Oxamyl
PESTICIDE NAME: Oxamyl
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Trade name(s): Vydate
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Manufacturer(s): E.I. du Pont de Nemours and Co., Inc.
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Biochemicals Dept.
1007 Market St.
Wilmington, DE. 19898
I. Basic information
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A. Molecular structure: C7H13N3O3S
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B. Chemical name: N-N-dimethyl-2-methylcarbamoyloxylmino-
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-2-(methylthio)acetamide or N', N'-dimethyl-N-[(methyl-
carbamoyl)oxy]-1-thiooxamimidate
C. Derivatives: no information available
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D. Molecular weight: 219.3 g/mole
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E. Solubility in water: 28g/100g (280,000 mg/l)
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F. Common physical appearance: colorless crystalline solid
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G. Oral LD50(rat): 5.4 mg/kg
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H. Pesticide classification: carbamate insecticide, nematicide
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I. Restricted use list (N.Y.): yes
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EPA priority pesticide list: no
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J. Crop use: apple, azalea, boxwood, cherry, mock orange, rose,
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potatoes, general pesticide on ornamental trees
II. Text
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Oxamyl is a widely studied carbamate insecticide and nematicide
used on potatoes, fruit and ornamental trees. It is highly soluble
(pK=6.2), available for leaching and is non-persistent in soil with
loss mainly due to decomposition. The breakdown of oxamyl follows
first-order kinetics degrading to <5% of parent compound within 1 month
of application.
Adsorption of oxamyl is faster than desorption and is due to ionic
interaction and long-range attractive forces. Adsorption increases up
to 30 hours after which equilibrium is achieved. The reaction rate
decreases when concentration is increased.
III. Soils information
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A. Degradation and transformation
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Oxamyl is non-persistent in soil with loss mainly due to
decomposition. There is hydrolysis of the carbamate group with no
measurable oxidation of the thioether function. Oxamyl breakdown
follows first-order kinetics and the rate of degradation is not
obviously correlated with any single soil property(6).
Due to the rapid decomposition of oxamyl, the scientific
literature does not contain a wealth of information on oxamyl
degradation and transformation. Most data is related to oxamyl
adsorption and desorption.
B. Adsorption and transport
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The adsorption of oxamyl is strongest on soils high in organic
matter(6,8). Adsorption on sandy loam is fairly weak and the
effectiveness is influenced by depth of incorporation of the
pesticide(8). The adsorption of oxamyl is not influenced by any single
soil property. Adsorption increases with time up to an asymptotic
maximum after 33hrs(3). The time of adsorptionincreases with
concentration increase(2,3) and with pH increase up to pH6.5 after
which adsorption rate decreases(3). Increasing ionic strength (up to
0.6) will lead to a lessening of adsorption. As ionic strength exceeds
0.6, the adsorption becomes constant(2). If clay is saturated with
individual ions, adsorption follows the order:Na>H>Ca(3) or
Al>Fe>Li>Na>K>Cs(2). From this it can be seen that as polarizing power
of the exchangeable cation decreases, adsorption decreases(2). A rise
in temperature causes adsorption to decrease possibly due to weakened
Van der Waals forces between oxamyl and the clay surface(3). The
adsorption rate constant has been found to be greater than desorption
at all temperatures therefore adsorption is faster than desorption(4).
Oxamyl is readily leached by rain. Spreading of the pesticide is
minimal therefore equilibrium is rapidly attained between mobile and
stationary phases. Under dry conditions upward movement of oxamyl
occurs but no large accumulations result(8).
The tables below present data concerning adsorption and desorption
of oxamyl. The reference is given in parentheses at the end of each
title.
Adsorption of oxamyl on cation-saturated clays(3)
Soil umole ox.add/g clay K(min-1)
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H-illite 392 1.4x10-4
1176 1.3x10-4
Na-illite 366 1.5x10-4
1099 1.4x10-4
Ca-illite 365 1.3x10-4
1095 1.2x10-4
H-kaolinite 163 1.6x10-4
489 1.5x10-4
Na-kaolinite 146 1.5x10-4
438 1.5x10-4
Ca-kaolinite 152 1.4x10-4
456 1.3x10-4
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Desorption of oxamyl with various solutions on cation-saturated
clays(3)
ox.ads.
Soil umol/gclay des.Ha2 O des.1M KCl des.0.05M BaCl2
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H-illite 196 23 83 80
Na-illite 208 42 101 101
Ca-illite 175 26 72 69
H-kaolin. 136 32 61 61
Na-kaolin. 140 46 83 80
Ca-kaolin. 127 36 80 80
***********************************************************************
Freundlich isotherm of oxamyl adsorption on cation-saturated
montmorillonite(2)
K 1/N
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Cation 15 25 35 15 25 35 (degrees C)
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Al 601.3 572.2 541.1 1.320 1.280 1.200
Fe 582.1 560.0 526.1 1.210 1.170 1.140
Li 575.1 550.2 516.6 0.820 0.800 0.780
Na 554.3 537.2 500.9 0.805 0.780 0.765
K 551.2 530.6 495.2 0.800 0.770 0.760
Cs 511.1 500.2 480.9 0.780 0.750 0.735
**********************************************************************
Rate constants as calculated by Lindstrom's model and by the
first-order kinetic rate law for the sorption of oxamyl on illites(4)
Rate Law method Lindstrom model(1970)
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Temp. K Adsorption Desorption Adsorption Desorption
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105xK1(sec-1) 106xK2(sec-1) 105xK1(sec-1) 106xK2(sec-1)
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Na-illite
293 1.44 1.54 1.51 1.60
303 2.10 3.56 2.16 3.41
313 3.16 7.41 3.06 7.22
323 4.52 15.00 4.40 14.91
H-illite
293 1.22 2.51 1.25 2.41
303 1.80 4.41 1.86 4.52
313 2.70 8.25 2.74 8.50
323 4.26 14.00 4.11 16.19
Ca-illite
293 1.15 3.00 1.12 3.01
303 1.90 6.23 1.72 5.38
313 2.70 10.00 2.57 9.71
323 3.84 16.24 3.60 17.46
***********************************************************************
Freundlich Constants for Adsorptive Capacity of Oxamyl on Na, H, and
Ca-montmorillonites(5)
Cation Temp. K l/n
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Na 30 537.0(7.0) 0.780(0.005)
45 478.6(6.3) 0.765(0.005)
60 467.7(4.6) 0.755(0.005)
H 30 524.8(6.2) 0.765(0.010)
45 475.7(1.9) 0.750(0.005)
60 457.1(3.1) 0.745(0.005)
Ca 30 518.8(2.2) 0.745(0.005)
45 467.7(3.0) 0.735(0.005)
60 446.7(4.3) 0.720(0.010)
***********************************************************************
Adsorption rates of oxamyl on bentonite with main constituent
montmorillonite (t**1**/**2 = half-life of adsorption process) (9)
"+"-sat.clay 104K1(min-1) t1/2 (h) ox.added(mmole/10gclay)
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H-montmor. 2.1 54.3 80.1
1.9 58.1 240.2
Na-montmor. 2.5 46.7 74.9
2.3 48.7 224.8
Ca-montmor. 2.2 55.2 75.5
2.0 57.4 226.5
**********************************************************************
Adsorption and desorption of oxamyl at 25degC on bentonite (main
constituent montmorillonite) by different desorbing solutions (9)
Cation ox.ads.(mmole/100g clay) ox.des(mmole/100g clay)by:
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H2O KCl BaCla2
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H 76.2 9.2 24.8 24.5
Na 79.6 26.2 57.4 59.3
Ca 73.0 4.7 23.6 23.0
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IV. References (*denotes key references)
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1.Bansal, O.P. 1983. Colloids and Surfaces. 7. 243-50.
__________________ Sci. 11. 379-88.
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*9.Singhal, J.P., S. Khan, and O.P. Bansal. 1978. Aust. J. Chem.
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31. 2151-6.
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in nature and may no longer be applicable.
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