Dimethachlor (Ref: CGA 17020)

Dimethachlor (Ref: CGA 17020)	Last updated: 09/04/2025
(Also known as: dimethachlore)

SUMMARY

Dimethachlor is a pre-emergence herbicide. It is highly soluble in water and has a low volatility. It is not expected to be persistent in soil systems but may be persistent in aquatic systems depending on local conditions. Based on its physico-chemical properties, dimethachlor is not expected to leach to groundwater. It is highly toxic to algae, moderately toxic to other aquatic species, birds and earthworms, and a low toxicity to honeybees. Dimethachlor has a moderate toxicity to mammals if ingested and is an irritant.

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: Mobile	Ecotoxicity Moderate alert: Birds acute ecotoxicity: Moderate; 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: Reproduction/development effects

GENERAL INFORMATION

Description

A herbicide used pre-emergence to control most annual grasses and broadleaved weeds

Example pests controlled

Loose silky-bent; Meadow grass; Brome; Slender foxtail; Common chickweed; Red dead-nettle; Mayweed

Example applications

Winter oilseed rape; Soybeans; Sugarbeet

Efficacy & activity

Efficacy established via field trials

Availability status

Current

Introduction & key dates

1977, introduced

GB regulatory status

GB COPR regulatory status

Approved

Date COPR inclusion expires

31/12/2029

GB LERAP status

Crop over 5m - See Authorisation for Crop LERAP Details

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Approved

Dossier rapporteur/co-rapporteur

Croatia/Austria

Date EC 1107/2009 inclusion expires

15/10/2026

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

Chemical structure

Isomerism

None

Chemical formula

C₁₃H₁₈ClNO₂

Canonical SMILES

CC1=C(C(=CC=C1)C)N(CCOC)C(=O)CCl

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

SCCDDNKJYDZXMM-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C13H18ClNO2/c1-10-5-4-6-11(2)13(10)15(7-8-17-3)12(16)9-14/h4-6H,7-9H2,1-3H3

2D structure diagram/image available?

Yes

General status

Pesticide type

Herbicide

Substance groups

Chloroacetamide herbicide

Minimum active substance purity

950 g kg⁻¹

Known relevant impurities

EU 2023 dossier: 2,6-dimethylaniline <= 0.5 g kg⁻¹

Substance origin

Synthetic

Mode of action

Selective, absorbed by new shoots of seedlings and roots. Inhibition of very long chain fatty acids (VLCFA, inhibition of cell division)

CAS RN

50563-36-5

EC number

256-625-6

CIPAC number

688

US EPA chemical code

PubChem CID

39722

CLP index number

616-031-00-3

Molecular mass

255.74

PIN (Preferred Identification Name)

2-chloro-N-(2,6-dimethylphenyl)-N-(2-methoxyethyl)acetamide

IUPAC name

2-chloro-N-(2-methoxyethyl)acet-2',6'-xylidide

CAS name

2-chloro-N-(2,6-dimethylphenyl)-N-(2-methoxyethyl)acetamide

Other status information

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

Physical state

Colourless crystals

Formulations

Property

Value

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

Ciba-Geigy

Example products using this active

Teridox 500EC

Formulation and application details

Usually supplied as an emulsifiable concentrate and used as a broadcast spray

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

2100

High

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

500000

Methanol

500000

Acetone

42000

Hexane

440000

Octanol

Melting point (°C)

46.3

Boiling point (°C)

Decomposes before boiling

Degradation point (°C)

300

Flashpoint (°C)

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

1.48 X 10⁰²

Calculated

Log P

2.17

at 25 °C

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.23

Dissociation constant pKa) at 25 °C

Not applicable

No dissociation

Vapour pressure at 20 °C (mPa)

2.3

at 25 °C

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)

2.8 X 10^-04

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

Negligible

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

Neutral solution: 215nm = 14461, 265nm = 486
Acidic solution: 215nm = 14768, 265nm = 572
Basic solution: 215nm = 9576, 265nm = 469

Surface tension (mN m⁻¹)

56.8

at 20 °C 99.5%

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Not readily biodegradable

Soil degradation (days) (aerobic)

DT₅₀ (typical)

7.37

Non-persistent

DT₅₀ (lab at 20 °C)

7.37

Non-persistent

DT₅₀ (field)

3.2

Non-persistent

DT₉₀ (lab at 20 °C)

27.8

Non-persistent

DT₉₀ (field)

10.5

DT₅₀ modelling endpoint

Note

EU dossier lab studies DT₅₀ range 2.3 (silt loam) - 15.6 (loamy sand) days, DT₉₀ range 11-65.9 days

Dissipation rate RL₅₀ (days) on plant matrix

Value

Note

Dissipation rate RL₅₀ (days) on and in plant matrix

Value

Note

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Stable

Note

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

Value

200

Persistent

Note

Stable pH 1 to pH 9, DT₅₀ 9.3 days at pH 13 up to 50 °C

Water-sediment DT₅₀ (days)

20.2

Fast

Water phase only DT₅₀ (days)

15.7

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

K_d (mL g⁻¹)

K_oc (mL g⁻¹)

Notes and range

Freundlich

K_f (mL g⁻¹)

4.20

Mobile

K_foc (mL g⁻¹)

¹/_n

0.91

Notes and range

EU dossier kf range 0.32-18.4, K_foc range 29.7-128 mL g⁻¹, ¹/_n range 0.760-0.939, Soils=10

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

1.09

Calculated

Low leachability

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

Value

2.50 X 10^-03

Calculated

Note

Potential for particle bound transport index

Low

Calculated

Potential for loss via drain flow

Mobile

Calculated

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

3.17

Calculated using the Atkinson method

Below the level of concern for long-range air transport

Bio-concentration factor

BCF (l kg⁻¹)

Estimated

Low potential

CT₅₀ (days)

Not available

Known soil metabolites

Metabolite

Major/Minor fraction

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

Estimated maximum occurrence fraction

Notes

N-(2,6-dimethylphenyl)-N-(2-methoxyethyl)oxalamic acid (Ref: CGA 50266)

Major fraction

0.355

((2,6-dimethylphenyl)-2-methoxyethyl)carbamoyl)methanesulfonic acid sodium salt (Ref: CGA 354742)

Major fraction

0.158

3-{2-[(2,6-dimethyl-phenyl)-(2-hy-droxyacetyl)amino]ethylsulfanyl}-2-hydroxypropionic acid

Aerobic

(2,6-dimethylphenylcarbamoyl)-methanesulfonic acid sodium salt (Ref: CGA 369873)

Aerobic

[(2,6-dimethylphenyl)-(2-sulfo-acetyl)amino]acetic acid sodium salt (Ref: CGA 373464)

Aerobic

2-[(2-hydroxyacetyl)-(2-methoxy-ethyl)amino]-3-methylbenzoic acid (Ref: SYN 530561)

Aerobic

2-[2-[N-(2-methoxyethyl)-2,6-dimethyl-anilino]-anilino]-2-oxo-ethyl]sulfinylacetic acid (Ref: SYN 547047)

Minor fraction

0.068

N-carboxymethyl-N-(2,6-dimethyl-phenyl)-oxalamic acid (Ref: CGA 102935)

Minor fraction

0.090

Aerobic

N-(2,6-dimethylphenyl)-N-(2-methoxyethyl)acetamide (Ref: CGA 42443)

Minor fraction

0.063

Anaerobic

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)

-{2-[(2,6-dimethyl-phenyl)-(2-hy-droxy-acetyl)-amino]-ethylsulfanyl}-2-hydroxy-propionic acid (Ref: SYN 528702)

Not relevant

(2,6-dimethylphenylcarbamoyl)-methanesulfonic acid sodium salt (Ref: CGA 369873)

Not relevant

[(2,6-dimethylphenyl)-(2-sulfo-acetyl)amino]acetic acid sodium salt (Ref: CGA 373464)

Not relevant

2-[(2-hydroxyacetyl)-(2-methoxy-ethyl)amino]-3-methylbenzoic acid (Ref: SYN 530561)

Not relevant

N-carboxymethyl-N-(2,6-dimethyl-phenyl)-oxalamic acid (Ref: CGA 102935)

Not relevant

N-(2,6-dimethylphenyl)-N-(2-methoxyethyl)oxalamic acid (Ref: CGA 50266)

Not relevant

((2,6-dimethylphenyl)-2-methoxyethyl)carbamoyl)methanesulfonic acid sodium salt (Ref: CGA 354742)

Not relevant

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

N-(2,6-dimethylphenyl)-N-(2-methoxyethyl)acetamide (Ref: CGA 42443)

Water; Sediment

2,6-dimethylaniline (Ref: CGA 72649)

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

>= 2000

Rat

Moderate

Mammals - Short term dietary NOEL

(mg kg⁻¹)

> 12

Rat 2 yr

High

(ppm diet)

> 300

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

267

Rat Reproductive NOAEL

Low

Birds - Acute LD₅₀ (mg kg⁻¹)

524

Coturnix japonica

Moderate

Birds - Short term dietary (LC₅₀/LD₅₀)

> 1470 mg kg bw⁻¹ day⁻¹

Coturnix japonica

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

102

Coturnix japonica as acid NOEL

Moderate

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

Eisenia foetida corr

Moderate

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

29.0

Eisenia foetida corr

Moderate

Soil micro-organisms

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

Dose: 7.5 kg ha⁻¹ 28 Day

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

> 1500

Echinochloa crusgalli
Vegetative vigour, ER₅₀
as g ha⁻¹

> 1500

Echinochloa crusgalli
Seedling emergence, ER₅₀
as g ha⁻¹

Honeybees (Apis spp.)

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

> 200

Apis mellifera

Low

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

> 300

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)

> 400

Bombus terrestris

Low

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

> 382.7

Bombus terrestris

Low

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)

2.5% Mortality at dose 1506 g ha⁻¹

Chrysoperla carnea

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

Aphidius rhopalosiphi Adult

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

655

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)

5.9

Oncorhynchus mykiss

Moderate

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

0.85

Oncorhynchus mykiss

Moderate

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

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

Daphnia magna

Moderate

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

2.3

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)

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

4.0

Chironomus riparius

Moderate

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

25.0

Chironomus riparius

Moderate

Aquatic plants (free-floating, growth) - Acute 7 day EC₅₀, biomass (mg l⁻¹)

0.066

Lemna gibba

Moderate

Aquatic plants (rooted, growth) - Acute 14 day EC₅₀, biomass (mg l⁻¹)

Algae - Acute 72 hour EC₅₀, growth (mg l⁻¹)

0.053

Desmodesmus subspicatus

Moderate

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)

>= 2000

Rat

Moderate

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

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

> 4.45

Rat 4 hr (nose only)

Other Mammal toxicity endpoints

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

0.1

Rat SF=100

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

0.5

Rat SF=100

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

0.5

Rat SF=100

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

0.1

Dog SF=100

Dermal penetration studies (%)

5.0-36%

concentration dependent

Dangerous Substances Directive 76/464

Exposure Routes

Public

No unacceptable risks to bystanders identified

Occupational

No unacceptable risks to operators or other workers identified with PPE/PPC

MRLs

European

EU MRL pesticide database

Great Britain

GB MRL Register

Notes

Drinking Water Standards

Drinking Water MAC (μg l⁻¹)

0.1

EU Dir 89/778/EC limit

Mammalian dose elimination route and rate

Approx 94% eliminated within 168 hrs via urine and bile

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

Respiratory tract irritant

Skin irritant

Skin sensitiser

Eye irritant

Phototoxicant

No data found

General human health issues

Possible liver, kidney and red blood cell toxicant at high dose

Handling issues

Property

Value and interpretation

General

Not explosive or oxidising
IMDG Transport Hazard Class 6.1
Not expected to auto-ignite; Not highly flammable

CLP classification 2013

Health: H302, H317
Environment: H400, H410

WHO Classification

II (Moderately hazardous)

UN Number

UN2811

Waste disposal & packaging

Packaging Group II (moderate danger)

Shelf-life, storage, stability and reactivity

Chemically stable under standard ambient conditions

TRANSLATIONS

Language

Name

English

dimethachlor

French

dimethachlore

German

Dimethachlor

Danish

dimethachlor

Italian

dimetaclor

Spanish

dimetacloro

Greek

dimethachlor

Polish

dimetachlor

Swedish

Hungarian

dimetaklor

Dutch

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