9637

• UCREFRP Catalog Number: 9637
• Author: American Society For Testing And Materials.
• Title: Standard Practice For Conducting Acute Toxicity Tests With Fishes, Microinvertebrates, And Amphibians.
• USFW Year: 1980.
• USFW - Doc Type: Philadelphia, PA.
• Copyright Material: YES

words, a measure of the susceptibility of the
test organisms to the toxicant under the condi-
tions of the test.

4. Significance

4.1 The results of acute toxicity tests provide
information about the immediate effects of
short-term exposure of test organisms to toxi-
cants under the experimental conditions. Re-
sults also provide information on the relative
toxicity of toxicants and the relative suscepti-
bility of species. Effects observed during an
acute toxicity test will probably occur ina field
situation as a result of an exposure under com-
parable conditions, but motile organisms may
sometimes avoid toxic conditions when possi-
ble. Toxicity to benthic organisms may be de-
pendent on sorption of toxicant by the sub-
strate. Temperature, pH, alkalinity, hardness,
salinity, and other water quality characteristics
may affect toxicity. Adverse effects other than
those obtained in acute tests, such as flavor
impairment and reduction in growth or repro-
duction, may occur at lower concentrations of
the toxicant. Acute toxicity tests may provide
a basis for a decision concerning the need for
additional tests in a hazard evaluation program.

5. Terminology

5.1 Acute toxicity tests are generally used to
determine the concentration of toxicant that
produces a specific adverse effect on a specified
percentage of test organisms in a short period
of time. Because death is normally an easily
detected and obviously important adverse ef-
fect, the most common acute toxicity test is the
acute lethality test. Experimentally, effect on
50 % of a group of test organisms is the most
reproducible and easily determined measure of
toxicity, and 96 h is often a convenient, useful
exposure duration. Therefore, the measure of
acute toxicity most often used with fishes,
macroinvertebrates, and amphibians is the 96-
h LC50, which is the statistically derived best
estimate of the concentration of toxicant lethal
to 50 % of the test organisms during a 96-h
exposure. The measure of acute toxicity most
often used with daphnids and midge larvae is
the 48-h EC50 (median effective concentration)
based on immobilization. The terms LC50 and
EC50 are consistent with the widely used toxi-
cological terms LD50 (median lethal dose) and
ED50 (median effective dose), respectively.

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The terms LC50 and EC50 should be used
whenever results are calculated based on the
concentration of toxicant in dilution water,
whereas the terms LD50 and ED50 should be
used whenever results are calculated based on
the quantity of toxicant that enters or is applied
directly to test organisms. For toxic agents or
tests for which neither concentration nor dose
are appropriate, such as tests with temperature,
the terms LL50 (median lethal level) and EL50
(median effective level) should be used.
5.2 Acute toxicity tests in which test orga-
nisms are exposed to test solutions containing
a toxicant can be conducted by at least four
techniques:
5.2.1 In the static 'technique, test solutions
and organisms are placed in chambers and kept
there for the duration of the test.
5.2.2 The recirculation technique is like the
static technique except that each test solution
is continuously circulated through an apparatus
designed to maintain water quality, and possi-
bly remove degraded, but not undegraded, tox-
icant by such means as flltration, aeration, and
sterilization and then returned to the test cham-
ber.
5.2.3 The renewal technique is like the static
technique except that test organisms are period-
ically exposed to fresh test solution of the same
composition, usually once every 24 h, either by
transferring the organisms from one test cham-
ber to another or by replacing test solution.
5.2.4 In the flow-through technique, test so-
lution flows through the test chamber on a
once-through basis throughout the test. Two
procedures can be used. In the first a large
volume of test solution is prepared before the
beginning of the test, and this solution flows
through the chamber. In the second and more
common procedure, fresh test solution is pre-
pared continuously or every few minutes just
before it enters the test chamber. In both pro-
cedures a metering system controls the flow of
test solution, and in the latter procedure the
metering system also controls the preparation
of test solution.
5.2.5 With any of these techniques a pump
or stirrer can be used to create a current in the
test chamber to accommodate particular spe-
cies, but this will often increase aeration and
volatilization.
5.3 In flow-through tests a "volume addi-
tion" is the placement into the test chamber of

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