Page 692 - The Toxicology of Fishes

672 The Toxicology of Fishes

are also more easily analyzed than in natural systems, there are several limitations. Temperature and
seasonal fluctuations and certain biotic components (invaders) not represented can significantly impact
results. Furthermore, all fish may not be adequately represented. Currently, no standardized laboratory
microcosm protocols with fish are available; however, standardized protocols are available for first
(primary consumers) and secondary (grazers, herbivores) trophic-level organisms including the detrital
(or recycling) level (ASTM, 2000).
Ideally, data from laboratory and field studies should be obtained for certain chemicals before widescale
use. In designing studies, considerations should be given to:

• Purpose (or objective) of the test—Tests used to develop numerical water or sediment quality
criteria for chemicals may be different than those tests used in support of chemical registration
or for routine monitoring or screening of effluents. Testing for a pesticide to be used on a
specific crop or an ornamental, for example, may not require as extensive a test battery as that
required for the development of numerical criteria.
• Characteristics of chemical—Chemicals with low solubility, volatility, susceptibility to sorption
or degradation, or other factors that affect their behavior will require special steps so the results
of toxicity tests are indicative and relevant to the way the chemical will behave in the environ-
ment. Chemicals that degrade rapidly and that are not analytically detectable in natural waters
after a few days may not require tests with long-term exposures. Measurements of test con-
centrations should be a requirement in all studies.
• Mode of action of chemical—Knowledge of the mode of action of the chemical will provide
information on the most likely biological endpoints to measure during and at the end of toxicity
tests.
• Pattern of use of chemical (or discharge)—A test that uses constant and continuous chemical
exposure will produce inaccurate results if organisms are only intermittently exposed. The latter
is important when considering that most pesticides in the field are used at different rates with
various time intervals in between applications, although chemical safety testing for pesticide
registration requires continuous exposure to constant concentrations of a pesticide.
• Interactive effects—Laboratory testing of single chemicals should consider any factors that
may affect toxicity and may include characteristics of the water (e.g., dissolved oxygen, humic
substances), temperature changes, and exposures to more than one chemical.
• Impact on characteristics of the ecosystem—Natural waters representative of oligotrophic,
mesotrophic, and eutrophic freshwater systems should be considered in toxicity tests. Whenever
possible, natural saltwater should also be used in testing instead of prepared saltwaters.
• Characteristics of test organisms—Indigenous non-target organisms should be considered in
testing, whenever possible.

No single test can provide enough information to assess the impact of toxicants on the aquatic environ-
ment. Ideally, a combination of tests should be used in the laboratory and field.

General Test Design

Fish toxicity testing in the laboratory follows a tier approach, progressing from simple short-term tests
to more complex longer-term tests based on results of previous tests. Although specific details of the
protocol for each toxicity test may differ, certain basic features are fundamental to the design and
analysis of all toxicity tests. Each protocol requires careful control and monitoring of conditions such
as pH, temperature, dissolved oxygen, exposure concentration, photoperiod, and water chemistry. Fish
are exposed in test chambers (e.g., glass tanks) to three to five different concentrations of a test material
(e.g., pesticide, industrial effluent, industrial chemical) in dilution water solutions. The criteria for
effects (e.g., mortality, growth, reproduction) and the type of test (i.e., acute or chronic) are established
before testing and are then evaluated by comparing chemically exposed (treated) organisms with