Page 970 - The Toxicology of Fishes

950 The Toxicology of Fishes

exposure, some biological response to the toxicant should occur and will be observable earlier, or at a
lower effluent concentration, than the acute endpoint. Sublethal toxicity tests can be short term or long
term. Short-term tests are partial life-cycle tests that measure the effects of effluents on critical life
stages. Long-term tests refer to full life-cycle exposures.
Two commonly employed chronic tests used to assess PME effects on fish are the fathead minnow
(Pimephales promelas) freshwater test and the inland silverside (Menidia beryllina) marine test. The
fathead minnow test measures the effects of effluents on larval growth and mortality after 7 days of
effluent exposure (Environment Canada, 1992b). The inland silverside survival and growth test is a 7-day
test where young fish (7 to 11 days old) are exposed to serial dilutions (five concentrations) of final
effluent from 6 to 100% to determine survival and growth (determined by weights) effects compared to
a control (USEPA, 1988). Growth effects are estimated using linear interpolation to determine the IC ,
25
the concentration (% v/v) at which growth is inhibited by 25% compared to control fish. More recently,
MacLatchy et al. (2004) have developed a short-term (7-day) exposure bioassay to evaluate reproductive
endocrine responses in a northern Atlantic saltwater fish, the mummichog (Fundulus heteroclitus). This
bioassay has been used to determine the efficacy of process changes for improving effluent quality and
to drive the fractionation and compound identification of individual waste streams from a pulp mill in
New Brunswick, Canada. The merits of acute and chronic toxicity tests are in their ability to rapidly
assess effluent quality from a biological perspective using a relatively cost-effective, standardized
approach with well-defined response endpoints (Rodier and Zeeman, 1994). Toxicity testing of PMEs
on fish has been used to assess the efficacy of effluent treatment in removing toxicity, to identify and
control in-plant sources of toxicity, and for routine monitoring of effluent quality (Kovacs and Megraw,
1996; Kovacs et al., 1996, 2003; McLeay and Associates, 1987). Threshold concentrations of PME that
are capable of causing effects have also been estimated from toxicity tests and compared to effluent
concentrations found in receiving waters. Using toxicity tests to assess field effects can be useful
providing the imitations of this approach are recognized (Kovacs et al., 1996). The main limitation is a
lack of environmental relevance because toxicity tests are conducted in the laboratory under tightly
controlled conditions with a single species. Other limitations include lack of consideration of additive
or synergistic effects of other chemical stressors or in combination with natural stressors (e.g., diurnal
temperature changes). The relevance of the results to other species and higher levels of biological
organization (e.g., populations) in complex field conditions has also not been adequately investigated
(Kovacs and Megraw, 1996; Kovacs et al., 1996). Robinson et al. (1994) reported that partial life-cycle
tests using fathead minnow could not predict field effects.

Life-Cycle Exposures
The predominant long-term sublethal toxicity test used with PMEs is the fathead minnow life-cycle test
(Kovacs et al., 1996; NCASI, 1985, 1998; Parrott et al., 2003; Robinson et al., 1994). In this test, fathead
minnow are exposed from the egg stage to sexual maturity and reproduction. Endpoints measured include
egg hatching, survival and growth of the parent generation, and hatching and larval survival of the first
generation of offspring (F ). Experimental duration for a single life cycle is typically around 200 days.
1
Primary advantages of a life-cycle test are that the effects of effluent exposure can be followed through
key developmental stages of a species under controlled laboratory conditions. In addition, these tests
allow for an evaluation of the population-level and multigenerational consequences of effluent exposure.
Although a variety of indicators are measured in these tests, application for pulp and paper effects
assessment has focused on fish reproductive health. Results from fathead minnow life-cycle tests show
that some indicators of fish reproduction are affected by PME exposure but at concentrations higher
than those found in receiving environments (Borton et al., 2003; NCASI, 1985; Parrott et al., 2000a;
Robinson, 1994). In addition, these effects do not consistently transfer to subsequent generations (Borton
et al., 2000a). Life-cycle tests have also been used to illustrate that mill process changes can reduce
reproductive effects on fish (Borton et al., 2003; Kovacs et al., 1995, 1996). Several studies have also
used fathead minnow life-cycle tests to determine the relevance of various biological indicators as
predictors of fish reproductive health after PME exposure. The intention is to develop a short-term assay
for assessing effluent effects that is predictive of longer term population consequences. NCASI (1985),