S-metolachlor (Ref: CGA 77102)

S-metolachlor (Ref: CGA 77102)	Last updated: 18/05/2025
(Also known as: alpha-metolachlor ; S-metholachlor; CGA 77101; S-metalachor)

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 Moderate alert: GUS: Transition state; Drainflow: Moderately mobile	Ecotoxicity Moderate alert: Fish acute ecotoxicity: Moderate; Fish chronic ecotoxicity: Moderate; Daphnia acute ecotoxicity: Moderate; Daphnia chronic ecotoxicity: Moderate; Bees acute oral ecotoxicity: Moderate; Earthworms acute ecotoxicity: Moderate; Earthworms chronic ecotoxicity: Moderate	Human health High alert: Endocrine disrupter; Reproduction/development effects

GENERAL INFORMATION

Description

Isomer herbicide mixture used to control grasses and some broadleaved weeds in a wide range of crops

Example pests controlled

Nightshade; Crabgrass; Pigweed; Foxtail; Yellow nutsedge; Witchgrass

Example applications

Corn; Soybeans; Beans & peas; Potatoes; Sugarbeet; Lupin; Sunflower; Fruit trees

Efficacy & activity

Efficacy demonstrated by extensive use and field trials

Availability status

Current

Introduction & key dates

circa 1998, introduced

GB regulatory status

GB COPR regulatory status

Approved

Date COPR inclusion expires

31/07/2028

GB LERAP status

Check label - may vary with formulation

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Not approved

Dossier rapporteur/co-rapporteur

Germany/France

Date EC 1107/2009 inclusion expires

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

Australia; Morocco

Chemical structure

Isomerism

Metolachlor exisits as the S- and R- entantiomers. S-metolachlor is a mixture of the S- and R-formats in an approximate ratio 88:12 .

Chemical formula

C₁₅H₂₂ClNO₂

Canonical SMILES

CCC1=CC=CC(=C1N(C(C)COC)C(=O)CCl)C

Isomeric SMILES

CCC1=CC=CC(=C1N([C@@H](C)COC)C(=O)CCl)C

International Chemical Identifier key (InChIKey)

WVQBLGZPHOPPFO-LBPRGKRZSA-N

International Chemical Identifier (InChI)

InChI=1S/C15H22ClNO2/c1-5-13-8-6-7-11(2)15(13)17(14(18)9-16)12(3)10-19-4/h6-8,12H,5,9-10H2,1-4H3/t12-/m0/s1

2D structure diagram/image available?

Yes

General status

Pesticide type

Herbicide

Substance groups

Chloroacetamide herbicide; Acetamide herbicide

Minimum active substance purity

960 g kg⁻¹

Known relevant impurities

EU dossier - None declared

Substance origin

Synthetic

Mode of action

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

CAS RN

87392-12-9

Alternative/old CAS RN

178961-20-1

EC number

618-004-1

CIPAC number

607

US EPA chemical code

108800

PubChem CID

11140605

CLP index number

607-432-00-4

Molecular mass

283.79

PIN (Preferred Identification Name)

mixture of 80–100% 2-chloro-N-(2-ethyl-6-methylphenyl)-N-[(2S)-1-methoxypropan-2-yl]acetamide and 20–0% 2-chloro-N-(2-ethyl-6-methylphenyl)-N-[(2R)-1-methoxypropan-2-yl]acetamide

IUPAC name

mix of: (aRS,1S)-2-chloro-6'-ethyl-N-(2-methoxy-1-methylethyl)acet-o-toluidide and 20–0% (aRS,1R)-2-chloro-6'-ethyl-N-(2-methoxy-1-methylethyl)acet-o-toluidide

CAS name

2-chloro-N-(2-ethyl-6-methylphenyl)-N-((1S)-2-methoxy-1-methylethyl)acetamide

Other status information

Possible groundwater contaminant

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

Clear straw-coloured liquid

Related substances & organisms

metolachlor

Formulations

Property

Value

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

Agriliance LLC
Syngenta
DuPont

Example products using this active

Dual Gold

Formulation and application details

Usually supplied as emulsifiable concentrates

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

480

at 25 °C

Moderate

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

Miscible

Acetone

Miscible

Methanol

Miscible

Toluene

Miscible

n-Hexane

Melting point (°C)

-61.1

Boiling point (°C)

334

Degradation point (°C)

290

Flashpoint (°C)

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

1.12 X 10⁰³

Calculated

Log P

3.05

at 25 °C

High

Fat solubility of residues

Solubility

Insoluble

Data type

Regulatory data - no accumulation of S-metolachlor residues in fat was observed in metabolism studies

Density (g ml⁻¹)

1.12

Dissociation constant pKa) at 25 °C

Not applicable

No dissociation

Vapour pressure at 20 °C (mPa)

3.7

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)

2.20 X 10^-03

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

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

266nm = 534
274nm = 443
>=290nm = 10

Surface tension (mN m⁻¹)

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Soil degradation (days) (aerobic)

DT₅₀ (typical)

51.8

Moderately persistent

DT₅₀ (lab at 20 °C)

51.8

Moderately persistent

DT₅₀ (field)

23.17

Non-persistent

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

111.8

DT₅₀ modelling endpoint

Note

EFSA 2018 lab studies DT₅₀ (normalised) range 10.3-221 days, Soils=21. Field studies DT₅₀ (measured) range 3.55-55.7 days, DT₉₀ (measured) range 27.6-256 days, Soils=17. EU 2003 dossier lab studies DT₅₀ range 7.6-37.6 days, DT₉₀ range 25.1-125 days; field studies DT₅₀ range 11-31 days, 6 soils, Europe, DT₉₀ range 36-148 days

Dissipation rate RL₅₀ (days) on plant matrix

Value

Note

Dissipation rate RL₅₀ (days) on and in plant matrix

Value

11.6

Note

Published literature RL₅₀ range 5.8-20.3 days, 3 field grown crops, various matrices, n=4

Aqueous photolysis DT₅₀ (days) at pH 7

Value

146

Stable

Note

Limited photolysis occurs

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

Value

Stable

Note

Stable pH 5 to 9 at 25 °C

Water-sediment DT₅₀ (days)

43.3

Moderately 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)

K_oc (mL g⁻¹)

Notes and range

Freundlich

K_f (mL g⁻¹)

3.63

Moderately mobile

K_foc (mL g⁻¹)

200.2

¹/_n

0.93

Notes and range

EU 2018 dossier K_f range 1.0-44.8 mL g⁻¹, K_foc range 112-368 mL g⁻¹, ¹/_n range 0.887-1.002, Soils=12

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

2.32

Calculated

Transition state

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

Value

1.01 X 10^-01

Calculated

Note

Potential for particle bound transport index

Low

Calculated

Potential for loss via drain flow

Moderately mobile

Calculated

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

2.3

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)

68.8

Whole fish

Low potential

CT₅₀ (days)

1.5

Known soil metabolites

Metabolite

Major/Minor fraction

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

Estimated maximum occurrence fraction

Notes

metolachlor ethane sulfonic acid (Ref: CGA 354743)

Major fraction

0.235

Syngenta verified

metolachlor oxanilic acid (Ref: CGA 51202)

Major fraction

0.211

Syngenta verified

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)

> 2000

Rat

Low

Mammals - Short term dietary NOEL

(mg kg⁻¹)

Dog

High

(ppm diet)

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

> 76

Unknown species Reproductive NOAEL

Moderate

Birds - Acute LD₅₀ (mg kg⁻¹)

>= 2510

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)

570

Moderate

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

< 26.65

Eisenia andrei corr

Moderate

Soil micro-organisms

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

Dose: 12.67 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)

> 200

Apis mellifera

Low

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

> 85

Apis mellifera

Moderate

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) as Mortality LR₅₀ g ha⁻¹

> 1.6

Aphidius rhopalosiphi

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

> 1.6

Typhlodromus pyri

Beneficial insects (Ground beetles)

0% Mortaliy at dose 960 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)

1.23

Oncorhynchus mykiss

Moderate

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

0.78

Pimephales promelas 35 day

Moderate

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

> 40.8

Danio rerio Embryo

Moderate

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

11.2

Daphnia magna

Moderate

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

5.2

Daphnia magna

Moderate

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

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

1.4

Mysidopsis bahia

Moderate

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

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

8.0

Chironomus riparius

Moderate

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

> 160

Chironomus riparius

Low

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

0.037

Lemna gibba 14 day

Moderate

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

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

0.017

Pseudokirchneriella subcapitata

Moderate

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

0.012

Pseudokirchneriella subcapitata 72 hr

Moderate

Mesocosm study data

NOEAEC mg l⁻¹

Marine bivalves – Acute EC₅₀ (mg l⁻¹)

> 0.01

Crassostrea gigas Embryo

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

Low

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

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

> 2.91

Rat 4 hr (nose only)

Other Mammal toxicity endpoints

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

0.1

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

None allocated

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

None allocated

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

0.15

Dermal penetration studies (%)

0.4-13%

concentration dependent

Dangerous Substances Directive 76/464

Exposure Routes

Public

Main risk for bystanders and residents arises from spray drift

Occupational

Acceptable levels with PPE/PPC

MRLs

European

EU MRL pesticide database

Great Britain

GB MRL Register

Notes

It is expected that EU MRLs will be amended in 2025

Drinking Water Standards

Drinking Water MAC (μg l⁻¹)

Mammalian dose elimination route and rate

Rapid and extensive via faeces (53%) and urine (42%) within 48 hrs

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

No data found

Respiratory tract irritant

Skin irritant

Skin sensitiser

Eye irritant

Phototoxicant

General human health issues

Possible liver and thyroid toxicant
US EPA - possible human carcinogen

Handling issues

Property

Value and interpretation

General

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

CLP classification 2013

Health: H317
Environment: H400, H410

WHO Classification

III (Slightly hazardous)

UN Number

UN3082

Waste disposal & packaging

Packaging Group III (minor danger)

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

S-metolachlor

French

S-metolachlore

German

S-Metolachlor

Danish

S-metolachlor

Italian

S-metolaclor

Spanish

S-metolachloro

Greek

S-metolachlor

Polish

S-metolachlor

Swedish

Hungarian

S-metolachlor

Dutch

S-metolachloor

Norwegian

Record last updated:	18/05/2025
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