A COMPARISON OF ACUTE TOXICITY EVALUATIONS AND EPA
WATER QUALITY CRITERIA WITH MACROINVERTEBRATE
COMMUNITY ANALYSES AT SITES OF ELECTROFINISHING
DISCHARGES TO STREAMS
Gerald M. Szal, Aquatic Biologist
Technical Services Branch
Massachusetts Division of Water Pollution Control
Westborough, Massachusetts 01581
BACKGROUND
In 1972 federal authorization for the use of aquatic toxicity tests in evaluating wastewater discharges was firmly established in the Clean Water Act (PL 92-500). Since that time the use of these
tests in federal and state water pollution assessment programs has been on the rise. They are an
important component of the National Pollutant Discharge Elimination System (NPDES) permit process in many parts of the country and are also being used in a variety of other capacities including
the assessment of freshwater and marine dredge spoils, and leachates from industrial waste sites.
Standard methods for certain of these tests were published by the U.S. Environmental Protection
Agency (EPA) in 1978 [1], and a revised and expanded edition of this text is expected for release
later in 1985.
Toxicity tests assess the potential of a substance to adversely affect the life process. There are
two basic types of tests: chronic and acute. Chronic tests are long term assays which usually encompass at least one life cycle of the organisms tested. An array of sublethal effects such as decrease in
fecundity, reduction in growth rates, or increase in tumor formation can be evaluated by such tests.
Acute tests are short term tests. They are usually conducted over only a portion of the life cycle
of the test organism. When the measured effect is mortality, results are often expressed as the toxicant
concentration level to 50% of the organisms tested (i.e., the LC,n)- Effects other than mortality, such
as the change in rate of certain physiological processes, may be reported as the percent toxicant
causing a fifty percent reduction in the measured effect (i.e., the EC,,,).
Toxicant concentrations inducing chronic alterations may be orders of magnitude lower than those
causing acute effects. For this reason, when acute tests are used to set effluent limits for a particular
discharge, LCws derived from these tests are usually divided by an "application factor" of from 2
to 1000 to protect organisms from chronic effects. Although chronic tests provide a more precise
estimate of "safe" instream levels of toxicants than acute tests, the latter are much less expensive
and still provide the analyst with information not accessible by other methods. As a result, many
state and federal regulatory agencies find the acute test more suitable than chronic tests for routine
monitoring of effluent discharges.
Two alternatives to toxicity tests commonly employed in effluent evaluations are chemical analysis
and aquatic community studies. The first is a comparison of known toxic components of effluents
to established criteria values. This method has the following shortcomings when compared with the
live organism approach: 1) there is a lack of criteria for all but the most common toxicants; 2)
synergistic and/or antagonistic interactions of components in a complex waste cannot be accounted
for; 3) site specifics of receiving waters (e.g., hardness, pH) cannot be incorporated into most chemical evaluations; and 4) the chemical approach relies on the previous identification of toxic components of a waste.
The second alternative, the instream community study, takes a completely different tack to effluent assessments than toxicity testing or chemical evaluations. While the latter are predictive and
speculative with regard to impact, the former establishes the severity of impact and describes its form.
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