Methamidophos (Ref: ENT 27396)	Last updated: 21/08/2024
(Also known as: acephate-metabolite; SRA 5172; BAY 71628)

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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 cholinesterase 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; Genotoxic; 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, introduced

GB regulatory status

GB COPR regulatory status	Not approved
Date COPR inclusion expires	Expired
GB LERAP status	No UK approval for use as a pesticide

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	Marine Pollutant; Rotterdam Convention (Class Ib) - subject to PIC regulations
Relevant Environmental Water Quality Standards	-
Herbicide Resistance Class (HRAC MoA class)	Not applicable
Herbicide Resistance Class (WSSA MoA class)	Not applicable
Insecticide Resistance Class (IRAC MoA class)	1B
Fungicide Resistance Class (FRAC MOA class)	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. If applied directly to plants or soil, drift is a concern & mitigation is advisable
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
Volatilisation as max % of applied dose lost	From plant surface	-	-	-
	From soil surface	-	-	-
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 (days) 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 (days) 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
Sediment phase only DT₅₀ (days)		-	-	-
Air degradation		As this parameter is not normally measured directly, a surrogate measure is used: ‘Photochemical oxidative DT₅₀’. Where data is available, this can be found in the Fate Indices section below.
Decay in stored produce DT₅₀		-

Soil adsorption and mobility

Property		Value	Source; quality score; and other information	Interpretation
Linear	Kd (mL g⁻¹)	-	H3 H = The US ARS pesticide properties database. Dataset is no longer available. 3 = Unverified data of known source	Very mobile
	Koc (mL g⁻¹)	1.0
	Notes and range	Other sources: 5.0 mL g⁻¹ (DW3)
Freundlich	Kf (mL g⁻¹)	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 (mL g⁻¹)	-
	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	-
Photochemical oxidative DT₅₀ (hrs) as indicator of long-range air transport risk		-	-	-
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 yr	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	-	-	-
	Notes	-
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) as Mortality LC₅₀ mg l⁻¹		> 321	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 Coccinella septempunctata Adult	-
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
Temperate Freshwater 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
Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)		-	-	-
Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)		-	-	-
Temperate Freshwater 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
Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)		-	-	-
Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (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 (free-floating, growth) - Acute 7 day EC₅₀, biomass (mg l⁻¹)		-	-	-
Aquatic plants (rooted, growth) - Acute 14 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	-	-	-
Marine bivalves		-	-	-

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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Record last updated:	21/08/2024
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