Determination of Biodegradability Using
Warburg Respirometric Techniques
J. V. HUNTER, Associate Professor,
H. HEUKELEKIAN, Professor and Chairman,
Department of Environmental Science,
Rutgers, The State University
New Brunswick, New Jersey
INTRODUCTION
The accumulation in the environment of many of the new organic materials
synthesized by man can be prevented by natural forces only through chemical,
photochemical, and biological or biochemical degradation. Although all these
share in the reduction of this pollutional burden, biological degradation is without
doubt the primary means by which most of this reduction occurs. There are many
biological agents through which these transformations can occur, including the
higher plants (1), but most attention has been paid to the microbial degradation of
these materials. This is due not only to their numbers and ubiquity in the land
and water environment, but also to their well established role in waste water
treatment. Unfortunately, many of these new and economically important compounds are partially or wholly resistant to microbial attack. This resistance has
caused considerable interest to be centered upon the concept of biological de-
gradability or biodegradability.
In essence, all that is implied by this term is the "ability" of a compound to
be oxidized by living organisms (micro-organisms) with the production of cell
matter, energy, and waste products. In actuality, the meaning of this term is not
quite so clear. This is due to the difficulties inherent in the definition itself and
in the methods used in its determination. As in any chemical reaction, two concepts are encountered -- rate and extent. The rate aspects of biodegradability
are most obvious in batch systems, in which a property is usually measured as a
function of time elapsed, but it is also inherent in continuous systems, in which a
certain contact time is specified. There is little about the rate aspects of the
definition to cause any confusion.
The extent to which a compound must be degraded before it may be considered "biodegradable" is a more complex concept. Few people would regard a
compound that undergoes only slight degradation as biodegradable. An intermediate position is occupied by the concept of "activity" loss (2). This means that
if the specific activity that renders the compound objectionable is lost through
microbial degradation, the compound would be considered biodegradable. This
would mean, for example, the loss of surfactant properties for ABS, herbicidial
properties for 2,4-D, pesticidial properties for DDT, taste and odor for chloro-
phenols, etc. Much of the work done in this and other fields has involved this
concept. A more severe criterion would demand the essentially complete conversion of the organic compound to cell matter, energy, C02- H2O minerals, etc.
(3). As the problem of the organic pollution of the environment will become more
acute with time, and as water quality criteria already have standards regarding
specific and general organic contaminants, this more severe standard forbiode-
gradability may achieve increasing recognition.
In addition to the complexities of defining biodegradability, there are further
complications arising from the methods and systems employed in its  actual
- 616 -