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Methamidophos (Ref: ENT 27396)
Last updated: 19/02/2021
(Also known as: acephate-metabolite; SRA 5172; BAY 71628)

SUMMARY
Methamidophos is an insecticide which no longer has approval for use in the EU. It is highly soluble in water and many organic solvents, and is volatile. It would not normally be expected to be persistent in soil or water systems. Methamidophos is highly toxic to mammals, and is a cholinestrase inhibitor and neurotoxin. It is highly toxic to birds and honeybees, and moderately toxic to most aquatic species and earthworms.
GENERAL INFORMATION
Description
An insecticide and acaricide used to control chewing and sucking pests. Also a pesticide transformation product
Example pests controlled
Aphids; Leaf beetles; Fruit borers; Flea beetles; Worms; Whiteflies; Thrips; Cabbage loopers; Colorado potato beetles; Potato tubeworms; Armyworms, Mites, Leafhoppers etc.
Example applications
Broccoli; Brussel sprouts; Cauliflower; Celery; Cotton; Beets; Potatoes; Hops, Vegetables; Corn; Tomatoes; Fruit including pome, stone and citrus fruits
Efficacy & activity
-
Availability status
Current
Introduction & key dates
circa 1972
UK regulatory status
UK COPR regulatory status
Not approved
Date COPR inclusion expires
Expired
UK LERAP status
No UK approval for use
EC Regulation 1107/2009 (repealing 91/414)
EC Regulation 1107/2009 status
Not approved
Dossier rapporteur/co-rapporteur
Italy
Date EC 1107/2009 inclusion expires
Expired
EU Candidate for substitution (CfS)
-
Listed in EU database
Yes
Approved for use (✓) under EC 1107/2009 in the following EU Member States
ATAustria
BEBelgium
BGBulgaria
CYCyprus
CZCzech Republic
DEGermany
DKDenmark
EEEstonia
ELGreece
                 
ESSpain
FIFinland
FRFrance
HRCroatia
HUHungary
IEIreland
ITItaly
LTLithuania
LULuxembourg
                 
LVLatvia
MTMalta
NLNetherlands
PLPoland
PTPortugal
RORomania
SESweden
SISlovenia
SKSlovakia
                 
Also used in
Also used in
Australia, USA
Chemical structure
Isomerism
A molecule with one chiral centre existing as the D-(+) and L-(-) isomers
Chemical formula
C₂H₈NO₂PS
Canonical SMILES
COP(=O)(N)SC
Isomeric SMILES
No data
International Chemical Identifier key (InChIKey)
NNKVPIKMPCQWCG-UHFFFAOYSA-N
International Chemical Identifier (InChI)
InChI=1S/C2H8NO2PS/c1-5-6(3,4)7-2/h1-2H3,(H2,3,4)
2D structure diagram/image available?
Yes
Cambridge Crystallographic Data Centre diagrams
Common Name Relationship Link
methamidophos -
General status
Pesticide type
Insecticide, Acaricide, Metabolite
Metabolite Type
Soil
Substance group
Organophosphate
Minimum active substance purity
-
Known relevant impurities
-
Substance origin
Synthetic
Mode of action
Systemic with contact and stomach action. Acetylcholinesterase (AChE) inhibitor.
CAS RN
10265-92-6
EC number
233-606-0
CIPAC number
355
US EPA chemical code
101201
PubChem CID
4096
Molecular mass
141.13
PIN (Preferred Identification Name)
-
IUPAC name
(RS)-(O,S-dimethyl phosphoramidothioate)
CAS name
O,S-dimethyl phosphoramidothioate
Other status information
Chemical subject to PIC regulations; Marine Pollutant; Rotterdam Convention (Class Ib)
Relevant Environmental Water Quality Standards
-
Herbicide Resistance Classification (HRAC)
Not applicable
Herbicide Resistance Classification (WSSA)
Not applicable
Insecticide Resistance Classification (IRAC)
1B
Fungicide Resistance Classification (FRAC)
Not applicable
Examples of recorded resistance
Aculops lycopersici, Apanteles plutellae, Aphis gossypii, Bemisia tabaci, Frankliniella occidentalis, many more
Physical state
Off-white crystalline solid
Can be a metabolite of:
Parent
Formation medium
Estimated maximum occurrence fraction
1107/2009 relevancy
acephate Soil - -
Formulations
Property
Value
Example manufacturers & suppliers of products using this active now or historically
  • Tahmabon
  • Patrole
  • Pillaron
  • Monitor
Example products using this active
  • Bayer CropScience
  • AgroCare
  • United Phosphorus
  • Chevron
  • Mobay
Formulation and application details
Usually supplied as a soluble concentrate
ENVIRONMENTAL FATE
Property
Value
Source; quality score; and other information
Interpretation
Solubility - In water at 20 °C (mg l⁻¹)
200000
K4 K = Research datasets, e.g. Pandora, Demetra
4 = Verified data
High
Solubility - In organic solvents at 20 °C (mg l⁻¹)
200000
C4 C = AGRITOX (click here )
4 = Verified data
Acetone
-
1000
C4 C = AGRITOX (click here )
4 = Verified data
Hexane
-
3500
C4 C = AGRITOX (click here )
4 = Verified data
Toluene
-
200000
C4 C = AGRITOX (click here )
4 = Verified data
Dichloromethane
-
Melting point (°C)
45
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
-
Boiling point (°C)
Decomposes before boiling
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
-
Degradation point (°C)
160
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
-
Flashpoint (°C)
212
Q2 Q = Miscellaneous internet resources
2 = Unverified data of unknown source
-
Octanol-water partition coefficient at pH 7, 20 °C
P
1.62 X 10-01 Calculated -
Log P
-0.79
H4 H = The US ARS pesticide properties database (click here )
4 = Verified data
Low
Bulk density (g ml⁻¹)
1.27
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
-
Dissociation constant pKa) at 25 °C
- - -
-
Vapour pressure at 20 °C (mPa)
2.3
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Low volatility
Henry's law constant at 25 °C (Pa m³ mol⁻¹)
1.60 X 10-06
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Non-volatile
Maximum UV-vis absorption L mol⁻¹ cm⁻¹
- - -
Surface tension (mN m⁻¹)
- - -
Degradation
Property
Value
Source; quality score; and other information
Interpretation
General biodegradability
-
Soil degradation (days) (aerobic)
DT₅₀ (typical)
3.5
K4 K = Research datasets, e.g. Pandora, Demetra
4 = Verified data
Non-persistent
DT₅₀ (lab at 20 °C)
4
Y4 Y = Germany's Federal Environment Agency (UBA) (click here )
4 = Verified data
Non-persistent
DT₅₀ (field)
4
H4 H = The US ARS pesticide properties database (click here )
4 = Verified data
Non-persistent
DT₉₀ (lab at 20 °C)
- - -
DT₉₀ (field)
- - -
DT₅₀ modelling endpoint
- - -
Note
Other sources: DT₅₀ 6 days (DW4); 1.9 days (F3)
Dissipation rate RL₅₀ on plant matrix
Value
2.8
R4 R = Peer reviewed scientific publications
4 = Verified data
-
Note
Published literature RL₅₀ range 0.8-4.7 days, 4 field & undercover grown crops, various matrices, n=4
Dissipation rate RL₅₀ on and in plant matrix
Value
5.9
R4 R = Peer reviewed scientific publications
4 = Verified data
-
Note
Published literature RL₅₀ range 0.9-15.2 days, 13 field & undercover grown crops, various matrices, n=25
Aqueous photolysis DT₅₀ (days) at pH 7
Value
90
C4 C = AGRITOX (click here )
4 = Verified data
Stable
Note
Insignificant degradation route
Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7
Value
5
C4 C = AGRITOX (click here )
4 = Verified data
Non-persistent
Note
-
Water-sediment DT₅₀ (days)
23.5
K3 K = Research datasets, e.g. Pandora, Demetra
3 = Unverified data of known source
Fast
Water phase only DT₅₀ (days)
16
K3 K = Research datasets, e.g. Pandora, Demetra
3 = Unverified data of known source
Slow
Soil adsorption and mobility
Property
Value
Source; quality score; and other information
Interpretation
Linear
Kd
-
H3 H = The US ARS pesticide properties database (click here )
3 = Unverified data of known source
Very mobile
Koc
1.0
Notes and range
Other sources: 5.0 mL g⁻¹ (DW3)
Freundlich
Kf
0.03
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
-
Kfoc
-
1/n
0.64
Notes and range
Clay loam, OM=3.3%, pH=5.8
pH sensitivity
-
Fate indices
Property
Value
Source; quality score; and other information
Interpretation
GUS leaching potential index
2.41 Calculated Transition state
SCI-GROW groundwater index (μg l⁻¹) for a 1 kg ha⁻¹ or 1 l ha⁻¹ application rate
Value
4.23 X 10-03 Calculated -
Note
-
Potential for particle bound transport index
Low Calculated -
Potential for loss via drain flow
Very mobile Calculated -
ECOTOXICOLOGY
Property
Value
Source; quality score; and other information
Interpretation
Bio-concentration factor
BCF (l kg⁻¹)
75
Q2 Q = Miscellaneous internet resources
2 = Unverified data of unknown source
Estimated
Low potential
CT₅₀ (days)
Not available -
Mammals - Acute oral LD₅₀ (mg kg⁻¹)
30
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Rat
High
Mammals - Short term dietary NOEL
(mg kg⁻¹)
0.1
L2 L = Pesticide manuals and hard copy reference books / other sources
2 = Unverified data of unknown source
Rat 2 year
High
(ppm diet)
- -
Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)
- - -
Birds - Acute LD₅₀ (mg kg⁻¹)
10
G4 G = Extension Toxicology network database EXTOXNET (click here )
4 = Verified data
Colinus virginianus
High
Birds - Short term dietary (LC₅₀/LD₅₀)
- - -
Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)
- - -
Fish - Acute 96 hour LC₅₀ (mg l⁻¹)
> 25
G4 G = Extension Toxicology network database EXTOXNET (click here )
4 = Verified data
Oncorhynchus mykiss
Moderate
Fish - Chronic 21 day NOEC (mg l⁻¹)
- - -
Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)
> 0.27
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Daphnia magna
Moderate
Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)
- - -
Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)
> 1.05
F3 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents (US EPA Databases Related to Pesticide Risk Assessment )
3 = Unverified data of known source
Americamysis bahia
Moderate
Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)
- - -
Sediment dwelling organisms - Chronic 28 day NOEC, static, water (mg l⁻¹)
- - -
Sediment dwelling organisms - Chronic 28 day NOEC, sediment (mg kg⁻¹)
- - -
Aquatic plants - Acute 7 day EC₅₀, biomass (mg l⁻¹)
- - -
Non-target plants
- - -
- - -
Algae - Acute 72 hour EC₅₀, growth (mg l⁻¹)
178
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Scenedemus subspicatus
Low
Algae - Chronic 96 hour NOEC, growth (mg l⁻¹)
- - -
Honeybees (Apis spp.)
Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
- - -
Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
> 0.22
K4 K = Research datasets, e.g. Pandora, Demetra
4 = Verified data
High
Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
- - -
Bumblebees (Bombus spp.)
Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
- - -
-
Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
- - -
-
Mason bees (Osmia spp.)
Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
- - -
Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
- - -
Other pollinators (1)
Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)
0.066
R4 R = Peer reviewed scientific publications
4 = Verified data
Melipona quadrifasciata
High
Mode of exposure
Oral
Other pollinators (2)
Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)
96.1
R4 R = Peer reviewed scientific publications
4 = Verified data
Melipona quadrifasciata
Moderate
Mode of exposure
Contact
Earthworms - Acute 14 day LC₅₀ (mg kg⁻¹)
34
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Eisenia foetida
Moderate
Earthworms - Chronic NOEC, reproduction (mg kg⁻¹)
- - -
Other soil macro-organisms
Acute LC₅₀ (mg kg⁻¹)
- - -
Chronic NOEC (mg kg⁻¹)
- - -
Other arthropod (1)
LR₅₀ g ha⁻¹
- - -
% Effect
Harmful [Dose: 900 g ha⁻¹]
AA3 AA = IOBC Database on classification of side effects to beneficial organisms, 2005
3 = Unverified data of known source
Typhlodromus pyri
-
Other arthropod (2)
LR₅₀ g ha⁻¹
- - -
% Effect
Harmful [Dose: 900 g ha⁻¹]
AA3 AA = IOBC Database on classification of side effects to beneficial organisms, 2005
3 = Unverified data of known source
Chrysoperla carnea
-
Soil micro-organisms
- - -
Mesocosm study data
NOEAEC mg l⁻¹
- - -
NOEAEC mg l⁻¹
- - -
HUMAN HEALTH AND PROTECTION
General
Property
Value
Source; quality score; and other information
Interpretation
Threshold of Toxicological Concern (Cramer Class)
High (class III) - -
Mammals - Acute oral LD₅₀ (mg kg⁻¹)
30
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Rat
High
Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)
69.0
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Rabbit
-
Mammals - Inhalation LC₅₀ (mg l⁻¹)
0.213
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Rat
-
Other Mammal toxicity endpoints
- - -
ADI - Acceptable Daily Intake (mg kg⁻¹ bw day⁻¹)
0.004
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
JMPR 1990
-
ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)
0.01
F5 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents (US EPA Databases Related to Pesticide Risk Assessment )
5 = Verified data used for regulatory purposes
JMPR 2003
-
AAOEL - Acute Acceptable Operator Exposure Level (mg kg⁻¹ bw day⁻¹)
- - -
AOEL - Acceptable Operator Exposure Level - Systemic (mg kg⁻¹ bw day⁻¹)
- - -
Dermal penetration studies (%)
- - -
Dangerous Substances Directive 76/464
List I; List II - -
Exposure Routes
Public
-
Occupational
Can be absorbed following ingestion, inhalation and skin contact
MRLs
European
EU MRL pesticide database 
Notes
-
Drinking Water Standards
- - -
Drinking Water MAC (μg l⁻¹)
- - -
Health issues
Specific human health issues
Carcinogen
Genotoxic
Endocrine disruptor
XNo, known not to cause a problem
A3 A = Chromosome aberration (EFSA database)
3 = Negative
;
B0 B = DNA damage/repair (EFSA database)
0 = No data
;
C0 C = Gene mutation (EFSA database)
0 = No data
;
D0 D = Genome mutation (EFSA database)
0 = No data
;
E1 E = Unspecified genotoxicity type (miscellaneous data source)
1 = Positive
No data found
Reproduction / development effects Acetyl cholinesterase inhibitor Neurotoxicant
?Possibly, status not identified
Yes, known to cause a problem
Yes, known to cause a problem
Respiratory tract irritant Skin irritant Skin sensitiser
XNo, known not to cause a problem
XNo, known not to cause a problem
No data found
Eye irritant Phototoxicant  
XNo, known not to cause a problem
No data found  
General human health issues
Highly toxic
Handling issues
Property
Value and interpretation
General
Prevent generation of dust
IMDG Transport Code is 6.1
CLP classification 2013
Health: H300, H311, H330
Environment: H400
EC Risk Classification
T+ - Very toxic: R26/28
T - Toxic: R24
N - Dangerous for the environment: R50
EC Safety Classification
S1/2, S28, S46, S36/37, S61
WHO Classification
Ib (Highly hazardous / Highly hazardous)
UN Number
2783
Waste disposal & packaging
-
TRANSLATIONS
Language
Name
English
methamidophos
French
methamidophos
German
Methamidophos
Danish
methamidophos
Italian
metamidofos
Spanish
metamidofos
Greek
methamidophos
Polish
metamidofos
Swedish
-
Hungarian
metamidofosz
Dutch
methamidofos

Record last updated: 19/02/2021
Contact: aeru@herts.ac.uk
Please cite as: Lewis, K.A., Tzilivakis, J., Warner, D. and Green, A. (2016) An international database for pesticide risk assessments and management. Human and Ecological Risk Assessment: An International Journal, 22(4), 1050-1064. DOI: 10.1080/10807039.2015.1133242