United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
vvEPA
Research and Development
EPA-600/S2-81-175/1 76 Oct 1981
Project Summary
Literature Study of the
Biodegradability of
Chemicals* in Water:
Volumes 1 and 2
John Geatmg
This project was initiated to compile
and review post-1974 literature refer-
ences on aqueous biodegradability of
chemicals to update a previous EPA
report.* Additionally, literature back
to 1913 was searched for inhibitory
effects of specific chemicals on
wastewater treatment processes.
Results are presented as an in-depth
hierarchical index and bibliography of
600 references. The index is searchable
at three levels: (1) chemical name or
chemical class. (2) name of micro-
organism or type of microbial popula-
tion affecting or being affected by the
chemical, and (3) wastewater treat-
ment process.
Also presented in the two-volume
project report are the results of a
successful feasibility study for predicting
biodegradabiiity solely from positive
or negative values assigned to standard
molecular substructural units of a
chemical compound. The predictability
accuracy was 93% for known bio-
degraable compounds and 68% for
nonbiodegradable compounds.
Brief abstracts of recent advances in
wastewater treatment technology
plus a guide to current Japanese and
West German commercial literature in
the field are included as a separate
section in the report.
Appendix F of Volume 1 lists 430
specific chemical compounds alphabet-
ically by principal name and synonym
classified from the literature search in
one of three categories: (1) biodegrad-
able, (2) nonbiodegradable, or (3)
nonbiodegradable/qualified.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory, Cincin-
nati. OH, to announce key findings of
the research projects that are fully
documented in separate reports (see
Project Reports ordering information
at back).
•Howard, P H , Saxena, J , Durkm, P R , and Ou, L -
T Review and Evaluation of Available Techniques
for Determining Persistence and Routes of
Degradation of Chemical Substances in the
Environment EPA-560/5-75-006, NTIS No PB
243-825 May 1975
Introduction
A comprehensive search was made of
the world's scientific and technical
literature for articles on applying
methods for studying biodegradability of
chemical substances in water. Also
covered were the effects of treating
chemicals in water by all biological
wastewater treatment processes, in-
cluding both aerobic and anaerobic
processes. After the literature search
and information gathering phase were
completed, the results were organized
into a permutated index by chemical
compounds or classes of compounds,
types of microorganisms involved in
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biodegradation, and by wastewater
treatment process or experimental
technique used. Volume 2 comprises
the complete index with 603 references.
A major aspect of biodegradability of
waste chemical substances in'water is
the potential correlation that may exist
between various structures, functional
groups, or positional relationships
within the structure. The obvious
advantage of foretelling the potential of
any specific compound to degrade (or
not) in a specific wastewater treatment
system without extensive experimenta-
tion is sufficient reason to conduct such
a study. A structure-activity algorithm
for predicting biodegradability was
developed from data in the 603 refer-
ences ( in Volume 2) and from a search
of eight scientific data bases.
Howard et al.'s previous report was
updated by including new or re-clustered
wastewater treatment processes and
equipment. These inclusions came from
searches of published literature reports,
review of manufacturers' advertise-
ments and material on file with the
Water Pollution Control Federation, and
through recommendations resulting
from direct contact with professionals
(e.g., manufacturer's representatives,
consultants, and operating engineers).
In addition, the literature on commercial
wastewater technology from West
Germany and Japan was searched for
relevant contributions (Volume 1).
A table of chemical contaminants
with adverse effects on water treatment
processes (focusing on specific chemical
contaminants found in wastewaters
and reported in earlier publications
(1913 to 1974) to have had negative
impact, i.e., toxicity and/or inhibition,
within municipal or industrial waste-
water treatment systems) is compiled in
Volume 1. The chemicals, their CAS
Registry Number, their effects, and the
literature sources, where given, were
intermeshed alphabetically for ease of
accession by the user (Volume 1).
Structure-Activity Study
(Volume 1)
The purpose of the structure-activity
work was to determine the feasibility of
developing a structure-activity model to
distinguish between biodegradable and
nonbiodegradable chemicals. Similar
models have been developed in the past
for a variety of biological endpoints,
including rat oral LD50, mutagenicity,
carcinogenicity, and teratogenicity.
The data were originally intended to
be presented for substructural analysis
as a list of compounds designated
degradable and a list designated non-
degradable. Unfortunately, the literature
in this field is not presented in such a
manner as to allow such clear-cut
interpretations of results, so a third list
of compounds, designated nondegrad-
able/qualified, was created. When
more reliable data were received, their
entries were transferred to the other
two lists. The remaining entries on this
third list were not used in constructing
the predictability algorithm. The largest
number of compounds from the literature
survey were found to be biodegradable.
For this reason, a subset of these
compounds was selected at random and
used in the structure-activity models.
Three types of parameters were
considered in the biodegradability
models: (1) molecular weight, (2)
octanol-water partition coefficient (log
p), and (3) Wiswesser line Notation
(WLN)-based substructural keys. Mo-
lecular weight is, of course, self-
evident. The partition coefficient was to
be used initially, but was not used in the
finally developed models because of the
great difficulty in obtaining accurate
numbers for a sufficient number of
compounds before completion of the
project. The 336 WLN-based keys are
based on a major modification of the
CROSSBOW program and are fully
described in Appendix B of Volume 1.
The statistical methodology used in
developing these models consisted of
stepwise discriminant analysis and
ridge regression procedures. An initial
discriminant equation was prepared
contrasting the biodegradable com-
pounds with the nonbiodegradable
chemicals. After multiple applications
of the statistical operations, those
substructural keys having the greatest
influence on biodegradability were
identified, those with least influence
were eliminated, and a final discriminant
analysis was performed. The final result
is a table of classification functions with
two values (a degradability function and
a nondegradability function) listed for
molecular weight and for each sub-
structural key. These functions are used
in the Probability Equation as described
in Figure 1 to predict the probability that
a compound is biodegradable.
The performance of the structure-
activity model on compounds of known
biodegradability is shown in Table 1. Of
292 degradable compounds, 270 or
92.5% were correctly classified whereas
39 of 57 (68.4%) nondegradable com-
pounds were correctly classified. A total
of 25 compounds could not be classified
by the model.
A serious limitation on general use of
the model is that classification functions
could be derived for only 39 substruc-
tural keys from data available in the
literature. Additionally, six keys were
found to have no significant influence
on biodegradability and six others had
such a variable influence that their
presence would not permit use of the
model.
Permutated Index
(Volume 2)
The in-depth hierarchical index and
accompanying compilation of biblio-
graphic citations were created to
provide the sanitary engineer, environ-
mental chemist, and microbiologist with
a concise and readily accessible source
of information on the biodegradation of
chemicals associated with wastewater
treatment plants.
The online retrieval of pertinent world
literature covers the period from 1974
to 1979 as well as articles published
during 1970 to 1973 that did not appeal
m Howard et al.'s previously published^
EPA study. Foreign language articles
are included to emphasize the worldwide
interest of this increasing environ-
mental problem.
The first level of the permutated index
is a listing of chemical names or
chemical classes. The final choice of
chemical names represents a third-
generation compromise involving utility
to professionals of widely diversified
chemical background; industrial
importance; an awareness of the
relative insensitivity of the biodegrad-
ability of closely related homologues to
the presence of nontoxic substituents;
and, finally, the traditional mechanics of
permutated index creation. Extensive
cross-indexing is included to assist the
investigator to locate readily the probable
sourcejs) of desired information.
The second level of the index consists
of the microbial populations responsible
for the biodegradation of the chemical
substances. Major classes of these
microbial populations, created to facil-
itate designation of the system with the
major role in the biodegradation process,
are as follows: activated sludge; micro-
bial population, mixed; microbial pop-
ulations as pure cultures; and microbial
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Compound: 2,4-Dmitrophenol
Substructural Keys.
Constant
Molecular weight
K3, Branching terminal nitro group - NO?
K65, One - OH group
K97, Aromatic 6-membered ring
K137, 1 benzene ring
Key
Degradable
Nondegradable
Constant
Molecular wt
K3
K65
K97
K137
-6340
0.023
0111
3 173
4.259
1.767
-9.758
0028
3.306
0.143
6614
-2.172
Step 1. Sum values for each key from degradable column
constant + molecular wt. + K3 + K65 + K97 + K137 -6.340 + 0.023 +
0 111 + 3.173 + 4.259 + 1.767 = 2.993
Step 2. Sum values for each key from nondegradable column
-9.758 + 0.028 + 3.306 + 0.143 + 6.614 + (-) 2 172 = -1.839
Step 3. Insert values from Steps 1 and 2 in the Probability Equation
P = exp (Step 1)/[exp (Step 1) + exp (Step 2)]
P = exp 2 993/[exp 2 993 + exp (-) 1.839]
Step 4. By inspect/on, the denominator is only slightly larger than the numerator,
indicating that P >0.9, i e., a high probability of biodegradation. In some
cases the inspection method of handling Step 3 will not work and the
exponential terms will have to be calculated. Probability values range
from 0 to 1, thee larger the number, the greater the probability of biodegra-
dation.
Figure 1. Example of calculation of probability of biodegradation
Table 1. Degradable Versus Nondegradable Classification Matrix Classified by
Discriminant Equation Evaluation
Actual
Classification
from Reference Literature
Degradable
Nondegradable
Degradable
(P > 0. 7)
N
270
9
%
92.5
15.8
Intermediate
(P = (0.3-0.6991)
N
16
9
%
5.5
15.8
Nondegradable
(P
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John Geating is with Franklin Research Center, Philadelphia, PA 19103.
Sidney A, Hannah is the EPA Project Officer (see below).
The complete reports, entitled "Literature Study of the Biodegradability of
Chemicals in Water":
Volume 1. Biodegradability Prediction, Advances in and Chemical Interfer-
ences with Wastewater Treatment (Order No. PB 82-100 843; Cost: $18.50,
subject to change)
Volume 2. Permutated Index of Chemicals, Microbial Populations, and
Wastewater Treatment Systems with Bibliography (Order No. PB 82-100850;
Cost: $14.00, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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