Chloridazon (Ref: BAS 119H)

Chloridazon (Ref: BAS 119H)	Last updated: 26/05/2025
(Also known as: pyrazon; pyrazone; PAC; chloridazone)

SUMMARY

Choridazon is a herbicide for broadleaved weeds and grass control. It has a moderate aqueous solubility and is not considered to be volatile. It is moderately persistent in soil system and can also be persistent in water systems under some conditions. It has a low oral mammalian toxicity and whilst it is a recognised skin and eye irritant no chronic health impacts have been identified. It shows moderate to low ecotoxicity to most species.

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: Birds chronic ecotoxicity: Moderate; Fish acute ecotoxicity: Moderate; Fish chronic ecotoxicity: Moderate; Daphnia chronic ecotoxicity: Moderate	Human health Moderate alert: Mammals chronic toxicity: Moderate; Reproduction/development effects; Neurotoxicant

GENERAL INFORMATION

Description

A residual pyridazinone herbicide for control of weeds in beet and other crops crops

Example pests controlled

Broadleaved and grass weeds including blackgrass, canary grass and wild oats

Example applications

Sugarbeet; Fodder beet; Red beet; Mangels; Onions; Shallots; Garlic; Ornamentals

Efficacy & activity

Availability status

Current

Introduction & key dates

1964, introduced

GB regulatory status

GB COPR regulatory status

Not approved

Date COPR inclusion expires

Not applicable

GB LERAP status

No UK approval for use as a plant protection agent

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Not approved

Dossier rapporteur/co-rapporteur

Germany/Poland

Date EC 1107/2009 inclusion expires

Not applicable

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

Chemical structure

Isomerism

Isomeric - the 4-amino-5-chloro-isomer is a common impurity

Chemical formula

C₁₀H₈ClN₃O

Canonical SMILES

C1=CC=C(C=C1)N2C(=O)C(=C(C=N2)N)Cl

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

WYKYKTKDBLFHCY-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C10H8ClN3O/c11-9-8(12)6-13-14(10(9)15)7-4-2-1-3-5-7/h1-6H,12H2

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
chloridazon	-

General status

Pesticide type

Herbicide

Substance groups

Pyridazinone herbicide

Minimum active substance purity

920 g kg⁻¹

Known relevant impurities

EU dossier - 5-chloro isomer <60 g/Kg

Substance origin

Synthetic

Mode of action

Selective, systemic. Inhibits photosynthesis (photosystem II).

CAS RN

1698-60-8

EC number

216-920-2

CIPAC number

111

US EPA chemical code

069601

PubChem CID

15546

CLP index number

606-035-00-3

Molecular mass

221.6

PIN (Preferred Identification Name)

5-amino-4-chloro-2-phenylpyridazin-3(2H)-one

IUPAC name

5-amino-4-chloro-2-phenylpyridazin-3(2H)-one

CAS name

5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone

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 crystalline solid

Formulations

Property

Value

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

AgriGuard
BASF
Nufarm
Sipcam
Du Pont

Example products using this active

Ashlade CP
Magnum
Pyramin DF
Takron
Questar
BREK

Formulation and application details

Supplied in a variety of formulations including suspension concentrates and wettable powders

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

422

Moderate

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

15100

Methanol

3700

Ethyl acetate

100

Toluene

190

Dichloromethane

Melting point (°C)

206

Boiling point (°C)

Decomposes before boiling

Degradation point (°C)

360

Flashpoint (°C)

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

1.55 X 10⁰¹

Calculated

Log P

1.19

Low

Fat solubility of residues

Solubility

Insoluble

Data type

Regulatory data

Density (g ml⁻¹)

1.51

Dissociation constant pKa) at 25 °C

3.38

Very weak acid

Vapour pressure at 20 °C (mPa)

1.0 X 10^-06

Low volatility

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

5.30 X 10^-10

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

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

210nm = 18577, 229nm = 25043, 286nm = 10088

Surface tension (mN m⁻¹)

72.0

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Soil degradation (days) (aerobic)

DT₅₀ (typical)

Moderately persistent

DT₅₀ (lab at 20 °C)

43.1

Moderately persistent

DT₅₀ (field)

18.6

Non-persistent

DT₉₀ (lab at 20 °C)

78.4

Moderately persistent

DT₉₀ (field)

60.8

DT₅₀ modelling endpoint

Note

EU dossier lab studies DT₅₀ range 8.6-173.9 days (normalised), DT₉₀ range 50-140 days (normalised); field studies DT₅₀ range 3-105 days (normalised), DT₉₀ range 9-349 days (normalised); Other sources: DT₅₀ 21.0 days (DW3)

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

Stable

Note

Stable at all pH for over 30 days

Water-sediment DT₅₀ (days)

137

Slow

Water phase only DT₅₀ (days)

51.5

Stable

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)

Moderately mobile

K_oc (mL g⁻¹)

120

Notes and range

Freundlich

K_f (mL g⁻¹)

1.1

Moderately mobile

K_foc (mL g⁻¹)

199

¹/_n

0.845

Notes and range

EU dossier K_f range 0.2-3.6 mL g⁻¹, K_foc range 89-340 mL g⁻¹, ¹/_n range 0.568-1.03, Soils=5

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

2.16

Calculated

Transition state

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

Value

7.56 X 10^-02

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

7.0

Calculated using the Atkinson method.

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

5-amino-4-chloro-3(2H)-pyridazinone

Major fraction

0.169

BASF verified

5-amino-4-chloro-2-methyl-3(2H)-pyridazinone

Minor fraction

BASF verified

5-(1-amino-1-desoxyglucopyranosyl)-4-chloropyridazin-3(2H)-one (metabolite A)

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)

5-amino-4-chloro-3(2H)-pyridazinone

Not relevant

0.015

5-amino-4-chloro-2-methyl-3(2H)-pyridazinone

Not relevant

0.01

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

chloridazon metabolite B-glucoside

Plant

5-amino-4-chloro-2-methyl-3(2H)-pyridazinone
Note: DT50 soil 144 days

chloridazon metabolite B-1

Plant

5-amino-4-chloro-2-(4-hydroxyphenyl)-3(2H)-pyridazinone

4-OH-chloridazon; BH 119-4-OH

Animal; Rat (Urine, Bile, Faeces)

5-amino-4-chloro-2-(4-sulfatophenyl)-3(2H)-pyridazinone

sulfate conjugate of BH 119-4-OH

Animal; Rat

5-amino-2-phenyl-3(2H)-pyridazinone

deschloro-chloridazon

Animal

5-amino-2-(4-sulfatophenyl)-3(2H)-pyridazinone

sulfate conjugate of deschloro-chloridazon

Rat

glucuronide of BH 119-4-OH

Rat

5-(1-amino-1-desoxyglucopyranosyl)-4-chloropyridazin-3(2H)-one; chloridazon metabolite A

Animal; Plant; Surface water

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

2140

Rat

Low

Mammals - Short term dietary NOEL

(mg kg⁻¹)

Rat 2 yr

High

(ppm diet)

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

148

Rat Reproductive NOAEL

Moderate

Birds - Acute LD₅₀ (mg kg⁻¹)

> 2000

Colinus virginianus

Low

Birds - Short term dietary (LC₅₀/LD₅₀)

> 1318 mg kg bw⁻¹ day⁻¹

Colinus virginianus

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

21.8

Colinus virginianus NOAEL

Moderate

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

> 1000

Eisenia foetida

Low

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

Soil micro-organisms

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

Dose: 26 mg kg⁻¹ soil

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)

7.1% Mortality at dose 3.82 kg ha⁻¹

Chrysoperla carnea Larva

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

> 4000

Aphidius rhopalosiphi

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

4000

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)

41.3

Oncorhynchus mykiss

Moderate

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

3.16

Oncorhynchus mykiss

Moderate

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

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

132.0

Daphnia magna

Low

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

6.23

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)

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

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

> 3.16

Lemna gibba

Moderate

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

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

> 3.0

Pseudokirchneriella subcapitata

Moderate

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

0.73

Unknown species

Moderate

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)

2140

Rat

Low

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

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

> 5.4

Rat 4 hr

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)

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

0.2

Dermal penetration studies (%)

Dangerous Substances Directive 76/464

Exposure Routes

Public

Acceptable risk for bystanders for proposed uses

Occupational

Acceptable risk for operators and other workers for proposed uses

MRLs

European

EU MRL pesticide database

Great Britain

GB MRL Register

Notes

EU expected to amend MRL in early 2023

Drinking Water Standards

Drinking Water MAC (μg l⁻¹)

Mammalian dose elimination route and rate

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

No data found

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

Respiratory tract irritant

Skin irritant

Skin sensitiser

Eye irritant

Phototoxicant

No data found

General human health issues

No further information available

Handling issues

Property

Value and interpretation

General

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

CLP classification 2013

Health: H317
Environment: H400, H410

WHO Classification

III (Slightly hazardous)

UN Number

Waste disposal & packaging

Packaging Group III (minor danger)

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

chloridazon

French

chloridazone

German

Chloridazon

Danish

chloridazon

Italian

chloridazon

Spanish

cloridazon; pirazona

Greek

Polish

chlorydazon

Swedish

kloridazon

Hungarian

chloridazon

Dutch

chloridazon

Norwegian

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