MCPA (Ref: BAS 009H)

MCPA (Ref: BAS 009H)	Last updated: 26/05/2025
(Also known as: metaxon; BAS 101H; BAS 141H; MCP; 2,4-MCPA; 2M-4C; MCPA acid)

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 High alert: GUS: High leachability; Drainflow: Mobile	Ecotoxicity Moderate alert: Birds acute ecotoxicity: Moderate; Birds chronic ecotoxicity: Moderate; Earthworms acute ecotoxicity: Moderate	Human health Moderate alert: Mammals acute toxicity: Moderate; Genotoxic; Reproduction/development effects

GENERAL INFORMATION

Description

A herbicide for control of annual and perennial weeds in cereals and other crops. Can also be a pesticide transformation product.

Example pests controlled

Annual and perennial broadleaved weeds including Charlock, Wild radish, Dandylion, Capeweed, Fat hen and Hedge mustards

Example applications

Wheat; Oats; Tritical; Rye; Establish grass; Lindseed; Asparagus; Citrus

Efficacy & activity

Effectiveness demonstrated via field trials.

Availability status

Current

Introduction & key dates

circa 1950, introduced

GB regulatory status

GB COPR regulatory status

Approved

Date COPR inclusion expires

31/10/2029

GB LERAP status

Check label - may vary with formulation

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Approved

Dossier rapporteur/co-rapporteur

Poland/Netherlands

Date EC 1107/2009 inclusion expires

15/08/2026

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

Australia; USA; Egypt

Chemical structure

Isomerism

None

Chemical formula

C₉H₉ClO₃

Canonical SMILES

CC1=C(C=CC(=C1)Cl)OCC(=O)O

Isomeric SMILES

International Chemical Identifier key (InChIKey)

WHKUVVPPKQRRBV-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C9H9ClO3/c1-6-4-7(10)2-3-8(6)13-5-9(11)12/h2-4H,5H2,1H3,(H,11,12)

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
MCPA	-

General status

Pesticide type

Herbicide; Metabolite

Metabolite Type

Soil

Substance groups

Aryloxyalkanoic acid herbicide; Phenoxyacetic herbicide

Minimum active substance purity

940 mg kg⁻¹

Known relevant impurities

EU 2022 dossier - None declared

Substance origin

Synthetic

Mode of action

Selective, systemic with translocation. Synthetic auxin.

CAS RN

94-74-6

EC number

202-360-6

CIPAC number

US EPA chemical code

030501

PubChem CID

7204

CLP index number

607-051-00-3

Molecular mass

200.62

PIN (Preferred Identification Name)

IUPAC name

4-chloro-o-tolyloxyacetic acid

CAS name

(4-chloro-2-methylphenoxy)acetic acid

Other status information

Potential groundwater contaminant

Relevant Environmental Water Quality Standards

UK Environment Agency non-statutory standard for the protection of freshwater aquatic life pH <7: 12 µg l⁻¹, pH >7 80 µg l⁻¹ as annual average; pH <7: 120 µg l⁻¹, pH >7 800 µg l⁻¹ as max acceptable conc. For salt water 80 µg l⁻¹ as annual average, 800 µg l⁻¹ as max acceptable conc. Non-statutory WHO drinking water guideline 0.002 mg l⁻¹

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

Raphanus raphanistrum, Sisymbrium orientale

Physical state

White crystalline powder

Related substances & organisms

MCPA-butotyl

MCPA-dimethylammonium

MCPA-isopropyl

MCPA-sodium

Can be a metabolite of:

Parent

Formation medium

Estimated maximum occurrence fraction

1107/2009 relevancy

MCPB

Soil

0.351

Major fraction

MCPA-etexyl

Soil

Major fraction

MCPA-thioethyl

Soil

0.857

Major fraction

Formulations

Property

Value

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

BASF
Bayer Environ
Dow AgroSciences
DuPont
Headland Agrochemicals
Luxan
Nufarm
Scotts

Example products using this active

Agritox
Agroxone
Cedar
Esteem
GoLow Power
Polo
Relay P
Spear
Tropotox Plus

Formulation and application details

Often supplied as soluble concentrate, wettable powder or emulsifiable concentrate

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

250000

at 25 °C

High

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

323

Hexane

289300

Ethyl acetate

775600

Methanol

26500

Toluene

Melting point (°C)

115.4

Boiling point (°C)

Decomposes before boiling

Degradation point (°C)

210

Flashpoint (°C)

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

1.55 X 10^-01

Calculated

Log P

-0.81

Low

Fat solubility of residues

Solubility

Insoluble

Data type

Regulatory data - observed in metabolism and farm animal feeding studies

Density (g ml⁻¹)

1.41

Dissociation constant pKa) at 25 °C

3.73

Weak acid

Vapour pressure at 20 °C (mPa)

0.4

at 32 °C

Low volatility. If applied directly to plants, drift is a concern & mitigation is advisable

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

1.460 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

No absorption >290nm

Surface tension (mN m⁻¹)

61.7

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Not readily biodegradable

Soil degradation (days) (aerobic)

DT₅₀ (typical)

12.07

Non-persistent

DT₅₀ (lab at 20 °C)

12.07

Non-persistent

DT₅₀ (field)

Non-persistent

DT₉₀ (lab at 20 °C)

53.7

Moderately persistent

DT₉₀ (field)

DT₅₀ modelling endpoint

Note

EU 2022 dossier lab studies DT₅₀ (normalised) range 3.12-34.9 days, Soils=8; DT₉₀ (measured) range 13.2-116.0 days, Soils=8

Dissipation rate RL₅₀ (days) on plant matrix

Value

Note

Dissipation rate RL₅₀ (days) on and in plant matrix

Value

4.2

Note

Published literature RL₅₀ range 2.9-6.2 days, 5 field crops, various matrices, n=6

Aqueous photolysis DT₅₀ (days) at pH 7

Value

0.558

Fast

Note

Rapid DT₅₀ ~ 1 hour pH 5 to pH 9 at 25 °C in test conditions, DT₅₀ 25.4 days in natural sunlight pH 5

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

Value

Stable

Note

Stable pH 5 to pH 9 at 25 °C

Water-sediment DT₅₀ (days)

Fast

Water phase only DT₅₀ (days)

13.5

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)

1.6

Mobile

K_oc (mL g⁻¹)

73.88

Notes and range

EU 2022 dossier K_d range 0.15-6.61 mL g⁻¹, K_oc range 19.05-183.61 mL g⁻¹, Soils=15

Freundlich

K_f (mL g⁻¹)

0.66

Mobile

K_foc (mL g⁻¹)

57.96

¹/_n

0.822

Notes and range

EU 2022 dossier K_f range 0.12-3.37 mL g⁻¹, K_foc range 9.4-157/0 mL g⁻¹, ¹/_n range 0.7-0.906, Soils=15

pH sensitivity

Yes - Adsorption decreases with increasing soil pH

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

3.13

Calculated

High leachability

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

Value

2.86 X 10^-01

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

20.32

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)

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

4-chloro 2-methylphenol

Major fraction

0.386

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)

962

Rat

Moderate

Mammals - Short term dietary NOEL

(mg kg⁻¹)

Rat

High

(ppm diet)

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

Birds - Acute LD₅₀ (mg kg⁻¹)

377

Colinus virginianus

Moderate

Birds - Short term dietary (LC₅₀/LD₅₀)

> 983 mg kg bw⁻¹ day⁻¹

Colinus virginianus

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

93.2

Colinus virginianus NOEC

Moderate

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

325

Eisenia foetida

Moderate

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

Soil micro-organisms

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

Dose: 10x field rate

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)

> 200

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)

Beneficial insects (Lacewings) as Mortality LR₅₀ g ha⁻¹

> 97.2

Chrysoperla carnea

Beneficial insects (Parasitic wasps)

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

> 97.2

Typhlodromus pyri

Beneficial insects (Ground beetles) as Mortality LR₅₀ g ha⁻¹

> 97.2

Poecilus cuppreus

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

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

> 100

Cyprinus carpio

Low

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

Pimephales promelas

Low

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

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

> 190

Daphnia magna

Low

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

56.0

Daphnia magna

Low

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, growth) - Acute 7 day EC₅₀, biomass (mg l⁻¹)

> 3.2

Lemna gibba

Moderate

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

0.44

Myriophyllum spicatum

Moderate

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

79.8

Pseudokirchneriella subcapitata

Low

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

Unknown species

Low

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)

962

Rat

Moderate

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

4000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

> 6.36

Rat 4 hr (nose only dust}

Other Mammal toxicity endpoints

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

0.05

Rat SF=100

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

0.15

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

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

0.04

Dermal penetration studies (%)

4-5

concentration dependent

Dangerous Substances Directive 76/464

List II

Exposure Routes

Public

May be absorbed through the skin

Occupational

Occupational exposure may occur through inhalation and dermal contact

MRLs

European

EU MRL pesticide database

Great Britain

GB MRL Register

Notes

Drinking Water Standards

Drinking Water MAC (μg l⁻¹)

Mammalian dose elimination route and rate

Rapidly and extensively excreted, mainly unchanged, following oral administration (90% within 48 hours)

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

General human health issues

Highly toxic
May cause hypotension
Possible liver, kidney & blood toxicant

Handling issues

Property

Value and interpretation

General

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

CLP classification 2013

Health: H302, H318
Environment: H400, H411

WHO Classification

II (Moderately hazardous)

UN Number

UN3345

Waste disposal & packaging

Packaging Group III (minor danger)

Shelf-life, storage, stability and reactivity

Chemically stable under standard ambient conditions

TRANSLATIONS

Language

Name

English

MCPA

French

MCPA

German

MCPA

Danish

MCPA

Italian

MCPA

Spanish

MCPA

Greek

MCPA

Polish

MCPA

Swedish

MCPA

Hungarian

MCPA

Dutch

MCPA

Norwegian

MCPA

Record last updated:	26/05/2025
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