Page 695 - The Toxicology of Fishes

Fish Toxicity Studies 675

ease of use in environmental litigation, and is useful for routine monitoring. Standardization can be
achieved by:

• Use of standard, well-written, and validated protocols
• Use of standard test species and disease-free organisms
• Use of reference toxicants

Standard test procedures, however, may not always be applicable for answering certain questions about
a particular aquatic system; for example, when evaluating the hazard of a chemical (or effluent) to an
indigenous fish community in a specific fresh- or saltwater system, it may not be practical to use standard
test species that are not normally present in these bodies of water. Furthermore, it may be desirable to
use water characteristic of the system and not standard laboratory-filtered water. Toxicity test protocols
also specify that exposures of organisms are for fixed and continuous concentrations of test substances
for a defined time period. As pointed out earlier, chemicals rarely enter the aquatic environment at a
continuous, fixed concentration but rather intermittently as pulses (or “slugs”) or as a one-time spill;
therefore, realistic environmental exposures typically include a one-time high exposure concentration
usually diluted to lower concentrations with time. A typical standard test in which all test conditions
are kept constant or maintained optimally may be inappropriate for predicting responses in a changing
natural system. In this case, site-specific conditions should be considered. This type of test design should
be customized to the situation, and a standardized test design would not be applicable. Alternatively, if
results are to be used to compare the toxicity of one chemical to another, rigid standardization is necessary.

Description of Test Methods

As previously pointed out, toxicity test methods may be categorized according to the length of exposure,
test situation, criteria for effects to be evaluated, and organisms to be tested. Some of the commonly
used tests and endpoints (effect criteria) that they measure are described below.

Acute Toxicity Tests

Before a definitive acute test is carried out with a particular chemical and species, few to no data may
be available; therefore, a range-finding acute test is conducted to pinpoint exposure concentrations for
the definitive acute test. Range-finding concentrations tested are normally spaced at intervals of a factor
of 10, and only two to four fish may be used per concentration. When the range-finding test defines the
smallest range between concentrations that produce mortality and no effects, the definitive test is
conducted with at least three, preferably five, concentrations to define the endpoint with greater accuracy
and precision. Accuracy is attained by closer spacing between concentrations and precision by using
more fish per concentration. Common acute effect criteria for fish include mortality; however, abnormal
behavior observations are also noted (e.g., swimming behavior, loss of equilibrium, color changes).
Tests are conducted for a predetermined length of exposure to estimate the 24-, 48-, 72-, or 96-hour
LC ; 95% confidence limits; and slope of the concentration–response curve. The LOEC and NOEC
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have also been reported in acute tests, but the LOEC and NOEC have shortcomings in that they are
affected by the study design (e.g., concentrations chosen, number and spacing of replicates in each
concentration) (Chapman et al., 1998). Much uncertainty is associated with these values, as they are
statistically determined using hypothesis testing, they do not have confidence intervals like point estimates
(e.g., LC , EC ), and they can only be compared by their ranges of values. In assessing acute hazards,
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the aquatic toxicology community is moving toward benchmark values such as the confidence interval
that result in an LC as a no-effect concentration. An acute test may also have a duration that is not
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predetermined, in which case it is referred to as a time-independent (TI) test. The acute TI test should
continue until acute toxicity (e.g., mortality) has stopped or nearly stopped and the toxicity curve indicates
that a threshold (or incipient) effect concentration can be estimated.