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methamidophos (Ref: ENT 27396)
** acephate-metabolite ** SRA 5172 ** BAY 71628 ** Translations

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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.

for methamidophos

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

Availability status: Current

Introduction & key dates: circa 1972

EC Regulation 1107/2009 (repealing 91/414):
Status Not approved
Dossier rapporteur/co-rapporteur Italy
Date inclusion expires Expired

Approved for use () or known to be used () in the following European countries:





























Also used in: Australia, USA

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
Chiral molecule Chiral, a specific isomer or a derivative of a chiral molecule
Chemical formula C2H8NO2PS
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)
Structure diagram/image available? Yes
Molecular mass (g mol-1) 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)
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
Related substances & organisms -

Can be a metabolite of:
Parent Formation medium Estimated maximum occurrence fraction 91/414 relevancy
acephate Soil     -

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
UK LERAP status No UK approval for use or outside scope
Formulation and application details Usually supplied as a soluble concentrate.


for methamidophos

Property Value Source/Quality Score/Other Information Interpretation
Solubility - In water at 20oC (mg l-1) 200000 K4 High
Solubility - In organic solvents at 20oC (mg l-1) 200000 C4 - Acetone -
1000 C4 - Hexane -
3500 C4 - Toluene -
200000 C4 - Dichloromethane -
Melting point (oC) 45 L3 -
Boiling point (oC) Decomposes before boiling L3 -
Degradation point (oC) 160 L3 -
Flashpoint (oC) 212 Q2 -
Octanol-water partition coefficient at pH 7, 20oC P 1.62 X 10-01 Calculated -
Log P -0.79 H4 Low
Bulk density (g ml-1)/Specific gravity 1.27 L3 -
Dissociation constant (pKa) at 25oC - - -
Vapour pressure at 25oC (mPa) 2.3 L3 Volatile
Henry's law constant at 25oC (Pa m3 mol-1) 1.60 X 10-06 L3 Non-volatile
Henry's law constant at 20oC (dimensionless) 1.10 X 10-09 K3 Non-volatile
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 - Calculated Low
Maximum UV-vis absorption L mol-1 cm-1 - - -
Surface tension (mN m-1) - - -

Property Value Source/Quality Score/Other Information Interpretation
Soil degradation (days) (aerobic) DT50 (typical) 3.5 K4 Non-persistent
DT50 (lab at 20oC) 4 Y4 Non-persistent
DT50 (field) 4 H4 Non-persistent
DT90 (lab at 20oC) - - -
DT90 (field) - - -
Note Other sources: DT50 6 days (DW4); 1.9 days (F3)
Plant matrix DT50 (days) Value 5.6 R4 -
Note DT50 range 0.7 - 17.0 days, 16 crops/plants, various matrices
Aqueous photolysis DT50 (days) at pH 7 Value 90 C4 Stable
Note Insignificant degradation route
Aqueous hydrolysis DT50 (days) at 20oC and pH 7 Value 5 C4 Non-persistent
Note -
Water-sediment DT50 (days) 23.5 K3 Fast
Water phase only DT50 (days) 16 K3 Slow

Soil adsorption and mobility:
Property Value Source/Quality Score/Other Information Interpretation
Linear Kd - H3 Very mobile
Koc 1.0
Notes and range Other sources: 5.0 mL/g (DW3)
Freundlich Kf 0.03 F4 -
Kfoc -
1/n 0.64
Notes and range Clay loam, OM=3.3%, pH=5.8
pH sensitivity -


for methamidophos

Property Value Source/Quality Score/Other Information Interpretation
Bio-concentration factor BCF (l kg-1) 75 Q2 Estimated Low potential
CT50 (days) Not available -
Mammals - Acute oral LD50 (mg kg-1) 30 F4 Rat High
Mammals - Short term dietary NOEL (mg kg-1) 0.1 L2 Rat, 2 year High
(ppm diet) - -
Birds - Acute LD50 (mg kg-1) 10 G4 Colinus virginianus High
Birds - Short term dietary (LC50/LD50) - - -
Fish - Acute 96 hour LC50 (mg l-1) > 25 G4 Oncorhynchus mykiss Moderate
Fish - Chronic 21 day NOEC (mg l-1) - - -
Aquatic invertebrates - Acute 48 hour EC50 (mg l-1) > 0.27 L3 Daphnia magna Moderate
Aquatic invertebrates - Chronic 21 day NOEC (mg l-1) - - -
Aquatic crustaceans - Acute 96 hour LC50 (mg l-1) > 1.05 F3 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 Scenedemus subspicatus Low
Algae - Chronic 96 hour NOEC, growth (mg l-1) - - -
Honeybees Contact acute 48 hour LD50 (μg bee-1) - - -
Oral acute 48 hour LD50 (μg bee-1) > 0.22 K4 High
Unknown mode acute 48 hour LD50 (μg bee-1) - - -
Earthworms - Acute 14 day LC50 (mg kg-1) 34 L3 Eisenia foetida Moderate
Earthworms - Chronic 14 day NOEC, reproduction (mg kg-1) - - -
Other soil macro-organisms - e.g. Collembola LR50 / EC50 / NOEC / % Effect - - -
Other arthropod (1) LR50 g ha-1 - - -
% Effect Harmful Dose: 900 g ha-1
AA3 Typhlodromus pyri
Other arthropod (2) LR50 g ha-1 - - -
% Effect Harmful Dose: 900 g ha-1
AA3 Chrysoperla carnea
Soil micro-organisms - - -
Mesocosm study data NOEAEC mg l-1 - - -
NOEAEC mg l-1 - - -


for methamidophos

Property Value Source/Quality Score/Other Information Interpretation
Threshold of Toxicological Concern (Cramer Class) High (class III) - -
Mammals - Acute oral LD50 (mg kg-1) 30 F4 Rat High
Mammals - Dermal LD50 (mg kg-1 body weight) 69.0 L3 Rabbit -
Mammals - Inhalation LC50 (mg l-1) 0.213 L3 Rat -
Other Mammal toxicity endpoints - -
ADI - Acceptable Daily Intake (mg kg-1bw day-1) 0.004 JMPR 1990 -
ARfD - Acute Reference Dose (mg kg-1bw day-1) 0.01 JMPR 2003 -
AOEL - Acceptable Operator Exposure Level - Systemic (mg kg-1bw day-1) - - -
Dermal penetration studies (%) - - -
Dangerous Substances Directive 76/464 List I; List II - -
Exposure Limits - - -
Exposure Routes Public -
Occupational Can be absorbed following ingestion, inhalation and skin contact
European MRLs Click here for the EU MRL pesticide database
Drinking Water MAC (μg l-1) - - -

Health issues:
Carcinogen Mutagen Endocrine disrupter Reproduction / development effects Cholinesterase inhibitor Neurotoxicant


Respiratory tract irritant Skin irritant Skin sensitiser Eye irritant Phototoxicant



General human health issues Highly toxic

: Yes, known to cause a problem
: No, known not to cause a problem
: Possibly, status not identified
- : No data found

Handling issues:
Property Value Source/Quality Score/Other Information 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
US EPA Classification (formulation) No consensus across products or no products available - -
UN Number 2783
Waste disposal & packaging -


for methamidophos

Language Name
English methamidophos
French methamidophos
German Methamidophos
Danish methamidophos
Italian metamidofos
Spanish metamidofos
Greek methamidophos
Slovenian metamidofos
Polish metamidofos
Swedish -
Hungarian metamidofosz
Dutch methamidofos

Record last updated: Sunday 14 August 2016