Oxydemeton-methyl (Ref: ENT 24964)

Oxydemeton-methyl (Ref: ENT 24964)	Last updated: 09/04/2025
(Also known as: methylmercaptophos oxide; R 2170; isomethylsystox sulfoxide; metaisosystox sulfoxide; BAY 21097)

SUMMARY

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; Reproduction/development effects; Acetyl cholinesterase inhibitor; Neurotoxicant

GENERAL INFORMATION

Description

An insecticide and acaricide for the control of insect pests in both food and non-food situations

Example pests controlled

Aphids including the green peach aphid, mustard aphid; Mites; Thrips; Sawflies

Example applications

Vegetables; Fruit; Field crops; Ornamental shrubs and trees

Efficacy & activity

Availability status

Current

Introduction & key dates

2002, first registered USA; 2006, first evaluated EU

GB regulatory status

GB COPR regulatory status

Not approved

Date COPR inclusion expires

Expired

GB LERAP status

No UK approval for use as a plant protection agent

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Not approved

Dossier rapporteur/co-rapporteur

France

Date EC 1107/2009 inclusion expires

Expired

EU Candidate for substitution (CfS)

Not applicable

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

Chemical structure

Isomerism

A molecule with one chiral centre

Chemical formula

C₆H₁₅O₄PS₂

Canonical SMILES

CCS(=O)CCSP(=O)(OC)OC

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

PMCVMORKVPSKHZ-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C6H15O4PS2/c1-4-13(8)6-5-12-11(7,9-2)10-3/h4-6H2,1-3H3

2D structure diagram/image available?

Yes

General status

Pesticide type

Insecticide

Substance groups

Organophosphate insecticide; Organothiophosphate insecticide

Minimum active substance purity

95%

Known relevant impurities

EU dossier - demeton-S-methyl <=3.5% and demeton-S-methyl sulfone <=2%

Substance origin

Synthetic

Mode of action

Systemic with contact and stomach action. Rapid knockdown effect. Acetylcholinesterase (AchE) inhibitor.

CAS RN

301-12-2

EC number

206-110-7

CIPAC number

171

US EPA chemical code

058702

PubChem CID

4618

CLP index number

015-046-00-7

Molecular mass

246.3

PIN (Preferred Identification Name)

IUPAC name

S-2-ethylsulfinylethyl O,O-dimethyl phosphorothioate

CAS name

S-(2-(ethylsulfinyl)ethyl) O,O-dimethyl phosphorothioate

Other status information

Potential groundwater contaminant; Chemical subject to PIC regulations; Subject to the provisions of the UK Poisons Act 1972

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)

Fungicide Resistance Class (FRAC MOA class)

Not applicable

Examples of recorded resistance

Aphis gossypii, Myzocallis coryli, Myzus persicae

Physical state

Colourless liquid

Formulations

Property

Value

Example manufacturers & suppliers of products using this active now or historically

Gowan
Amico Pesticides
Makhteshim Agan
Bayer
Mobay

Example products using this active

Metasystox 250EC
Oxydemetchem
Safasystox

Formulation and application details

Usually supplied as an emsulsifiable concentrate

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C (mg l⁻¹)

1200000

High

Solubility - In organic solvents at 20 °C (mg l⁻¹)

n-Hexane

250000

Toluene

250000

1-Octanol

250000

Acetone

Melting point (°C)

-49

Boiling point (°C)

Decomposes before boiling

Degradation point (°C)

Flashpoint (°C)

80.5

Octanol-water partition coefficient at pH 7, 20 °C

1.82 X 10^-01

Calculated

Log P

-0.74

Low

Fat solubility of residues

Solubility

Insoluble

Data type

Regulatory data

Density (g ml⁻¹)

1.31

Dissociation constant pKa) at 25 °C

Not applicable

Not determinable

Vapour pressure at 20 °C (mPa)

2.0

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)

4.00 X 10^-07

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

24 hr

Volatilisation is not considered critical for air pollution

From soil surface

24 hr

Volatilisation is not considered critical for air pollution

Maximum UV-vis absorption L mol⁻¹ cm⁻¹

Maxima at 213nm = 1356

Surface tension (mN m⁻¹)

66.0

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Soil degradation (days) (aerobic)

DT₅₀ (typical)

Non-persistent

DT₅₀ (lab at 20 °C)

Non-persistent

DT₅₀ (field)

Non-persistent

DT₉₀ (lab at 20 °C)

3.32

Non-persistent

DT₉₀ (field)

2.66

DT₅₀ modelling endpoint

Note

EU dossier Lab studies DT₅₀ range 0.4-3.2 days, DT₉₀ range 1.3-10.6 days at 25°C; Field studies DT₅₀ raneg 1.49-3.82 days, DT₉₀ range 4.9-12.7 days

Dissipation rate RL₅₀ (days) on plant matrix

Value

Note

Dissipation rate RL₅₀ (days) on and in plant matrix

Value

3.6

Note

Published literature RL₅₀ range 3.1-4.0 days, 2 field crops, various matrices, n=2

Aqueous photolysis DT₅₀ (days) at pH 7

Value

222

Stable

Note

Not significant route of degradation. DT₅₀ 187 days daylight, 257 days in dark, pH 5, 38 deg N, Spring

Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7

Value

Moderately persistent

Note

pH sensitive: DT₅₀ 96.3 days at pH 5, 41 days at pH 7, 2.4 days at pH 4, all at 25 °C. 73 days at pH 7 and 20 °C

Water-sediment DT₅₀ (days)

Fast

Water phase only DT₅₀ (days)

Moderately fast

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

K_d (mL g⁻¹)

Very mobile

K_oc (mL g⁻¹)

Notes and range

Freundlich

K_f (mL g⁻¹)

0.36

Mobile

K_foc (mL g⁻¹)

¹/_n

0.928

Notes and range

EU dossier K_f range 0.01-0.89 mL g⁻¹, kfoc range 2-58 mL g⁻¹, ¹/_n range 0.83-1.14, Soils=4

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

1.77

Calculated

Low leachability

SCI-GROW groundwater index (μg l⁻¹) for a 1 kg ha⁻¹ or 1 l ha⁻¹ application rate

Value

4.32 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

1.22

Calculated using the Atkinson method

Below the level of concern for long-range air transport

Bio-concentration factor

BCF (l kg⁻¹)

Low risk

Based on LogP < 3

Low risk

CT₅₀ (days)

No data

Known soil metabolites

Metabolite

Major/Minor fraction

$Click here for further information on Major/Minor fraction$

Estimated maximum occurrence fraction

Notes

dimethyl phosphate

Major fraction

0.458

Aerobic

2-ethylsulfinyl ethane sulfonic acid

Major fraction

0.390

2-ethylsulfonyl ethane sulfonic acid

Major fraction

0.265

S-[2(ethylsulfonyl)ethyl]O,O-dimethylphoshorothioate

Minor fraction

0.063

Aerobic

1-(ethylsulfonyl)-2-(methylsulfonyl) ethane

Minor fraction

0.095

Aerobic

Known groundwater metabolites

Metabolite

EC SANCO/221/2000 relevancy

ADI (mg kg⁻¹ bodyweight day⁻¹)

WHO drinking water guidance value (μg L⁻¹ day⁻¹)

1-(ethylsulfonyl)-2-(methylsulfonyl) ethane

Relevancy unknown

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

O-methyl-S-[2(ethylsulfinyl)ethyl] phoshorothioate

oxydemeton-methyl metabolite M06

Plant; Surface water; Sediment

O-methyl-S-[2(ethylsulfonyl)ethyl] phoshorothioate

oxydemeton-methyl metabolite M07

Plant; Surface water; Sediment

dimethyl phosphate

DMP

Surface water

S-[2(ethylthio)ethyl]O,O-dimethylphoshorothioate. Pesticide common name: demeton-S-methyl

oxydemeton-methyl metabolite M02

Surface water; Sediment

bis-2-[(ethylsulfinyl)-ethyl]disulfide

oxydemeton-methyl metabolite M11

Surface water; Sediment

2-ethylsulfinyl-ethyl mercaptan

oxydemeton-methyl metabolite M21

Surface water; Sediment

S-[2(ethylsulfonyl)ethyl]O,O-dimethylphoshorothioate

demeton-S-methylsulphon; oxydemeton-methyl metabolite M01

Plant; Surface water; Sediment

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

Rat

High

Mammals - Short term dietary NOEL

(mg kg⁻¹)

0.1

Dog 1 yr

High

(ppm diet)

Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)

Birds - Acute LD₅₀ (mg kg⁻¹)

Colinus virginianus

High

Birds - Short term dietary (LC₅₀/LD₅₀)

361 mg kg bw⁻¹ day⁻¹

Colinus virginianus

Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)

Earthworms - Acute 14 day LC₅₀ (mg kg⁻¹)

115

Eisenia foetida

Moderate

Earthworms - Chronic NOEC, reproduction (mg kg⁻¹)

0.55

Eisenia foetida 56 day

Moderate

Soil micro-organisms

Nitrogen mineralisation: No significant adverse effect [Dose: 5 kg ha⁻¹]
Carbon mineralisation: No significant adverse effect [Dose: 6 kg ha⁻¹]

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)

0.175

Apis mellifera

High

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

0.2

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)

0.75

Bombus terrestris 24 hr

High

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)

0.133

Megachile rotundata

High

Mode of exposure

Oral

Other bee species (2)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

0.0082

Nomia melanderi

High

Mode of exposure

Oral

Beneficial insects (Ladybirds) as Mortality LR₅₀ g ha⁻¹

4.3

Coccinella septempunctata Larva

Beneficial insects (Lacewings) as Mortality LR₅₀ g ha⁻¹

< 37.5

Chrysoperla carnea

Beneficial insects (Parasitic wasps) as Mortality LR₅₀ g ha⁻¹ 48 hr

> 0.375

Aphidius rhopalosiphi

Beneficial insects (Predatory mites) as Mortality LR₅₀ g ha⁻¹ 7 day

11.0

Typhlodromus pyri

Beneficial insects (Ground beetles)

36.7% Mortality at dose 37.5 g ha⁻¹

Poecilus cupreus

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Temperate Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

Oncorhynchus mykiss

Moderate

Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)

1.8

Oncorhynchus mykiss

Moderate

Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

Temperate Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

0.11

Daphnia magna

Moderate

Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)

0.027

Daphnia magna

Moderate

Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)

0.011

Chironomus riparius 48 hr

High

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)

> 100

Scenedesmus subspicatus

Low

Algae - Chronic 96 hour NOEC, growth (mg l⁻¹)

Mesocosm study data

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)

Rat

High

Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)

112

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

0.471

Rat

Other Mammal toxicity endpoints

ADI - Acceptable Daily Intake (mg kg⁻¹ bw day⁻¹)

0.0003

Rat SF=100

ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)

0.0015

Rat SF=100

AAOEL - Acute Acceptable Operator Exposure Level (mg kg⁻¹ bw day⁻¹)

AOEL - Acceptable Operator Exposure Level - Systemic (mg kg⁻¹ bw day⁻¹)

0.001

Rat SF=100

Dermal penetration studies (%)

20.0

Dangerous Substances Directive 76/464

List II

Exposure Routes

Public

Possible risk to bystanders

Occupational

Possible exposure risk during treatment of orchards

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

; ; ; ;

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

Respiratory tract irritant

Skin irritant

Skin sensitiser

No data found

Eye irritant

Phototoxicant

No data found

General human health issues

Highly toxic

Handling issues

Property

Value and interpretation

General

Not explosive
IMDG Transport Hazard Class 6.1
Flammable liquid

CLP classification 2013

Health: H301, H311
Environment: H400

WHO Classification

Ib (Highly hazardous)

UN Number

UN2784

Waste disposal & packaging

Packaging Group II (moderate danger)

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

oxydemeton-methyl

French

oxydemeton-methyle

German

Oxydemeton-methyl

Danish

oxydemeton-methyl

Italian

ossidemeton-metil

Spanish

oxidemeton metil

Greek

oxydemeton-methyl

Polish

oksydemeton metylu

Swedish

Hungarian

oxidemeton-methyl

Dutch

oxydemeton-methyl

Norwegian

Record last updated:	09/04/2025
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