Fenthion-ethyl (Ref: ENT 25,636)

Fenthion-ethyl (Ref: ENT 25,636)	Last updated: 28/01/2026
(Also known as: ethyl fenthion; BAY S 1751)

GENERAL INFORMATION

Description

An obsolete insecticide

Examples of veterinary uses

Examples of species treated

Approval status

VMR 2013/2033 approval status (GB/UK)

EU Regulatory approval status

Chemical structure

Isomerism

Fenthion-ethyl exhibits stereoisomerism due to the presence of a chiral phosphorus atom. The tetrahedral phosphorus centre is bonded to four distinct groups: two ethoxy groups, a sulphur atom (via the P=S bond), and a 3-methyl-4-(methylthio)phenoxy group, creating a chiral centre. This results in a pair of enantiomers.

Chemical formula

C₁₂H₁₉O₃PS₂

Canonical SMILES

CCOP(=S)(OCC)OC1=CC(=C(C=C1)SC)C

Isomeric SMILES

International Chemical Identifier key (InChIKey)

WGWJBWHBOKETRC-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C12H19O3PS2/c1-5-13-16(17,14-6-2)15-11-7-8-12(18-4)10(3)9-11/h7-9H,5-6H2,1-4H3

2D structure diagram/image available?

Yes

General status

Veterinary substance type

Substance groups

Organophosphate insecticide

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Acetylcholinesterase (AchE) inhibitor.

Molecular targets

CAS RN

1716-09-2

EC number

216-999-3

CIPAC number

US EPA chemical code

Not applicable

PubChem CID

CLP index number

015-048-00-8

Therapeutic Class

ATCvet Code

Controlled Drug?

Regulation 37/2010 MRL Classification

Molecular mass

306.37

PIN (Preferred Identification Name)

O,O-diethyl O-[3-methyl-4-(methylsulfanyl)phenyl] phosphorothioate

IUPAC name

O,O-diethyl O-[3-methyl-4-(methylthio)phenyl] phosphorothioate

CAS name

O,O-diethyl O-[3-methyl-4-(methylthio)phenyl] phosphorothioate

Global Governance status: Listed (✓) under

UK Poisons List Order 1972	Rotterdam Convention	Montreal Protocol
XNo The Poisons List Order 1972	XNo Rotterdam Convention	XNo Montreal Protocol
Stockholm Convention	OSPAR	EU Water Framework Directive
XNo Stockholm Convention	XNo OSPAR	XNo EU Water Framework Directive

Relevant Environmental Water Quality Standards

Forever chemical

Other status information

PAN Bad Actor Chemical

Physical state

Commercial

Property

Value

Availability status

Not applicable

Introduction & key dates

Not applicable

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

Bayer CropScience

Example products using this active

Lucijet

Formulation and application details

Mainly formulated as emulsifiable concentrates

Commercial production

Fenthion-ethyl was produced by adapting the standard organophosphorothioate assembly used across the fenthion family. Commercial manufacture began with preparation of the phosphorothiochloridate intermediate, generated from inexpensive phosphorus trichloride and sulphur chemistry under controlled conditions. This activated phosphorus species was then reacted with the appropriate ethyl-substituted thioether alcohol to form the O-alkyl phosphorothioate framework that defines fenthion-ethyl. Producers focused on achieving clean substitution at phosphorus, managing sulphur-based impurities, and purifying the resulting ester to technical grade suitable for formulation.

Impact on climate of production and use

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C at pH 7 (mg l⁻¹)

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

Melting point (°C)

Boiling point (°C)

361

Degradation point (°C)

Flashpoint (°C)

172

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

3.09 X 10⁰⁴

Calculated

Log P

4.49

High

Fat solubility of residues

Solubility

Soluble

Data type

Regulatory data - observed in metabolism and farm animal feeding studies

Density (g ml⁻¹)

Dissociation constant pKa) at 25 °C

Vapour pressure at 20 °C (mPa)

Henry's law constant at 25 °C (Pa m³ mol⁻¹)

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)

Refractive Index

1.533

Environmental release

Degradation

Property

Value

Source; quality score; and other information

Interpretation

Soil degradation (days) (aerobic)

DT₅₀ (typical)

DT₅₀ (lab at 20 °C)

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

Note

Manure DT₅₀ (days)

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Note

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

Value

Note

Water-sediment DT₅₀ (days)

Water phase only DT₅₀ (days)

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)

K_oc (mL g⁻¹)

Notes and range

Freundlich

K_f (mL g⁻¹)

K_foc (mL g⁻¹)

¹/_n

Notes and range

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

Bio-concentration factor

BCF (l kg⁻¹)

CT₅₀ (days)

Known soil metabolites

Metabolite

Major/Minor fraction

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

Estimated maximum occurrence fraction

Notes

fenthion (Ref: OMS 2)

Major fraction

Known groundwater metabolites

None

Other known metabolites

None

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)

(ppm diet)

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

Birds - Acute LD₅₀ (mg kg⁻¹)

Birds - Short term dietary (LC₅₀/LD₅₀)

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

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

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

Soil micro-organisms

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

Vegetative vigour ER₅₀ (g ha⁻¹)

Seedling emergence ER₅₀ (g ha⁻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)

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)

Mode of exposure

Other bee species (2)

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

Mode of exposure

Beneficial insects (Ladybirds)

Beneficial insects (Lacewings)

Beneficial insects (Parasitic wasps)

Beneficial insects (Predatory mites)

Beneficial insects (Ground beetles)

Beneficial insects (Butterflies)

Contact

Notes

Oral

Notes

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

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

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)

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)

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, fonds growth, fresh) - 7 day (mg l⁻¹)

Aquatic plants (rooted, growth rate, fresh) - 14 day (mg l⁻¹)

Algae - Acute (growth rate, fresh; mg l⁻¹)

Algae - Chronic (growth rate, fresh; 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)

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

Intraperitoneal LD₅₀ = 22 mg kg⁻¹

Rat

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

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

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

Exposure Routes

Public

Occupational

Mammalian dose elimination route and rate

Health issues

Specific human health issues (hazard-based)

Carcinogen

Genotoxic

Endocrine disruptor

No data found

; ; ; ;

No data found

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

No data found

Respiratory tract irritant

Skin irritant

Skin sensitiser

No data found

Eye irritant

Phototoxicant

No data found

General human health issues

May cause Headache, dizziness, nausea, vomiting, abdominal cramps and diarrhoea
May depress the respiratory system

Handling issues

Property

Value and interpretation

General

No information available

CLP classification 2013

Health: H300, H330, H311
Environment: H410

WHO Classification

Ib (Highly hazardous)

UN Number

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

fenthion-ethyl

French

fenthion-éthyl

German

Danish

Italian

Spanish

Greek

Polish

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	28/01/2026
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