Page 954 - The Toxicology of Fishes

934 The Toxicology of Fishes

FIGURE 24.1 Photographs of pulp mills, pulp mill effluent discharge, field sampling, and examples of target sentinel
species: creek chub (Semotilus atromaculatus) and slimy sculpin (Cottus cognatus).

discharges was capable of affecting fish at concentrations lower than previously suspected. It has since
become clear that some PMEs impact the reproductive health of fish, yet the factors determining which
mills will cause effects are unknown (Environment Canada, 2003; Lowell et al., 2004; Sandström, 1996).
Various countries have used different strategies for regulating PME discharges (Folke, 1996). Regu-
lations can focus on the technology used, the treatment required, chemical concentrations in the effluent,
the biological toxicity, or maintenance of a specified level of receiving environment quality. In Canada,
for example, chlorinated dioxins in some effluents and evidence of continued environmental issues at
modernized mills resulted in amendments in 1992 to the Canadian Pulp and Paper Effluent Regulation
under the federal Fisheries Act (Environment Canada, 1992a, 1997a). Under the revised regulation, final
effluents could not be acutely lethal to fish, and limits were set for the discharge of organic compounds
(measured as biochemical oxygen demand) and chlorinated dioxins. Furthermore, amendments included
an Environmental Effects Monitoring (EEM) requirement, where each mill is required to monitor receiv-
ing waters and effluent quality on a cyclical basis (Environment Canada, 1998). To meet these more
stringent regulations, the Canadian pulp and paper industry made a significant investment to modify the
processes used to whiten pulp (i.e., substituted elemental chlorine with chlorine dioxide in the bleaching
process), and most mills installed biological effluent treatment systems (Folke, 1996; Karels and Oikari,
2000; Kovacs et al., 2003; Munkittrick et al., 2000a). These process changes virtually eliminated acute
lethality of PMEs to fish and the discharge of persistent chlorinated organic compounds such as dioxins.
Similar regulatory changes and mill process improvements have occurred internationally (Folke, 1996).
Improvements in effluent quality have changed the types of responses measured in receiving environ-
ments exposed to PMEs. If effects are observed, they are sublethal in nature. In Canada to date, the
dominant response pattern of freshwater benthos is one of nutrient enrichment (Environment Canada,
2003; Lowell et al., 2004). The dominant fish response patterns include nutrient enrichment (increased
condition, liver and gonad size) and altered energy allocation (increased condition and liver size,
decreased gonad size). These results are consistent with those reported for some mills in the United
States (Adams et al., 1992; Sepúlveda et al., 2003) and Scandinavia (Karels et al., 1999; Larsson and
Forlin, 2002).