Page 967 - The Toxicology of Fishes

Case Study: Pulp and Paper Mill Impacts 947

(Munkittrick et al., 2000b). For example, on the Wapiti River in Alberta, Canada, monitoring illustrated
that nutrient enrichment was the dominant effect of PME discharge and increased algal biomass affected
benthic invertebrate communities and fish populations from the bottom-up (Culp et al., 2004; Dubé et
al., 2004). Future studies at this site now focus on establishing relationships between nutrient levels and
algal biomass accrual in an effort to reduce PME effects (Cash et al., 2004).

Indicators for Assessing PME Effects in Fish
Changes in fish exposed to PMEs could be evident at all levels of organization, including biochemical,
organ, individual, population, and community. Selecting the level of organization to be used for assess-
ment purposes depends on the study objectives and management targets (Adams et al., 1992; Karels et
al., 2001; Larsson et al., 2000; Munkittrick et al., 2000b). It is not reasonable to monitor all levels of
biological organization and require a “zero-tolerance” for change. It is also not reasonable to monitor
only at the highest levels of biological organization and determine a change is unacceptable after a
species has been pushed to extinction (Munkittrick et al., 2000b). In general, as the level of biological
organization increases from individual to community, the ecological relevance increases, the time lag
for detecting changes relative to stressor exposure increases, and the specificity of the response decreases
(Munkittrick et al., 2000b). These factors must be recognized when the level (or levels) of organization
is selected for assessment purposes.
Biochemical, physiological, and pathological variables have been very useful as indicators for detecting
responses in fish exposed to PMEs (see tables) (Andersson et al., 1988; Larsson et al., 2000, 2003;
Munkittrick et al., 1998). These indicators are used to assess the status of important biological functions
including growth, condition, and energy metabolism; liver function; reproduction; immune defense;
pathology; and hematology. In the last decade, some indicators used to assess exposure to PMEs that
have received attention include changes in liver weight and condition as an indication of effects on
energy stores; changes in gonad weight, sex ratios, fecundity, age at sexual maturation, egg size, and
sex steroid hormones to assess effects on reproduction; changes in growth as an indication of energy
allocation; and changes in the induction of liver detoxification enzymes.
Current strategies recommend that a suite of indicators be measured to reflect both population and
physiological functions of the individual organisms that might be affected by PME (Larsson et al., 2000;
Munkittrick et al., 1998, 2000a). This information can serve to build a weight-of-evidence approach to
establish what the effect of the effluent is, what types of chemicals might be responsible, and their
potential mechanism of action; however, it is critical to understand that the roles of many biochemical
and physiological indicators in fish are not understood, and any conclusions on the effects of effluents
based on these indicators must be interpreted in that context of uncertainty.

Liver Detoxification Enzymes
In mammals, the cytochrome P450-dependent mixed-function oxidase or mixed-function oxygenase
(MFO) system is responsible for initiating the biotransformation of various organic compounds, including
xenobiotic contaminants (e.g., pesticides, dioxin) and endogenous compounds such as steroid hormones
(Jimenez and Stegeman, 1990). Upon exposure to foreign aromatic compounds, MFO enzymes are
rapidly induced, and, as a result, they can be used as biological indicators of contaminant exposure
(Hodson et al., 1991; Jimenez and Stegeman, 1990). They are mentioned specifically in this chapter as
they have been used extensively to assess fish responses to PME. Exposure to secondary treated BKPMEs
has been shown to induce MFO enzymes (Hodson, 1996; Munkittrick et al., 1994; Oikari and Holmbom,
1996; Soimasuo et al., 1998a,b); however, enzyme induction is not always correlated with other indicators
of fish health, including changes in sex steroid levels, liver size, and gonad size (Hodson, 1996;
Munkittrick et al., 1994; Swanson et al., 1992). Although MFO induction has not been mechanistically
linked to other indicators of fish health, it is still commonly used in conjunction with a suite of other
indicators to indicate effluent exposure (Larsson et al., 2000; Martel et al., 1996). Specifics on liver
detoxification enzymes can be found in other sections of this text.