28 TOXICITY EVALUATION OF PERSISTENT ORGANIC
CONTAMINANTS
James R. Hartman, Graduate Student
Clifford R. Lange, Graduate Student
Mark R. Matsumoto, Assistant Professor
A. Scott Weber, Assistant Professor
Department of Civil Engineering
State University of New York at Buffalo
Buffalo, New York 14260
INTRODUCTION
Since the end of World War II, the development rate of new xenobiotic chemicals has increased
rapidly. The United States Environmental Protection Agency's (EPA) chemical inventory list contains
more than 62,000 industrial substances excluding foods, drugs, cosmetics, and pesticides.1
A large number of xenobiotic chemicals are resistant to biological degradation, or are degraded at
very low rates. This resistance to biodegradation is termed persistence. Persistence of xenobiotics can
be attributed to: 1) the inhibitory nature of the chemical substance to the microorganisms; and/or
2) the microorganisms' lack of necessary enzymatic pathways necessary for the breakdown of specific
compound(s).
Many of the existing procedures for assessing the biodegradability (persistence) of xenobiotics rely
upon assessing the performance of bench-scale biological reactors which have specific wastes or
chemicals as a part of their influent. However, such investigations are useful only in determining the
effect of specific wastes or compounds on treatment performance. Thus, while pilot testing has an
important function, the factors which cause persistence cannot be established.
Establishing the cause of persistence is an important step in determining how to deal with a
compound which resists biodegradation. For example, when the enzymatic pathways required for
degradation are lacking, the course of action may be to induce the enzymes via acclimation. Alternately, the addition of bacteria which possess the desired pathways, a process termed bioaugmentation, may also be used as a means of overcoming enzymatic deficiencies.
However, if persistence is due to inhibition or toxicity, dilution or selective removal of these
compounds to levels which are less inhibitory may be required before biological treatment. In cases of
extreme inhibition, biological treatment may be impossible, and removal must be accomplished by
physical and/or chemical means.
Clearly, what is needed to design effective systems for the biological treatment of xenobiotics is a
methodology which can be used to determine the degree and cause of persistence. However, differentiation between persistence due to inhibition and enzyme deficiency is difficult and use of a single
experimental test can lead to erroneous conclusions.
The primary objective of the study described in this paper was to examine various, easily performed
tests that could be used for assessing persistence of xenobiotic chemicals and determine the relative
merits of each test. The ultimate goal of this research is to develop an approach for assessing the
degree and cause of persistence associated with xenobiotic biodegradation and thereby determine
operating conditions which are favorable for biological treatment of specific wastes and compounds.
EXPERIMENTAL METHODS
A series of experimental studies were performed using selected synthetic chemicals known to be
inhibitory and persistent. Testing was separated into three categories: 1) methods testing persistence;
2) methods testing acute toxicity; and 3) methods measuring metabolic activity as an indication of the
combined effect of acute toxicity and/or enzyme deficiency persistence.
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