Diclofop-methyl (Ref: HOE 023408)

Diclofop-methyl (Ref: HOE 023408)	Last updated: 22/08/2025
(Also known as: dichlofop variant; AE F023408)

SUMMARY

Diclofop-methyl is a grass weed herbicide. It has a low aqueous solubility, a low risk of leaching to groundwater and is relatively volatile. It is non-persistent in soils but may be persistent in aquatic systems under certain conditions. It is moderately toxic to mammals if ingested and there is some concern that exposure may cause cancer or adverse reproduction / developmental effects. It is moderately toxic to birds, most aquatic organisms, earthworms and honeybees but is not toxic to honeybees.

Hazard 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. These hazard alerts do not take account of usage patterns or exposure, thus do not represent risk.

Environmental fate	Ecotoxicity	Human health
Environmental fate Moderate alert: Potential for particle bound transport: Medium	Ecotoxicity Moderate alert: Birds chronic ecotoxicity: Moderate; Fish acute ecotoxicity: Moderate; Fish chronic ecotoxicity: Moderate; Daphnia acute ecotoxicity: Moderate; Daphnia chronic ecotoxicity: Moderate; Earthworms acute ecotoxicity: Moderate; Earthworms chronic ecotoxicity: Moderate	Human health High alert: Mammals chronic toxicity: High

GENERAL INFORMATION

Description

A herbicide used for post-emergence control of annual grasses including wild oats

Example pests controlled

Annual ryegrass, Barbgrass; Wild oats; Cowfoot grass

Example applications

Cereals including wheat, barley, triticale, rye; Linseed; Lupins; Canola; Peas; Poppies; Turf

Efficacy & activity

GB regulatory status

GB COPR regulatory status

Approved

Date COPR inclusion expires

31/05/2026

GB LERAP status

None

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Approved

Dossier rapporteur/co-rapporteur

France

Date EC 1107/2009 inclusion expires

31/08/2026

EU Candidate for substitution (CfS)

Yes - low ADI / ARfD / AOEL

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

Diclofop-methyl exhibits chiral isomerism, meaning it exists as two enantiomers: the R- and S-forms. These arise due to the presence of a chiral centrr in its structure, specifically at the carbon atom adjacent to the ester group. Commercial formulations of diclofop-methyl are typically racemic mixtures, containing equal proportions of both enantiomers.

Chemical formula

C₁₆H₁₄Cl₂O₄

Canonical SMILES

CC(C(=O)OC)OC1=CC=C(C=C1)OC2=C(C=C(C=C2)Cl)Cl

Isomeric SMILES

Clc2cc(Cl)ccc2Oc1ccc(OC(C(=O)OC)C)cc1

International Chemical Identifier key (InChIKey)

BACHBFVBHLGWSL-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C16H14Cl2O4/c1-10(16(19)20-2)21-12-4-6-13(7-5-12)22-15-8-3-11(17)9-14(15)18/h3-10H,1-2H3

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
diclofop-methyl	Unstated isomer

General status

Pesticide type

Herbicide

Substance groups

Aryloxyphenoxypropionate herbicide

Minimum active substance purity

930-980 g kg⁻¹

Known relevant impurities

EU dossier - None declared

Substance origin

Synthetic

Mode of action

Selective, systemic with contact action. Acetyl CoA carboxylase inhibitor (ACCase) - distrupts fatty acid biosynthesis and lipid formation.

CAS RN

51338-27-3

EC number

257-141-8

CIPAC number

358.201

US EPA chemical code

110902

PubChem CID

39985

CLP index number

607-165-00-3

Molecular mass

341.19

PIN (Preferred Identification Name)

rac-methyl (2R)-2-(4-(2,4-dichlorophenoxy)phenoxy)propanoate

IUPAC name

methyl (RS)-2-(4-(2,4-dichlorophenoxy)phenoxy)propionate

CAS name

methyl 2-(4-(2,4-dichlorophenoxy)phenoxy)propanoate

Forever chemical

Other status information

Severe Marine Pollutant

Relevant Environmental Water Quality Standards

Herbicide Resistance Class (HRAC MoA class)

Herbicide Resistance Class (WSSA MoA class)

Insecticide Resistance Class (IRAC MoA class)

Not applicable

Fungicide Resistance Class (FRAC MOA class)

Not applicable

Examples of recorded resistance

Alopecurus myosuroides, Avena fatua, Avena sterilis, Lolium multiflorum

Physical state

White crystalline powder

Related substances & organisms

diclofop

diclofop-phenol

Commercial

Property

Value

Availability status

Current

Introduction & key dates

1975, first reported

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

Bayer CropScience
Industrial Quimica key SA SPAIN
Hoechst

Example products using this active

Keylofop
Tigress Ultral
Illoxan 36 EC
Lolium
Avena

Formulation and application details

Usually supplied as an emulsifiable concentrate

Commercial production

The commercial production of diclofop-methyl typically involves a multi-step organic synthesis starting from phenoxyacetic acid derivatives. The key intermediate is diclofop acid, which is synthesised by chlorinating and etherifying specific aromatic compounds to introduce the 2,4-dichlorophenoxy moiety. This acid is then esterified with methanol in the presence of an acid catalyst, commonly sulphuric acid or a similar agent, to form diclofop-methyl, the active herbicidal ester.

Impact on climate of production and use

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

0.39

Low

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

500000

Acetone

500000

Toluene

500000

Dichloromethane

49700

n-Hexane

Melting point (°C)

Boiling point (°C)

370

Degradation point (°C)

Flashpoint (°C)

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

6.31 X 10⁰⁴

Calculated

Log P

4.8

High

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.4

at 28.5 °C

Dissociation constant pKa) at 25 °C

Not applicable

No dissociation, neither acid nor base

Vapour pressure at 20 °C (mPa)

2.5 X 10^-02

Low volatility

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

1.05 X 10^-05

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

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

220nm = 51969, 229nm = 16030, 283nm = 3218, 291nm = 2495

Surface tension (mN m⁻¹)

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)

0.31

Non-persistent

DT₅₀ (field)

19.0

Non-persistent

DT₉₀ (lab at 20 °C)

1.5

Non-persistent

DT₉₀ (field)

113.2

DT₅₀ modelling endpoint

Note

EU dossier lab studies DT₅₀ range 0.1-1.1 days, DT₉₀ range 0.5-3.6 days; field studies DT₅₀ range 6.7-38.5 days, DT₉₀ range 39.6-241.5 days

Dissipation rate RL₅₀ (days) on plant matrix

Value

Note

Dissipation rate RL₅₀ (days) on and in plant matrix

Value

1.4

Note

Chinese cabbage leaves, n=1

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Slow

Note

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

Value

31.7

Moderately persistent

Note

pH sensitive: 363 days at pH 5, 31.7 days at pH 7, 0.52 days at pH 9 - all at 25 °C, darkness

Water-sediment DT₅₀ (days)

0.06

Fast

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)

118.7

Non-mobile

K_foc (mL g⁻¹)

20869

¹/_n

1.04

Notes and range

EU dossier K_f range 80-157.3 mL g⁻¹, K_foc range 15084-26654 mL g⁻¹, ¹/_n range 1.01-1.08, Soils=2

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

-0.41

Calculated

Low leachability

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

Value

5.35 X 10^-03

Calculated

Note

Estimated concentrations of chemicals with Koc values greater than 9995 ml g⁻¹ are beyond the scope of the regression data used in SCI-GROW development. If there are concerns for such chemicals, a higher tier groundwater exposure assessment should be considered, regardless of the concentration returned by SCI-GROW

Potential for particle bound transport index

Medium

Calculated

Potential for loss via drain flow

Non-mobile

Calculated

Photochemical oxidative DT₅₀ (hrs) as indicator of long-range air transport risk

13.44

Calculated using the Atkinson method. Assumed 1.5E+06 OH/cm³, 12 hr

Below the level of concern for long-range air transport

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

diclofop (Ref: AE F021079)

Major fraction

0.87

diclofop-phenol

Minor fraction

0.059

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)

> 512

Rat

Moderate

Mammals - Short term dietary NOEL

(mg kg⁻¹)

Rat

High

(ppm diet)

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

Unknown species Reproductive NOAEL

High

Birds - Acute LD₅₀ (mg kg⁻¹)

> 2250

Coturnix japonica

Low

Birds - Short term dietary (LC₅₀/LD₅₀)

> 1104 mg kg bw⁻¹ day⁻¹

Coturnix japonica

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

Colinus virginianus

Moderate

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

> 500

Eisenia foetida corr

Moderate

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

Eisenia foetida corr

Moderate

Soil micro-organisms

Nitrogen mineralisation: No significant adverse effect
Carbon mineralisation: No significant adverse effect

Dose: 5.67 kg ha⁻¹ 5x field rate

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

Vegetative vigour ER₅₀ (g ha⁻¹)

116

Lolium perenne

Seedling emergence ER₅₀ (g ha⁻¹)

Lolium perenne

Honeybees (Apis spp.)

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

> 100

Apis mellifera

Low

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

> 131

Apis mellifera

Low

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)

9.76% Mortality at dose 1134 g ha⁻¹

Coccinella septempunctata

Beneficial insects (Lacewings)

Beneficial insects (Parasitic wasps) as Mortality LR₅₀ g ha⁻¹, Std lab test

30.12

Aphidius rhopalosiphi

Moderate

Beneficial insects (Predatory mites) as Mortality LR₅₀ g ha⁻¹, Std lab test

> 30.24

Typhlodromus pyri

Moderate

Beneficial insects (Ground beetles)

18.0% Mortality at dose 1.134 kg 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)

0.31

Oncorhynchus mykiss

Moderate

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

0.083

Oncorhynchus mykiss

Moderate

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

1.17

Danio rerio EC₅₀ Embryo

Moderate

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

0.23

Daphnia magna

Moderate

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

0.081

Daphnia magna Reproduction

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)

Sediment dwelling organisms - Chronic 28 day NOEC, static, water (mg l⁻¹)

10.0

Chironomus riparius as acid

Moderate

Sediment dwelling organisms - Chronic 28 day NOEC, sediment (mg kg⁻¹)

Aquatic Plants (free-floating, fonds growth, fresh) - 7 day (mg l⁻¹) (EC₅₀, Semi-static)

> 1.12

Lemna gibba

Moderate

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

Algae - Acute (growth rate, fresh; mg l⁻¹) (72 hr ErC₅₀, Static)

> 2.196

Raphidocelis subcapitata

Moderate

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)

> 512

Rat

Moderate

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

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

> 1.36

Rat 4 hr (nose only)

Other Mammal toxicity endpoints

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

0.001

Rat as diclofop

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

0.03

Rat as diclofop

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

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

0.003

Rat as diclofop

Dermal penetration studies (%)

1.2-11.1

concentration dependent

Dangerous Substances Directive 76/464

Exposure Routes

Public

Slight risk to the public from treated recreational areas such as golf courses

Occupational

PPE/PPC advised to minimise exposure

MRLs

European

EU MRL pesticide database

Great Britain

GB MRL Register

Notes

Drinking Water Standards

Drinking Water MAC (μg l⁻¹)

0.006

Mammalian dose elimination route and rate

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

Eye irritant

Phototoxicant

No data found

General human health issues

Kidney and liver toxicant
May cause bronchopneumonia or pulmonary oedema
US EPA - likely to be human carcinogen

Handling issues

Property

Value and interpretation

General

Not explosive or oxiding
Not expected to auto-ignite; Not highly flammable
IMDG Transport Hazard Class 9

CLP classification 2013

Health: H302, H317
Environment: H400, H410

WHO Classification

III (Slightly hazardous)

UN Number

UN3077

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

diclofop-methyl

French

diclofop-methyl

German

Diclofop-methyl

Danish

diclofop-methyl

Italian

diclofop-metile

Spanish

diclofop-metil

Greek

Polish

dichlofop metylowy

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	22/08/2025
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