Azinphos-methyl

86-50-0

Active ingredient in insecticides; acaricide; cholinesterase
inhibitor.

Brown waxy solid.

Odour threshold: detection: 0.0002 mg/kg water (Sigworth 1964).

317.34

The adsorption coefficients of azinphos-methyl were determined
in aqueous solutions with three soils.
soil type               % organic carbon           Ka
sandy loam                    1.4                 3.33
silt loam                     1.8                11.04
high organic silt loam        4.6                28.50
(PESREG)

Azinphos-methyl (from 0.13 to 13 ppm) adsorption coefficients
determined by the Freundlich equation were 16.75 (silt loam),
7.6 (sandy loam) and 9.85 (silty clay). 
Desorbed amounts (4
desorption equilbrations) of azinphos-methyl ranged from 32 to
40% (silt loam), 47 to 68% (sandy loam) and 56 to 67% (silt
clay) (PESREG).

The adsorption and desorption coefficients and constants of
azinphos-methyl were determined in aqueous solutions with four
soil types.
              % organic      adsorption       desorption
soil type       matter       Ka     Koc       Kd     Koc
_______________________________________________________________
silt loam         2.9        12.7   829       16.9  1102
sandy loam        1.1         4.0   693        6.8  1164
sand              1.0         6.8  1282        9.1  1722
clay loam         2.2         8.4   723       11.7  1006
_______________________________________________________________
(PESREG).

Rf-values of azinphos-methyl on soil thin-layer plates varies
0.11 - 0.24 (six different soils) (PESREG).

In soil column study (silt loam soil, aerobic conditions,
incubated 28 days, rainfall 45 days, 1.25 cm daily) 4.4 % of
the applied original radioactivity was found in the leachate.
90 % was retained in the upper 5 cm (PESREG).

The leaching behaviour of azinphos-methyl was studied in the
laboratory with and without ageing soil (two different soils).

Without prior ageing of the parent compound in the soil about
10 - 5 % of the applied radioactivity were translocated into
the leachate of soils. 
About 0.2 - 0.3 % of unchanged parent
compound were recovered from the leachate of both soils.

Degradation products were desmethyl azinphos-methyl,
hydroxymethyl benzazimide/benzazimide and methyl benzazimide
sulfonic acid.

In the study the ageing periods of soils were 30, 62 and 92
days, and rainfall 393 ml/48hr. 
No parent compound could be
detected in the leachate at any time after ageing of the parent
compound in the soil. 
Methyl benzazimidesulfonic acid was the
only metabolite being detectable in the leachate (max conc.
about 5 %) (PESREG).

In the soil column studies azinphos-methyl (1.0 - 1.25 kg/ha)
wasn't found (analysis unit 0.004 - 0.1 mg/l) in the leachate
of six soil samples after two days rainfall (153 - 200 mm)
(PESREG).

Solubility in organic solvents (g/1000 ml):
n-hexane            <1
dichloromethane   >200
2-prapanol        1-10
toluene           >200
(PESREG).

Decomposition begins at 90°C and highly exotermic from 110°C
(PESREG).

Dust-air mixture may be explosive, if the is dust over 500 g/m3
in the air (Gusation *) (PESREG).

The photolysis (high intensity mercury lamp) half-life of
(C-14) azinphos-methyl in a sandy loam soil was 9 days.

The photolysis products were benzazimide and/or
hyrdoxymethyl benzazimide (after 10 days 4 %), azinphos-methyl
oxygen analog, methyl benzazimide and
bis-(benzazimide-N-methyl) sulfide (PESREG).

Azinphos-methyl (3.38 kg/ha) was irradiated with natural
sunlight. 80% of the parent was recovered after 31 days
exposure. 
The estimated half-life of azinphos-methyl under
these study conditions was 99 days (PESREG).

The photolysis (high intensity mercury lamp) half-life of
(C-14) azinphos-methyl in an aqueous solution (pH 4) was 9.4
hours. 
The photolysis products were benzazimide and/or
hyrdoxymethyl benzazimide (after 48 hours about 40%),
anthranilic acid (after 48 hours about 10%) and methyl
benzazimide. 
No volatile degradation products were formed
(PESREG).

Aqueous azinphos-methyl (10.3 ppm) was irradiated with natural
sunlight. 
The half-life was 76.7 hours. 
Photolysis products
were benzazimide and anthranilic acid (PESREG).

The half-lives of azinophos-methyl in water and on glass beads:
                       half-lives (days)
            in water          dry glass beads   wet glass beads
temp pH 8.6  pH 9.6  pH 10.7
_______________________________________________________________
 6°C   36.4     4.95     3.9         99                91
25°C   27.9     2.40     2.0         66                10
40°C    7.2     0.65     0.41        48                 1
_______________________________________________________________
(PESREG).

The half-life of azinophos-methyl was 23.1 days (30°C) and
50 days (calc.) 
(22°C) at pH 7 (PESREG).

The hydrolysis half-lives of azinophos-methyl in buffer
solutions:
         concentration       temperature     half-life
pH          (ppm)                (°C)         (days)
_______________________________________________________________
4             1                   30            39
4            10                   30            42
4             1                   40            18
4            10                   40            21

7             1                   30            23
7            10                   30            25
7             1                   40            11
7            10                   40            12

9             1                   30            2.2
9            10                   30            2.5
9             1                   40            1.1
9            10                   40            1.3
_______________________________________________________________
The major hydrolysis products were
pH 4, 7 and 9
benzazimide and/or hydroxymethyl benzazimide;
bis-(benzazimide-N-methyl) sulfide;
pH 4 and 7
mercaptomethyl benzazimide;
pH 7 and 9
anthranilic acid (PESREG).

The half-life of azinophos-methyl was 38.9 days (30°C) and 87
days (calc.) 
(22°C) at pH 4 (PESREG).

The half-life of azinophos-methyl was 2.2 days (30°C) and 4.1
days (calc.) 
(22°C) at pH 9 (PESREG).

The degradation behaviour of azinphos-methyl was studied in the
laboratory under aerobic conditions with two soils. 
After an
incubation period of 30 days about 6.8 - 8.6 % of applied active
ingredient could be extracted from the soils. 
After 92 days the
proportion of parent compound was about 4.6 - 6.2 %.

The following degradation products were detected:
desmethyl azinphos-methyl;
hydroxymethyl benzazimide/benzazimide;
methylsulfinyl-methyl-benzazimide;
methylsulfonyl-methyl benzazimide;
methyl benzazimide sulfonic acid (PESREG).

The degradation of azinphos-methyl was investigated in sandy
loam soil under aerobic conditions. 
The degradation rate of
azinphos-methyl did not follow strictly first order kinetics
over the 365 day period. 
A half-life value can be estimated for
azinphos-methyl through 95% degradation and was shown to be 44
days. 
The degradation products were azinphos-methyl oxygen
analog, mercaptomethyl benzazimide, benzazimide and/or
hydroxymethyl benzazimide and bis-methyl benzazimide sulfide
(PESREG).

The half-life of azinphos-methyl in sterile soil (sandy loam
soil) was 355 days (PESREG).

The degradation of azinphos-methyl was studied in the
laboratorytests on two different soils. 
Approx. 19 - 9 % of the 
C-14 activity applied was eliminated as 14CO2 222 - 552 days 
after application of (carbonyl-C-14) azinphos-methyl. 
Also the
degradation of (phenyl-UL-C-14) azinphos-methyl was studied in
the soil. 
Approx. 10 % of the applied C-14 activity was
eliminated as 14CO2 365 days after application (PESREG).

The half-life of azinphos-methyl under anaerobic soil (sandy
loam soil) conditions was 68 days following 30 days in aerobic
soil. 
No additional metabolites were formed under anaerobic
conditions (PESREG).

Azinphos-methyl oxygen analog;
Benzazimide and/or hydroxymethyl benzazimide;
bis-(benzazimide-N-methyl) sulfide;
mercaptomethyl benzazimide;
anthranilic acid;

The major metabolic pathway in the degradation of
azinphos-methyl is hydrolysis of the phosphorous ester
resulting in mercaptomethyl benzazimide or hydroxymethyl
benzazimide and their dimethyl (mono or di) thiophosphoric
acids. 
Minor metabolic pathways are
1) oxidative desulfurization with formation of azinphos-methyl
oxygen analog,
2) hydrolysis of the phosphorous-methoxy group to yield either
desmethyl azinphos-methyl or desmethyl oxygen analog  and
3) isomerization of the methoxy-oxygen and phosphorothiono-
sulfur to ultimately give the desmethyl azinphos-methyl
S-methyl isomer; further degradation of these products occurs by
hydrolysis of the phosphorous ester linkage between the
phosphorus and the benzazimide moiety.

Azinphos-methyl oxygen analog is the only
metabolite/degradation product which exhibits cholinesterase
inhibition activity. 
Azinphos-methyl itself shows only slight
activity (PESREG).

In diet; no mortality occurred in rats fed 1 mg/kg/day for 60
days (Martin 1968).

NCI carcinogenesis bioassay completed: results indefinite,rat;
results negative, mus (Lewis & Sweet 1984).

The no-reproduction-effect concentration is 35 ppm, 20 week-diet
Anas platyrhyncos.

There was apparent treatment-related decrease in the percent
hatched, 101 ppm, 20 week-diet, Anas platyrhyncos 
(GLP)(PESREG).

LOEC is 35 ppm based on the decresed body weight gains of the
adult Anas platyrhyncos in 20 week-diet (GLP)(PESREG).

LC50, 59 mg/kg, 14d, Eisenia foetida, OECD No 207
LLC, 32 mg/kg, 14d Eisenia foetida, OECD No 207
NOEC, 1 mg/kg, 14d, Eisenia foetida, OECD No 207
(PESREG).

LD50, 0.000063 mg/bee, 460 g a.i./ha (Smart & Stevenson 1982).

LD50, 0.000423 mg/bee, 48hr, at 26.7 °C (Atkins & Anderson 1967)

Pteronarcys dorsata:
0.0211 mg/l, 96hr LC50; 0.0049 mg/l, 30d LC50
Acroneuria lycorias:
0.0015 mg/l, 30d LC50; 0.00136 mg/l, 30 day, no effect
Ophiogomphus rupinsulensis:
0.012 mg/l, 96hr LC50; 0.0022 mg/l, 30d LC50;
0.00173 mg/l, 30d, no effect
Hydropsyche bettoni:
0.0074 mg/l, 30d LC50; 0.00494 mg/l, 30d no effect
Ephemerella subvaria:
0.0045 mg/l, 30d LC50; 0.0025 mg/l, 30d, no effect
(Verschueren 1983).

Pteronarcys californica: 0.0015 mg/l, 96hr LC50 (Sanders & Cope
1968).

Significant differences were recognized on soil respiration
between azinphos-methyl treated and untreated soil:

                      mg azinphos-    days      soil respirati
    soil              methyl         after       significant
                      /kg in         treat-      difference
                      soil           ment      carbon dioxide
________________________________________________________________
LOAMY SAND
without lucerne-grass  1.07            7             +
                      10.67            7             +
                       1.07           14             +
                      10.67           21             +
with lucerne-grass     1.07            7             +
                       1.07           14             +
                      10.67           14             +
                       1.07           21             +
                      10.67           21             +
SANDY SILT
without lucerne-grass 10.67            7             +
                       1.07           14             +
                      10.67           14             +
with lucerne-grass     1.07           21             +
________________________________________________________________
(PESREG)

Significant differences in mineralization of nitrogen were
observed between azinphos-methyl treated and control soil
samples:
                      mg azinphos-  days      significant
                      methyl       after      difference
    soil              /kg in       treat-  ammonium   nitrat
                      soil          ment
_______________________________________________________________

loamy sand              1.07          0        +         +
                        1.07          7                  +
                       10.67          7                  +
                        1.07         14                  +
                       10.67         14                  +
                        1.07         21        +         +
                       10.67         21        +         +
                        1.07         28                  +
                       10.67         28                  +
                        1.07         42                  +
                       10.67         42                  +
                        1.07         56                  +
                       10.67         56                  +
sandy silt              1.07         14                  +
                       10.67         14                  +
                       10.67         42                  +
loamy sand after        1.07         21        +         +
amendment with ammonium10.67         21        +         +
                        1.07         28        +
                       10.67         28        +
sandy silt after        1.07          0                  +
amendment with ammomium10.67          0                  +
                        1.07         14        +         +
                       10.67         56        +         +
________________________________________________________________
(PESREG)

Azinphos-methyl (at 2 to 10000 ppm) did not inhibit the bacteria
and actinomycetes, but it (at 2 to 10 ppm) caused 4 to 18%
inhibition of the four fungi (Aspergillus niger, Penicillium
daleae, Trichoderma viride and Phycomyces nitens) (PESREG).

Crustacean: Gammarus pseudolimneaus: 0.00010 mg/l, 30 day, no
effect (Sanders 1972).

Aplexa hypnorum: LC50, 4 d, > 3.69 mg/l (Holcombe et al. 1987).

Mollusca:
EC50, 96hr, 4.7 mg/l, Crassostrea virginica
NOEC, 96hr, 2.0 mg/l, Crassostrea virginica
EPA, PESREG

Salmo gairdneri, larvae: 0.00098 mg/l, 60 days post-hatch, 25 %
larvae survival.

The maximum acceptable toxicant concentration of
azinphos-methyl for Salmo gairdneri was estimated to be
>0.00044 mg/l and <0.00098 mg/l. 
(GLP)(PESREG)

Salmo gairdneri (early life stages), 47 days:
The maximum acceptable toxicant concentration was 0.00029 mg/l.

(PESREG).

Based on the statistical analysis of adult mean length,
survival and youn/adult/reproduction day from the 21-day
Daphnia magna dynamic life cycle study, the MATC (maximum
acceptable toxicant concentration) limits were estimated to be
(C-14) azinphos-methyl mean measured concentrations of 0.00025
and 0.00040 mg/l (PESREG).