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Methamidophos (Ref: ENT 27396)
(Also known as: acephate-metabolite; SRA 5172; BAY 71628)
SUMMARY
Methamidophos is an insecticide for the control of sucking and chewing pests. 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.
Data alerts

The following alerts are based on the data in the tables below. An absence of an alert does not imply the substance has no implications for human health, biodiversity or the environment but just that we do not have the data to form a judgement.

Environmental fate Ecotoxicity Human health
Environmental fate
High alert:
Drainflow: Very mobile
Ecotoxicity
High alert:
Birds acute ecotoxicity: High; Bees acute contact ecotoxicity: High; Bees acute oral ecotoxicity: High
Human health
High alert:
Mammals acute toxicity: High; Acetyl cholinesterase inhibitor; Neurotoxicant
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
                 
Approved for use (✓) under EC 1107/2009 by Mutual Recognition of Authorisation and/or national regulations in the following EEA countries
ISIceland
NONorway
                 
Additional information
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 groups
Organophosphate insecticide; Organothiophosphate insecticide; Organophosphate acaricide; Organothiophosphate acaricide; Phosphoramidothioate insecticide; Phosphoramidothioate acaricide
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
CLP index number
015-095-00-4
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
  • Bayer CropScience
  • AgroCare
  • United Phosphorus
  • Chevron
  • Mobay
Example products using this active
  • Tahmabon
  • Patrole
  • Pillaron
  • Monitor
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; these datasets no longer available). Norman Ecotoxicology database. (click here )
4 = Verified data
 High
Solubility - In organic solvents at 20 °C (mg l⁻¹)
200000
C4 C = AGRITOX dataset. Dataset is no longer available.
4 = Verified data
Acetone		 -
1000
C4 C = AGRITOX dataset. Dataset is no longer available.
4 = Verified data
Hexane		 -
3500
C4 C = AGRITOX dataset. Dataset is no longer available.
4 = Verified data
Toluene		 -
200000
C4 C = AGRITOX dataset. Dataset is no longer available.
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 data from online sources
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. Dataset is no longer available.
4 = Verified data
 Low
Fat solubility of residues
Solubility
- - -
Data type
- - -
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; these datasets no longer available). Norman Ecotoxicology database. (click here )
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. Dataset is no longer available.
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 dataset. Dataset is no longer available.
4 = Verified data
 Stable
Note
Insignificant degradation route
Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7
Value
5
C4 C = AGRITOX dataset. Dataset is no longer available.
4 = Verified data
 Non-persistent
Note
-
Water-sediment DT₅₀ (days)
23.5
K3 K = Research datasets (e.g. Pandora, Demetra; these datasets no longer available). Norman Ecotoxicology database. (click here )
3 = Unverified data of known source
 Fast
Water phase only DT₅₀ (days)
16
K3 K = Research datasets (e.g. Pandora, Demetra; these datasets no longer available). Norman Ecotoxicology database. (click here )
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. Dataset is no longer available.
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 / FAO data, IPCS INCHEM data (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 -
Bio-concentration factor
BCF (l kg⁻¹)
75
Q2 Q = Miscellaneous data from online sources
2 = Unverified data of unknown source
Estimated		 Low potential
CT₅₀ (days)
Not available -
Known metabolites

None
ECOTOXICOLOGY
Terrestrial ecotoxicology
Property
Value
Source; quality score; and other information
Interpretation
Mammals - Acute oral LD₅₀ (mg kg⁻¹)
30
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (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. Available online but no longer updated. (click here )
4 = Verified data
Colinus virginianus		 High
Birds - Short term dietary (LC₅₀/LD₅₀)
- - -
Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)
- - -
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)
- - -
Soil micro-organisms
- - -
Collembola
Acute LC₅₀ (mg kg⁻¹)
- - -
Chronic NOEC (mg kg⁻¹)
- - -
Non-target plants
- - -
- - -
Honeybees (Apis spp.)
Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
0.97
K3 K = Research datasets (e.g. Pandora, Demetra; these datasets no longer available). Norman Ecotoxicology database. (click here )
3 = Unverified data of known source
Apis mellifera		 High
Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
> 0.22
K3 K = Research datasets (e.g. Pandora, Demetra; these datasets no longer available). Norman Ecotoxicology database. (click here )
3 = Unverified data of known source
Apis mellifera		 High
Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
- - -
Chronic
- - -
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 bee species (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 bee species (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
Beneficial insects (Ladybirds)
- - -
Beneficial insects (Lacewings)
Harmful at 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		 -
Beneficial insects (Parasitic wasps)
- - -
Beneficial insects (Predatory mites)
Harmful at 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		 -
Beneficial insects (Ground beetles)
- - -
Aquatic ecotoxicology
Property
Value
Source; quality score; and other information
Interpretation
Fish - Acute 96 hour LC₅₀ (mg l⁻¹)
> 25
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (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 / FAO data, IPCS INCHEM data (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)
- - -
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
Scenedesmus subspicatus		 Low
Algae - Chronic 96 hour NOEC, growth (mg l⁻¹)
- - -
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 / FAO data, IPCS INCHEM data (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)
0.001
A5 A = EU regulatory and evaluation data as published by EC, EFSA (RAR, DAR & Conclusion dossiers), EMA (e.g. EU Annex III PIC DGD) (EU - Pesticides database; EFSA Scientific Publications )
5 = Verified data used for regulatory purposes
 -
ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)
0.003
A5 A = EU regulatory and evaluation data as published by EC, EFSA (RAR, DAR & Conclusion dossiers), EMA (e.g. EU Annex III PIC DGD) (EU - Pesticides database; EFSA Scientific Publications )
5 = Verified data used for regulatory purposes
 -
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 
Great Britain
GB MRL Register 
Notes
-
Drinking Water Standards
- - -
Drinking Water MAC (μg l⁻¹)
- - -
Mammalian dose elimination route and rate
- - -
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 Hazard Class 6.1
CLP classification 2013
Health: H300, H311, H330
Environment: H400
WHO Classification
Ib (Highly hazardous)
UN Number
UN2783
Waste disposal & packaging
Packaging Group III (minor danger)
Shelf-life, storage, stability and reactivity
-
TRANSLATIONS
Language
Name
English
methamidophos
French
methamidophos
German
Methamidophos
Danish
methamidophos
Italian
metamidofos
Spanish
metamidofos
Greek
methamidophos
Polish
metamidofos
Swedish
-
Hungarian
metamidofosz
Dutch
methamidofos
Norwegian
-
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