MCPB (Ref: MB 3046)

MCPB (Ref: MB 3046)	Last updated: 09/04/2025
(Also known as: 2,4-MCPB; L-338; MCPB 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 Moderate alert: Drainflow: Moderately mobile	Ecotoxicity Moderate alert: Birds acute ecotoxicity: Moderate; Fish acute ecotoxicity: Moderate; Daphnia acute ecotoxicity: Moderate; Bees acute oral ecotoxicity: Moderate; Earthworms acute ecotoxicity: Moderate	Human health High alert: Mammals chronic toxicity: High

GENERAL INFORMATION

Description

A herbicide for post-emergence control of annual and perennial broadleaved weeds

Example pests controlled

Thistles; Docks; Buttercups; Fat hen; Shepherds purse; Nightshade; Nettles; Plantains; Ragwort; Hedge mustard; Bindweed

Example applications

Newly sown pastures; Clover seed crops; Peas; cereals undersown with ryegrass or clover

Efficacy & activity

MCPB has been tested in field development trials which demonstrated its efficacy

Availability status

Current

Introduction & key dates

circa 1960, introduced

GB regulatory status

GB COPR regulatory status

Approved

Date COPR inclusion expires

31/10/2029

GB LERAP status

None

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

Chemical structure

Isomerism

None

Chemical formula

C₁₁H₁₃ClO₃

Canonical SMILES

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

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

LLWADFLAOKUBDR-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C11H13ClO3/c1-8-7-9(12)4-5-10(8)15-6-2-3-11(13)14/h4-5,7H,2-3,6H2,1H3,(H,13,14)

2D structure diagram/image available?

Yes

General status

Pesticide type

Herbicide

Substance groups

Aryloxyalkanoic acid herbicide; Phenoxyacetic herbicide

Minimum active substance purity

950 g kg⁻¹

Known relevant impurities

EU 2022 dossier - 4-chloro-2-methylphenol (PCOC)

Substance origin

Synthetic

Mode of action

Selective, systemic, absorbed by leaves and roots with translocation. Synthetic auxin.

CAS RN

94-81-5

EC number

202-365-3

CIPAC number

US EPA chemical code

019201

PubChem CID

7207

CLP index number

607-053-00-4

Molecular mass

228.67

PIN (Preferred Identification Name)

4-(4-chloro-2-methylphenoxy)butanoic acid

IUPAC name

4-(4-chloro-o-tolyloxy)butyric acid

CAS name

4-(4-chloro-2-methylphenoxy)butanoic acid

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

White powdery solid

Formulations

Property

Value

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

BASF
Headland
Nufarm
United Phosphorus

Example products using this active

Butoxone
Tropotox
Tropotox Plus
Thistrol

Formulation and application details

Often supplied as soluble concentrate or in liquid formulations

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

60.4

Moderate

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

313000

Acetone

169000

Dichloromethane

266

Hexane

150000

Ethanol

Melting point (°C)

101.5

Boiling point (°C)

Decomposes before boiling

Degradation point (°C)

245

Flashpoint (°C)

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

2.14 X 10⁰¹

Calculated

Log P

1.33

Low

Fat solubility of residues

Solubility

Insoluble

Data type

Regulatory data - observed in metabolism and farm animal feeding studies

Density (g ml⁻¹)

1.233

Dissociation constant pKa) at 25 °C

4.6

Weak acid

Vapour pressure at 20 °C (mPa)

0.053

at 25 °C

Low volatility

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

9.4 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

Water: 290nm=9700, 280nm=1750, 286nm=1530
).1M HCl: 2890nm=9700, 280nm=1760, 287nm=1530
0.1M NaOH: 229nm=9590, 280nm=1760, 287nm=1530

Surface tension (mN m⁻¹)

70.0

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Not readily biodegradable

Soil degradation (days) (aerobic)

DT₅₀ (typical)

3.65

Non-persistent

DT₅₀ (lab at 20 °C)

3.65

Non-persistent

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

16.9

Non-persistent

DT₉₀ (field)

DT₅₀ modelling endpoint

Note

EU 2022 dossier Lab studies DT₅₀ (Normalised) range 1.7-6.82 days, DT₉₀ (measured) range 7.8-28.7 days, Soils=3

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

2.8

Moderately fast

Note

Rapid photolysis at pH 5 to pH 9 under irradiated conditions

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

Value

Stable

Note

Stable pH 5 to pH 9, 30 days

Water-sediment DT₅₀ (days)

Fast

Water phase only DT₅₀ (days)

9.7

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)

1.93

Moderately mobile

K_oc (mL g⁻¹)

104.7

Notes and range

EU 2022 Dossier K_d range 0.26-5.59 mL g⁻¹, K_oc range 31.1-280 mL g⁻¹, Soils=8

Freundlich

K_f (mL g⁻¹)

1.41

Moderately mobile

K_foc (mL g⁻¹)

101.95

¹/_n

0.902

Notes and range

EU 2022 dossier K_f range 0.22-7.89 mL g⁻¹, K_foc range 27.28-423.96 mL g⁻¹, ¹/_n range 0.854-0.936, Soils=8

pH sensitivity

Adsorption increases as pH decreases

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

1.12

Calculated

Low leachability

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

Value

2.77 X 10^-03

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

12.67

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 risk

Based on LogP < 3

Low risk

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

MCPA (Ref: BAS 009H)

Major fraction

0.351

cloxyfonac

Minor fraction

0.095

Known groundwater metabolites

None

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

benzoic acid

Water

O-cresol

2,4-dihydroxyphenol formate

2-hydroxyphenol format

Water

4-(4-hydroxy-o-tolyloxy) benzoic acid

Water

4-hydroxy-2-methylphenoxyacetic acid

OHMPA

Water

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)

Rat 2 yr

(ppm diet)

> 100

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

Rat NOEL

High

Birds - Acute LD₅₀ (mg kg⁻¹)

282

Colinus virginianus

Moderate

Birds - Short term dietary (LC₅₀/LD₅₀)

> 5000 mg kg feed⁻¹

Colinus virginianus

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

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

> 263

Eisenia foetida

Moderate

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

Soil micro-organisms

Nitrogen mineralisation: Effect noted but recovery by day 42
Carbon mineralisation: No significant adverse effect

Dose: 10 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)

> 100

Apis mellifera

Low

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

> 81.8

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

> 4000

Aphidius rhopalosiphi

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

> 2000

Typhlodromus pyri

Beneficial insects (Ground beetles)

0% Mortality at dose 2.25 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)

4.3

Oncorhynchus mykiss

Moderate

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

Oncorhynchus mykiss

Low

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)

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)

Lemna gibba

Low

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

0.745

Myriophyllum spicatum

Moderate

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

41.0

Pseudokirchneriella subcapitata

Low

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

Low

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

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

> 1.14

Rat 4 hr

Other Mammal toxicity endpoints

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

0.01

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

0.05

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)

0.06

Dermal penetration studies (%)

0.4-10.0

Concentration dependent

Dangerous Substances Directive 76/464

Exposure Routes

Public

{No unacceptable risks anticipated

Occupational

Occupational exposure may occur through dermal contact and inhalation of dust and sprays - PPE/PPC advised

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

Extensively metabolised - 85% and 5% via urine and faeces respectively with 48hrs of dose

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

Harmful or fatal if swallowed
Possible kidney and blood toxicant

Handling issues

Property

Value and interpretation

General

Not explosive
IMDG Transport Hazard Class 9
Not expected to auto-ignite; Not highly flammable
Product may be corrosive

CLP classification 2013

Health: H302
Environment: H400, H410

WHO Classification

II (Moderately hazardous)

UN Number

UN3082

Waste disposal & packaging

Packaging Group III (minor danger)

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

MCPB

French

MCPB

German

MCPB

Danish

MCPB

Italian

MCPB

Spanish

MCPB

Greek

MCPB

Polish

MCPB

Swedish

MCPB

Hungarian

MCPB

Dutch

MCPB

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