Fenchlorphos (Ref: Dow ET-14)

Fenchlorphos (Ref: Dow ET-14)	Last updated: 04/09/2025
(Also known as: ronnel; fenclofos; dermaphos; dermafos; Dow ET-57)

GENERAL INFORMATION

Description

An organophosphate insecticide once used in veterinary medicine for parasite management but now mainly obsolete

Examples of veterinary uses

Used for scabies management

Examples of species treated

Cattle; Sheep

Approval status

VMR 2013/2033 approval status (GB/UK)

Not approved

EU Regulatory approval status

Not approved

Chemical structure

Isomerism

None

Chemical formula

C₈H₈Cl₃O₃PS

Canonical SMILES

COP(=S)(OC)OC1=CC(=C(C=C1Cl)Cl)Cl

Isomeric SMILES

International Chemical Identifier key (InChIKey)

JHJOOSLFWRRSGU-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C8H8Cl3O3PS/c1-12-15(16,13-2)14-8-4-6(10)5(9)3-7(8)11/h3-4H,1-2H3

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
fenchlorphos	-

General status

Veterinary substance type

Insecticide

Substance groups

Organophosphate insecticide; Organothiophosphate insecticide; Phenyl organothiophosphate insecticide

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Systemic. Acetylcholinesterase (AchE) inhibitor.

Molecular targets

[Cholinesterase, Inhibitor]

CAS RN

299-84-3

EC number

206-082-6

CIPAC number

112

US EPA chemical code

PubChem CID

9298

CLP index number

015-052-00-X

Therapeutic Class

ATCvet Code

None allocated

Controlled Drug?

Regulation 37/2010 MRL Classification

Molecular mass

321.55

PIN (Preferred Identification Name)

O,O-dimethyl O-(2,4,5-trichlorophenyl) phosphorothioate

IUPAC name

O,O-dimethyl O-2,4,5-trichlorophenyl phosphorothioate

CAS name

O,O-dimethyl O-(2,4,5-trichlorophenyl) phosphorothioate

Forever chemical

Other status information

Relevant Environmental Water Quality Standards

UK Environment Agency non-statutory standard for the protection of aquatic life in freshwater and saltwater: 0.03 µg l⁻¹ as annual average, 0.1 µg l⁻¹ as max acceptable conc.

Physical state

Colourless to light tan coloured crystalline powder

Commercial

Property

Product

Manufacturer

Authorisation Route

Legal Class (GB/UK)

Availability status

Considered obsolete but may be available in some countries

Introduction & key dates

1984, first registered USA

Example products (past and present) using this active

Formulation and application details

Commercial production

The production of fenchlorphos involves a two-step synthetic process starting with 2,4,5-trichlorophenol as the key aromatic precursor. In the first step, this compound reacts with phosphorus oxychloride or dimethyl phosphorochloridothioate in the presence of a base such as pyridine or triethylamine, facilitating the formation of the O,O-dimethyl O-(2,4,5-trichlorophenyl) phosphorothioate structure. This reaction is carried out under controlled temperature and anhydrous conditions to prevent hydrolysis.

Impact on climate of production and use

Data for the amount of life cycle GHGs produced by fenchlorphos are not available in the public domain. However, whilst estimates vary, more general data suggests that between 14 and 19 kilograms of CO₂e is emitted per kilogram of insecticide produced.

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

40.0

Moderate

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

9080000

Acetone

3470000

Chloroform

5950000

Toluene

5030000

Xylene

Melting point (°C)

Boiling point (°C)

Degradation point (°C)

Flashpoint (°C)

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

7.59 X 10⁰⁴

Calculated

Log P

4.88

High

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.58

Dissociation constant pKa) at 25 °C

Vapour pressure at 20 °C (mPa)

110

Highly volatile. 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)

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

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)

Non-mobile

K_oc (mL g⁻¹)

10232

Notes and range

Estimated

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 metabolites

None

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

500

Rat

Moderate

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)

> 3500

Anas platyrhynchos

Low

Birds - Short term dietary (LC₅₀/LD₅₀)

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

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

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

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)

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

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

0.74

Oncorhynchus mykiss juvenile 48 hr

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)

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)

500

Rat

Moderate

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

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

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

List II

Exposure Routes

Public

Occupational

May be absorbed through the skin

Mammalian dose elimination route and rate

Mainly excreted in urine

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

No data found

; ; ; ;

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

Harmful in contact skin or if swallowed

Handling issues

Property

Value and interpretation

General

Prevent generation of dust
Incompatible with alkaline pesticides
IMDG Transport Hazard Class 6.1

CLP classification 2013

Health: H302, H312
Environment: H400, H410

WHO Classification

II (Moderately hazardous)

UN Number

UN2811

Waste disposal & packaging

Packaging Group III (minor danger)

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

fenchlorphos

French

fenchlorphos

German

Fenchlorphos

Danish

Italian

Spanish

fenclorfos

Greek

Polish

fenchlorfos

Swedish

Hungarian

Dutch

fenchloorfos

Norwegian

Record last updated:	04/09/2025
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