Mechanisms of composition change and toxic potentiation of chloramidophos emulsifiable concentrate during storage

Article abstract of DOI:10.1021/jf803188f

Storage instability is one of the serious problems that greatly restrict pesticide use. Routine checks on the composition and toxicity of 30% emulsifiable concentrates (EC) of chloramidophos (CP) during storage indicated that 78.6% of the active ingredien

Full text of DOI:10.1021/jf803188f

930 J. Agric. Food Chem. 2009, 57, 930–937
Mechanisms of Composition Change and Toxic
Potentiation of Chloramidophos Emulsifiable
Concentrate during Storage
SHANSHAN ZHOU,†,‡ DATONG ZHANG,† HUAYUN YANG,† YING ZHANG,‡ AND
†,
WEIPING LIU *
Research Center of Green Chirality, College of Biological and Environmental Engineering, Zhejiang
University of Technology, Hangzhou 310032, People’s Republic of China; and Institute of
Environmental Science, College of Environmental and Resource Sciences, Zhejiang University,
Hangzhou 310027, People’s Republic of China
Storage instability is one of the serious problems that greatly restrict pesticide use. Routine checks
on the composition and toxicity of 30% emulsifiable concentrates (EC) of chloramidophos (CP) during
storage indicated that 78.6% of the active ingredient had decreased, whereas the anti-acetylcho-
linesterase (AChE) activity of the formulation was potentiated by 3.5 times. To understand the
mechanism for these changes, detailed knowledge of the products present and their effects on anti-
AChE potential deserves attention. It was likely that the basis for these changes was methanol, the
cosolvent of CP EC, because when the purified CP was stored in methanol at 50 °C for 2 weeks, CP
drop and toxic potentiation similar to those observed in CP EC also appeared. The major products
of the CP-methanol reaction mixture were isolated and identified by HPLC and GC-MS, respectively,
and their inhibitory potentials against AChE and effectiveness as potentiators were assessed. Following
redetermination of the main product (O,S-dimethyl-[(2,2,2)-trichloro-1-methoxyethyl]phosphorami-
dothioate (MCP)) and high anti-AChE material (methamidophos), which were preconfirmed in the
reaction mixture in CP EC, it was successfully demonstrated that the majority of CP in the formulation
had been transformed to a new stable compound, MCP. Meanwhile, formation of another product,
methamidophos, resulted in toxic potentiation.
KEYWORDS: Chloramidophos; pesticide formulation; storage stability; toxic potentiation
INTRODUCTION
A new organophosphorus insecticide, chloramidophos (CP,
O,S-dimethyl (2,2,2-trichloro-1-hydroxyethyl)phosphoramidot-
hioate; also known as chloramine phosphorus; Figure 1) was
provisionally registered as an effective alternative to Me in 2005
and has been widely applied in some provinces in China. Our
Methamidophos (Me, O,S-dimethylphosphoramidothioate;
Figure 1), which was first registered in 1972, is a broad-
spectrum acaricide-insecticide used to control pests on veg-
etables and various crops such as cotton, tobacco, and
potatoes (1, 2). It has even been one of the top 10 organophos-
phorus pesticides (OPs) sold worldwide (3) and is greatly
responsible for humans surviving hunger and poverty. Me has
also been the most used pesticide in China, accounting for >15%
of China’s 1.2 million tons of annual pesticide application (4, 5).
However, as a highly hazardous pesticide (2, 6), Me has caused
numerous poisoning cases (2, 7, 8), and the authorities of China
have stated that all of the production, sale, and use of Me must
be completely banned before December 31, 2008 (9). As a result,
to fill this great gap in agrochemicals, it has been desirable to
introduce some safe and cost-effective substitutes.
* Author to whom correspondence should be addressed (telephone
+86-571-8832-0666; fax +86-571-8832-0884; e-mail wliu@
zjut.edu.cn).
† Research Center of Green Chirality, Zhejiang University of
Technology.
Figure 1. Compound structures of Me, CP, CSP, MCP, SP, MCPA, and
CDPAT.
‡ Institute of Environmental Science, Zhejiang University.
10.1021/jf803188f CCC: $40.75  2009 American Chemical Society
Published on Web 01/08/2009

Instability of a Formulated Pesticide during Storage
J. Agric. Food Chem., Vol. 57, No. 3, 2009 931
previous study using a thermal assay found that the stability of
CP in the solid phase was poor but that it could be improved
when it was inclusion-complexed with ꢀ-cyclodextrin (10). The
present study instead focused on the storage stability of the
exclusively commercial formulation of CP, that is, 30%
emulsifiable concentrates (EC). Because the formulated pesticide
is often stored for long periods, a variety of toxic agents that
are not present originally may form. Moreover, in some cases,
the toxicological properties of the formulations will be modified
by the newly formed compounds, and therefore samples must
be re-evaluated for purity depending on the storage conditions.
One of the most famous examples is the potentiating activity
of the S-methyl isomer of malathion on the mammalian toxicity
of its tropically stored water-dispersible powder formulation
(11). If the formulations of OPs contain a hydroxylic organic
solvent, like the 30% EC of CP which includes methanol as
the cosolvent, the storage stability of the formulation should
be carefully examined for possible changes in chemical com-
position and biological action, because hydroxylic organic
solvents may catalyze the hydrolysis or directly replace amide
or ester groupings within the OPs (12, 13). In this study, we
discovered that the amount of the active ingredient in CP EC
had greatly decreased during its half-year of storage at room
temperature. Contrary to expectation, the acetylcholinesterase
(AChE) inhibitory potential of this formulated CP increased after
storage. With the purpose of finding the particular mechanisms
of disappearance of CP in the stored CP EC, the products
produced were identified. Moreover, their inhibitory potentials
against AChE and effectiveness as potentiators were determined
to assess the relationship of CP drop and toxic potentiation.
These corresponding results may offer useful evidence to
determine whether CP EC can continuously be used in
agriculture.
MATERIALS AND METHODS
Chemicals. Racemic Me with a purity of 99.0% was purchased from
Kefa New Technology Development Co. (Shenyang, China). The
analytical standard (>98%), technical grade (about 90%), and 30% EC
(trade name, Rosi Ling; certificate LS20051354) of CP as well as the
analytical standard (about 97.3%) of O,O-dimethyl-(2,2,2-trichloro-1-
hydroxyethyl)phosphoramidothioate (CSP; Figure 1) were kindly
provided by Wuhan Zhongxin Chemical Engineering Co. Ltd. (Wuhan,
China). Acetylthiocholine iodide (ATCh-I), 5,5′-dithiobis(2-nitrobenzoic
acid) (DTNB), and AChE from E. electricus (EE-AChE, type V-S)
were purchased from Sigma Chemical Co. (St. Louis, MO).
O,S-Dimethyl-[(2,2,2)-trichloro-1-methoxyethyl]phosphoramidot-
hioate (MCP; Figure 1) was synthesized on the basis of our previous
patent (14). Briefly, the technical CP (10.0 g) was stored in 20 mL of
methanol at 50 ( 1 °C in the dark for 7 days and then evaporated
under vacuum, reprecipitated from ethano,l and filtered. The crude
product was further purified by silica gel chromatography, yielding the
desired MCP as a white powder. The purity (>98%) of the compound
was determined by HPLC: 1H NMR (400 MHz, CDCl3) δ 2.37 (3H, d,
J ) 15.2 Hz, -SCH3), 3.69 (3H, s, C-OCH3), 3.84 (3H, d, J ) 12.8
Hz, P-OCH3), 3.95 (1H, t, J ) 21.2 Hz, NH), 4.93 (1H, dd, J ) 4.0,
18.4 Hz, -CH-); 13C NMR (100 MHz, CDCl3) δ 12.42 (-SCH3),
53.63 (P-OCH3), 58.47 (-OCH3), 91.73 (-CCl3), 100.33 (-CH-);
MS [electrospray ionization (ESI)], m/z calcd, 302.3 ([M] + H+); found,
302.3. Elemental analysis (%): calcd C, 19.85; H, 3.66; N, 4.63; found
C, 19.73; H, 3.56; N, 4.47.
Other chemicals and solvents were of analytical or HPLC grade.
General Information. HPLC analyses were carried out on a Jasco
LC-2000 series HPLC system (Jasco, Tokyo, Japan) equipped with a
variable-wavelength UV-2075 detector. GC-MS was conducted on a
TraceGC 2000 equipped with a TraceMS mass selective detector
(Finnigan, MA). 1H NMR and 13C NMR spectra were recorded in
CDCl3 on a Varian Mercury Plus 400 (400 and 100 MHz, respectively)

932 J. Agric. Food Chem., Vol. 57, No. 3, 2009
Zhou et al.
Figure 2. Representative HPLC chromatogram of the stored CP-methanol solution. Peaks: 1, Me; 2, CSP; 3, CP; 4, MCPA; 5 and 6, MCP. The
operating conditions are shown in Table 1 (isolation).
NMR spectrometer (Palo Alto, CA) at room temperature. Direct
injection mass spectra were measured with a Finnigan Trace DSQ mass
spectrometer (ESI) (Silicon Valley, CA). Elemental analysis was
performed using a Thermo Finnigan Flash EA 1112 Elemental Analyzer
(Milan, Italy). AChE activity was determined by a Bio-Rad model 680
microplate reader (Bio-Rad Laboratories).
Storage of Technical and Commercial Products of CP at Room
Temperature. Samples (5.0 g) of freshly prepared CP (in both technical
and formulated states) were sealed in glass ampules and placed at room
temperature for half a year (February-July; daily mean temperature
ranging from 0 to 30 °C; average temperature about 20 °C). At the
end of storage, aliquots were analyzed for the CP by HPLC and tested
for acute cholinergic toxicity against EE-AChE. Corresponding data
of recently manufactured technical (purity about 90%) and 30% EC of
CP were also measured for comparison.
Thermal Storage of the Analytical Standard of CP in Methanol.
A solution of 750 mg of CP (>98%) in 1.5 mL of anhydrous methanol
was closed in a vial and warmed at 50 ( 1 °C for 2 weeks. At 0, 7,
and 14 days, aliquots were taken out for determination of their anti-
AChE potentials against EE-AChE and identification of the main
products. The extent of the anti-AChE activity of the decided products
was also evaluated.
Figure 3. Mass spectra of compound 1 (a) and analytical standard of
Me (b). RT represents the retention time of the sample from the GC
spectra.
Isolation and Characterization of the Main Products in the
CP-Methanol Reaction Mixture (RM). Aliquots from the 14-day
RT samples were injected into a semipreparative C18 column to isolate
the main products. The detailed parameters for separation of the main
products are shown in Table 1. The isolated products were manually
collected at the column outlet and immediately extracted with dichlo-
romethane/acetone ) 1:1. They were evaporated under vacuum and
redissolved in ethyl acetate. All of the separated products were then
identified by GC-MS.
Table 2. Data Relating to Active Ingredient Content and Anti-AChE
Activity of Technical and Formulated CP before and after Storagea
30% ECb
technical productb
active
AChE IC50,
mg L-1 c
active
AChE IC50,
mg L-1c
ingredient, %
ingredient, %
GC-MS Analysis. A HP-5 MS fused silica capillary column (30 m
× 0.25 mm, film thickness ) 0.25 µm, cross-linked 5% diphenyl and
95% dimethylpolysiloxane, Agilent, Wilmington, DE) was used with
nitrogen as the carrier gas (1.0 mL/min). The injection port temperature
was 180 °C, the interface was 280 °C, and the oven temperature was
increased by 10 °C/min from 80 to 250 °C. Electron impact ionization
was performed at 70 eV. The MS scan range was set from 25 to 500
Da.
Quantification of the Products and CP. Quantities of the decided
products and CP were measured using HPLC by comparing the area
of the peaks with that of the standards. Table 1 provides the operating
conditions. Samples for the HPLC assay were dissolved with CH3CN
with a concentration of 5 g L-1. Except for those reagents of analytical
grade, the other samples were filtered through a 0.45 µm pore membrane
filter.
beforec
afterd
29.60
6.32
31.09 ( 1.22
8.82 ( 0.32
88.82
81.29
16.81 ( 0.66
20.00 ( 0.70
a All values are means ( SDs of the mean (n ) 4). b Both the formulated and
technical CP were resolved in acetone at proper concentration. c Freshly prepared.
d Stored for half a year at room temperature.
Working solutions of the enzymes were made in 0.1 M potassium
phosphate buffer (pH 8.0), in which the hydrolysis rates of ATCh-I
were approximately 0.05-0.10 absorbance unit/min. In a typical
experiment, each of five test tubes containing 180 µL of diluted enzyme
solution was treated with 20 µL solutions of inhibitors at various
concentrations that inhibited enzymatic activity by 10-90%. At the
same time, control samples were also prepared using 20 µL of PBS
(pH 8.0) in place of the inhibitor solution. The final concentrations of
solvents (acetone or ethanol) in both the AChE-inhibitor solution and
AChE-control solution were fixed at 0.5% (v/v). Each solvent had
been confirmed not to react with the inhibitors during the experiment
AChE Inhibition Assay in Vitro. Anti-AChE potentials of the
samples were determined by calculating their respective concentrations
that inhibited half of the AChE (from E. electricus) activity (IC50).

Instability of a Formulated Pesticide during Storage
J. Agric. Food Chem., Vol. 57, No. 3, 2009 933
Figure 4. Mass spectra of compound 2 (a), CSP (b), and SP (c) and HPLC of compound 2 (d) and CSP (e). The HPLC conditions are shown in Table
1 (quantification).
period, and their effects on AChE inhibition were negligible. The
mixture was incubated at 37 °C for 30 min, and then 20 µL of the
AChE-inhibitor solution (or AChE-control solution) was taken to
measure the residual activity of AChE.
AChE activity was spectrophotometrically determined at 37 °C
according to a modified Ellman method (15). All of the above tests
and measurements were performed in four replicates. IC50 was
calculated by the logit transition model (16).
of CP EC are very complicated, including the solvent benzene,
a cosolvent methanol, a skin penetration promoter azone, and
many polymer emulsifiers. In addition to the complexity of
the formulated substances, materials for the synthesis of the
technical CP also involve a lot of impurities (such as the
technical Me with the purity of only 73%). Therefore, isolation
of the compounds that were produced by the decomposition of
CP in the formulation is very difficult. As an alternative method,
we initially supposed that some certain formulation constituents
are the main factors inducing the instability of CP. Then,
following storage of highly purified CP with the proposed
formulating ingredient, an effort was made to purify the main
products as well as the potentiating materials out of the RM.
Mechanisms responsible for the changes in CP EC cannot be
concluded until the identity of the products of the main reaction
or high-anti-AChE compounds have been confirmed in the RM
of CP EC.
Statistical Analysis. All data are expressed as mean ( SD. Student’s
t test at a significance level of 0.05 was used to compare the differences
between groups.
RESULTS AND DISCUSSION
Effect of Storage on Technical and Formulated CP. This
study arose from the changes observed in both composition and
AChE inhibitory potential (Table 2) of CP EC during its half-
year storage at room temperature. Table 1 provides data which
show that the anti-AChE activity of CP EC was potentiated by
a factor of about 3.5 times after storage, whereas 78.6% of the
active ingredient CP synchronously disappeared. In contrast to
the formulated CP, AChE inhibition of the technical CP that
was stored under the same condition was decreased only a little
compared to that of a fresh solution. This result is likely because
of a minor degradation of CP during the period of storage, as
determined by HPLC (Table 2). As far as it is possible to
discriminate between the technical and formulated versions of
CP, it is reasonable to presume that some new compounds with
high anti-AChE potential have formed in the stored CP EC,
and the formulating agents are likely responsible for the
instability of CP when it is formulated. The formulating agents
Chloramidophos is a hemiaminal and thus reactive in acidic
alcohols, such as methanol (17). Therefore, we suppose that
these reactions may play an important role in the decomposition
and anti-AChE activity change of CP in EC, and thus we
analyzed the spontaneous reactions of CP in methanol in this
study. First, we mixed the analytical standard of CP with
methanol and then incubated the solution at 50 ( 1 °C. The
major products in the heated CP-methanol solution were
collected and characterized by semipreparative HPLC and GC-
MS, respectively. Then, the amount of the decided products and
their anti-AChE contributions to that of the RM were evaluated
for determining the mechanisms from both composition and

934 J. Agric. Food Chem., Vol. 57, No. 3, 2009
Zhou et al.
Figure 5. Mass spectrum of compound 4 and its probable interpretations.
toxicological points of view. Concentrations of the key products
(product of the main reaction or high anti-AChE material) were
further determined in the CP EC by HPLC as previously
suggested.
compound 4 and its probable interpretation are shown in Figure
5. The structure of compound 5 was concluded to be the same
as that of compound 6 because both total ion current chromato-
grams showed three peaks and the retention times as well as
the fragmentation patterns of each corresponding peak were
identical. As an example, Figure 6 gives the mass spectra of
compound 5 and the probable interpretation. The fragment ion
data suggested that peaks 2 and 3 were assigned as MCP,
whereas the structure of peak 1 was considered to be O,S-
dimethyl 2,2,2-trichloroethylidenephosphoramidothioate (CD-
PAT; Figure 1), a thermal breakdown product of MCP in the
GC. Data from the GC-MS provided evidence that compounds
5 and 6 are two diastereomers of MCP. Confirmation was further
accomplished by comparison with the synthesized material.
Mechanisms of Instability of the Formulated CP. The use
of HPLC to isolate a minor amount of products in the
CP-methanol RM is generally a rapid and convenient method.
However, because of the low sensitivity of the UV signal, we
obtained only four products. Table 3 contains data for the
amount of the various products and CP in the total CP-methanol
mixture. Also included are data for the inhibitory potential of
the product (or CP) itself to AChE and their effects on the anti-
AChE activity of the RM. On the basis of the results shown in
Table 2, it can be calculated that four chemicals, that is, Me,
CSP, MCP, and CP, accounted for about 90% of the total
amount of the RM. Furthermore, supposing that the enzyme
Characterization of the Main Products in the Heated
CP-Methanol Solution. In consideration of the decomposition
of CP at the injection port of the GC, the individual products
were preliminarily isolated, extracted, and then subjected to GC-
MS analysis. HPLC analysis on the semipreparative C18 column
indicated five compounds other than the original chemical CP
(Figure 2). By GC-MS, compound 1 was confirmed as Me
through a good agreement of retention time and mass spectra
of compound 1 with those of the authentic sample (Figure 3).
The chemical structure of compound 2 was also initially
assumed through a comparison of the data from the GC-MS of
the extracted substance with those of a standard sample of CSP
(Figure 4). As shown in Figure 3, the mass spectra of both
compound 2 and CSP were virtually identical, however, with
that of spermine (SP, O,O-dimethyl phosphoramidothioate;
Figure 1), which may be attributable to their consistent thermal
degradation in the GC. Uniform retention time measured by
HPLC (Figure 3) further manifested that CSP is compound 2.
The structure of compound 3 corresponds to CP. Compound 4
was tentatively assigned as O,O-dimethyl-[(2,2,2)-trichloro-1-
methoxyethyl]phosphoramidate (MCPA; Figure 1) on the basis
of its MS fragmentation pattern. The mass spectrum of

Instability of a Formulated Pesticide during Storage
J. Agric. Food Chem., Vol. 57, No. 3, 2009 935
Figure 6. Mass spectra of compound 5 and its probable interpretations. Three peaks with retention times, respectively, at 11.00, 12.76, and 12.85 min
are obtained in the GC spectra of compound 5.
inhibitory actions of all compounds are independent, these four
compounds contributed about 97% of the inhibition of AChE.
Consequently, other products, including MCPA and those not
identified, seem to be less important to the composition or
toxicological aspect of this research and therefore were not
pursued in the present study.
Similar changes in both composition and anti-AChE potential
found in the CP EC solution were identified again after heating

936 J. Agric. Food Chem., Vol. 57, No. 3, 2009
Zhou et al.
Table 3. Effects of the Decided Products and CP on Acetylcholinesterase Inhibitory Potential of the Total Reaction Mixture
compounds
IC50 of the mixturea b (mg L-1
)
,
time (days)
0
Me
CP
CSP
MCP
IC50 (mg L-1
amountc (%)
)
0.36
ND
0
9.19
98.23
>50.00
1.56
39.65
ND
0
9.19
toxic contributiond (%)
100.00
CN
7
amount (%)
toxic contribution (%)
2.95
74.00
5.55
5.45
2.42
CN
78.75
17.93
9.03
8.27
14
amount (%)
toxic contribution (%)
3.37
77.42
1.90
1.71
1.40
CN
82.58
17.22
a Mixture is the aliquot taken from the CP-methanol mixture warmed at 50 °C. b IC50: ) concentration of inhibitor leading to half-inhibition of EE-AChE activity in 30
c
min. Amount % ) concentrations of samples/5 mg L-1. Quantification of the products and CP was accomplished by comparing the area of the peaks with that of the
standards. ND, not detected. d Contribution % ) (amount % × IC50 of mixture at the corresponding time)/IC50 of the pure product. CN, can be neglected.
Figure 7. Possible transformation mechanisms of CP to MCP and Me in CP EC.
of the purified CP in anhydrous methanol. On the one hand,
the content of CP greatly dropped. Storage of CP in methanol
for 7 days resulted in a breakdown of 94.3% to other
compounds, whereas there was 98.2% decomposition after 14
days. On the other hand, the anti-AChE potential of the stored
CP-methanol solution was increased, but much milder than in
CP EC (IC50 at 9.19 mg L-1 at 1 day to 8.27 mg L-1 at 14 days).
Meanwhile, MCP was formed with a mass percent up to 82.6%,
suggesting that the majority of CP was reacted with methanol by
nucleophilic addition, incorporating the methoxyl group into the
molecule in place of the hydroxyl group (Figure 7). This similar
reaction between CP and methanol also can be extrapolated to
the formulation, because peaks relevant to MCP were then
successfully checked out in the stored CP EC (data not shown).
By quantitative analysis, it can be estimated that about 80% of
the disappeared active ingredient of CP EC has been changed
to MCP. In theory, the anti-AChE potential of MCP should be
weaker than that of CP because the anti-cholinesterase activity
of OPs in vitro has been manifested to be closely related to
their hydrophilicity (18). In the present study, we found a
credible result that the IC50 of MCP was about 4.3 times larger
than that of CP (Table 3). For this reason, contribution of MCP
to the anti-AChE activity was only about 18%, even though its
contribution to total mass was >80%, implying that MCP must
not be a potentiator. By contrast, another product Me was about
25.5 times more active toward inhibiting AChE than CP (Table
3), leading to a small quantity of Me greatly responsible for
the AChE inhibitory activity of the CP-methanol RM. For
example, 3% of the total mass contributed >75% of the AChE
inhibitory potential of the RM (Table 2). We further estimated
that if the mass percent of Me in CP EC increased to 4.1%
after storage, the anti-AChE activity would be potentiated to
3.5 times, whereas the actual amount of Me in CP EC
determined by HPLC was 3.8%. Thus, it can be considered that
theformation of Me is probably the main factor for enhancement
of the anti-AChE activity of CP EC during storage. A previous
study concerning two isomers of CP, that is, (CH3O)2P-
(S)NHCH(OH)CCl3 and (CH3O)2P(O)NHCH(OH)CCl3, showed
that these two chemicals could reversibly decompose to
(CH3O)2P(S)NH2 and chloral or (CH3O)2P(O)NH2 and chloral
(19), respectively. As a result, we believe that decomposition
of CP is one of the mechanisms for theformation of Me in CP
EC (Figure 7). CSP is the major impurity of the analytical
standard of CP. As shown in Table 2, the concentration of CSP
first increased and then decreased, meaning that it was unstable
in the RM. Moreover, the contribution of CSP to the anti-AChE
activity was neglected. We therefore never measured its
concentration in CP EC.
In conclusion, these results provide two new pieces of
information. On the one hand, 30% EC, the exclusive formula-
tion of CP used in China, is advised to be limited for sale for
two reasons: first, the active ingredient, CP, is unstable and
easily decreases and, second, Me, a highly toxic and banned
insecticide, will form during storage. On the other hand, MCP,
the newly formed organophosphorus compound, seems to be
stable in this type of formulation because its amount was
constant during storage. As we mentioned, instability was one
of the key factors in stopping application of CP EC in pest
control. Stability of MCP may make it a good substitute for
CP. Furthermore, although the inhibitory potency of MCP to
the target enzyme measured in vitro was only one-fourth of the
paternal insecticide (Table 3), the comparable in vivo activities
of 30% emulsion in water of MCP with those of 30% CP EC
toward both Leucania separate and Pluteua xylostella (14)
additionally imply its application future. Also, because instability
of CP in EC is closely responsible for the hydroxylic organic

Instability of a Formulated Pesticide during Storage
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ABBREVIATIONS USED
AChE, acetylcholinesterase; ATCh-I, acetylthiocholine iodide;
CDPAT, O,S-dimethyl-2,2,2-trichloroethylidenephosphoramid-
othioate; CP, chloramidophos; CSP, O,O-dimethyl-(2,2,2-
trichloro-1-hydroxyethyl)phosphoramidothioate; DTNB, 5,5′-
dithiobis(2-nitrobenzoic acid); EC, emulsifiable concentrates;
EE-AChE, AChE from E. electricus; IC50, concentration of
inhibitor leading to half-inhibition of AChE activity in 30 min;
Me, methamidophos; MCP, O,S-dimethyl-[(2,2,2)-trichloro-1-
methoxyethyl]phosphoramidothioate; MCPA, O,O-dimethyl-
[(2,2,2)-trichloro-1-methoxyethyl]phosphoramidate; OPs, orga-
nophosphorus pesticides; RM, reaction mixtures; SP, O,O-
dimethyl phosphoramidothioate.
ACKNOWLEDGMENT
We thank the Gao Tingyao Environmental Science and
Technology Development Foundation of Tongji University,
Shanghai, China.
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Received for review October 13, 2008. Revised manuscript received
December 6, 2008. Accepted December 9, 2008. This work was
supported by the National Basic Research Program of China
(2009CB421603), the Program for Changjiang Scholars and Innovative
Research Team in University (No. IRT 0653), and the National Natural
Science Foundation of China (No. 20837002, 30771255).
JF803188F