Abiological loss of endosulfan and related chlorinated organic compounds from aqueous systems in the presence and absence of oxygen

Environmental Pollution 115 (2001) 219–230
www.elsevier.com/locate/envpol

Abiological loss of endosulfan and related chlorinated organic
compounds from aqueous systems in the presence and absence of
oxygen
T.F. Guerin *
3/32 Wolli Creek Road, Banksia, Sydney, New South Wales 2216 Australia
Received 24 July 2000; accepted 25 January 2001

‘‘Capsule’’: Endosulfan, related OC pesticides, and major degradation products are studied in aquatic systems and factors
influencing persistence, and implications to biodegradation studies are explored.
Abstract
Endosulfan is a cyclodiene organochlorine currently widely used as an insecticide throughout the world. This study reports that
the endosulfan isomers can be readily dissipated from aqueous systems at neutral pH in the absence of biological material or
chemical catalysts, in the presence or absence of oxygen. The study showed that aldrin, dieldrin, and endosulfan exhibit bi-phasic
loss from water in unsealed and butyl rubber sealed vessels. Half-lives are substantially increased for endosulfan I when oxygen is
removed from the incubation vessel. The study conditions, where PTFE was used, were such that loss due to volatilization and
alkaline chemical hydrolysis was eliminated. Half-lives determined from these data indicate that the parent isomers are much less
persistent than the related cyclodienes, aldrin and dieldrin, confirming the findings of previous studies. The major oxidation product
of endosulfans I and II, endosulfan sulfate, is less volatile and can persist longer than either of the parent isomers. Endosulfan
sulfate was not formed in any of the treatments suggesting that it would not be formed in aerated waters in the absence of microbial
activity or strong chemical oxidants. Since endosulfan sulfate is formed in many environments through biological oxidation, and is
only slowly degraded (both chemically in sterile media and biologically), it represents a predominant residue of technical grade
endosulfan, which finds its way into aerobic and anaerobic aquatic environments. The data obtained contributes to and confirms
the existing body of half-life data on endosulfan I and II and its major oxidation product, endosulfan sulfate. The half-life data
generated from the current study can be used in models for predicting the loss of chlorinated cyclodiene compounds from aqueous
systems. The findings also highlight the importance of critically reviewing half-life data, to determine what the predominant processes are that are acting on the compounds under study. # 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Endosulfan; Degradation; Pesticide; Half-lives; Hydrolysis; Non-biological degradation; Bi-phasic loss; Persistence; Abiotic loss; Biodegradation; Endosulfan sulfate; Toxicity; Physico-chemical; Risk

1. Introduction
Endosulfan is a cyclodiene organochlorine possessing
a labile, cyclic sulfite diester group. Endosulfan is a
widely used agricultural chemical and it has been detected in an increasing number of environmental samples
in recent years (Guerin and Kennedy, 1991; Guerin,
1993; Mansingh and Wilson, 1995; Mansingh et al.,
1997; Miles and Pfeuffer, 1997; Guerin, 1999b). Of key
* Present address: Shell Engineering Ltd, NSW State Office, PO
Box 26, Granville 2142 NSW, Australia. E-mail address: turlough.
guerin@shell.com.au.
E-mail addresses: turloughg@hotmail.com, turlough.guerin@
bigpond.com (T.F. Guerin).

concern regarding its widespread distribution, particularly in water environments, is its high acute toxicity to
fish (Table 1). There are, however, relatively few studies
describing the fate of endosulfan in aquatic systems
(Greve, 1971; Walker et al., 1988; Peterson and Batley,
1991; Singh et al., 1991; Guerin and Kennedy, 1992;
Guerin, 1993; Peterson and Batley, 1993; Mansingh and
Wilson, 1995; Mansingh et al., 1997; Miles and Pfeuffer,
1997). In addition, it has not been extensively determined to what extent losses of the endosulfan isomers
result from chemical degradation as opposed to dissipation by other means, such as volatilization and
adsorption, in aqueous systems (Guerin and Kennedy,
1992; Guerin, 1993). Although there are a number of
reports describing biological oxidation of endosulfan to

0269-7491/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0269-7491(01)00112-9

220

T.F. Guerin / Environmental Pollution 115 (2001) 219–230

Table 1
Overview of acute toxicity of key endosulfan compoundsa
Compound

Table 2
Liquid-phase physico-chemical properties of major endosulfan compounds

Toxicity LD50 (mg kgÀ1)
Insects

Endosulfan I
Endosulfan II
Endosulfan sulfate
Endosulfan diol

Fish

Birds

Mammals

5.5
9.0
9.5
>500

0.001–0.01b
0.001–0.01
0.001–0.01
1–10

26–1000
26–1000
–c
–

9.4–40
177
8–76
>1500

a
Summarized from the literature (Guerin, 1993; Anonymous,
1998).
b
The lower the lethal dose, i.e. LD50 value, the higher the toxicity.
c
–, indicates that there was no data available.

the sulfate, there is no clear evidence for its formation in
sterile soils or water (Guerin, 1993). This indicates that
living organisms may be necessary to bring about the
oxidation of endosulfan to form endosulfan sulfate in
the environment. Previous studies have also reported
that isomerization can occur between the parent isomers
in aqueous systems, with the reaction favouring formation of endosulfan I (a-endosulfan; Schmidt et al.,
1997).
The primary aim of the research described in this
paper was to determine the half-life of the parent endosulfan compounds in sterile aqueous solutions with and
without the presence of oxygen. A further aim was to
determine whether endosulfan sulfate could be formed
under these conditions.

2. Materials and methods
2.1. Chemicals
Endosulfan and its degradation products were a gift
from Hoechst, Germany. Aldrin and dieldrin were provided by Shell Chemicals, Australia. cis- and transAldrin diol were kindly provided by Shell Chemicals
Research, UK. Hexane (Nanograde) and methanol
(ChromAR) were purchased from Mallinckrodt Chemicals. The key physico-chemical properties of the endosulfan compounds are summarized in Table 2.
2.2. Incubation conditions in aerobic study
The pesticides, endosulfan I, II, aldrin and dieldrin and
the endosulfan degradation product, endosulfan sulfate
(100–500 ppm in 10 ml methanol) were added to either
Nanopure-filtered, distilled and deionized water, sterilized by autoclaving at 121 C for 20 min, or sterilized
100 mM potassium phosphate-buffered yeast mannitol
medium with filtered (45 m) soil extract (10% v/v of a 50
g lÀ1 soil in water extract; (Guerin, 1993) in 4 ml Wheaton vials, to give final amounts of 1–5 mg lÀ1. The headspace volume was 2 ml in the vials. The quantities of 1–5

Compound

Log Kow v.p. (Pa)a,b Hc
Solubility in
water (S) ppma

Endosulfan I
0.51
Endosulfan II
0.45
Endosulfan sulfate
0.48
Endosulfan diol
300.0

3.6
3.83
3.66
3.68

0.0004
8.0Â10À5
3.7Â10À5
2.3Â10À6

0.72
0.04
0.03
1.3Â10À4

a
Values reported are from the PhysProp and DATALOG Databases from Syracuse Research Corporation where available (Meylan
and Howard, 2000). Values for endosulfan diol are from elsewhere
(Guerin and Kennedy, 1992; Guerin, 1993).
b
Vapor pressure in units of Pa.
c
Henry’s constant (H)=v.p./S in units of Pa m3 molÀ1, calculated
from the v.p. and S data reported in this table.

mg lÀ1 pesticide used in this study reflects those commonly used in studies of the microbial degradation of
pesticides, and in aquatic toxicology, where bioassays
are performed. The medium was also sterilized by
autoclaving for 20 min at 121 C. It is also noted that the
quantities of added pesticide meant that these compounds were close to the limits of the solubility for these
compounds in the aqueous phase (Table 2). Duplicate
vials were made of unsilanized borosilicate glass and
prepared according to the protocol described (Guerin,
1993). The medium contents have previously been
described (Guerin, 1993). Vessels were sealed with either
Polytetrafluoroethylene (PTFE)-lined butyl rubber seals
(Wheaton, Millville NJ, USA supplied by Edwards
Instrument, Narellan, Australia) or non-PTFE-lined
butyl rubber stoppers. Duplicate vessels were kept at
30 Æ 0.5 C, in an incubator for 30 days. No further
attempt was made to artificially aerate the incubation
flasks during the course of the experiment, and sterile
air at atmospheric pressure from a laminar flow cabinet
was used as the gas atmosphere in the headspace of
the flasks. The media was kept sterile throughout the
experiment, and this was checked by heterotrophic plate
counts and microscopic examination (Guerin, 1993).
The pH of the media was adjusted to 7 Æ 0.05 with KOH
or HCl prior to dispensing into the incubation vessels.
Incubation vessels were kept in the dark.
Surface microlayer subsamples were also taken, in
triplicate, after 4 h (30 C) from vessels set aside especially to determine whether there was any difference in
pesticide concentration at the liquid–air interface. This
was performed by withdrawing a volume of 100 ml from
the surface, an amount equivalent to the top 0.9 mm
of the medium, using a pipette. The pipette was rinsed
with solvent and the medium extracted as previously
described (Guerin and Kennedy, 1992). An equivalent
volume removed from the medium bulk was also analyzed for pesticides.


2.3. Incubation conditions in oxygen-limited study

3. Results and discussion

The incubations conditions were as before except
the incubation vessels were evacuated with N2 gas
at the commencement of the incubation period. Resazurin was added to the medium and this dye remained
in its reduced form throughout the entire incubation
period (i.e. clear) in all the incubation vessels.

221

3.1. Analysis using 0–30 day data

2.4. Extraction, recovery and analysis of parent
pesticides and degradation products
Duplicate incubation vessels containing the aqueous
media (2 ml) had their contents quantitatively transferred (i.e. sacrificed) into the reservoir of a 10 ml
liquid–liquid partitioning device (Mixxor1 by Genex)
and were extracted, recoveries determined, and analyses
conducted according to the method previously described (Guerin and Kennedy, 1992). Samples were
taken on days 0, 2, 4, 6, 8, 15 and 30. A total solvent
volume of 10 ml hexane/acetone/methanol/medium
(15:5:2:2) was also added to the Mixxor1 reservoirs.
The piston of the Mixxor1 was moved 60 times in its
reservoir to partition the pesticides into the solvent
phase. After the phases were allowed to separate ($1
min), the solvent layer was decanted off the aqueous
phase directly from the Mixxors1 into volumetric flasks
and the total volumes were made to either 10 or 25 ml
with hexane. Subsamples were dried with anhydrous
sodium sulfate prior to analysis by GC–ECD.
2.5. Analysis of data
Half-lives for all the compounds were determined.
The data analysis was conducted in three stages. During the initial data analysis (incorporating the data
collected at all sampling times, i.e. 0–30 days), the
square root of the correlation coefficient (r2) was determined from the log exponential decay plots i.e. log
100ÂC/Co vs t plots using the trend line function in
Microsoft Excel 2000 (Microsoft). In the second stage
of the analyses, data were analyzed, excluding the data
at day 15 and 30, to determine whether the pesticide
loss was bi-phasic, that is, exponential during the initial
phases of the experiment (0–8 days), followed by a later
linear phase (8–30 days). Where there was bi-phasic (i.e.
non-first-order or non-linear) loss occurring, evident
from the 100ÂlogC/Co vs t plots, 8–30 day data was
plotted and half-lives were also calculated using this
data. Multivariate analysis were conducted to compare
sets of data using the regression function in Microsoft
Excel 2000 (Microsoft). This generated P-values (5%
level of significance) for these comparisons. Univariate
analyses were conducted on individual treatments (e.g.
aldrin, unsealed, 0–30 days) to determine P values (5%
level of significance).

For each of the treatments, a line was plotted through
the data to determine whether the data collected at
all the sampling times fitted an exponential decay curve.
Since the concentration data was plotted as log values,
then an exponential decay plot would be a straight line
on such graphs.
The dissipation of aldrin and dieldrin from PTFE
sealed vessels observed the first order decay model. This
was also the case with the data from dissipation of
endosulfan I and II from the unsealed and PTFE sealed
flasks, and the dissipation of endosulfan sulfate from
unsealed, BRS and PTFE sealed flasks. This is illustrated in Fig. 1A–C.
These data indicated, however, that the first order
exponential decay model did not adequately describe the
losses of pesticide over the entire period of the experiment (0–30 days), particularly for losses of the more
volatile pesticides from the unsealed and butyl rubber
sealed vessels.
The dissipation of endosulfan I and II from water in
PTFE-sealed vessels (r2=0.93) and endosulfan sulfate
from water in unsealed vessels (r2=0.95) fitted the first
order decay model well, and therefore a single half-life
value was adequate to describe the loss of these compounds within these treatments. There was a significant
difference (P0.05) between the pesticide half-lives in
the butyl rubber sealed and PTFE-sealed flasks, and the
unsealed and PTFE-sealed vessels, but no differences
were measured between the butyl rubber sealed and the
unsealed vessels. The half-lives of the compounds in
each of the aerobic treatments are recorded in Table 3.
3.2. Analysis using 0–8 day data
The data that were obtained earlier in the trial (i.e. up
to the 8th day of incubation, only) for the unsealed and
BRS sealed treatments, generally showed larger r2
values and an improved fit to the first order exponential
decay model (compare columns 2, 3, 5, 6 in Table 3).
In the unsealed and butyl rubber sealed treatments, it
was found that data from the first 8 days fitted the
model of first order exponential decay better than data
from over the entire experiment (i.e. 30 days). These
findings indicated that the loss of pesticides from the
aqueous media, particularly in the butyl rubber-sealed
and the unsealed vessels, did display a first order exponential decay, but only over the initial phase of the
experiment. Volatilization from the unsealed vessels, and
absorption by butyl rubber in the butyl rubber sealed
vessels, could explain these losses early in the experiment.
As with the 0–30 day data, there was a significant difference (P0.05) between the pesticide half-lives in the

222


butyl rubber sealed and PTFE-sealed flasks, and the
unsealed and PTFE-sealed vessels, but no differences
were measured between the butyl rubber sealed and the
unsealed vessels. The 0–8 day data for aldrin, dieldrin
and endosulfan are plotted in Fig. 2A and B.
3.3. Analysis of 8–30 day data
When the 8–30 day data from the unsealed treatments
was analyzed, increased half-lives were obtained. These
half-lives increased from 0.5, 2, and 14 (for the 0–8 day
data), to 78, 46, and 29 days for aldrin, dieldrin, and
endosulfan I, respectively. These increased half-lives
reflected the predominant dissipation processes which
were acting on the compounds after the initial fast rate
of loss due to volatilization. These longer term rates of
loss reflecting the chemical degradation and slow desorption processes, showed that there was an 18–75Â
increase in the half-life length when data from 8–30 days
was considered. These slower processes were chemical
degradation and slow desorption of the compounds
from the glass and through the aqueous media, and
subsequent volatilization (Fig. 3).
3.4. Losses of aldrin and dieldrin
There were high rates of loss of aldrin and dieldrin
from both unsealed incubation vessels and flasks sealed
with butyl rubber when the 0–30 day data was considered. In the butyl rubber sealed vessels, aldrin and
dieldrin had largely disappeared at the 30th day, with
half-lives of 2.9 and 3.7 days, respectively. These results
were similar to the values of 0.5 and 2 days for half-lives
in the open flasks. The only difference in the pattern of
loss between these two treatments was that the initial
rate of dieldrin disappearance in the unsealed vessels
was slightly higher than in the butyl rubber sealed vessels. In contrast, when aldrin and dieldrin were incubated in similar sterile media or in water alone with
PTFE-lined butyl rubber seals, there was a considerably
slower rate of loss. The half-lives under these conditions
were 58 and 22 days, respectively.
Losses of aldrin and dieldrin were very low under
conditions of limited oxygen with half-life values of 134
and 46 days, respectively (Fig. 4A and Table 7).
The bi-phasic pattern of loss was particularly pronounced for aldrin, dieldrin and endosulfan I loss from
unsealed flasks (Table 4). A possible reason for this
non-first order loss could have been that a large proportion of pesticide was concentrated at the liquid–air
interface (surface microlayer) as previously reported
(Guerin and Kennedy, 1992). As a consequence, these
pesticides would be expected to volatilize early in the
experiment because of their close proximity to the liquid–
air interface. Peterson and Batley (1991) have also
suggested this mechanism as a reason for the loss of

Fig. 1. Dissipation of chlorinated compounds under oxygenated conditions (0–30 day data) (A) aldrin and dieldrin, (B) endosulfan I and
II, and (C) endosulfan sulfate.

endosulfan from aqueous media in laboratory experiments. After this surface quantity had entirely volatilized, further losses must have come from the solution
bulk through the process of diffusion. Therefore
another possible reason for this bi-phasic loss may be
due to a rim effect, where the more rapid diffusion
occurs at high adsorptions (i.e. at concentrations higher
than the compound’s solubility in the aqueous medium

223

Table 3
Half-lives (r2 values) in days for pesticide loss using the first order exponential decay model on data from various timesa
Compound

Unsealed (days)
0–30

Aldrin
Dieldrin
Endosulfan I
Endosulfan II
Endosulfan sulfate
a
b

13.6
2.8
25.8
18.0
37.3

BRS-sealed (days)

0–8
(0.37)
(0.65)
(0.83)
(0.90)
(0.95)

0.52
2.01
13.8
)200b
51.8

8–30
(0.73)
(0.98)
(0.89)
(0.001)
(0.48)

77.9
46.4
29.0
18.2
35.3

0–30
(0.55)
(0.90)
(0.93)
(0.91)
(1.0)

1.1
3.4
7.9
12.7
34.0

PTFE-sealed (days)

0–8
(0.79)
(0.94)
(0.83)
(0.83)
(0.5)

2.9
3.7
6.6
9.6
12.4

8–30
(0.98)
(0.98)
(0.96)
(0.96)
(0.78)

21.6
2.3
3.0
5.7
68.9

0–30
(0.71)
(0.99)
(0.66)
(0.63)
(0.18)

200b
75
21.7
24.2
102.5

0–8
(0.22)
(0.54)
(0.93)
(0.93)
(0.56)

57.8
21.8
13.8
36.2
65.1

(0.34)
(0.82)
(0.89)
(0.36)
(0.37)

Unsealed=cotton wool was used to stopper the flasks, BRS=butyl rubber sealed vessels, and PTFE=Teflon-lined butyl rubber seals.
Values of 200 and )200 days were given because of the relatively short time of the trials (30 days).

Fig. 2. Dissipation of chlorinated compounds under oxygenated conditions (0–8 day data) (A) aldrin and dieldrin, and (B) endosulfan I
and II.

early in the experiment) across the glass to the surface.
As the pesticide levels decrease in the vessels, the
amounts remaining after the initial high losses will more
closely approximate the upper limits of the compound’s
solubility. This may explain, at least in part, why the
pesticide loss is slower after 8–30 days incubation as
the forces of solubilization would tend to override those
exerted by volatilization (Guerin and Kennedy, 1992;
Guerin, 1993).

In the current study, approximately 40–50% of the
originally applied pesticides recovered from the vessels
containing aqueous medium (1–5 mg mlÀ1 originally
added), was found to be concentrated at the interfaces
of the system. Also, an attempt was made to subsample
the liquid–air interface and measure the pesticide concentration. However, there was no detectable difference
between the surface sample and that in the bulk of the
medium. Therefore, the pesticides must have accumulated at the liquid–glass interface only under these
conditions. Although it is possible that a slower rate
of hydrolysis could occur at this interface, insulated
from the effect of the hydroxyl ion, this is unlikely to
explain the increased half-lives for the endosulfan isomers reported in this study with effective sealing. A
similar increase in half-life was also observed for the
more stable compounds such as dieldrin, when the flasks
were sealed with PTFE.
This distribution to the glass-medium interface was
observed when the compounds under study were added
to either water or microbial growth media. An homogenous distribution of pesticide throughout the entire
system was achieved by adding 0.1% Tween 80. All of
the compounds studied were distributed throughout the
system in a similar fashion, and all responded similarly
to the detergent treatment in both the sterile distilled
water and growth medium. There was a greater distribution of all the pesticides to the liquid–glass interface in the vessels containing pure water. A similar effect
was observed by Peterson and Batley (1991) when they
subsampled from a larger total volume of water containing both endosulfan isomers at lower concentrations
(0.1 ppm) in polycarbonate vessels. These findings
and the results from the current study therefore illustrate the importance of avoiding subsampling when
analyzing aqueous extracts containing relatively high
concentrations of endosulfan and related cyclodienes.
The distribution of pesticides in aqueous systems is of
particular importance in microbial degradation studies
where the availability of the compound is likely to
affect its degradation. Thus, when the pesticide is added
in small amounts of solvent to the aqueous phase (as
has generally been reported in microbial pesticide

224


Fig. 3. Experimental vessel and graphical presentation of bi-phasic loss.

degradation studies, often followed by evaporation of
solvents with N2 gas), its distribution in the incubation
vessel will tend to be associated with the interfaces. The
geometry of the incubation vessel as well as the constituents of the medium will effect the pesticide distribution. In microbial degradation experiments, where
insoluble compounds are added in methanol or a similar
solvent, an apparent increase in pesticide concentration
with time will be observed in the bulk of the medium,
once exponential growth commences and lipids increase
in quantity. This effect may be overcome by completely
sacrificing the entire treatment incubation flasks at each
sampling time.
The inclusion of the very chemically stable cyclodienes,
aldrin and dieldrin, in PTFE-sealed vessels in this study
provided internal controls that indicated disappearance
predominantly from physical losses, thereby providing
the maximum limits of these processes in the system
studied. The experimental conditions were too mild and
the incubation period was too short to allow substantial
chemical degradation of these compounds. The persistence of aldrin and dieldrin in these incubations therefore
represents the maximum limits for either slow volatilization or other possible processes such as irreversible
binding to container surfaces. Thus, any differences

between the persistence of these internal controls and
that of the endosulfan compounds represents the actual
disappearance by chemical reaction. The very slow rate
of disappearance of aldrin and dieldrin in the PTFEsealed vessels in both water and growth medium confirmed that the system was well sealed.
3.5. Dissipation of endosulfan isomers
In both the butyl rubber sealed and the unsealed vessels, the endosulfan isomers were lost at fast rates. After
8 days of incubation, the calculated half-lives of endosulfans I and II in the butyl rubber sealed flasks were 7.9
and 12.7 days, respectively. When endosulfans I and II
were incubated in unsealed vessels, the half-lives varied
from 13.8 to 29 and 18 to )200 days, respectively. In
both the butyl rubber sealed and the unsealed flasks,
comparing 0–8 day data, endosulfan I loss was higher
than that of endosulfan II. This result reinforces previous findings that endosulfan I is more volatile than
endosulfan II (Goebel et al., 1982; Worthing and
Walker, 1987; Singh et al., 1991; Guerin and Kennedy,
1992; Guerin, 1993).
When the vessels were sealed with PTFE, rates of
disappearance for both isomers in both water and


Fig. 4. Dissipation of chlorinated compounds under oxygen-limited
conditions (0–30 day data) (A) aldrin, dieldrin, endosulfan I and II
(1 ppm), and (B) endosulfan I and II (10 ppm), and (C) endosulfan
sulfate (5 and 50 ppm).

microbial growth medium were considerably lower
comparing 0–30 day data. The half-lives were 21.7 and
24.2 days for endosulfans I and II, respectively. Under
oxygen-limited conditions, the half-lives of endosulfan
I and II, were )200 and 58 days, respectively (Fig. 4A,
B and Table 7). The effect of PTFE sealing was to substantially reduce the volatilization of the parent compounds from the flasks.

225

It was clear from the butyl rubber sealed and unsealed
treatments that endosulfan I is more volatile than
endosulfan II. Given the relative chemical inertness of
the PTFE-sealed systems and that traces of endosulfan
diol were detected in the same system, it is reasonable to
conclude that both endosulfan isomers were chemically
degraded in the aqueous incubations. Based on this
data, endosulfan II may be more chemically labile than
endosulfan I.
In previous studies, it has been observed that endosulfan II also disappeared at a faster rate than endosulfan
I. Under aerobic conditions at a lower temperature of
22 C, the half-lives of endosulfans I and II in a potassium phosphate buffered, minimal salts medium (pH
6.5), were 88 and 40 days, respectively (Miles and Moy,
1979). In their paper no mention was made on how the
vessels were sealed. The half-lives of endosulfans I and
II in non-sterile seawater (pH 8.0) were 4.9 and 2.2
days, respectively (Cotham and Bidleman, 1989). These
incubations were carried out aerobically and at 20oC
under laboratory lighting. In another study, incubations in lake water showed that the half-life of endosulfan I was 35 days at pH 7 and 105 days at pH 5.5
(Greve, 1971). It was shown in the same study that
when iron hydroxide gel is mixed with water, the rate of
hydrolysis is considerably accelerated. Other researchers have reported half-lives of 10–43 days under controlled laboratory conditions, at pH values of 8.5
(Southan and Kennedy, 1995), and values of 3 days
for both isomers in laboratory water columns of unreported pH (Logan and Barry, 1996). Guerin (1999a)
has reported losses of endosulfan I under sterile anaerobic conditions, as part of a 30-day anaerobic biodegradation study, with losses of endosulfan I at 20, 10
and 2% (of that originally applied) when this compound was added at 1, 2, and 10 ppm, respectively,
indicating rates of loss are dependent on the mass of
added pesticide. The latter findings are consistent with
water insoluble pesticides desorbing from the glass surface into the medium. Also, in the Guerin (1999a) study,
when microorganisms were present, half-lives of endosulfan I varied between 5 and 15 days, substantially
increasing its loss. It has also been shown that endosulfan losses can be significantly minimized from water
solutions if the incubation vessels are sealed to prevent
volatilization (Guerin and Kennedy, 1992; Guerin,
1993). Several biodegradation studies in liquid culture
have demonstrated the importance of sealing incubation
vessels with Teflon or PTFE as previously discussed
(Guerin, 1995, and references cited therein). However,
not all biodegradation studies have employed PTFE
and this should be considered as a critical criterion
when reviewing and evaluating degradation data
reported in the literature. It was noted that there was no
interconversion between isomers under the conditions
described in the current study.

226


Table 4
Summary of bi-phasic loss data from trials with unsealed vessels
Phase of trial (days)

Main loss mechanisms

Relative rate of loss

Calculated half-lives (days)
Aldrin

Initial (0–8)
Latter (8–30)

Volatilization
Desorption, chemical degradation

The role of pH is important, particularly when the
rates of endosulfan loss are compared across different
studies. This is because the endosulfan isomers are susceptible to alkaline hydrolysis (Goebel et al., 1982).
Thus, rates of hydrolysis at pH 8 will be a $10 times
faster than the rates at pH 7. Some differences in the
half-lives previously reported may be due to differences
in temperature, which may also affect the hydrolysis
rates of pesticides. Since endosulfans I and II are volatile, the temperature at which the experiments are carried out is also very important.
In the current study there was no significant difference
(P0.05) in the degradation rates of either endosulfan
isomer comparing incubation in water and in the
microbial growth medium. This indicates that the soil,
peptone, or yeast extract and inorganic minerals had no
measurable effect on the persistence of the isomers.
3.6. Losses of endosulfan sulfate
In all of the experiments conducted, endosulfan sulfate was relatively stable and considerably more persistent than the parent isomers. The half-life of endosulfan
sulfate in the sterile water was calculated at 103 days
when sealed with PTFE compared with 30 days in the
unsealed vessels. Its persistence in the vessels sealed with
butyl rubber (10 day half life), compared with that in
the unsealed vessels (30 day half-life), was not significant, and this was likely to be due to the wide variation in the analysis of endosulfan sulfate data as
previously reported by (Guerin et al., 1992).
The data on the dissipation of endosulfan sulfate
from the PTFE-sealed vessels fitted the model of first
order exponential decay poorly, when all the sampling
times were analyzed. The very low r2 values obtained
with endosulfan sulfate in the PTFE-sealed vessels,
suggests little or no relationship between endosulfan
sulfate concentrations and time. However, from the
extraction and analysis of endosulfan sulfate previously
reported (Guerin and Kennedy, 1992), it is likely that
analytical error was also important and contributed to
the very low r2 values. Endosulfan sulfate was even
more stable under conditions of limited oxygen, with
half-lives typically )200 days (Fig. 4C and Table 5).
The results of the dissipation of endosulfan sulfate
therefore indicate a limitation of calculating the half-life
of this compound using the approach described here.

Fast
Slow

Dieldrin

Endosulfan I

0.52
77.9

2.01
46.4

13.8
29

This approach is more appropriate for determining the
half-lives of the parent isomers, where the differences
between the half-lives are not as great, and where analytical variation is low.
Miles and Moy (1979) have also reported on the persistence of endosulfan sulfate in aqueous media and
have given a value for its half-life, under the previously
described conditions, as 140 days. The reported persistence of endosulfan sulfate in the aqueous systems
studied in the current work, and from this report in the
literature, indicates that this endosulfan transformation
product is likely to remain in water environments much
longer than the parent isomers. It has previously been
shown not to be readily biodegradable. However, in real
environments, there may be other processes of endosulfan sulfate removal such as strong adsorption to soil
and sediment particles. It should be recognized that
because of the relatively short time frame of the trials,
the r2 values and corresponding half-life data for endosulfan sulfate, has been included in the data set for the
sake of completeness and these do not represent definitive values. Further research would be needed to determine definitive values for the persistence of this
compound in aqueous systems.
3.7. The role of volatilization in pesticide disappearance
From the increased losses in the open vessel incubations, it is evident that the endosulfan dissipation in
these treatments was primarily owing to volatilization.
The rates of volatilization of the endosulfan isomers
in the open-vessel experiments were similar to those
from the butyl rubber sealed experiments. These results
indicated that volatilization of these compounds from
the aqueous media has a similar effect as that of the
butyl rubber seals. Aldrin and dieldrin were also lost at
fast rates in similar incubations, confirming that
absorption into the butyl rubber seals was the major
cause of loss (Guerin and Kennedy, 1992). Extraction
and analysis of the butyl rubber seals after the incubation indicated that all the cyclodienes had become
absorbed into this sealing material.
No hydrolysis products of endosulfan, endosulfan
sulfate, aldrin or dieldrin were detected in hexane–
acetone extracts from the open or butyl rubber sealed
treatments. Thus, it is evident that the major cause of
dissipation of all compounds in the unsealed flasks was

227

Table 5
Half-lives for pesticide loss under oxygen-limited conditions using the first order exponential decay model (0–30 days)a
Compound

1 ppmb

10 ppmc

Half-life (days)
Aldrin
Dieldrin
Endosulfan I
Endosulfan II
Endosulfan sulfate

r2

Half-life (days)

r2

134
46
)200
58
)200

0.003
0.14
0.001
0.24
0.43

–
–
200
97
)200

–
–
0.001
0.71
0.01

a

PTFE-lined butyl rubber sealed vessel, evacuated 7Â prior to incubation (see methods); values 200 days were given because of the relatively
short time of the trials (30 days). Values of )200 indicated that the calculated half-lives were greater than 1000 days.
b
5 ppm of endosulfan sulfate was used because of its higher analytical detection limits.
c
50 ppm of endosulfan sulfate was used because of its higher analytical detection limits.

volatilization, and absorption in the butyl rubber sealed
flasks, rather than chemical degradation.
Volatilization from uninoculated controls in aerobic
microbial degradation studies is likely to be a significant
factor in overall pesticide disappearance in unsealed
systems, particularly with organochlorine pesticides
such as endosulfan. In one study, 30% of applied
endosulfan I was reported to have volatilized from a
seawater/sediment microcosm (sealed with polyurethane) during the first 4 days of the experiment
(Cotham and Bidleman, 1989). Others demonstrated
that polystyrene absorbed both endosulfan isomers
strongly, compared with glass (Peterson and Batley,
1991). The current findings therefore confirm these
findings, and illustrate the importance of sealing aqueous systems containing these compounds, with an inert
material such as PTFE.
The high volatilization rate of endosulfan I, is due to
its low water solubility and relatively high vapor pressure, or its high Henry’s constant. The ratio of liquidphase vapor pressure and solubility, or solid-phase
vapor pressure and solubility, provides a value for the
Henry’s constant. This relationship may be used to
show the difference in the relative rates of volatilization
of the parent endosulfan isomers and of the recalcitrant
cyclodienes, aldrin and dieldrin. In illustrating the
importance of the Henry’s constant of a compound, it is
convenient to introduce the concept of fugacity. The
fugacity is the escaping tendency of a compound from a
particular phase. This can be expressed mathematically
as f=C/Z. In this expression, f is the fugacity (units of
pressure Pa), C is the concentration (units of mol mÀ3)
and Z is the fugacity capacity (units of mol mÀ3 PaÀ1).
Each compound has its own fugacity and at equilibrium, compounds will accumulate in phases with
the lowest fugacity, or highest Z values. So in water, the
fugacity capacity is the inverse of the compound’s Henry’s constant (H) (Guerin and Kennedy, 1992). This is
described by the equation, Z=Zwater=1/H. The calculated fugacities of the cyclodiene compounds under
study are equivalent to their vapor pressure values in

the same phase because the concentration (C) is equal to
their water solubilities for the solid compounds.
In calculating the Henry’s constant, values for water
solubility and vapour pressure must be for the same
phase, that is, both for the liquid-phase or both for the
solid-phase. The values presented in Table 2 are for
the solid-phase for each of the pesticides.
Some of the behavior observed in the butyl rubbersealed and unsealed vessels can be accounted for by
differences in their calculated fugacities. The fastest
rates of disappearance from both of these treatments
were that of aldrin, which also had the lowest Z value,
or greatest fugacity. From the vapor pressure and solubility data obtained from the literature, endosulfan I has
a Henry’s constant of 0.72, approximately 18 times
that of endosulfan II (H=0.04), which correlates well
with the greater rate of disappearance from the nonPTFE-sealed vessels (consistent with volatilization and
absorption mechanisms of loss). Aldrin had the highest
Henry constant of 4.95, while dieldrin was lower at 0.53.
3.8. Detection and analysis of potential hydrolysis
products of endosulfan
Trace levels of the hydrolysis product, endosulfan
diol, were detected after 30 days incubation in flasks
containing either parent isomer of endosulfan at the
beginning of the experiment. The recovery treatments
showed that this degradation product was extracted
when spiked into zero time vessels. The identity of
endosulfan diol was confirmed using two different gas
chromatographic columns (Guerin and Kennedy, 1992).
The highest concentrations of endosulfan diol were
detected in the PTFE-sealed incubations. With endosulfan I, these concentrations were 0.08–0.1 ppm of
endosulfan diol after 30 days. This rate of endosulfan
diol formation correlates well for the calculated half-life
of endosulfan I of approximately 22 days in the sterile
media. This rate of formation, however, was not stoichiometric, as approximately 0.5 ppm of endosulfan
diol would have been expected to form over this period

228


if there was complete transformation. Some of the difference between the amount of endosulfan diol expected
and that which was observed, may have been due to the
reduced extraction efficiency of the endosulfan diol.
Higher concentrations of 0.1–0.15 ppm endosulfan diol
were detected in the endosulfan II incubations under the
same conditions, consistent with its lower chemical stability. Much lower amounts of endosulfan diol (0.01
ppm) were detected in the endosulfan sulfate incubations after 30 days, and then only in PTFE-sealed incubations. These findings correlate well with the observed
stability of this compound under these conditions.
The potential hydrolysis products of dieldrin, cis- and
trans-aldrin diol, were not detected in any of the treatment incubations containing dieldrin, although the
underivatized standard compounds were chromatographed successfully under the conditions described for
analyzing the parent compounds (Guerin et al., 1992).
Given the highly recalcitrant nature of dieldrin, and the
mild incubation conditions of water and growth medium, no hydrolysis products were expected to form.
Polytetrafluoroethylene (PTFE) exhibits chemical and
physical properties which, when coated onto butyl or
silicone rubber, make it suitable for sealing aqueous
media that is in contact with semi-volatile or hydrophobic compounds such a the cyclodiene pesticides.
These characteristics of PTFE are its high resistance to
heat, inertness to chemical attack over a wide range of
temperatures, low moisture absorption and permeability (0.01% in 24 h), high physical strength, very

high thermal stability, and flexibility. Because of
its high resistance to temperature, it is also autoclavable (Schlanger and Baumgartner, 1980; Guerin, 1993).
However, dry heat and radiation may also sterilize it.
These properties are listed in Table 6. Since this material
is impermeable to gases, including N2, O2, H2, and CO2,
it can also be used to maintain anaerobic conditions in
flasks containing media for the growth of microorganisms. Of these properties, its high chemical resistance is
of greatest importance in biodegradation studies as it
prevents absorption of the compounds under study, into
the sealing material.

4. Conclusions
This study reports that the endosulfan isomers can be
dissipated from simple aqueous systems at neutral pH in
the absence of biological material or chemical catalysts.
When the incubation vessels are sealed with PTFE, then
endosulfan II is more readily degraded than endosulfan
I, a phenomenon already observed in various aqueous
systems. The study also showed that under PTFE-sealed
conditions, but in oxygen-limited conditions, the halflives are more than doubled indicating that the parent
isomers of endosulfan are more stable under these conditions. This result is in contrast to that obtained in
unsealed systems, where the loss of endosulfan I is
greater than that of endosulfan II. Half-lives determined
from the data indicate that the parent isomers are much

Table 6
Physico-chemical properties of polytetrafluoroethylene (PTFE)
Inertness to chemical attack
Low moisture absorption and permeability
Impermeable to N2, O2, H2 and CO2
High physical strength and high thermal stability
Low coefficient of friction
Very low dielectric constant and excellent electrical insulator
Non-stick (anti-adhesion) surfaces
Flexible, making suitable for sealing vessels in biodegradation or dissipation studies

Table 7
Implications and recommendations from the current study
1.

The endosulfan isomers, like aldrin and dieldrin, volatilize readily from incubation vessels containing microbial growth media, which are
unsealed, or sealed with butyl rubber.
Published values for half-lives of volatile and semi-volatile values should be critically reviewed prior to use in modelling their degradation to
see whether the study has taken bi-phasic effects into account and use the data accordingly.
Biodegradation assays should include sterilized cells as a control to minimize glass surface binding effectsa.
Half-life values generated in the current study can be used in modelling the dissipation of the endosulfan and related compounds from
aqueous systems.
When endosulfan (or aldrin and dieldrin) are added to aqueous media at levels higher than their solubility in water, adsorption effects are
likely to retain the pesticide at the glass-media interfaces until microbial growth becomes significant, and causes it to desorb. Therefore in
sterile treatments, entire vessels should be extracted without prior subsampling, particularly with compounds that have low water solubility.
Anaerobic biodegradation assays should be sealed with Teflon-lined butyl rubber to avoid pesticide absorption, while maintaining an oxygen
impermeable seal.

2.
3.
4.
5.

6.
a

Particularly in aerobic studies where the medium surface has direct contact with the atmosphere through a cotton wool plug.


less persistent than the related cyclodienes, aldrin and
dieldrin. However, the major oxidation product of
endosulfans I and II, endosulfan sulfate, is less volatile
and can persist longer than either of the parent isomers.
Endosulfan sulfate was not formed in any of the
treatments in the current study. This suggests that
endosulfan sulfate would not be formed in aerated
waters in the absence of microbial activity or strong
chemical oxidants. Since endosulfan sulfate is formed in
many natural environments through biological oxidation, and is only slowly degraded (both chemically in
sterile media and biologically), it represents a predominant residue of endosulfan in aerobic aquatic
environments.
Both the endosulfan isomers dissipated from the
incubation vessels at faster rates when the vessel was
sealed with butyl rubber, than when they were sealed
with PTFE. Conversely, the relatively inert PTFE seals
greatly reduced losses from volatilization and absorption, thus providing the necessary conditions for studying the chemical degradation of the cyclodienes.
Analysis of the data on the dissipation of the cyclodienes has indicated that the loss of the more volatile
cyclodienes, aldrin, dieldrin and endosulfan I, from
unsealed and butyl rubber sealed treatments, is bi-phasic.
The fact that there was very little difference between
the rates of dissipation of aldrin and dieldrin from
media sealed with butyl rubber and that which were
unsealed, showed that butyl rubber sealing was ineffective. As known from previous biodegradation studies,
such a rubber seal is therefore unsuitable for microbial
degradation studies when endosulfan or other volatile/
semi-volatile compounds are studied. Although butyl
rubber has a very low permeability towards oxygen, it
has a high affinity for organic compounds (e.g. hexane
and volatile organochlorine pesticides). Conversely,
PTFE, due to its very low coefficient of friction and
resistance to chemical reaction, has an extremely low
porosity to volatile/semi-volatile organic compounds.
PTFE-lined rubber therefore provides an ideal seal for
anaerobic degradation studies with compounds of high
volatility, for example see Guerin (1999a).
A significant finding was the complete absence of the
formation of endosulfan sulfate. This is a toxic degradation product (Table 1), and is the major oxidative
product of endosulfan in the environment. This was true
for both sterile incubations and incubations containing
soil extracts in the well defined liquid media used for
cultivating anaerobic and aerobic bacteria. From the
current study, it is unlikely that endosulfan sulfate
forms in naturally occurring waters under anaerobic
conditions, either with or without microorganisms present. However, endosulfan diol was formed in the sterile
incubations, indicating that this degradation product
may be formed in the absence of any microbial activity.
Furthermore, under the conditions described, there was

229

no interconversion between the parent isomers of endosulfan during the study period.
Further implications for studying the behaviour of
chlorinated organic compounds in aqueous systems are
also given (Table 7). It is imperative that in any aqueous
incubation containing volatile/semi-volatile organic
compounds, such as endosulfan, aldrin or dieldrin, special precautions must be taken to reduce volatilization.
An important demonstration in this study is that of the
necessity to seal aqueous incubation vessels with Teflonlined butyl rubber seals to prevent volatilization which
would have otherwise reduced the apparent half-lives of
the compounds under study. For these volatile organochlorines, unlined butyl rubber was shown to be ineffective as a vessel stopper, and may even enhance the
loss of these compounds from sterile aqueous media.
These findings are fundamental to the design of future
biodegradation experiments as losses of these compounds due to volatilization, as well as from chemical
hydrolysis, are also likely to occur. These losses can
confound the results of biodegradation experiments,
making it difficult to determine which losses are actually
a result of biological activity. Therefore, these findings
were applied to the design of experiments aimed at
determining the role of indigenous soil microorganisms
in the biodegradation of endosulfan under anaerobic
conditions and have allowed the biodegradation potential of indigenous populations of anaerobic microorganisms to be determined (Guerin, 1999a).

References
Anonymous, 1998. Review of endosulfan. Australia, National Registration Authority for Agricultural and Veterinary Chemicals, Canberra.
Cotham, W.E., Bidleman, T.F., 1989. Degradation of malathion,
endosulfan, and fenvalerate in seawater and seawater/sediment
microcosms. Journal of Agricultural and Food Chemistry 37,
824–828.
Goebel, H., Gorbach, S.G., Knauf, W., Rimpau, R.H., Huttenbach,
H., 1982. Properties, effects, residues and analytics of the insecticide
endosulfan. Residue Reviews 83, 1–122.
Greve, P.A., 1971. De persistentie van endosulfan in oppervlaktewater. Ghent Rijksinstituut Mededlingen 36, 439–447.
Guerin, T. F. 1993. The relative significance of biodegradation and
physico-chemical dissipation of endosulfan from water and soil.
Department of Agricultural Chemistry and Soil Science University
of Sydney, Sydney, New South Wales, Australia, pp. 240.
Guerin, T.F., 1995. Anaerobic biodegradation of the chlorinated
hydrocarbon endosulfan. In: Hinchee, R.E., Hoeppel, R.E., Anderson, D.B. (Eds.), Bioremediation of Recalcitrant Organics, Vol. 7.
Battelle Press, Ohio, pp. 157–164.
Guerin, T.F., 1999a. The anaerobic degradation of endosulfan by
indigenous microorganisms from low-oxygen soils and sediments.
Environmental Pollution 106, 13–21.
Guerin, T.F., 1999b. Natural attenuation of a low mobility chlorinated insecticide in low-level and high-level contaminated soil: a
feasibility study. Remediation 9, 51–63.
Guerin, T.F., Kennedy, I.R., 1991. The biodegradation of endosulfan
in cotton growing soils. The Australian Cotton Grower 12, 13–15.

230


Guerin, T.F., Kennedy, I.R., 1992. Distribution and dissipation of
endosulfan and related cyclodienes in sterile aqueous systems:
implications for studies on biodegradation. Journal of Agricultural
and Food Chemistry 40, 2315–2323.
Guerin, T.F., Kimber, S.W.L., Kennedy, I.R., 1992. Efficient one-step
method for the extraction of cyclodiene pesticides from aqueous
media and the analysis of their metabolites. Journal of Agricultural
Food and Chemistry 40, 2309–2314.
Logan, D.C., Barry, M.J., 1996. The fate of endosulfan in aquatic
microcosms and effects on benthic communities. Intersect ’96, Sydney, Australia, RACI, P155.
Mansingh, A., Robinson, D.E., Dalip, K.M., 1997. Insecticide contamination of the Jamaican environment. Trends in Analytical
Chemistry 16, 115–123.
Mansingh, A., Wilson, A., 1995. Insecticide contamination of Jamaican environment III. Baseline studies on the status of insecticidal
pollution of Kingston Harbour. Marine Pollution Bulletin 30,
640–645.
Meylan, B., Howard, P., 2000. PhysProp and Datalog Databases.
Syracuse Research Corporation. (http://esc.syrres.com).
Miles, C.J., Pfeuffer, R.J., 1997. Pesticides in canals of south Florida.
Archives of Environmental Contamination and Toxicology 32,
337–345.
Miles, J.R.W., Moy, P., 1979. Degradation of endosulfan and its
metabolites by a mixed culture of soil microorganisms. Bulletin of
Environmental Contamination and Toxicology 23, 13–19.

Peterson, S.M., Batley, G.E., 1991. Fate and Transport of Endosulfan
and Diuron in Aquatic Ecosystems. CSIRO Division of Coal and
Energy Technology, Sydney, New South Wales.
Peterson, S.M., Batley, G.E., 1993. The fate of endosulfan in aquatic
ecosystems. Environmental Pollution 82, 143–152.
Schlanger, L.M., Baumgartner, E.R., 1980. Fluoroplastics. Modern
Plastics Encyclopedia 57, 31–34.
Schmidt, W.F., Hapeman, C.J., Fettinger, J.C., Rice, C.P., Bilboulian,
S., 1997. Structure and asymmetry in the isomeric conversion of
beta- to alpha-endosulfan. Journal of Agricultural and Food
Chemistry 45, 1023–1026.
Singh, N.C., Dasgupta, T.P., Roberts, E.V., Mansingh, A., 1991.
Dynamics of pesticides in tropical conditions. Kinetic studies of
volatilization, hydrolysis and photolysis of dieldrin and a- and bendosulfan. Journal of Agricultural Food Chemistry 39, 575–579.
Southan, S.K., Kennedy, I.R., 1995. Dissipation of the pesticide
endosulfan from cotton field runoff water using an improved apparatus for the simulation of field conditions. Fourth Environmental
Chemistry Symposium, Darwin, RACI, EO-22.
Walker, W.W., Cripe, C.R., Pritchard, P.H., Bourquin, A.W., 1988.
Biological and abiotic degradation of xenobiotic compounds in in
vitro estuarine water and sediment/water systems. Chemosphere 17,
2255–2270.
Worthing, C.R., Walker, S.B., 1987. The Pesticide Manual: a World
Compendium. The British Crop Protection Council, 1081, Thornton Heath, UK.

Abiological loss of endosulfan and related chlorinated organic compounds from aqueous systems in the presence and absence of oxygen

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (19)

Similaire à Abiological loss of endosulfan and related chlorinated organic compounds from aqueous systems in the presence and absence of oxygen

Similaire à Abiological loss of endosulfan and related chlorinated organic compounds from aqueous systems in the presence and absence of oxygen (20)

Plus de Turlough Guerin GAICD FGIA

Plus de Turlough Guerin GAICD FGIA (20)

Dernier

Dernier (20)

Abiological loss of endosulfan and related chlorinated organic compounds from aqueous systems in the presence and absence of oxygen