Biological field and laboratory methods for measuring the quality of ...

1.0 GENERAL CONSIDERATIONS
The term BIOASSAY includes any test in
which organisms are used to detect or measure
the presence or effect of one or more substances
or conditions. The organism responses measured
in these tests include: mortality, growth rate,
standing crop (biomass), reproduction, stimulation
or inhibition of metabolic or enzyme
systems, changes in behavior, histopathology,
and flesh tainting (in shellfish and fish). The
ultimate purpose of bioassays is to predict the
response of native populations of aquatic organisms
to specific changes within the natural
environment. Whenever possible, therefore, tests
should be carried out with species that are native
(indigenous) to the receiving water used as the
diluent for the biJassay. Bioassays are important
because in most cases the success of a water
pollution control program must be judged in
terms of the effects of water quality on the condition
of the indigenous communities of aquatic
organisms. Also, in many cases, bioassays are
more sensitive than chemical analyses.
Two general kinds of bioassays are recognized:
• laboratory tests conducted to determine the
effects of a substance on a species; more or
less arbitrary conditions are employed;
• in situ tests conducted to determine the
effects of a specific natural environment;
the test organisms are held in "containers"
through which the water circulates freely.
The general principles and methods of conducting
laboratory bioassays presented in
Standard Methods for the Examination of Water
and Waste Water, 13th edition (APHA, 1971)
apply to most bioassays, and the described
methods can be used with many types of aquatic
organisms with only slight modification.
The following are suggested improvements to
the methods given in Standard Methods, 13 th
edition (APHA, 1971).
BIOASSAY
• The 48- and 96-hour LC50 values are
presently important for determining compliance
with water quality standards as
established by various pollution control
authorities. Short-term threshold information
can be derived by reporting LC50
values at 24-hour intervals to demonstrate
the shape of the toxicity curve.
• Reports of LC50's should state the method
of calculation used and the statistical confidence
limits when possible.
• Rubber or plastic materials should be used
in bioassay equipment only after consideration
has been given to the possibility of
the leaching of substances such as plasticizers
or sorption of toxicants.
• Test materials should be administered in
such a way that their physical and chemical
behavior approximates that in natural
systems.
Biological tests can be conducted in any kind
of water with proper precautions, and although
most tests have been conducted in freshwater,
the same general principles apply to brackish
and salt waters. The literature contains a great
many formulations for artificial seawater. Of
these, a modification of the Kester et ai. (1967)
formulation (LaRoche et aI., 1970; Zaroogian et
aI., 1969) seems to support the greatest variety
of marine organisms. When metal-containing
wastes are to be bioassayed, omitting EDTA and
controlling trace metals, as described by Davey
et ai. (1970), is recommended.
Using a standard toxicant and a parallel series
in a standard medium is recommended to help
assess variations due to experimental technique
and the condition of the organisms. Such tests
are also useful in distinguishing effects due to an
altered character of the effluent from changes
in the sensitivity of the organism, or from
changes in the quality of the receiving water.