluent