Competitive degradation and detoxification of carbamate insecticides by membrane anodic fenton treatment

Article abstract of DOI:10.1021/jf034311f

The competitive degradation of six carbamate insecticides by membrane anodic Fenton treatment (AFT), a new Fenton treatment technology, was carried out in this study. The carbamates studied were dioxacarb, carbaryl, fenobucarb, promecarb, bendiocarb, and carbofuran. The results indicate that AFT can effectively degrade these insecticides in both single component and multicomponent systems. The carbamates compete for hydroxyl radicals, and their kinetics obey the previously developed AFT kinetic model quite well. Hydroxyl radical reaction rate constants were obtained, and they decrease in the following order: dioxacarb ≈ carbaryl > fenobucarb > promecarb > bendiocarb > carbofuran. The AFT is shown to have higher treatment efficiency at higher temperature. Degradation products of the carbamates were determined by gas chromatography/mass spectrometry, and it appears that degradation can be initiated by hydroxyl radical attack at different sites in the molecule, depending on the individual structure of the compound. Substituted phenols are the commonly seen degradation products. The AFT treatment can efficiently remove the chemical oxygen demand of the carbamate mixture, significantly increasing the biodegradability. Earthworm studies show that the AFT is also an effective detoxification process.

Full text of DOI:10.1021/jf034311f

5382 J. Agric. Food Chem. 2003, 51, 5382−5390
Competitive Degradation and Detoxification of Carbamate
Insecticides by Membrane Anodic Fenton Treatment
QIQUAN WANG AND ANN T. LEMLEY*
Graduate Field of Environmental Toxicology, TXA, MVR Hall, Cornell University,
Ithaca, New York 14853-4401
The competitive degradation of six carbamate insecticides by membrane anodic Fenton treatment
(AFT), a new Fenton treatment technology, was carried out in this study. The carbamates studied
were dioxacarb, carbaryl, fenobucarb, promecarb, bendiocarb, and carbofuran. The results indicate
that AFT can effectively degrade these insecticides in both single component and multicomponent
systems. The carbamates compete for hydroxyl radicals, and their kinetics obey the previously
developed AFT kinetic model quite well. Hydroxyl radical reaction rate constants were obtained, and
they decrease in the following order: dioxacarb ≈ carbaryl > fenobucarb > promecarb > bendiocarb
> carbofuran. The AFT is shown to have higher treatment efficiency at higher temperature.
Degradation products of the carbamates were determined by gas chromatography/mass spectrometry,
and it appears that degradation can be initiated by hydroxyl radical attack at different sites in the
molecule, depending on the individual structure of the compound. Substituted phenols are the
commonly seen degradation products. The AFT treatment can efficiently remove the chemical oxygen
demand of the carbamate mixture, significantly increasing the biodegradability. Earthworm studies
show that the AFT is also an effective detoxification process.
KEYWORDS: Carbamate; insecticide; degradation; detoxification; Fenton; wastewater treatment;
earthworm; toxicity; anodic; dioxacarb; carbaryl; bendiocarb; fenobucarb; promecarb; carbofuran
INTRODUCTION
tages of classic Fenton treatment (17, 19, 20) and electrochemi-
cal Fenton treatment (21, 22), AFT was developed as an
alternative for treating small-scale pesticide wastewater on site
(23, 24). An ion exchange membrane was subsequently added
to the AFT system in the degradation of carbaryl, making AFT
technology more convenient and practical for potential scale-
up. High treatment efficiency and strong functional stability of
the membrane were observed (25). Timely and reliable waste
treatment decreases potential pollution from the rinsing of
pesticide containers and application equipment and from the
disposal of unwanted pesticides. On the basis of the degradation
of 2,4-D by AFT, a kinetic model (also known as the AFT
model) was developed to better understand AFT reaction
mechanisms and to optimize the operating conditions (26). This
model was also found to be appropriate in fitting degradation
kinetics of diazinon by AFT (27).
After the ban or restriction on various chlorinated hydrocarbon
insecticides, such as 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-
ethane and lindane, carbamate insecticides gained prominence
in many developed countries. They are now widely used in the
U.S. and throughout the world (1). Contamination by carbamate
insecticides has been extensively reported, however, and has
become an environmental concern (2-8). There are also
questions about the health effects of carbamates, making
environmental cleanup and wastewater treatment a high priority
(9-11).
Among the causes of pesticide pollution, the disposal of rinse
water from pesticide containers and spray equipment and the
disposal of unused, unwanted, or obsolete pesticide stocks has
become a major problem and has received extensive attention
nationally and internationally (12-14). Thus, efficient, low cost,
fast, and easily operated technologies are badly needed for
farmers or commercial applicators to treat these small-scale but
high concentration pesticide wastewaters on site.
To understand the degradation kinetics of each component
by AFT in a multiple component system, this study investigated
the competitive degradation of six carbamate insecticides. The
compounds included carbaryl (1-naphthyl methylcarbamate),
carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methyl-
carbamate), dioxacarb (2-(1,3-dioxolan-2-yl)phenyl methylcar-
bamate), bendiocarb (2,2-dimethyl-1,3-benzodixol-4-yl meth-
ylcarbamate), promecarb (3-isopropyl-5-methylphenyl methylcar-
bamate), and fenobucarb (2-(1-methylpropyl)phenyl methylcar-
bamate). Considerable work has been reported in the literature
Fenton technologies seem more attractive than other advanced
oxidation processes due to their effectiveness on a broad
spectrum of compounds, strong oxidation activity, fast kinetics,
and equipment simplicity (14-19). To overcome the disadvan-
* To whom correspondence should be addressed. Tel: 607-255-3151.
Fax: 607-255-1093. E-mail: ATL2@cornell.edu.
10.1021/jf034311f CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/01/2003

Competitive Degradation and Detoxification of Carbamate
J. Agric. Food Chem., Vol. 51, No. 18, 2003 5383
compounds were added to the solution. Carbamates were studied
individually in experiments where temperature was controlled at 10 (
0.1, 18 ( 0.1, 25 ( 0.1, or 33 ( 0.1 °C.
about the environmental behavior of carbaryl and carbofuran;
however, papers about the other four carbamates are very
limited. As shown by Mabury and Crosby (28), there is a
relationship between pesticide reactivity toward hydroxyl
radicals and environmental behavior. Information about these
carbamates acquired from this study will supplement the
knowledge about carbamates in the environment both directly
and indirectly. The objectives of this study are (i) to exam the
appropriateness of the AFT model for the degradation kinetics
of different carbamate mixtures; (ii) to derive rate constants for
reaction with hydroxyl radicals generated by AFT; (iii) to
investigate the temperature dependency of degradation and
calculate activation energies; (iv) to determine the effect of AFT
on the biodegradability of these carbamates; (v) to identify
degradation products by AFT and propose possible degradation
pathways; and (vi) to estimate the detoxification of carbamate
insecticides by AFT.
Analysis of Carbamate and Hydrogen Peroxide Concentration.
The concentration of carbamates was analyzed by a HP 1090 HPLC
equipped with a diode array detector. For analysis of carbofuran,
carbaryl, bendiocarb, dioxacarb, and the mixture containing carbofuran
and one or two of these carbamates, the mobile phase was composed
of acetonitrile and water (40:60, pH adjusted to 3 using phosphoric
acid). For analysis of promecarb, fenobucarb, and the mixture of
carbofuran with one of these carbamates, the mobile phase was
composed of acetonitrile and water (70:30, pH 3). A C18 5 µm 250
mm × 4.6 mm (i.d.) PRISM RP column was used for separation. The
detector wavelength was set at 220 ( 20 nm with 450 ( 80 nm as the
reference. Under the first operating conditions, the retention times of
carbofuran, carbaryl, bendiocarb, and dioxacarb were 10.36, 11.85, 9.12,
and 4.87 min, respectively. Under the second operating conditions, the
retention times of carbofuran, promecarb, and fenobucarb were 3.55,
5.26, and 5.00 min, respectively. The concentration of hydrogen
peroxide was determined by titration using standard potassium per-
manganate solution (29).
MATERIALS AND METHODS
Determination of COD and BOD5. Under typical operating
conditions, a mixture of six carbamates with individual concentrations
of 50 µM was treated by membrane AFT. At different treatment times,
the AFT was stopped and samples were taken from the anodic half-
cell for COD and BOD5 determination. To adjust pH, phosphate buffer
(NaH2PO4 and Na2HPO4, each at 1.0 M) was added at a ratio of 1.0
mL per 50 mL sample to each sample to adjust pH. Fresh catalase
solution (1.0 mg/mL in 0.5 M phosphate buffer solution) was
subsequently added at the same ratio as that of buffer to decompose
the residual hydrogen peroxide.
Chemicals, Test Organisms, and Membrane. Carbaryl (99%),
carbofuran (99%), dioxacarb (98%), bendiocarb (99%), fenobucarb
(99%), and promecarb (98%) were purchased from Chem Services
(West Chester, PA). Hydrogen peroxide (analytic grade), magnesium
sulfate (analytic grade), potassium dichromate (analytic grade), potas-
sium permanganate (analytic grade), acetonitrile (HPLC grade), and
water (HPLC grade) were purchased from Mallinckrodt (Paris, KY).
Sodium chloride (certified), phosphoric acid (analytic grade), potassium
phosphate monobasic (certified), ferrous chloride (certified), sodium
hydroxide (certified), starch soluble (certified), sodium thiosulfate
(certified), potassium iodide (certified), sodium fluoride (certified), and
methylene chloride (HPLC grade) were purchased from Fisher Scientific
(Fair Lawn, NJ). Sulfuric acid (analytic grade) was purchased from
EM Science (Gibbstown, NJ). Potassium phosphate dibasic, ammonium
sulfate, calcium chloride, calcium carbonate, ferrous ammonium sulfate,
and silver sulfate were all certified reagents and were purchased from
GFS Chemicals (Columbus, OH). Manganese sulfate (certified) was
purchased from Sigma (St. Louis, MO). Mercury sulfate (certified) and
1,10-phenanthroline (99%) were purchased from Aldrich (Milwaukee,
WI). Fine sand and sphagnum peat moss were purchased from K-mart.
Kaolinte clay was purchased from Lagula Clay Co. (City of Industry,
CA).
COD was determined using the dichromate method, and BOD5 was
determined using the iodometric method with azide modification (30).
To remove the interference from iron ion, sodium fluoride was used
prior to the addition of sulfuric acid during the process of BOD5
determination.
GC/MS Identification of Degradation Products. Each insecticide
of the six carbamates was degraded individually by AFT under typical
operating conditions. After a 2 min treatment, 15 mL of anodic solution
was withdrawn and immediately extracted with 3 mL of methylene
chloride. After separation from the aqueous solution, the organic phase
was dried with anhydrous sodium sulfate. The sample was then analyzed
by an Agilent 6890N Network GC system equipped with an Agilent
5973 Network mass selective detector and Agilent 7683 series injector.
The GC/MS conditions were as follows: a 30 m × 0.25 mm (i.d.)
fused silica capillary column with 0.25 µm film thickness (HP 19091S-
433) and helium carrier gas (10.50 psi) was used; initial temperature
was 80 °C, increasing at 10 °C/min to 210 °C, at 30 °C/min from 210
to 305 °C, and then kept at 305 °C for 5 min; the injector port
temperature was 220 °C; and the detector temperature was 250 °C.
The structures of the degradation products were identified by interpret-
ing the MS spectra obtained in this work and by checking with available
standard spectra.
The sludge inoculated for the BOD5 determination (as defined by
APHA) was taken from the domestic sewage treatment plant of Ithaca,
NY. Earthworms (Eisenia foetida) were purchased from Carolina
Biological Supply (Burlington, NC). The anion exchange membrane
(ESC-7001), with an electrical resistance of 8 ohm cm-2 in 1 M NaCl
solution at 25 °C, was purchased from Electrosynthesis (Lancaster, NY).
Degradation of Carbamates by AFT. A schematic of the membrane
AFT apparatus was shown and specified in our previous work (25).
Under typical operating conditions, 200 mL of different concentrations
of carbamate(s) with 0.02 M NaCl and 200 mL of 0.08 M NaCl were
added to the anodic and cathodic half-cells, respectively. The ferrous
ion was delivered to the anodic half-cell by electrolysis at 0.050 Amp.
The hydrogen peroxide solution of 0.311 M was added to the anodic
half-cell by a peristaltic pump at 0.50 mL/min. The delivery ratio of
H2O2 to Fe2+ was 10:1. The temperature was controlled at 25 ( 0.1
°C by a HAAKE K20 water circulator serving as a water bath. The
power supply was turned on to initiate electrolysis when the first drop
of hydrogen peroxide was added to the anodic half-cell. At different
treatment times, 1.0 mL of anodic solution was taken out and put into
a 2 mL GC vial containing 0.10 mL of methanol (for quenching
subsequently generated hydroxyl radicals) and was analyzed for
carbamate concentration(s) using HPLC. Treatments were repeated for
a total of three replicates.
Earthworm Toxicity Assay. Earthworms were exposed to the AFT
treatment effluents in artificial soil, which was comprised of fine sand
(69%, dry weight), kaolinite clay (20%), sphagnum peat moss (10%),
and calcium carbonate (1%) (31). To prepare effluents, a mixture of
the six carbamate pesticides (80 µM each) was subjected to AFT under
typical operating conditions. At 0, 3, and 10 min, the AFT was stopped
and samples were taken from the anodic half-cell. One hundred
milliliters of effluent was added to 300 g (dry weight) of artificial soil
and thoroughly mixed in a plastic zip bag. With the addition of effluent,
the moisture content of the soil was adjusted to 40-45%. The spiked
soil was then transferred to a 500 mL plastic jar. Ten earthworms with
individual weights of 0.15-0.25 g were washed, dried on filter paper,
weighed, and then placed on the surface of the soil. Earthworms that
did not burrow into the soil after 5 min were replaced. All exposures
were conducted at 20 ( 1 °C with an 8:16 h light:dark cycle. Evaporated
moisture was determined gravimetrically and replaced daily. All tests
were conducted in triplicate.
The degradation kinetics of carbofuran were investigated using initial
concentrations that ranged from 30 to 200 µM. When investigating
competitive degradation between carbofuran and other carbamates, the
concentration of each insecticide was 50 µM, and two or three

5384 J. Agric. Food Chem., Vol. 51, No. 18, 2003
Wang and Lemley
The soil was hand-sorted after 1, 5, 7, and 10 days to determine the
mortality and the decrease of average body weight of living earthworms.
Earthworms that had no response to a mild mechanical touch were
regarded as dead. After each assessment, soil and earthworms were
put back in the original jars and the weight was recorded as the basis
for the next day’s moisture compensation.
AFT Kinetic Model. The derivation of the AFT kinetic model was
published in our previous paper (25). Assumptions for setting up the
model include the following: (i) the concentration of ferrous ion, which
is constantly generated by electrolysis and continuously consumed by
reacting with hydrogen peroxide, is constant; (ii) hydrogen peroxide
can be accumulated during the treatment; (iii) the Fenton reaction and
the hydroxyl radical reaction with the target compound obey second-
order kinetics; and (iv) the instantaneous concentration of hydroxyl
radical is proportional to its generation rate. With these assumptions,
the degradation kinetics of the target organic compound can be
described by the following equation:
[C]t
[C]0
1
2
2 2
ln
) - Kλπων0 t
(1)
where K ) kk′ (µM-2 min-2), k (µM-1 min-1), and k′ (µM-1 min-1
)
are the second-order rate constants of the Fenton reaction and the
reaction between hydroxyl radical and target compound, respectively;
[C]0 (µM) and [C]t (µM) are the concentrations of the target compound
at 0 and t min, respectively; λ(min) and π(min) are the average life of
the hydroxyl radical and ferrous ion, respectively; ω is a constant related
to the delivery ratio of hydrogen peroxide to ferrous ion and to the
consumption ratio of hydrogen peroxide; ν0 (µM min-1) is the delivery
rate of ferrous ion by electrolysis; and t (min) is time. Kλπω, the
degradation rate parameter, signifies the degradation rate when the
delivery rate of ferrous ion is fixed.
Figure 1. Competitive oxidation of carbamates by membrane AFT in two
component (a) and three component (b) systems. Points are experimental
data. Lines are fitting results using the AFT model.
RESULTS AND DISCUSSION
Competitive Degradation and Hydroxyl Reaction Rate
Constants. In our previous studies, we showed that the AFT
model could successfully fit the degradation kinetics of several
target compounds in a single component system (25-27). The
fit of the AFT model to the kinetics of coexisting compounds
in a multitarget system has not yet been demonstrated. In this
work, the competitive degradation between carbofuran and either
one or two other carbamate(s) was carried out and fitted by the
AFT model. Some of these results are shown in Figure 1. Both
carbofuran and coexisting carbamate(s) can be efficiently
degraded at different rates during the membrane AFT treatment.
The degradation kinetics of each of the coexisting carbamates
in either a two target or three target system are fitted very well
by the AFT model. All values of rate parameters (Kλπω) and
regression coefficients (r) of each coexisting carbamate in the
competitive system investigated in this study are listed in Table
1.
Table 1. Rate Parameters (Kλπω) and Regression Coefficients (r) of
Each Coexisting Carbamate
competitive system
Kλπω (µM-2
)
r
carbofuran (1) + carbaryl (2)
(1) (6.875 ± 0.086) × 10-5
(2) (1.178 ± 0.238) × 10-4
(1) (7.769 ± 0.089) × 10-5
(2) (9.897 ± 0.083) × 10-5
(1) (6.375 ± 0.109) × 10-5
(2) (1.109 ± 0.420) × 10-4
(1) (6.802 ± 0.076) × 10-5
(2) (1.076 ± 0.166) × 10-4
(1) (6.965 ± 0.096) × 10-5
(2) (1.039 ± 0.053) × 10-4
(1) (4.538 ± 0.106) × 10-5
(2) (8.179 ± 0.036) × 10-5
(3) (9.060 ± 0.156) × 10-5
0.999
0.999
0.999
0.999
0.998
0.993
0.999
0.998
0.999
0.999
0.997
0.999
0.998
carbofuran (1) + bendiocarb (2)
carbofuran (1) + dioxacarb (2)
carbofuran (1) + fenobucarb (2)
carbofuran (1) + promecarb (2)
carbofuran (1) + carbaryl (2) +
dioxacarb (3)
Because λ, π, ω, and ν0 should be the same for each of the
coexisting targets in the same solution and k (the Fenton reaction
rate constant) is a constant, the difference in degradation rate
should be determined by k′, the hydroxyl radical reaction rate
constant for a given pesticide. Thus, the degradation rates of
coexisting compounds in the same solution are proportional to
their hydroxyl radical reaction rate constants. The following
equation can describe the ratio of coexisting carbamates
rate constants of other carbamates can be calculated from eq 2
and are listed in Table 2. This method of deriving rate constants
requires analysis of each pesticide to develop the degradation
curve and is called the direct method. According to the data
listed in Table 2, the reactivity of these carbamates toward
hydroxyl radicals is in the following order: dioxacarb ≈ carbaryl
> fenobucarb > promecarb > bendiocarb > carbofuran.
As described in our previous work (26), we can also calculate
the hydroxyl radical reaction rate constant of the coexisting
carbamates from the difference of carbofuran Kλπω values
between that obtained from a pure 50 µM carbofuran solution
and that from 50 µM carbofuran coexisting with another 50
µM carbamate. This method is called the indirect method. This
method does not require the concentration analysis of each
carbamate during degradation to obtain its degradation rate
k1′ (Kλπω)1
)
(2)
k2′
(Kλπω)2
where k1′ and k2′ are hydroxyl radical reaction rate constants
for coexisting compounds 1 and 2, respectively. According to
Haag and Yao (32), the hydroxyl radical reaction rate constant
for carbofuran (k′) is 7 × 109 M-1 s-1. The hydroxyl reaction

Competitive Degradation and Detoxification of Carbamate
J. Agric. Food Chem., Vol. 51, No. 18, 2003 5385
Table 2. Hydroxyl Reaction Rate Constants (k′) of Each Coexisting
Carbamate Derived from Direct and Indirect Methods
Table 3. Kλπω Values at Different Temperatures and Pseudo
Activation Energies (E ) of Carbamates by Membrane AFT
a
k′ (M-1 s-1) from
direct method
k′ (M-1 s-1) from
indirect method
carbamate
dioxacarb
temp (K)
Kλπω (µM-2
)
E (kJ/mol)
a
carbamate
283.2
291.2
298.2
306.2
283.2
291.2
298.2
306.2
283.2
291.2
298.2
306.2
283.2
291.2
298.2
306.2
283.2
291.2
298.2
306.2
283.2
291.2
298.2
306.2
(1.128 ± 0.031) × 10-4
(1.705 ± 0.072) × 10-4
(1.978 ± 0.089) × 10-4
(2.917 ± 0.143) × 10-4
(7.028 ± 0.036) × 10-5
(9.043 ± 0.096) × 10-5
(1.048 ± 0.011) × 10-4
(1.330 ± 0.028) × 10-4
(6.081 ± 0.063) × 10-5
(7.534 ± 0.066) × 10-5
(8.722 ± 0.056) × 10-5
(1.020 ± 0.013) × 10-4
(6.130 ± 0.112) × 10-5
(8.047 ± 0.172) × 10-5
(8.805 ± 0.169) × 10-5
(9.888 ± 0.079) × 10-5
(6.869 ± 0.079) × 10-5
(8.030 ± 0.066) × 10-5
(9.123 ± 0.122) × 10-5
(9.911 ± 0.116) × 10-5
(5.995 ± 0.116) × 10-5
(6.773 ± 0.073) × 10-5
(7.074 ± 0.060) × 10-5
(7.686 ± 0.119) × 10-5
26.4
13.3
16.4
14.9
11.9
7.7
dioxacarb
carbaryl
fenobucarb
promecarb
bendiocarb
carbofuran
1.2 × 1010
1.2 × 1010
1.1 × 1010
1.0 × 1010
8.9 × 109
7 × 109a
1.1 × 1010
1.0 × 1010
1.0 × 1010
9.9 × 109
8.3 × 109
carbaryl
fenobucarb
promecarb
bendiocarb
carbofuran
a Data from Hagg and Yao (36).
parameter, but it does require an accurate correlation between
the Kλπω value and the initial concentration of carbofuran to
estimate the equivalent carbofuran concentration of the coexist-
ing target compound. This correlation was obtained in a previous
study of carbofuran (33).
ln(Kλπω) ) -4.478 - 1.062 lnCinitial
(3)
The calculated rate constant values of these coexisting carbam-
ates using the indirect method are also listed in Table 2. The
two calculation methods yielded consistently similar rate
constants, confirming that the indirect method is reliable and
acceptable. The application of the indirect method in obtaining
hydroxyl radical reaction rate constants is quite convenient,
especially when a large number of compounds is simultaneously
studied. As compared with our data from this study and with
data from Haag and Yao (32), Mabury and Crosby’s data appear
to be systematically lower (28). This difference might result
from the fact that in their PNDA model they do not account
for the consumption of hydroxyl radicals by species other than
the probe parent compound and the PNDA. Our previous
pesticide rate constants calculated with these same methods (26)
compared well with literature values from Haag and Yao (32).
Effect of Temperature on Degradation. Degradation of the
carbamates by membrane AFT at different temperatures obeys
the AFT model very well (regression coefficients not shown).
All Kλπω values are listed in Table 3. The Kλπω value
increases with increasing temperature. Because the delivery rate
of Fenton reagent was kept constant for all treatments and the
hydroxyl radical reaction and Fenton reaction are fast reactions,
the degradation rate parameter can also be used to signify the
treatment efficiency. An increasing Kλπω value with temper-
ature indicates that a higher AFT treatment efficiency can be
attained at a higher temperature.
On the basis of the changes of Kλπω with the temperature,
pseudo activation energies for the degradation of each carbamate
by membrane AFT (a combination of the Fenton reaction and
the hydroxyl radical reaction with the insecticide) were calcu-
lated using the Arrhenius equation (25). These activation
energies are also listed in Table 3. As compared with those for
hydrolysis of carbamates, ranging from 50 to 110 kJ/mol (7,
34, 35), these activation energies are much lower, indicating
that carbamates are thermodynamically easier to degrade by
AFT as compared to hydrolysis in an acidic/alkaline aqueous
environment. Additionally, no correlation between the hydroxyl
reaction rate constants and the activation energies of the
carbamates by AFT was found. This implies that these carbam-
ates may undergo different first steps in the degradation process.
If they underwent the same initial degradation reaction, this
result would indicate that the reactions between these carbamates
and hydroxyl radicals are a kinetically controlled process.
Figure 2. Changes of carbofuran concentration, COD, BOD , and BOD /
COD during the degradation of the carbamate mixture by membrane AFT.
5
5
Improvement on Biodegradability. During AFT treatment
of a mixture of the six carbamates (each concentration at 50
µM), both the carbofuran and the total COD can be effectively
removed (Figure 2a). About 10 min of treatment can completely
remove 50 µM carbofuran from the mixture. Because the
degradation rate of carbofuran by AFT is the lowest among those
of the six carbamates in the mixture, all other coexisting
carbamates should have already been degraded within 10 min
of treatment. The efficiency for total COD is slightly lower as

5386 J. Agric. Food Chem., Vol. 51, No. 18, 2003
Wang and Lemley
Table 4. Retention Times (tr) and MS Spectra of the Degradation Products of Carbamates Determined by GC/MS
carbamate
dioxacarb
degradation products
parent compound (1a)
tr (min)
MS spectrum, m/z (%)
+•
14.08
223 (M , 0.1), 193 (0.1), 178 (1), 167 (8),
166 (76), 165 (58), 150 (2), 149 (23),
148 (4), 135 (5), 123 (6), 122 (55),
121 (100), 107 (16), 105 (8),
104 (13), 94 (14), 93 (8), 92 (6)
167 (4), 166 (M ,42), 165 (35), 150 (1),
+•
2-(1,3-dioxolan-2-yl)phenol (1b)
9.17
149 (6), 135 (1), 123 (4), 122 (40),
121 (100), 108 (2), 107 (17), 105 (6),
104 (12), 95 (2), 94 (11), 93 (8), 92 (3)
+•
(2-hydroxylethyl)salicylate (1c)
2-hydroxyl benzaldehyde (1d)
parent compound (2a)
10.58
4.39
182 (M ,13), 165 (4), 164 (37), 138 (4),
122 (6), 121 (50), 120 (100), 94 (2),
93 (14), 92 (42), 86 (3), 84 (5)
+•
124 (1), 123 (8), 122 (M ,100), 121 (93.3),
105 (1), 104 (13), 94 (6), 93 (20),
92 (3), 88 (2), 86 (11), 84 (17)
+•
fenobucarb
11.47
12.53
7.21
207 (M ,0.5), 176 (0.3), 151 (3), 150 (29),
135 (2), 122 (9), 121 (100), 115 (2),
107 (8), 103 (7), 91 (12)
+1
2-(1-methylpropyl)phenyl formate (2b)
2-(1-methylpropyl)phenol (2c)
2-acetyl phenol (2d)
179 (M , 2), 165 (3), 164 (26), 123 (2),
122 (21), 121 (100), 107 (7.2),
103 (14), 93 (4), 91 (14)
+•
151 (3), 150 (M ,23), 135 (2), 133 (1),
122 (9), 121 (100), 119 (2),
115 (3), 107 (12), 103 (16), 91 (15)
+•
5.86
137 (4), 136 (M ,48), 122 (8), 121 (100),
118 (1), 107 (1), 94 (3), 93 (21),
92 (3), 89 (2), 86 (5), 84 (7)
207 (M ,2), 151 (8), 150 (73), 136 (10),
+•
promecarb
parent compound (3a)
12.40
7.73
135 (100), 133 (3), 122 (4), 121 (5),
115 (5), 107 (6), 105 (6), 91 (16)
+•
3-isopropyl-5-methylphenyl formate (3b)
178 (M ,0.1), 151 (3), 150 (38), 136 (10),
135 (100), 122 (4), 121 (6), 117 (6),
115 (9), 107 (11), 105 (6), 91 (21)
223 (M ,1), 167 (6), 166 (47), 152 (11),
+•
3-(2-hydroxyl-isopropyl) 5-methylphenyl
methylcarbamate (3c)
13.92
10.66
10.23
9.77
151 (100), 135 (7.3), 123 (5),
107 (9), 91 (8)
+•
3-acetyl-5-hydroxyl benzaldehyde (3d)
3-isopropyl-5-hydroxyl benzaldehyde (3e)
3-methyl-5-(2-hydroxy-2-propyl)phenol (3f)
165 (9), 164 (M ,82), 150 (12), 149 (100),
135 (23), 131 (5), 121 (26.5),
107 (21), 103 (25), 91 (36)
+•
165 (3), 164 (M ,24), 150 (5), 136 (33),
135 (100), 121 (21), 117 (21), 117 (8),
115 (16), 107 (19), 105 (10), 91 (40)
+•
167 (8), 166 (M ,65), 152 (10), 151 (100),
148 (4), 135 (9), 123 (8), 121 (5),
119 (3), 109 (12), 108 (12),
107 (21), 91 (12)
224 (1), 223 (M ,11), 167 (4), 166 (42),
152 (9), 151 (100), 149 (2),
+•
bendiocarb
carbofuran
parent compound (4a)
12.16
7.58
126 (43), 123 (7)
+•
2,2-dimethyl-1,3-benzodixol-4-yl formate (4b)
2,2-dimethyl-1,3-benzodixol-4-ol (4c)
parent compound (5a)
195 (4), 194 (M ,35), 179 (8), 166 (14),
152 (10), 151 (100), 127 (5),
126 (70), 125 (6), 123 (7)
+•
7.21
167 (6), 166 (M ,62), 152 (9), 151 (9100),
149 (1), 128 (1), 127 (6), 126 (87),
125 (6), 123 (9)
+•
12.98
222 (0.8), 221 (M ,6), 206 (0.1), 191 (0.1),
177 (0.3), 166 (1), 165 (11), 164 (100),
150 (6), 149 (57), 147 (8), 131 (16),
123 (14), 122 (16)
+•
2,3-dihydro-2,2-dimethylbenzofuran-7-yl formate (5b)
2,3-dihydro-2,2-dimethylbenzofuran-7-ol (5c)
8.74
7.63
193 (7), 192 (M ,43), 164 (58), 149 (100),
145 (10), 135 (7), 131 (36),
123 (32), 122 (30)
+•
166 (1), 165 (11), 164 (M ,100), 150 (8),
149 (85), 147 (14), 146 (6), 145 (8),
136 (3), 135 (6), 132 (4), 131 (34),
123 (27), 122 (28), 121 (24)
+•
2-hydro-3-hydroxyl-2,2-dimethylbenzofuran-7-ol (5d)
9.59
181 (5), 180 (M ,38), 163 (2), 162 (8),
161 (12), 151 (14), 147 (33),
138 (11), 137 (100), 134 (6),
123 (9), 121 (11)

Competitive Degradation and Detoxification of Carbamate
J. Agric. Food Chem., Vol. 51, No. 18, 2003 5387
MS spectrum, m/z (%)
Table 4. (Continued)
carbamate
carbofuran
degradation products
tr (min)
+•
2-hydro-3-oxo-2,2-dimethylbenzofuran-7-ol (5e)
9.02
179 (12), 178 (M ,100), 177 (39), 164 (5),
163 (34), 161 (5), 160 (4), 150 (6),
149 (6), 137 (63), 136 (13), 135 (36),
122 (3), 121 (6)
+•
carbaryl
parent compound (6a)
1-naphthol (6b)
12.31
9.00
201 (M ,3), 146 (1), 145 (11), 144 (100),
128 (1), 127 (3), 126 (1), 117 (3),
116 (28), 115 (56), 114 (3), 113 (2),
89 (7), 88 (2), 87 (2)
+•
146 (M ,1), 145 (11), 144 (100), 126 (1),
117 (4), 116 (41), 115 (89), 114 (4),
113 (3), 100 (1), 98 (1), 90 (2), 89 (10),
88 (3), 87 (3), 86 (2), 85 (1)
+•
1,4-naphtho-quinone (6c)
8.10
160 (M ,10), 159 (11), 158 (100), 131 (9),
130 (39), 104 (59), 103 (9), 102 (53)
+•
(phthalic acid-O-)yl N-methylcarbamate (6d)
12.60
223 (M ,5), 205 (4), 150 (10), 149 (100),
105 (4), 104 (5), 97 (4), 85 (3), 83 (3)
Figure 3. Degradation pathways of dioxacarb and fenobucarb by
membrane AFT.
compared with the removal efficiency of parent compounds.
After 10 min of treatment, 27% COD still remains, indicating
the existence of a significant amount of degradation products
with substantial COD values.
Figure 4. Degradation pathways of bendiocarb and carbofuran by
membrane AFT.
After AFT treatment, the BOD5 value of the carbamate
mixture gradually increased from 4.9 at 0 min to 22.5 mg/L at
3 min and was maintained at this level for 15 min (Figure 2b).
The increased BOD5 demonstrated that the mixture became more
utilizable for bacteria through the AFT treatment. BOD5/COD
is usually used as a parameter to assess the biodegradability of
certain organics in water, and compounds with a ratio greater
than 0.3 are regarded as biodegradable (36). The value of BOD5/
COD for the carbamate mixture prior to AFT treatment was
only 0.04, illustrating that the carbamates are biorefractory or
toxic. As shown in Figure 2b, BOD5/COD can be dramatically
increased by AFT treatment. After a 3 min treatment, the BOD5/
COD reached 0.34, indicating that the waste was more likely
to be biodegradable. A 15 min treatment raised the BOD5/COD
ratio of the carbamate mixture solution to 0.71. Thus, AFT is a
very effective preliminary treatment method for refractory or
toxic organics. The effluents from the AFT can be combined
with common sewage for further treatment.
Degradation Pathways of Carbamates by AFT. Degrada-
tion products of carbamates identified by GC/MS analysis and
their MS spectra are listed in Table 4. Because of the sensitivity
limit of the MS detector, low concentration, and the difficulty
of volatilization in the GC inlet port, some degradation
compounds may not have been detected. On the basis of the

5388 J. Agric. Food Chem., Vol. 51, No. 18, 2003
Wang and Lemley
Figure 5. Degradation pathways of promecarb and carbaryl by membrane AFT.
identified degradation products, degradation pathways of these
carbamates by membrane AFT are proposed. Figure 3 shows
the degradation pathway of dioxacarb (1a) and fenobucarb (2a).
The carbamate branch seems to be the first target attacked by
hydroxyl radicals. The cleavage of the carbamate branch results
in a substituted phenol (1b and 2c). Subsequently, hydroxyl
radicals begin to attack remaining ring substituents. For di-
oxacarb, the dioxolane ring opens and salicylate (1c) is formed.
Further attack can remove the hydroxyethyl branch to form
2-hydroxy benzaldehyde (1d). For fenobucarb, hydroxyl attack
removes the ethyl and forms a carbonyl in its place, generating
2-acetyl phenol (2d).
Bendiocarb (4a) and carbofuran (5a) have very similar
structures. The only difference is that bendiocarb has a 1,3-
dioxol-ring, while carbofuran has a furan ring. Their degradation
pathways are also similar (Figure 4). As described above, attack
of the carbamate branch by hydroxyl radicals is the first step.
The carbamate can be deaminated, generating formates (4b and
5b). Continuous attack removes the formate group, giving rise
to the substituted phenol (4c and 5c), which has been found
after photodegradation of bendiocarb (37) and carbofuran (38).
Moreover, carbofuran can further react with hydroxyl radicals
at the 3-C of the furan ring substituting the hydroxy group for
the H atom (5d) and forming carbonyl (5e) by subsequent
hydroxyl radical attacks.
the common initial target of hydroxyl radicals. The degradation
products resulting from this attack, substituted phenols, are the
commonly seen degradation products for each of them. Some
of these phenols can also be found in photolysis (37-39) and
hydrolysis (40, 41) of carbamates. For promecarb and carbaryl,
hydroxyl radicals can also initiate attack at the alkyl site. Thus,
the degradation of carbamates by the AFT can be initiated by
hydroxyl radical attack at different sites on carbamate molecules.
This is consistent with the result obtained in the temperature
experiments, confirming that these carbamates undergo different
first steps in the degradation process.
Reduction of Toxicity. Earthworms are important contribu-
tors to soil fertility and therefore need protection from agro-
chemicals and industrial compounds. Hence, the earthworm
toxicity test is widely used to predict the potential impact of
pesticides on earthworm populations in agricultural land and
to model the potential hazard of industrial chemicals to the
terrestrial ecosystem (42). It has been reported that carbamates
are very toxic to earthworms and can kill them rapidly (43). A
more recent study found that carbaryl strongly inhibits earth-
worm acetylcholinesterase and may also competitively inhibit
biotransformations relying on cytochrome P-450 (44).
The toxicity changes of carbamate mixtures treated by AFT
were examined using earthworm E. foetida in this study.
Earthworms suffered no mortality when exposed to a combined
carbamate concentration of 48 µmol in 300 g of soil (0.16 µmol/
g) for 10 days. Because of the limited solubility of some of the
carbamates, the concentrations could not be increased suf-
ficiently to observe acutely toxic levels. However, changes in
average earthworm weight, a sensitive parameter of sublethal
toxicity (31), showed that AFT treatment reduced the overall
toxicity of the carbamate mixture (Figure 6). Almost no
significant difference in average weight loss was found between
earthworms exposed to a 10 min treatment effluent and the blank
control. In summary, the untreated carbamate mixture was more
toxic to earthworms than treatment effluents, and longer AFT
treatment times decreased toxicity.
The degradation products of promecarb and carbaryl suggest
that the carbamate branch need not always be the first target
attacked by hydroxyl radicals (Figure 5). The hydroxyl radical
can react with and remove the carbamate branch of carbamate
insecticides, leading to substituted phenols (6b and 3d-f).
Concurrently, hydroxyl radicals can also initially attack the alkyl
group. For carbaryl, hydroxyl radicals can open one aromatic
ring of naphthalene to generate product 6d (27). For promecarb,
hydroxyl radicals can attack the isopropyl group by substituting
a hydroxy group for the H atom to form product 3c.
From the overall degradation pathways of these six carbam-
ates by membrane AFT, it appears that the carbamate branch is

Competitive Degradation and Detoxification of Carbamate
J. Agric. Food Chem., Vol. 51, No. 18, 2003 5389
ACKNOWLEDGMENT
We sincerely appreciate the assistance of Emily Scherer for
sample preparation methods for toxicity testing and Tatyana
Dokuchayeva for operation of GC/MS.
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Received for review March 28, 2003. Revised manuscript received July
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JF034311F