Difethialone (Ref: OMS 3053)

Difethialone (Ref: OMS 3053)	Last updated: 23/05/2025
(Also known as: LM 2219)

SUMMARY

Difethialone is a rodenticide not approved for use in Europe but is still used elsewhere. It is relatively volatile, has low potential to leach to groundwater but is highly persistent in soils. It is highly toxic to humans and considered to produce adverse effects on the reproduction system. it is also highly toxic to birds and aquatic life.

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; Fish acute ecotoxicity: High; Daphnia acute ecotoxicity: High	Human health High alert: Mammals acute toxicity: High; Reproduction/development effects Warning: Significant data are missing

GENERAL INFORMATION

Description

A rodenticide for use against warfarin-resistant and warfarin-susceptible strains of Rattus norvegicus and Mus musculus

Example pests controlled

Rodent damage

Example applications

Rats; Mice; Other small rodents

Efficacy & activity

Availability status

Current

Introduction & key dates

1989, registered France

GB regulatory status

GB COPR regulatory status

Not approved

Date COPR inclusion expires

Expired

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

Norway

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

Australia; USA

Chemical structure

Isomerism

A molecule with 2 chiral centres

Chemical formula

C₃₁H₂₃BrO₂S

Canonical SMILES

C1C(CC2=CC=CC=C2C1C3=C(SC4=CC=CC=C4C3=O)O)C5=CC=C(C=C5)C6=CC=C(C=C6)Br

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

JHELOZJAKXYVBE-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C31H23BrO2S/c32-24-15-13-20(14-16-24)19-9-11-21(12-10-19)23-17-22-5-1-2-6-25(22)27(18-23)29-30(33)26-7-3-4-8-28(26)35-31(29)34/h1-16,23,27,33H,17-18H2

2D structure diagram/image available?

Yes

General status

Pesticide type

Rodenticide

Substance groups

Coumarin rodenrticide

Minimum active substance purity

976 g kg⁻¹

Known relevant impurities

EU dossier - None declared

Substance origin

Synthetic

Mode of action

Anticoagulant, locks onto the rodent's liver enzyme

CAS RN

104653-34-1

EC number

600-594-7

CIPAC number

549

US EPA chemical code

128967

PubChem CID

91771

CLP index number

607-717-00-3

Molecular mass

539.48

PIN (Preferred Identification Name)

3-[(1E,3E)-3-(4'-bromo[1,1'-biphenyl]-4-yl)-1,2,3,4-tetrahydronaphthalen-1-yl]-4-hydroxy-2H-1-benzothiopyran-2-one where the ratios of the racemates (1RS,3RS) to (1RS,3SR) lie within the ranges 0–15 to 85–100 respectively

IUPAC name

3-[3-(4'-bromo[1,1'-biphenyl]-4-yl)-1,2,3,4-tetrahydro-1-naphthalenyl]-4-hydroxy-2H-1-benzothiopyran-2-one

CAS name

Other status information

Relevant Environmental Water Quality Standards

Herbicide Resistance Class (HRAC MoA class)

Not applicable

Herbicide Resistance Class (WSSA MoA class)

Not applicable

Insecticide Resistance Class (IRAC MoA class)

Not applicable

Fungicide Resistance Class (FRAC MOA class)

Not applicable

Examples of recorded resistance

Physical state

White-yellow powder

Formulations

Property

Value

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

Kukbo Science Co. Ltd.
Bayer CropScience

Example products using this active

Veteran Pellet
Veteran Wax Block
Rodilon Rat Bait

Formulation and application details

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

0.392

Low

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

100000

Acetone

14000

Dichloromethane

470

Methanol

200

Hexane

Melting point (°C)

235

Boiling point (°C)

Degradation point (°C)

Flashpoint (°C)

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

1.95 X 10⁰⁶

Calculated

Log P

6.29

High

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.36

Dissociation constant pKa) at 25 °C

Vapour pressure at 20 °C (mPa)

0.0133

Low volatility

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

1.02 X 10^-01

Moderately volatile

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

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

Maxima at 234nm, 260nm and 330nm

Surface tension (mN m⁻¹)

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Soil degradation (days) (aerobic)

DT₅₀ (typical)

635

Very persistent

DT₅₀ (lab at 20 °C)

635

Very persistent

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

DT₅₀ modelling endpoint

Note

EU dossier lab studies DT₅₀ range 417-976 days, at 12 °C

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

Note

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

Value

Note

Water-sediment DT₅₀ (days)

Water phase only DT₅₀ (days)

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)

54000000

Notes and range

Freundlich

K_f (mL g⁻¹)

K_foc (mL g⁻¹)

¹/_n

Notes and range

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

-10.46

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)

39974

High potential

CT₅₀ (days)

Not available

Known metabolites

None

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

0.56

Rat

High

Mammals - Short term dietary NOEL

(mg kg⁻¹)

(ppm diet)

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

Birds - Acute LD₅₀ (mg kg⁻¹)

0.264

Colinus virginianus

High

Birds - Short term dietary (LC₅₀/LD₅₀)

0.56 mg kg feed⁻¹

Colinus virginianus

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

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

> 1000

Low

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)

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

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)

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)

0.051

Oncorhynchus mykiss

High

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

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

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

0.0044

Daphnia magna

High

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

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)

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

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

> 0.18

Pseudokirchneriella subcapitata

Moderate

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

0.032

Selenastrum capricornutum Growth

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)

0.56

Rat

High

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

5.3

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

0.005

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

May be absorbed through the skin

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

; ; ; ;

No data found

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

No data found

Respiratory tract irritant

Skin irritant

Skin sensitiser

No data found

Eye irritant

Phototoxicant

No data found

General human health issues

Highly toxic
May cause severe haemorrhage leading to death

Handling issues

Property

Value and interpretation

General

Not explosive or oxidising
IMDG Transport Hazard Class 6.1

CLP classification 2013

Health: H300, H310, H330, H360d, H372
Environment: H400, H410

WHO Classification

Ia (Extremely hazardous)

UN Number

UN3027

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

difethialone

French

difethialone

German

Difethialone

Danish

difethialon

Italian

difetialone

Spanish

difetialone

Greek

Polish

difetialon

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	23/05/2025
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