Difenacoum

Difenacoum	Last updated: 04/02/2024
(Also known as: difenacume; coumarin)

SUMMARY

Difenacoum is a second generation anticoagulant rodenticide that is not approved for use in many countries. It has a low aqueous solubility, a low volatility, and would not generally be expected to leach to groundwater. It may be very persistent in soil systems under certain conditions. In water systems the predominant degradation process is photolysis. it is highly toxic to mammals with some evidence indicating that it may cause negative reproduction and/or fertility effects. There are gaps in ecotoxicological data but it is known to be highly toxic to birds and fish and moderately toxic to aquatic invertebrates.

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

GENERAL INFORMATION

Description

A rodenticide effective against rats and mice resistant to other anticoagulants

Example pests controlled

Rats; Mice; Other small rodents

Example applications

Rats; Mice; Other small rodents

Efficacy & activity

Availability status

Current

Introduction & key dates

1976, introduced

UK regulatory status

UK COPR regulatory status

Not approved

Date COPR inclusion expires

Expired

UK LERAP status

No UK approval for use

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Not approved

Dossier rapporteur/co-rapporteur

Finland

Date EC 1107/2009 inclusion expires

Expired

EU Candidate for substitution (CfS)

Not applicble

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

A chiral molecule - mixed stereochemistry

Chemical formula

C₃₁H₂₄O₃

Canonical SMILES

C1C(CC2=CC=CC=C2C1C3=C(C4=CC=CC=C4OC3=O)O)C5=CC=C(C=C5)C6=CC=CC=C6

Isomeric SMILES

International Chemical Identifier key (InChIKey)

FVQITOLOYMWVFU-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C31H24O3/c32-30-26-12-6-7-13-28(26)34-31(33)29(30)27-19-24(18-23-10-4-5-11-25(23)27)22-16-14-21(15-17-22)20-8-2-1-3-9-20/h1-17,24,27,32H,18-19H2

2D structure diagram/image available?

Yes

General status

Pesticide type

Rodenticide

Substance groups

Coumarin rodenticide

Minimum active substance purity

Known relevant impurities

EU dossier - None declared

Substance origin

Synthetic

Mode of action

2nd generation anticoagulant

CAS RN

56073-07-5

EC number

259-978-4

CIPAC number

514

US EPA chemical code

11901

PubChem CID

54676884

CLP index number

607-157-00-X

Molecular mass

444.52

PIN (Preferred Identification Name)

3-((1E,3E)-3-(1,1'-biphenyl)-4-yl-1,2,3,4-tetrahydronaphthalen-1-yl)-4-hydroxy-2H-1-benzopyran-2-one

IUPAC name

3-((1RS,3RS;1RS,3SR)-3-biphenyl-4-yl-1,2,3,4-tetrahydro-1-naphthyl)-4-hydroxycoumarin

CAS name

3-(3-(1,1'-biphenyl)-4-yl-1,2,3,4-tetrahydro-1-naphthalenyl)-4-hydroxy-2H-1-benzopyran-2-one

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

Colourless crystalline powder

Formulations

Property

Value

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

Killgerm
Sorex
ICI Plant Protection

Example products using this active

Neokil
Sakarat D
Sorexa Gel
Neosorexa pellets
Ratak

Formulation and application details

Usually supplied as ready-to-use baits

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

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

1.7

Low

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

7600

Acetone

3700

Ethyl acetate

1200

Methanol

19600

Dichloromethane

Melting point (°C)

213

Boiling point (°C)

Decomposes before boiling

Degradation point (°C)

300

Flashpoint (°C)

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

3.98 X 10⁰⁷

Calculated

Log P

7.6

High

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.27

Dissociation constant pKa) at 25 °C

4.84

Weak acid

Vapour pressure at 20 °C (mPa)

1.9 X 10^-08

Low volatility

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

5.0 X 10^-09

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

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

259.4nm = 466001
310.6nm = 171001

Surface tension (mN m⁻¹)

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Soil degradation (days) (aerobic)

DT₅₀ (typical)

290

Persistent

DT₅₀ (lab at 20 °C)

439

Very persistent

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

DT₅₀ modelling endpoint

Note

EU dossier lab studies DT₅₀ 439 days Speyer 2.2 soil, aerobic conditions

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

0.34

Fast

Note

pH sensitive: 3.3 hrs at pH 5, 8.1 hrs at pH 7, 7.3 hrs at pH 9

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

Value

1000

Very persistent

Note

Stable at 25 °C

Water-sediment DT₅₀ (days)

Water 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)

170700

Notes and range

EU dossier K_oc range 17-426579 mL g⁻¹ - estimated by HPLC

Freundlich

K_f (mL g⁻¹)

K_foc (mL g⁻¹)

¹/_n

Notes and range

pH sensitivity

Higher adsorption at lower pH

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

-3.26

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)

9010

Estimated

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)

1.8

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)

Colinus virginianus

High

Birds - Short term dietary (LC₅₀/LD₅₀)

3.5 mg kg bw⁻¹ day⁻¹

Colinus virginianus

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

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

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

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)

0.064

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)

0.52

Daphnia magna

Moderate

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 - Acute 7 day EC₅₀, biomass (mg l⁻¹)

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

0.32

Selenastrum capricornutum

Moderate

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

Mesocosm study data

NOEAEC mg l⁻¹

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)

1.8

Rat

High

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

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

0.005

Rat 4 hr (head only)

Other Mammal toxicity endpoints

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

None allocated

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)

0.000017

Rabbit SF=300

Dermal penetration studies (%)

3.0

Dangerous Substances Directive 76/464

Exposure Routes

Public

Occupational

Exceptable risks for operators even with out PPE/PPC

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

Eye irritant

Phototoxicant

No data found

General human health issues

Highly toxic
May cause blood coagulation and haemorrhaging
Vapour may cause dizziness or suffocation

Handling issues

Property

Value and interpretation

General

Prevent generation of dust
Not explosive or oxidising but vapour may form explosive mixtures with air
IMDG Transport Hazard Class 6.1
Not expected to auto-ignite; Not highly flammable

CLP classification 2013

Health: H300, H310, H330, H372, H360D
Environment: H400, H410

WHO Classification

Ia (Extremely hazardous)

UN Number

UN3027

Waste disposal & packaging

Packaging Group I (great danger)

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

difenacoum

French

difenacoum

German

Difenacoum

Danish

difenacoum

Italian

difenacum

Spanish

difenacum

Greek

difenacoum

Polish

difenakum

Swedish

difenakum

Hungarian

Dutch

difenacum

Norwegian

Record last updated:	04/02/2024
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