EPA 904-R-97-003
THE ANAEROBIC DEGRADATION
OF SELECTED
CHLORINATED HYDROCARBON PESTICIDES
by
David W. Hill and Perry L. McCarty
9/27/1966
reprinted by:
U. S. Environmental Protection Agency
Region 4, Water Division,'Wetlands Section
61 Forsyth Street, S. W.
Atlanta, Georgia, U. S. A. 30303-3415
(404) 562-9900 voice
(404) 562-8339 TTY/TDD
(800) 241-1754 voice
WEB site: http://www.epa.gov/docs/Region4Wet/wetlands.html
e-mail: burnett.thomasSepamail.epa.gov
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THE ANAEROBIC DEGRADATION OF SELECTED
CHLORINATED HYDROCARBON PESTICIDES
by
David W. Hill* and Perry L. McCarty
Respectively, Doctoral Candidate and Associate Professor
of Sanitary Engineering
Department of Civil Engineering
Stanford University
Stanford, California
*Now a Research Sanitary Engineer with the Federal Water Pollution
Control Administration, Southeast Water Laboratory, Athens, Georgia.
Presented on September 27, 1966 at the Water'Pollution Control Federation
Meeting, Kansas City, Kansas.
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THE ANAEROBIC DEGRADATION OF SELECTED CHLORINATED
HYDROCARBON PESTICIDES
'by David W. Hill and Perry L. McCarty
The persistence of many of the modern organic pesticides in the
environment has led to a great deal of concern over their possible harm-
ful effects upon both wildlife and human beings. The most persistent of
the organic pesticides are the chlorinated hydrocarbon insecticides and
certain associated epoxides, commonly referred to as a group simply as the
chlorinated hydrocarbons. Residues of these pesticides have been measured
in soils more than a decade after application and traces have been found
in almost all major U. S. rivers as well as in fish in the open sea.
Chlorinated hydrocarbon residues in natural waters are of particular
concern because of their great toxicity to many aquatic organisms, because
of their possible adverse effect on man through his drinking water sup-
plies, and because of their tendency to concentrate in living matter which
sometimes results in the death of higher species such as fish and birds.
The extremely hydrophobic nature of most of the chlorinated hydrocarbons
allows them to concentrate on particulate matter which may settle to form
the bottom muds of streams and lakes. There, the pesticides may poison
bottom feeding species, they may be churned up and carried along with sedi-
ment during periods of turbulent flow, or they may be desorbed to maintain
a continuous feed of pesticides to the overlying water.
It is important in estimating the quantities of pesticides trans-
ported by a river, or in estimating the build-up of pesticides in a
reservoir, lake, or bay, to have some indication of rates of degradation
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or of rates of conversion to other forms. Most transport studies conducted
to date have assumed indefinite persistence of all measurable pesticides
from which it could only be concluded that there was a continuing increase
in the level of pesticide residues, while it may actually be that pesticides
slowly degrade so that an equilibrium state is eventually reached.
The assumption has frequently been made in the past that if a substance
is very resistant to aerobic degradation, then it will probably not degrade
at all under anaerobic conditions. This assumption has been applied to the
persistence of chlorinated hydrocarbons in the water environment; yet the
results of this study have shown that many of these pesticides degrade more
quickly under biologically active anaerobic conditions than under correspond-
ing aerobic conditions.
The term "degradation" is used here in a broad sense to refer to any
measurable chemical change in a pesticide under natural environmental con-
ditions. This degradation may be "complete degradation" to inorganic end
products or "partial degradation" to other organic products. With this def-
inition it can be stated that chlorinated hydrocarbons degrade without in-
ferring that they are converted completely to inorganic end products.
PESTICIDES STUDIED
The structures of the eight pesticides studied in this investigation
are shown in Figure 1. DDT and DDD are indicated by schematic structures;
while the remaining pesticides are illustrated by three-dimensional draw-
ings as their schematic structures do not differentiate between possible
isomers.
Consumption of these pesticides represents more than 60% of the total
U. S. consumption of chlorinated hydrocarbon compounds. In chemical
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structure they represent a range of different types of chlorinated
hydrocarbons. DDT and ODD represent chlorinated diphenyl compounds with
the basic "DDT carbon skeleton"; lindane represents the benzene hexachloride
isomers; aldrin and heptachlor are unsaturated cyclodienes; and heptachlor
epoxide, dieldrin, and endrin are epoxidized cyclodienes. Contrasting
studies of anaerobic versus aerobic degradation were restricted to DDT,
lindane, aldrin, and heptachlor epoxide to obtain a representative of each
structure, which was well separated from the others on a gas chromatogram.
PREVIOUS STUDIES
The persistence of various chlorinated hydrocarbons in different parts
of the environment has been extensively documented. Soil pesticide residuals
have received the greatest study, and Wheatley (33) lists half lives ranging
from 25-40 years for DDT down to 15-20 weeks for lindane.
Pesticide residues in water have been receiving increasing attention in
recent years, and measurable concentrations of chlorinated hydrocarbons have
been found in almost all the major U. S. rivers (31). Ordinary background
levels of dieldrin, endrin, DDT, DDE, heptachlor, aldrin, DDD and BHC (in
order of frequency of occurrence) were found in the parts-per-trillion range
in water (1 ppt to 1 ppb) (9, 13, 31) ; and a Mississippi River study showed
that many pesticide residues in bottom muds were found at concentrations
greater than 0.1 ppm (5).
The persistence of chlorinated hydrocarbon pesticides in the aquatic en-
vironment is documented mainly in reports of field studies made following in-
dividual applications of pesticides. Residues of DDT generally disappear
fairly rapidly from water only to reappear in greater concentrations in sedi-
ments, vegetation, and aquatic fauna in which they are much more persistent
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(7, 11, 12). Perhaps the classic example is the persistence of more than 1000
ppm of DDD in fish and birds at Clear Lake, California, more than a year fol-
lowing a parts-per-billion application to the lake water (18). A total of
0.05 ppm application of toxaphene to Clayton Lake, New Mexico, persisted in
the water at a level of 0.001 ppm for more than one and one-half years (19).
EXPERIMENTAL PROCEDURE
The conditions that received the greatest amount of study in this inves-
tigation were active anaerobic conditions that were idealized or made very
favorable for degradation. Here, pesticides were mixed continuously at 35°C
with thick, biologically active anaerobic digested sewage sludge obtained
from the Menlo Park Sewage Treatment Plant. This environment was chosen to
obtain a clear indication of degradation which would probably occur only
slowly in less favorable, natural environments.
It must be stressed that the anaerobic conditions used in this study
were ideal in the sense that an active culture of anaerobic methane producing
and sulfate reducing bacteria were present. It is not implied that these
particular microorganisms were necessarily involved in the degradation which
occurred, but only that their presence in an active state is a useful indi-
cator of the conditions under discussion. Significant anaerobic pesticide
degradation would probably not occur under conditions which would not be con-
ductive to the growth of these particular organisms because under such condi-
tions many less resistant materials such as fatty acids are not biologically
destroyed.
Most of the apparatus was designed with variable volume gas reservoirs
as shown in Figure 2. Closed systems were used to minimize pesticide
losses by codistillation with water, and the variable volume gas reservoir
was essential to avoid excessive pressures in thick-sludge anaerobic units
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in Which gas production occurred. Sampling was facilitated with this
design because application of pressure to the acid-salt confining fluid
would force sludge out the withdrawal tube.
Pesticide analysis was performed by gas chromatography following
organic solvent extraction and clean-up procedures. Samples for analysis
were centrifuged and a separate determination was made for pesticides in
the supernatant liquor and that sorbed to the suspended solids.
The preferred extraction procedure from water or from centrifuged
supernatant liquor was to place a small volume of hexane (generally 10 ml)
in a separatory funnel on top of the liquid to be extracted (generally
about 80 ml). The contents were shaken gently on a horizontal shaker for
one hour with the separatory funnel on its side; the water layer was re-
moved and discarded; the volume of hexane was measured; and an aliquot was
injected directly into a gas chromatograph. (An electron capture gas
chromatograph was the most suitable for this procedure as no further pesti-
cide concentration step was required).
The extraction preferred for centrifuged suspended solids was largely
a modification of a procedure designed for pesticide extraction from dairy
products reported by Langlois, Stemp, and Liska (23). The centrifuged
solids were scraped into a large mortar and ground uniformly into about 25
grams of Florisil. The 60-100 mesh Florisil, obtained from the Floridin
Company, Tallahassee, Florida, was previously activated at 600°C for three
hours, cooled, mixed thoroughly with 5% water, and stored in an airtight
container for at least 48 hours prior to use. Five hundred milliliters of
20% methylene chloride in petroleum ether was mixed in successive increments
with the mixture of ground solids and Florisil and then was decanted into
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the top of a liquid chromatographic column packed with four inches of
Florisil. The solvent was eluted through the column into a Kuderna-
Danish evaporator and evaporated to about 5 ml. The walls and joints of
the evaporator were then rinsed and the solvent was concentrated further
by evaporation through a micro-Snyder column. Evaporation was continued
to dryness to remove all the methylene chloride using a gentle stream of air
directed into the ampule after placement in a flask of hot water to prevent
condensation. Finally, the residue was redissolved in 2 ml of hexane, and
an aliquot was suitably diluted and injected into a gas chromatbgraph.
All solvents were redistilled prior to use, and all glassware was care-
fully washed and. given a final rinse with acetone. Teflon stopcocks were
soaked in acetone while not in use to help minimize contamination from pesti-
cides which strongly adsorbed on Teflon. Pesticide extraction efficiency
with both preferred methods was approximately 100%.
The gas chromatographs used during the course of this investigation
were a tnicrocoulometric gas chrotnatograph of the type manufactured by
Dohrmann Instruments Company and an electron capture Hy-Fi Gas Chromatograph
manufactured by Wilkens Instrument and Research, Inc. (now Varian Aerograph).
These instruments are described adequately in the literature.
Other analyses were performed using techniques essentially as described
in the llth Edition of Standard Methods (30).
EXPERIMENTAL RESULTS
o
Degradation in Thick Anaerobic Sludge at 35 C
o
Experiments with thick anaerobic digested sewage sludge at 35 C formed
the major portion of this investigation as it was with this material that
degradation was the most pronounced.
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All concentrations of pesticide products are reported as equivalent
concentrations of the parent pesticide. Calculations were made by comparing
peak areas generated by the pesticide products with those generated by the
parent pesticide injected as a standard. The one exception was DDD formed
from DDT which is reported as DDD as determined from DDD standards. The pH
of the sludge varied from one experiment to another but it remained generally
in the range of 7 to 8. All pesticides were dissolved in acetone prior to
injection in the units. The sludge for the first two studies with lindane
was diluted 1:1 with deaerated tap water to produce an average total dry
solids concentration of 1.5% of which an average of 56% was volatile solids.
The sludge was seived and placed under nitrogen in the apparatus described
previously. Units were agitated on horizontal shakers because the sludge
was too thick to stir with magnetic stirring bars.
In the first study two units were dosed with one and ten ppm lindane,
respectively; and a third unit was maintained as a control. [Throughout
this discussion pesticide concentrations expressed as parts per million (ppm)
refer to micrograms of pesticide per milliliter of sample and parts per
billion (ppb) refer to micrograms of pesticide per liter of sample!] The
results of this experiment, indicated in Figure 3, show an immediate and
sharp decrease in the total concentration of lindane in both units.
The second study was performed to determine if this rapid anaerobic
degradation of lindane was a biological or a chemical phenomenon. Four
units were prepared of which two were heavily poisoned with a total of 4 gm/1
of cobaltous and mercuric salts. One active and one poisoned unit were dosed
with 10 ppm lindane each, and the other two units were maintained as controls.
The results of this experiment shown in Figure 4 indicate a very significant
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difference between the rates of degradation in these two units. The half
life of lindane in the active unit was in the order of 1 day while that in
the poisoned unit was approximately 170 days*
The third study was designed to measure the degradation of other
chlorinated hydrocarbon pesticides in thick biologically active anaerobic
sludge at 35°C. Total solids averaged 4% by weight of sludge and volatile
solids averaged 48% of the total solids. Each pesticide was dissolved in
350 jul of acetone and injected into a separate one-gallon bottle containing
3500 ml of undiluted, seived, digested sewage sludge under nitrogen; giving
a 1 ppm concentration of pesticide in each bottle which was connected to a
gas reservoir as shown in Figure 2. These units were also agitated on hori-
zontal shakers.
The results of this study are shown in Figure 5. DDT was converted
almost immediately to DDD, which was identified by its characteristic re-
tention time on two types of chromatographic columns; and the DDD was de-
graded gradually but steadily with a half life of less than one week. Aldrin
was degraded at approximately the same rate as DDD. Heptachlor was converted
to an unidentified early elution product whose retention time on a Dow-
Corning 200 Silicone Oil chromatographic column was three-quarters that of
heptachlor. This product persisted for at least 42 days but was degraded
completely within 266 days.
The fourth study with thick anaerobic sludge was conducted to measure
the degradation of large doses of pesticides added in combinations to units
containing sludge of different characteristics. Two combinations of pesti-
cides were each added to a Thick Sludge unit (7.2% total solids) and to
three units (4% total solids) used previously in the third study. Of these
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three units one was lightly poisoned with one-half gram per liter of
mercurous chloride as mercury, and two were left unchanged (Active I and
Active II). The first combination of pesticides used was lindane, aldrin,
heptachlor epoxide, and DDT in concentrations of 40, 40, 100, and 100 ppm,
respectively; and the second combination was heptachlor, dieldrin, and
endrin; 10, 30, and 150 ppm, respectively. These concentrations were
chosen to give approximately the same peak heights on the gas chromato-
graphic chart.
The results of this study are shown in Figures 6 and 7. Lindane de-
graded very rapidly in all units and was the only pesticide to show a sig-
nificantly greater persistence in the lightly poisoned unit than in the
active units. Other differences between the units were largely masked by
the variability of the results. However, slightly faster degradation rates
were suggested for lindane and aldrin in the Thick Sludge unit than in
other units. DDT and heptachlor were observed only in samples taken
initially, 20 minutes after injection of the pesticides. All later analyses
of samples for these compounds showed only DDD and "heptachlor early elution,"
respectively, to be present. Several degradation products of endrin were
observed. The first and most clearly defined product had a relative reten-
tion time of about 2.34 on a Dow-11 column; three other less distinct
products were formed later with relative retention times ranging from 2.12
to 5.55 on a Dow-11 column. These products were not formed from heptachlor
or dieldrin, the other pesticides added in the mixture, because the products
were observed in greater concentrations than the total added heptachlor
and because dieldrin persisted in almost its initially injected concentration.
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Degradation gollowing Daily Pesticide Injections into Dilute Sludges
Daily injections of a pesticide mixture were made into dilute sludges
contained in five-gallon units illustrated in Figure 2. The daily injections
were made to examine variations in pesticide degradation rates which might
be caused fry repeated doses of pesticides; and dilute sludge was used to
allow measurement of pesticide degradation at slower rates than observed
previously in the thick sludge studies at 35°C. With dilute sludge it was
possible to maintain aerobic conditions in some units to allow a comparison
of aerobic and anaerobic rates of pesticide degradation. Degradation products
were again measured as the parent pesticide with the exception of DDD which
was measured as DDD. Lindane, aldrin, heptachlor epoxide, and DDT were
chosen as easily separable and as representative pesticides for these studies,
and were injected daily for 57 days in quantities calculated to give incre-
mental increases of 0.4, 0.4, 1.0, and 1.0 ppm, respectively.
Three units were initially set up for comparison of degradation at
20 C: (1) an aerobic unit containing diluted aerated digested sludge mixed
under oxygen, (2) an anaerobic unit containing diluted digested sludge mixed
under nitrogen, and (3) an autoclaved unit containing a suspension of fine
glass beads, 0.0029 centimeters in diameter, mixed in BOD dilution water
under nitrogen. The 11 grams of beads added to 18 liters of water was the
maximum that could be suspended with a 50 watt magnetic stirrer and had a
total surface area equal to that of the walls of the bottle. The beads
served as an adsorption surface for the pesticides and were removed along
with periodic water samples in order to measure the adsorbed pesticide
concentrations.
The sludge used was digested sewage sludge diluted 19 to 1 with either
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deaerated or oxygenated tap water. The sludge was initially the same for
both the anaerobic and aerobic units, but that for the aerobic unit was
aerated for five days and seeded with one liter of dilute activated
sludge before being transferred to the five-gallon test unit. Alkalinity
was kept low, initially between 300 to 400 tug/1 as CaCO^, and the pH was
kept at approximately 7 by varying the CO content of the confined gas.
The confined gases were changed periodically to maintain a high level of
dissolved oxygen in the aerobic unit and to avoid a large CO, increase in
either sludge unit. Dissolved oxygen in the aerobic unit began at 1 ppm
and rose to 26 ppm by day 118; ORF in the anaerobic unit ranged from -453 mv
to a high of -100 mv. Total suspended solids averaged 0.2570 in both sludge
units and volatile solids were approximately 59% of the suspended solids.
The results of the first study are shown in Figure 8. In the anaerobic
unit DDT converted to DDD within a period of two days; no further DDT was
detected even though daily additions of 1.0 ppm DDT were continued. By day
41 a waxy scum had accumulated in the autoclaved glass bead unit that proved
to be fine glass beads coated with a sufficient quantity of pesticides to
cause them to float. This scum layer continued to grow and was probably
the cause of the apparent decrease in DDT concentration in the autoclaved
glass bead unit between day 57 and 118. The anaerobic degradation of lin-
dane and aldrin was slightly greater than the corresponding aerobic degra-
dation. Lindane appeared to degrade steadily under anaerobic conditions at
an approximate rate of 0.1 ppm per day; a continuation of this rate from day
57 to 118 would have left a residue of 11.3 ppm lindane, which checks fairly
closely with the 10.4 ppm measured. There was no significant degradation of
heptachlor epoxide in any of the units.
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The second study with daily pesticide injections into dilute sludges
was conducted primarily at 35°C. A total of five units were used: three
at 35°C were set up similarly to those in the previous experiment at 20°C;
an additional anaerobic unit at 20°C was set up, also similar to the pre-
vious one except that the sludge was older; and an autoclaved sludge unit
at 35°C was set up the same as the anaerobic units except that it was also
autoclaved for 12 hours and cooled prior to pesticide injection. The 20°C
unit was used as a check on the constancy of the sludge from one experiment
to the next, and the 35°C autoclaved sludge u»iL was added to examine the'
importance of biological activity on anaerobic pesticide degradation. The
measured sludge characteristics were essentially the same as in the previous
experiment.
The results of this study are shown in Figure 9. Conversion of DDT
to DDD was again noted only under anaerobic conditions. The conversion
was almost immediate in the biologically active anaerobic units at both 20°C
and 35°C, and it was peculiarly delayed in the autoclaved anaerobic unit.
Apparently this unit became contaminated and the conversion to DDD began
sometime between day 14 and 41. By day 57 the conversion was complete and
the resultant DDD concentration was approximately one-half that in the active
anaerobic unit at 35°C. Aerobic degradation of DDT was apparent at 35°C,
although it had not been clearly defined previously at 20°C.
Anaerobic lindane degradation appeared to be very temperature sensi-
tive because at 35°C it proceeded at a rate of approximately 0.3 ppm per day
which was contrasted with very little degradation at 20°C in this experiment.
The contrast between these and the previous 20°C results suggest that the
biological activity of the sludge might have decreased during the time inter-
val of 1 1/2 months between the two experiments while the undiluted sludge
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was stored at 20°C.
A slight amount of aldrin degradation was noted in all three
anaerobic units, the active units at 20°C and 35°C and the autoclaved
sludge unit at 35°C. These results suggest that neither temperature nor
biological activity are significant in influencing the rate of anaerobic
aldrin degradation.
No significant degradation of heptachlor epoxide was noted in any of
the units.
Sorption and Desorption £f Pesticides in Water
Sorption and desorption tests were conducted to determine the relative
uptake of pesticides by suspended particulate matter. Strong sorption of
pesticides on particulate matter in streams and subsequent settling in
still water would allow the pesticides to be carried to the bottom where
anaerobic conditions often prevail. Adsorption from phosphate buffered
water onto bentonite clay was explored as an index to adsorption on inor-
ganic particulate matter; and sorption on algae was investigated as these
organisms frequently occur in significant concentrations in lakes and
streams. Algae eventually die and settle to the bottom where they may
decay anaerobically. The importance of the anaerobic degradation of pesti-
cides is thus highlighted when algae are present. The algae were a mixed
culture consisting primarily of Vaucheria. possibly V. sessilis or a similar
filamentous species. The algae were homogenized in a blender before being
dosed with pesticides to facilitate the taking of representative samples.
For comparison, a single test of adsorption and desorption for some of the
pesticides was also made with fine sand (115-250 mesh).
The adsorption isotherms obtained for'the pesticides tested with
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bentonite clay are presented in Figure 10, and detailed sorption data for
all three sorbing media are illustrated for DDT in Figure 11. Sorption
was fairly reversible for all media tested, and the extent of sorption was
in the inverse order of pesticide solubility.
Sorption on algae was approximately one to two orders of magnitude
greater than adsorption from the same water concentration of pesticide on
bentonite, and adsorption on sand was about one order of magnitude less than
on bentonite. The isotherms show that sorption on particulate matter was
significant for all the pesticides tested. For example, a turbid river con-
taining 0.1 ppb DDT in solution and carrying a suspended load of 100 ppm
bentonite clay would be carrying slightly more DDT on the clay than in
solution. Similar relationships can be obtained with these isotherms for
other pesticides.
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DISCUSSION
As a group the chlorinated hydrocarbon pesticides are resistant to
any change. They have been found throughout the environment and are con-
tained even in rain water (34). On the basis of the assumption that per-
sistent compounds do not degrade under anaerobic conditions, they would be
expected to persist indefinitely in anaerobic muds.
Comparison of Anaerobic and Aerobic Degradation of Chlorinated Hydrocarbon
Pesticides
The results of this study show, however, that such a sweeping generality
cannot be applied to the anaerobic environment. All of the chlorinated hydro-
carbons tested showed some degradation under anaerobic conditions; and all
of them, with the exception of dieldrin and heptachlor epoxide, consistently
showed more degradation under anaerobic conditions than under corresponding
aerobic conditions.
DDT showed the most striking qualitative difference between anaerobic
and aerobic degradation. Under anaerobic conditions it converted very
rapidly to DDD, but under aerobic conditions with several mg/1 of dissolved
oxygen DDT remained unchanged as DDT.
The identification of DDD as a degradation product of DDT was supported
by reports in the literature by other investigators who also identified DDD
as a common product of DDT (3, 4, 10, 14, 15, 20, 26, 27). Castro (10)
demonstrated a chemical conversion of DDT to DDD under nitrogen using
ferrous deuteroporphyrin as a reducing cofactor; and Miskus, Blair, and
Casida (26) extended these findings to aqueous systems using hematin and hemo-
globin as reducing porphyrins. In both studies anaerobic conditions were
essential to preserve the reduced state of the porphyrins needed for the re-
action. Miskus, Blair, and Casida .also showed that DDD was the only
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signlficant metabolic product of DDT produced by unsterllized, stagnating
bovine rumen fluid.
On the basis of these studies it appears that the conversion of DDT
to DDD requires a reducing cofactor. If conditions are not sufficiently
aerobic to oxidize all such cofactors, it seems probable that some conver-
sion to DDD may occur even in the presence of a slight amount of dissolved
oxygen. In the study cited above, Miskus, Blair, and Casida demonstrated a
variable amount of this conversion in surface water from Clear Lake,
California; and in preliminary experiments for this investigation the authors
observed a variable amount of the DDT Co DDD conversion in dilute sludges
containing traces of dissolved oxygen.
DDT also degraded aerobically, but in sludges containing several mg/1
of dissolved oxygen the extractable residual remained as DDT in greater con-
centrations than the corresponding anaerobic DDD residuals (all concentrations
measured in ppm of the identified pesticide).
Lindane degraded much more rapidly under anaerobic conditions than
under aerobic conditions at 35°C, but at 20°C this difference was much less
pronounced. Aldrin also degraded more rapidly under anaerobic conditions,
but the differences between anaerobic and aerobic rates were not as great
as for lindane. Heptachlor epoxide showed varying results, most of which
indicated very little degradation under either anaerobic or aerobic con-
ditions; although some anaerobic degradation was noted in thick sludge.
Many extractable degradation products were observed under anaerobic
conditions, but very few were found in the aerobic sludges. This obser-
vation suggests that small changes in pesticide molecules may be more
common under anaerobic conditions.
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Importance of Biological Activity
'It has been fairly well established that none of the chlorinated
hydrocarbon pesticides are used by any organism as a carbon source for
metabolism. Okey and Bogan (28) arrived at this conclusion after a series
of Warburg experiments; and Alexander (1, 2) has justified this conclusion
at some length. However, in this study and in other studies (6, 16, 17,
24, 32), pesticide degradation or change has been found to occur most
readily under conditions of significant biological activity. It seems likely
that tuese changes are enzymatic in nature and related more to detoxification
mechanisms than to metabolism. Radioactive tracer studies with the cyclodiene
insecticides (21, 22, 25, 29) have suggested that the final products formed
by biological processes are frequently water-soluble compounds that are
easily excreted by organisms. It also seems possible that the degradation
noted in microbial sludges may be caused by extracellular enzymes, which
would cause a desorption of the more soluble degradation products.
Of the pesticides studied lindane was by far the most sensitive to
biological activity, as it was also to temperature. Although the anaerobic
conversion of DDT to DDD was rapid, the "delayed reaction" conversion in the
anaerobic, autoclaved sludge suggested that at least a minimum of biological
activity was required for this conversion. Anaerobic aldrin degradation was
also increased by biological activity but only slightly compared to that of
lindane.
Reaction Kinetics
Although this investigation was not a study of the kinetics of pesti-
cide degradation some comments can be made about the rates of degradation
observed.
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It appears that anaerobic lindane degradation was a function -of the
concentrations of lindane and of the sludge. In the thick sludge experi-
ments lindane degradation appeared to follow first order kinetics as it
was proportionally faster for larger concentrations of lindane. In dilute
sludge, however, degradation appeared to proceed at a constant rate, zero
order kinetics, probably because the degrading capacity of the sludge was
saturated. Aerobic lindane degradation was too slight to classify.
The anaerobic conversion of DDT to DDD was too rapid to classify,
but the subsequent degradation of DDD in thick sludge following a 1 ppm
dose of DDT appeared to follow a fairly smooth curve characteristic of
first order kinetics with a half life of about 4 days. Slower degradations
of DDD in both thick and dilute anaerobic sludges following larger doses of
DDT suggested that the degrading capacity of the sludge became exhausted,
possibly because a complexing capacity of the sludge for DDD became satu-
rated or because degrading organisms became poisoned. Aerobic degradation
of DDT in dilute sludge was too variable to classify at 20°C but at 35°C
zero order kinetics were suggested.
The anaerobic degradation ofaldrin in both thick and dilute sludges
suggested first order kinetics. Aerobic degradation of aldrin and degra-
dations of other pesticides were not classified.
Relative Rates of the Anaerobic Degradation £f_ Chlorinated Hydrocarbon
Pesticides
The results of the thick sludge experiments showed that all the
chlorinated hydrocarbon pesticides studied degraded under suitable an-
aerobic conditions. Dieldrin was almost an exception, but it degraded
eventually in the third thick sludge experiment as shown by a final ex-
traction using the methylene chloride technique.
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An approximate ranking of the pesticides studied and their extractable
degradation products according to increasing persistence under anaerobic con-
ditions is: lindane, heptachlor, DDT, ODD, aldrin, endrin, heptachlor
epoxide, and dieldrin. Reservations are made concerning the relative order
of DDT, DDD, aldrin, and endrin because of small variations in relative rates
of degradation from one experiment to another.
Possible Degradations in the Natural Environment
The anaerobic environment can be very biologically active and can
cause significant degradation of the. notoriously persistent chlorinated
hydrocarbon pesticides. This fact must be recognized and evaluated in
making long term predictions of aquatic pesticide residue levels.
Greater degradation of resistant chlorinated hydrocarbon pesticides
should be expected in lakes, streams, reservoirs, or other bodies of water
in which anaerobic bottoms are prevalent than in those that are aerobic
throughout. The amount of degradation would depend on temperature, bio-
logical activity in the anaerobic bottoms, and probably on many other
factors not evaluated here. If anaerobic conditions are widespread such
as in Clear Lake, California, with its bottom of soft black ooze (18),
residues of DDT in particular would be expected to be very small because
of its very rapid anaerobic conversion to DDD.
Studies by other investigators have indicated that virtually no deg-
radation occurs at freezing temperatures. However, when anaerobic muds
in algae ponds or in natural waterways reach temperatures of 20°C or
warmer, a significant amount of degradation can be expected for lindane,
aldrin, DDT, DDD, heptachlor, and possibly endrin. Heptachlor epoxide
and dieldrin would persist longer. The restrictions currently being
-------
-20-
placed on the sale and use of dieldrin would help reduce some of the
problems caused by this most persistent pesticide; and if the presence
of heptachlor epoxide could somehow be limited, a fairly effective an-
aerobic treatment pond could possibly be built to remove the other pesti-
cides.
-------
-21-
qONCLUSIONS
The following conclusions can be drawn from this study:
1. Many chlorinated hydrocarbon pesticides were degraded under
suitable, biologically active, anaerobic conditions.
2. Degradation of most of the chlorinated hydrocarbon pesticides
studied was more rapid under anaerobic than under corresponding aerobic
conditions; exceptions were heptachlor epoxide and probably dieldrin,
which were very persistent in both environments.
3. Extractable degradation products were more common under anaerobic
than under corresponding aerobic conditions.
4. The pesticides studied and their extractable degradation products
can be ranked in the following approximate order of increasing persistence
under anaerobic conditions: lindane, heptachlor, DDT, DDD, aldrin, endrin,
heptachlor epoxide, and dieldrin.
5. The anaerobic degradation of lindane was greatly increased with
increased biological activity and was generally more rapid in anaerobic
than in corresponding aerobic environments.
6. DDT converted very rapidly to DDD under anaerobic conditions,
but under aerobic conditions of several milligrams per liter of dissolved
oxygen it persisted as DDT.
7. Under anaerobic conditions heptachlor converted quickly to extract-
able degradation products which in turn were more persistent than the
initial heptachlor.
8. Endrin also formed extractable degradation products under anaerobic
conditions.
9. The increase of temperature from 20 C to 35°C produced no signifi-
cant increases in pesticide degradation rates except for the anaerobic
-------
-22-
degradation of lindane and the aerobic degradation of DDT.
10. The chlorinated hydrocarbon pesticides were more strongly sorbed
by algae than by bentonite clay.
11. The adsorption of the chlorinated hydrocarbon pesticides was
inversely related to their solubilities.
ACKNOWLEDGMENTS
This investigation was supported by Research Grant WP-715 from the
Federal Water Pollution Control Administration.
The generosity of Dr. Dale M. Coulson of Stanford Research Institute
in granting the use of his instruments, particularly at the beginning of
this study, is gratefully acknowledged.
-------
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-------
13. Dugan, P. R. , Pfister, R. M. , Sprague, M. L. , "Evaluation of the Extent
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-------
26. Miskus, R. P., Blair, D. P., and Casida, J. E., "Conversion of DDT
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in Sea Water," Journal of the Fisheries Research Board of Canada. 18,
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-------
Cl
Cl
Cl- C-CI
I
Cl
DDT
Cl
Cl
I
Cl -C - Cl
I
H
ODD
ALDRIN
LINDANE
H
DIELDRIN
Cl
HEPTACHLOR
Cl
,H
HEPTACHLOR EPOXIDC
FIGURE 1. Structures of Pesticides Studied.
-------
T 7-—OVERFLOW
V J RESERVOIR
GAS VENT
TO LOW
PRESSURE
AIR VALVE
WITHDRAWAL
TUBE
— TEST UNIT
INJECTION PORT
(ON FIVE-GALLON
UNITS ONLY)
MAGNETIC STIRRER
8 SUPPORT BLOCKS
PIEZOMETER TUBE
(PRESSURE INDICATOR)
GAS RESERVOIR
(PRIMARILY N2 OR 02)
TO OTHER UNITS
CONFINING FLUID
RESERVOIR
FIGURE 2. Schematic Diagram of Closed System with Variable Volume
Gas Reservoir Used for Pesticide Degradation Studies.
-------
100
*
I
o
UJ
cr
t 4 • • 10
DAYS AFTER PESTICIDE INJECTION
FIGURE 3. Anaerobic Degradation of Lindane in Sludge at 35 C.
-------
10
Q.
Q.
O
<
2
UJ
tr
2 6
UJ
z
ACTIVE
POIS(
NED
4O 80 120 I6O
DAYS AFTER PESTICIDE INJECTION
200
.0
FIGURE 4 .Anaerobic Degradation of Lindane in Active and Poisoned Sludge at 35 C
-------
I ppm DDT
ADDED
E
a
a. 1.0
1
0 0.8
Z
z
— 0.6
Z (
LJ
Q» O 4
LJ
O
— 0.2
— i
H -
CO
n
i i i r>
1 ppm HEPTACHLOR
ADDED
i
— —
L /— HEPTACHLOR /—"HEPTACHLOR EARLY ELUTION" _
m A A J
.20 40 60 200 300
DAYS AFTER PESTICIDE INJECTION
20 40" 60 " 200 300
DAYS AFTER PESTICIDE INJECTION
ppm ALDRIN
ADDED
20 40 60 200
DAYS AFTER PESTICIDE INJECTION
LEGEND
O MEASURED CONCENTRATION OF INJECTED PESTICIDE
A MEASURED CONCENTRATION OF APPARENT DEGRADATION
PRODUCT
FIGURE 5. Anaerobic Degradation of Single Pesticides in Thick Sludge at 35 C.
-------
50
40 ppm LIN DANE
ADDED
POISONED
ACTIVE I •
THICK SLUOOC
10 20 30 40 50
DAYS AFTER PESTICIDE INJECTION
10 20 30 40 SO
DAYS AFTER PESTICIDE INJECTION
60
100 ppm
H E PTACHLOR EPOXIDE
ADDED
40 ppm ALDRIN
ADDED
40
•2
0.
10 20 JO 40 SO
DAYS AFTER PESTICIDE INJECTION
30 ppm DIELDRIN
ADDED
ACTIVE t
THICK SLUOOE
POISONED-
10 20 30 40 SO
DAYS AFTER PESTICIDE INJECTION
60
FIGURE 6. Anaerobic Degradation of Pesticide Mixtures in Thick Sludge at 35 C
(Pesticides without Extractable Degradation Products).
-------
*\
£ 80
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100 ppm DDT
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1 . ALL UNIT* (OOTI
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J^ ""'lO 20 v JO 40 50 6
DAYS AFTER PESTICIDE INJECTION
' '
DDT PRODUCT
( DDD)
, — THICK ILUDtE
/
•*•», / J ACTIVE I
f^^^T^ «"-
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ADDED
K o
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\ /— ACTIVC H
V
\ \ , THICK SLUDtE
^v ^v
\ \*V\ / ACTIVf I
-D V\Xv
10 20 JO 40 50 61
DAYS AFTER PESTICIDE INJECTION
E N D Rl N PRODUCTS
ACTIVE II v
\
THICK ILUDCE — i \
\ POItONID \ \
"^-^^^^^^ •
/'^^-'^ o
ri in 90 \n Ait «vn
10 20 30 40 50 60
DAYS AFTER PESTICIDE INJECTION
DAYS AFTER PESTICIDE INJECTION
DAYS AFTER PESTICIDE INJECTION
(J
FIGURE 7. Anaerobic Degradation of Pesticide Mixtures in Thick Sludge at 35 C
(Pesticides with Extractable Degradation Products).
-------
40 SO 60 70 »0
DAYS AFTCftlNITIA. PESTICIDE INJECTION
20 30
40 SO tO '0 60
DAYS AFTER INI TIAL PESTICIDE It.'JECTION
40 50 (0 70 60
DAYS AFTER INITIAL CCSTICIDE IUECTION
40 SO «0 TO
DAYS AFTERINITIM. PESTKIDC IIUECTIOI/
FIGURE 8. Pesticide Degradation in Dilute Sludge at 20 C
(Daily Injection Units).
-------
O 20 JO 40 60
OATS AFTCH INITIAL PESTICIDE INJECTION
D 00
I PRODUCED FROM DDT)
10 10 >o «o so
DAT* AFTCK INITIAL PESTICIDE INJECTION
FIGURE 9. Pesticide Degradation in Dilute Sludge Primarily at 35 C
(Daily Injection Units).
-------
10,000
aoi
0.01
I IJO
WATER CONCENTRATION (ppb)
100
IOOO
FIGURE 11. DDT Adsorption and Desorption from Several Materials
in Buffered Water, 20° C.
------- |