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Metolachlor (Ref: CGA 24705)
Last updated: 22/02/2024
(Also known as: metolachlore)

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; Earthworms acute ecotoxicity: Moderate
Human health
High alert:
Endocrine disrupter
GENERAL INFORMATION
Description
A pre-emergence herbicide used to control certain weeds in a variety of situations
Example pests controlled
Broad-leaved; Annual grassy weeds
Example applications
Corn; Soybeans; Sorghum; Potatoes; Cotton; Safflower; Stone fruits; Nuts; Woody ornamentals
Efficacy & activity
-
Availability status
Current
Introduction & key dates
1976, introduced
UK regulatory status
UK COPR regulatory status
Not approved
Date COPR inclusion expires
Not applicable
UK LERAP status
No UK approval for use
EC Regulation 1107/2009 (repealing 91/414)
EC Regulation 1107/2009 status
Not approved
Dossier rapporteur/co-rapporteur
Not applicable
Date EC 1107/2009 inclusion expires
Not applicable
EU Candidate for substitution (CfS)
Not applicable
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
Chemical structure
Isomerism
A molecule with two chiral centres. The technical product is an isomeric mixture containing both the R- and S-enantiomers
Chemical formula
C₁₅H₂₂ClNO₂
Canonical SMILES
CCC1=CC=CC(=C1N(C(C)COC)C(=O)CCl)C
Isomeric SMILES
No data
International Chemical Identifier key (InChIKey)
WVQBLGZPHOPPFO-UHFFFAOYSA-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
2D structure diagram/image available?
Yes
Cambridge Crystallographic Data Centre diagrams
Common Name Relationship Link
S-metolachlor S-isomer
General status
Pesticide type
Herbicide
Substance groups
Chloroacetanilide herbicide
Minimum active substance purity
>95%
Known relevant impurities
-
Substance origin
Synthetic
Mode of action
Selective, reduces seed germination. Inhibition of VLCFA (inhibition of cell division).
CAS RN
51218-45-2
EC number
257-060-8
CIPAC number
400
US EPA chemical code
108801
PubChem CID
4169
CLP index number
No data found
Molecular mass
283.79
PIN (Preferred Identification Name)
-
IUPAC name
2-chloro-N-(6-ethyl-o-tolyl)-N-[(1RS)-2-methoxy-1-methylethyl]acetamide
CAS name
2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide
Other status information
Potential groundwater contaminant
Relevant Environmental Water Quality Standards
-
Herbicide Resistance Class (HRAC MoA class)
K3
Herbicide Resistance Class (WSSA MoA class)
15
Insecticide Resistance Class (IRAC MoA class)
Not applicable
Fungicide Resistance Class (FRAC MOA class)
Not applicable
Examples of recorded resistance
Lolium rigidum
Physical state
Tan to colourless oily liquid
Related substances & organisms
Formulations
Property
Value
Example manufacturers & suppliers of products using this active now or historically
  • Ciba-Geigy
  • BOC Sciences
Example products using this active
  • Dual
  • Bicep
  • Pennant
  • Pimagram
Formulation and application details
Usually formulated as an emulsifiable concentrate
ENVIRONMENTAL FATE
Property
Value
Source; quality score; and other information
Interpretation
Solubility - In water at 20 °C (mg l⁻¹)
530
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
High
Solubility - In organic solvents at 20 °C (mg l⁻¹)
Miscible
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Benzene
-
Miscible
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Acetone
-
Miscible
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Hexane
-
Miscible
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Xylene
-
Melting point (°C)
-51.05
E4 E = Manufacturers safety data sheets
4 = Verified data
-
Boiling point (°C)
406.8
E4 E = Manufacturers safety data sheets
4 = Verified data
-
Degradation point (°C)
- - -
Flashpoint (°C)
190
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
-
Octanol-water partition coefficient at pH 7, 20 °C
P
2.51 X 1003 Calculated -
Log P
3.4
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
High
Fat solubility of residues
Solubility
- - -
Data type
- - -
Density (g ml⁻¹)
1.12
E4 E = Manufacturers safety data sheets
4 = Verified data
-
Dissociation constant pKa) at 25 °C
Not applicable
R4 R = Peer reviewed scientific publications
4 = Verified data
-
No dissociation
Vapour pressure at 20 °C (mPa)
1.7
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
Low volatility
Henry's law constant at 25 °C (Pa m³ mol⁻¹)
2.40 X 10-03
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Non-volatile
Maximum UV-vis absorption L mol⁻¹ cm⁻¹
- - -
Surface tension (mN m⁻¹)
- - -
Degradation
Property
Value
Source; quality score; and other information
Interpretation
General biodegradability
-
Soil degradation (days) (aerobic)
DT₅₀ (typical)
90
DW4 DW = Don Wauchope personal database for Pka data: Wauchope, R. D. and Edwards, J. Dissociation constants for pesticide active ingredients: a database and comparison with predicted values. Dataset is no longer available.
4 = Verified data
Moderately persistent
DT₅₀ (lab at 20 °C)
15
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Non-persistent
DT₅₀ (field)
21
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Non-persistent
DT₉₀ (lab at 20 °C)
- - -
DT₉₀ (field)
- - -
DT₅₀ modelling endpoint
- - -
Note
General literature lab studies DT₅₀ range 8-38 days, field studies DT₅₀ range 11-31 days (Switerland and France): Other sources: DT₅₀ 6-100 days (R3), 26 days at 25 °C (R4
Dissipation rate RL₅₀ on plant matrix
Value
- - -
Note
-
Dissipation rate RL₅₀ on and in plant matrix
Value
9.1
R4 R = Peer reviewed scientific publications
4 = Verified data
-
Note
Published literature RL₅₀ range 1.0-17.4 days, 3 field & undercover grown crops, various matrices, n=3
Aqueous photolysis DT₅₀ (days) at pH 7
Value
Stable
Q2 Q = Miscellaneous data from online sources
2 = Unverified data of unknown source
Stable
Note
-
Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7
Value
Stable
Q2 Q = Miscellaneous data from online sources
2 = Unverified data of unknown source
Stable
Note
-
Water-sediment DT₅₀ (days)
365
Q2 Q = Miscellaneous data from online sources
2 = Unverified data of unknown source
Stable
Water phase only DT₅₀ (days)
88
Q2 Q = Miscellaneous data from online sources
2 = Unverified data of unknown source
Stable
Soil adsorption and mobility
Property
Value
Source; quality score; and other information
Interpretation
Linear
Kd
0.67
R4 R = Peer reviewed scientific publications
4 = Verified data
Moderately mobile
Koc
120
Notes and range
Literature value: Kd range 0.33-1.64 mL g⁻¹, Koc range 50.0-540 mL g⁻¹, soils=33; Other sources: 120.2-309.0 mL g⁻¹ (R3), Log Koc 2.26 at 25 °C (R4)
Freundlich
Kf
0.93
R4 R = Peer reviewed scientific publications
4 = Verified data
Moderately mobile
Kfoc
163
1/n
0.888
Notes and range
Literature values: Study 1 - Kf range 0.07-2.57 mL g⁻¹, Kfoc range 51.7-600 mL g⁻¹, 1/n range 0.55-1.35, Soils=36; study 2 - Kf range 4.8-26.7 mL g⁻¹, Kfoc range 421-3679 mL g⁻¹, 1/n range 0.47-1.10, soils=5 (R4)
pH sensitivity
-
Fate indices
Property
Value
Source; quality score; and other information
Interpretation
GUS leaching potential index
2.36 Calculated Transition state
SCI-GROW groundwater index (μg l⁻¹) for a 1 kg ha⁻¹ or 1 l ha⁻¹ application rate
Value
1.03 X 10-01 Calculated -
Note
-
Potential for particle bound transport index
Low Calculated -
Potential for loss via drain flow
Moderately mobile Calculated -
Bio-concentration factor
BCF (l kg⁻¹)
68.8
Q3 Q = Miscellaneous data from online sources
3 = Unverified data of known source
Whole fish
Low potential
CT₅₀ (days)
1.5 -
Known soil metabolites
Metabolite
Major/Minor fraction
Estimated maximum occurrence fraction
Notes
metolachlor oxanilic acid (Ref: CGA 51202)
Major fraction 0.1 -
metolachlor ethane sulfonic acid (Ref: CGA 354743)
Major fraction 0.10 -
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)
> 1200
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
Rat
Moderate
Mammals - Short term dietary NOEL
(mg kg⁻¹)
90
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
Rat
High
(ppm diet)
- -
Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)
- - -
Birds - Acute LD₅₀ (mg kg⁻¹)
> 2000
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
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)
140
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
Moderate
Earthworms - Chronic NOEC, reproduction (mg kg⁻¹)
- - -
Soil micro-organisms
- - -
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)
> 110
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Apis mellifera
Low
Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
110
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Low
Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)
- - -
Chronic
- - -
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)
> 3.9
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
Oncorhynchus mykiss
Moderate
Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)
1.0
P3 P = Other non-EU, UK or US Governments and Regulators
3 = Unverified data of known source
Cyprinodon variegatus
Moderate
Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)
9.57
F3 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
3 = Unverified data of known source
Danio rerio EC₅₀ Embryo
Moderate
Temperate Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)
> 23.5
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
Daphnia magna
Moderate
Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)
> 0.707
F3 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
3 = Unverified data of known source
Daphnia magna LOEC
Moderate
Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)
> 0.9
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Ceriodaphnia dubia
Moderate
Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)
4.2
F3 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
3 = Unverified data of known source
Americamysis bahia
Moderate
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 - Acute 7 day EC₅₀, biomass (mg l⁻¹)
> 0.043
F3 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
3 = Unverified data of known source
Lemna gibba
Moderate
Algae - Acute 72 hour EC₅₀, growth (mg l⁻¹)
> 57.1
F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment )
4 = Verified data
Pseudokirchneriella subcapitata
Low
Algae - Chronic 96 hour NOEC, growth (mg l⁻¹)
3.0
P3 P = Other non-EU, UK or US Governments and Regulators
3 = Unverified data of known source
Anabaena sp.
Low
Mesocosm study data
NOEAEC mg l⁻¹
- - -
NOEAEC mg l⁻¹
- - -
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)
> 1200
G4 G = Extension Toxicology network database EXTOXNET. Available online but no longer updated. (click here )
4 = Verified data
Rat
Moderate
Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)
5050
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Rat
-
Mammals - Inhalation LC₅₀ (mg l⁻¹)
2.02
L3 L = Pesticide manuals and hard copy reference books / other sources
3 = Unverified data of known source
Rat
-
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
- - -
Exposure Routes
Public
-
Occupational
-
MRLs
European
EU MRL pesticide database 
Great Britain
GB MRL Register 
Notes
-
Drinking Water Standards
Non-statutory WHO drinking water guideline 0.01 mg l⁻¹
B5 B = UK CRD and ACP Evaluation Documents / and other DEFRA (UK) documents; Also Chemicals Regulation Division, Health and Safety Executive (HSE), UK (click here )
5 = Verified data used for regulatory purposes
UK EA QS database 2018
-
Drinking Water MAC (μg l⁻¹)
- - -
Mammalian dose elimination route and rate
- - -
Health issues
Specific human health issues
Carcinogen
Genotoxic
Endocrine disruptor
?Possibly, status not identified
A3 A = Chromosome aberration (EFSA database)
3 = Negative
;
B0 B = DNA damage/repair (EFSA database)
0 = No data
;
C0 C = Gene mutation (EFSA database)
0 = No data
;
D0 D = Genome mutation (EFSA database)
0 = No data
;
E3 E = Unspecified genotoxicity type (miscellaneous data source)
3 = Negative
Yes, known to cause a problem
Reproduction / development effects Acetyl cholinesterase inhibitor Neurotoxicant
?Possibly, status not identified
XNo, known not to cause a problem
XNo, known not to cause a problem
Respiratory tract irritant Skin irritant Skin sensitiser
XNo, known not to cause a problem
Yes, known to cause a problem
?Possibly, status not identified
Eye irritant Phototoxicant  
Yes, known to cause a problem
No data found  
General human health issues
May cause convulsions, diarrhoea, jaundice, weakness, nausea, sweating and dizziness
US EPA - possible human carcinogen
Endocrine issues - Pregnane X cellular receptor activation
Handling issues
Property
Value and interpretation
General
No information available
CLP classification 2013
Health: H317
Environment: H400, H410
WHO Classification
III (Slightly hazardous)
UN Number
-
Waste disposal & packaging
-
Shelf-life, storage, stability and reactivity
Limited shelf-life
TRANSLATIONS
Language
Name
English
metolachlor
French
metolachlore
German
Metolachlor
Danish
metolachlor
Italian
metolaclor
Spanish
metolacloro
Greek
metolachlor
Polish
metolachlor
Swedish
-
Hungarian
metolachlor
Dutch
metolachloor
Norwegian
-

Record last updated: 22/02/2024
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