Diquat

Diquat	Last updated: 18/12/2024
(Also known as: diquat ion; reglone; reglon)

SUMMARY

Diquat is a contact desiccant and herbicide that is normally used as the dibromide salt. As the salt it is highly soluble in water, has a low risk of leaching to groundwater and is volatile. It is very persistent in soil but rapidly degrades in aquatic systems. The dibromide salt is moderately toxic to mammals and is a known irritant but no other significant human health issues have been identified. The dibromide salt is moderately toxic to birds, most aquatic organisms, honeybees and earthworms.

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: Very persistent; Potential for particle bound transport: High	Ecotoxicity High alert: Birds acute ecotoxicity: High; Birds chronic ecotoxicity: High	Human health High alert: Mammals chronic toxicity: High

GENERAL INFORMATION

Description

A non-residual bupyridyl herbicide and crop desiccant, normally used as the dibromide salt, to control broad-leaved weeds and grasses

Example pests controlled

Water lettuce; Water hyacynth; Duckweed; Pennywort; Annual bluegrass; Fescue; Henbit; Buttercup

Example applications

Potatoes; Oilseed rape; Fruit including apples, pears, peaches, plums, citrus, olive, grapes; Tomatoes; Sunflowers; Vegetables including beans & peas, carrots, onions, chicory; Sugarbeet

Efficacy & activity

Availability status

Current

Introduction & key dates

1958, first described

GB regulatory status

GB COPR regulatory status

Not approved

Date COPR inclusion expires

Expired

GB LERAP status

No UK approval for use as a pesticide

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Not approved

Dossier rapporteur/co-rapporteur

UK/Sweden

Date EC 1107/2009 inclusion expires

Expired

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

Chemical structure

Isomerism

None

Chemical formula

C₁₂H₁₂N₂

Canonical SMILES

C1C[N+]2=CC=CC=C2C3=CC=CC=[N+]31

Isomeric SMILES

International Chemical Identifier key (InChIKey)

SYJFEGQWDCRVNX-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C12H12N2/c1-3-7-13-9-10-14-8-4-2-6-12(14)11(13)5-1/h1-8H,9-10H2/q+2

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
diquat dibromide	Variant

General status

Pesticide type

Herbicide

Substance groups

Quarternary ammonium herbicide

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Non-selective, contact absorbed through foliage, some desiccant action. Photosystem I (electron transport) inhibitor.

CAS RN

2764-72-9

EC number

220-433-0

CIPAC number

US EPA chemical code

032202

PubChem CID

6795

CLP index number

No data found

Molecular mass

184.24

PIN (Preferred Identification Name)

6,7-dihydrodipyrido[1,2-a:2',1'-c]pyrazine-5,8-diium

IUPAC name

9,10-dihydro-8a,10a-diazoniaphenanthrene

CAS name

6,7-dihydrodipyrido[1,2-a:2',1'-c]pyrazinediium

Other status information

Potential groundwater contaminant; PAN listed Highly Hazardous Chemical

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)

Note applicable

Examples of recorded resistance

Monochoria korsakowii

Physical state

Yellow crystalline solid

Related substances & organisms

diquat dibromide

diquat dichloride

Formulations

Property

Value

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

BOC Sciences

Example products using this active

Formulation and application details

Normally formulated as the dibromide salt

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

718000

High

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

25000

Methanol

100

Acetone

100

Hexane

100

Ethyl acetate

Melting point (°C)

Decomposes before melting

Boiling point (°C)

Decomposes before boiling

Degradation point (°C)

Flashpoint (°C)

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

2.51 X 10^-05

Calculated

Log P

-4.6

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.61

Dissociation constant pKa) at 25 °C

Vapour pressure at 20 °C (mPa)

1.00 X 10^-03

Low volatility

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

5.0 X 10^-12

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

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)

2345

Very persistent

DT₅₀ (lab at 20 °C)

2345

Very persistent

DT₅₀ (field)

5500

Very persistent

DT₉₀ (lab at 20 °C)

10478

Very persistent

DT₉₀ (field)

DT₅₀ modelling endpoint

Note

EU data lab studies DT₅₀ range 598 to >1000 days, DT₉₀ range from 1985 to 20509 days; Field studies DT₅₀ 10-20 years

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

Moderately fast

Note

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

Value

Stable

Note

Stable at all environmentally relevant pH's

Water-sediment DT₅₀ (days)

>1000

Stable

Water phase only DT₅₀ (days)

1.0

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)

Non-mobile

K_oc (mL g⁻¹)

2185000

Notes and range

Industry data

Freundlich

K_f (mL g⁻¹)

23099

Non-mobile

K_foc (mL g⁻¹)

1078792

¹/_n

0.869

Notes and range

EU dossier K_f range 144-70308 mL.g, K_foc range 6857-2511015 mL g⁻¹, ¹/_n range 0.589-1065, soils=4

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

-7.60

Calculated

Low leachability

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

Value

5.35 X 10^-03

Calculated

Note

Estimated concentrations of chemicals with Koc values greater than 9995 ml g⁻¹ are beyond the scope of the regression data used in SCI-GROW development. If there are concerns for such chemicals, a higher tier groundwater exposure assessment should be considered, regardless of the concentration returned by SCI-GROW

Potential for particle bound transport index

High

Calculated

Potential for loss via drain flow

Non-mobile

Calculated

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

Bio-concentration factor

BCF (l kg⁻¹)

Low risk

Based on LogP < 3

Low risk

CT₅₀ (days)

Known soil metabolites

Metabolite

Major/Minor fraction

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

Estimated maximum occurrence fraction

Notes

1-oxo-1,2,3,4-tetrahydropyrido(1,2-a)pyrazin-5-ium (Ref: R32245)

Minor fraction

Known groundwater metabolites

None

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

1-oxo-1,2,3,4-tetrahydropyrido(1,2-a)pyrazin-5-ium (Ref: R32245)

TOPPS

Plant; Poultry; Eggs; Surface water (photolysis)

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

214

Rat

Moderate

Mammals - Short term dietary NOEL

(mg kg⁻¹)

0.5

Rat

High

(ppm diet)

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

6.7

Rat Reproductive NOAEL

High

Birds - Acute LD₅₀ (mg kg⁻¹)

Anas platyrhynchos

High

Birds - Short term dietary (LC₅₀/LD₅₀)

721 mg kg feed⁻¹

Coturnix japonica

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

0.5

Anas platyrhynchos

High

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

94.3

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: >160 mg kg⁻¹ soil

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

< 10

Folsomia candida

Non-target plants

Honeybees (Apis spp.)

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

as diquat ion

Moderate

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

as diquat ion

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

3.2

Aphidius rhopalosiphi

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

2.9

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)

21.0

Oncorhynchus mykiss

Moderate

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

0.12

Oncorhynchus mykiss

Moderate

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

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

1.2

Daphnia magna

Moderate

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

0.125

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)

100

Chironomus riparius

Moderate

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

0.0032

Lemna gibba

High

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

0.011

Pseudokirchneriella subcapitata

Moderate

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)

214

Rat

Moderate

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

400

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

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

0.002

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

0.01

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

Not applicable

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

0.0002

Dermal penetration studies (%)

Dangerous Substances Directive 76/464

Exposure Routes

Public

Slight risk of dietary exposure

Occupational

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

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

Potential liver, kidney, stomach and intestine toxicant

Handling issues

Property

Value and interpretation

General

IMDG Transport Hazard Class 6.1

CLP classification 2013

Health: H335, H302, H317, H330, H372, H315, H319
Environment: H400, H410

WHO Classification

II (Moderately hazardous)

UN Number

UN2811

Waste disposal & packaging

Packaging Group II (moderate danger)

Shelf-life, storage, stability and reactivity

Limited shelf-life

TRANSLATIONS

Language

Name

English

diquat

French

diquat

German

Deiquat

Danish

diquat

Italian

diquat

Spanish

dicuat

Greek

diquat

Polish

dikwatu

Swedish

dikvat

Hungarian

diquat

Dutch

diquat

Norwegian

Record last updated:	18/12/2024
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