Bithionol

Bithionol	Last updated: 23/10/2025
(Also known as: bithionolate; bisoxyphen)

SUMMARY

Bithionol is a multi-use chemical that is now largely obsolete. It was once used as a fungicide, wood preservative and also has veterinary applications. It has a very low aqueous solubility but little else is known about its environmental fate or its ecotoxicology. This substance is highly toxic to mammals via the oral route.

GENERAL INFORMATION

Description

A bridged diphenyl drug with antibacterial and anthelmintic properties which is now largely obsolete

Examples of veterinary uses

Used to treat tapeworms (Anoplocephala perfoliata) and liver flukes (Fasciola hepatica)

Examples of species treated

Horses; Sheep

Approval status

VMR 2013/2033 approval status (GB/UK)

Not approved

EU Regulatory approval status

Not approved

Chemical structure

Isomerism

None

Chemical formula

C₁₂H₆Cl₄O₂S

Canonical SMILES

C1=C(C=C(C(=C1Cl)O)SC2=CC(=CC(=C2O)Cl)Cl)Cl

Isomeric SMILES

International Chemical Identifier key (InChIKey)

JFIOVJDNOJYLKP-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C12H6Cl4O2S/c13-5-1-7(15)11(17)9(3-5)19-10-4-6(14)2-8(16)12(10)18/h1-4,17-18H

2D structure diagram/image available?

Yes

Cambridge Crystallographic Data Centre diagrams

Common Name	Relationship	Link
bithionol	-
bithional sulfoxide	Variant

General status

Veterinary substance type

Anthelmintic, Antiparasitic

Other bioactivity & uses

Therapeutic drug; Wood preservative; Biocide

Substance groups

Bridged diphenyl fungicide

Minimum active substance purity

>97%

Known relevant impurities

Substance origin

Synthetic

Mode of action

An uncoupler of oxidative phosphorylation

Molecular targets

[Induced myeloid leukemia cell differentiation protein Mcl-1, Inhibitor], [Calpain, Inhibitor], [Estrogen receptor, Inhibitor], [Estrogen receptor beta, Inhibitor]

CAS RN

97-18-7

EC number

202-565-0

CIPAC number

None allocated

US EPA chemical code

064201

PubChem CID

2406

CLP index number

No data found

Therapeutic Class

Anthelmintics: Antitrematodals: Other antitrematodal agents

ATCvet Code

QP02BX01

Controlled Drug?

Regulation 37/2010 MRL Classification

Molecular mass

356.05

PIN (Preferred Identification Name)

2,2'-sulfanediylbis(4,6-dichlorophenol)

IUPAC name

2,2'-thiobis(4,6-dichlorophenol)

CAS name

2,2'-thiobis(4,6-dichlorophenol)

Global Governance status: Listed (✓) under

UK Poisons List Order 1972	Rotterdam Convention	Montreal Protocol
XNo The Poisons List Order 1972	XNo Rotterdam Convention	XNo Montreal Protocol
Stockholm Convention	OSPAR	EU Water Framework Directive
XNo Stockholm Convention	✓ (Section B)Yes (Section B) OSPAR	XNo EU Water Framework Directive

Relevant Environmental Water Quality Standards

Forever chemical

Other status information

Marine pollutant

Physical state

White crystalline powder with a faint odour

Commercial

Property

Value

Availability status

Considered obsolete but may be available in some countries

Introduction & key dates

1950s, first synthesis & charcaterisation; 1960s, introduction for vet use; 2013, not approved UK

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

Merck
Ciba-Geigy AG
AdvaCare Pharma

Example products using this active

Bitin
Bithin
Bithional

Formulation and application details

Usually formulated for topical use

Commercial production

Bithionol is synthesised through a condensation reaction involving chlorinated phenols and sulphur-containing reagents. The process typically begins with 2-hydroxy-3,5-dichlorophenol, which undergoes coupling via a sulphur bridge to form the symmetrical molecule of bithionol.

Impact on climate of production and use

Published GHG data is not available for most pharmaceuticals. However, according to industry, global averages suggest producing 1 kg of a typical active pharmaceutical ingredient can range from 10 to 100 kg CO₂e for small molecule drugs and potentially up to 1000 kg CO₂e for complex biologicals such as vaccines, depending on the drug type, its formulation, complexity of synthesis, solvent recovery, and energy sources used.

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C at pH 7 (mg l⁻¹)

4.0

Low

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

Melting point (°C)

188

Boiling point (°C)

445

Degradation point (°C)

Flashpoint (°C)

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

8.13 X 10⁰⁵

Calculated

Log P

5.91

High

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

1.73

Dissociation constant pKa) at 25 °C

4.82

pKa(2)=10.50

Vapour pressure at 20 °C (mPa)

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

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)

Refractive Index

Environmental release

Degradation

Property

Value

Source; quality score; and other information

Interpretation

Soil degradation (days) (aerobic)

DT₅₀ (typical)

DT₅₀ (lab at 20 °C)

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

Note

Manure DT₅₀ (days)

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)

K_oc (mL g⁻¹)

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

Bio-concentration factor

BCF (l kg⁻¹)

CT₅₀ (days)

Known metabolites

None

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

7.0

Rat

High

Mammals - Short Term Oral NOAEL (mg kg⁻¹ bw d⁻¹)

Mammals - Long Term (Chronic) Oral NOAEL (mg kg⁻¹ bw d⁻¹)

Birds - Acute LD₅₀ (mg kg⁻¹)

Birds - Short term dietary LC₅₀ (mg kg⁻¹ bw d⁻¹)

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

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

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

Soil micro-organisms

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

Vegetative vigour ER₅₀ (g ha⁻¹)

Seedling emergence ER₅₀ (g ha⁻¹)

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)

Beneficial insects (Butterflies)

Contact

Notes

Oral

Notes

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

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

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)

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, fonds growth, fresh) - 7 day (mg l⁻¹)

Aquatic plants (rooted, growth rate, fresh) - 14 day (mg l⁻¹)

Algae - Acute (growth rate, fresh; mg l⁻¹)

Algae - Chronic (growth rate, fresh; 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)

7.0

Rat

High

Mammals - Short Term Oral NOAEL (mg kg⁻¹ bw d⁻¹)

Mammals - Long Term (Chronic) Oral NOAEL (mg kg⁻¹ bw d⁻¹)

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

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

Intraperitoneal LD₅₀ = 100 mg kg⁻¹

Mouse

Intravenous LD₅₀ = 18.0 mg kg⁻¹

Mouse

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

Mammalian dose elimination route and rate

Unclear

Health issues

Specific human health issues (hazard-based)

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

May cause skin disorders
Toxic if ingested
May cause diarrhoea and fatigue

Handling issues

Property

Value and interpretation

General

IMDG Transport Hazard Class 6.1
When heated to decomposition will emit toxic fumes of hydrogen chloride and sulfur oxides

CLP classification 2013

WHO Classification

Not listed - determined as Ia (Extremely hazardous / Not listed)

UN Number

UN2811

Waste disposal & packaging

Packaging Group II (moderate danger)

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

bithionol

French

bithionol

German

Danish

Italian

Spanish

bitionol

Greek

Polish

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	23/10/2025
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

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