Arsenous oxide	Last updated: 22/08/2024
(Also known as: arsenious acid; arsenic trioxide; arsenic (III) oxide; arsenic (3+) oxide; diarsenic trioxide; arsenic sesquioxide)

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SUMMARY

Arsenous oxide was once used as a rodenticide and in sheep dips. It is no longer approved for use in most countries due to its toxicity to humans and the environment. Arsenous oxide is highly toxic to all mammals, is a carcinogen, a reproduction toxin and highly corrosive. It is quite soluble in aqueous solution but practically insoluble in most organic solvents. It is also toxic to most fauna and flora.

GENERAL INFORMATION

Description	A now obsolete antiparasitic agent
Availability status	Considered obsolete but may be available in some countries
Introduction & key dates	circa 16th century, introduced
Examples of veterinary uses	Used, historically, in sheep dips
Examples of species treated	Sheep

Approval status

VMR 2013/2033 approval status (GB/UK)	Not approved
EU Regulatory approval status	Not approved

Chemical structure

Isomerism	None
Chemical formula	As₂O₃
Canonical SMILES	[O-2].[O-2].[O-2].[As+3].[As+3]
Isomeric SMILES	-
International Chemical Identifier key (InChIKey)	QTLQKAJBUDWPIB-UHFFFAOYSA-N
International Chemical Identifier (InChI)	InChI=1S/2As.3O/q2*+3;3*-2
2D structure diagram/image available?	Yes

General status

Veterinary substance type	Antiparasitic
Substance groups	Inorganic compound
Minimum active substance purity	-
Known relevant impurities	-
Substance origin	Synthetic
Mode of action	Inhibits sulfhydral enzymes
Molecular targets	[Sulfhydral enzymes, Inhibitor]
CAS RN	1327-53-3
Alternative/old CAS RN	28380-38-3
EC number	215–481–4
CIPAC number	250
US EPA chemical code	-
PubChem CID	14888
CLP index number	033-003-00-0
Therapeutic Class	-
ATCvet Code	Not allocated
Controlled Drug?	No
Regulation 37/2010 MRL Classification	-
Molecular mass	197.84
PIN (Preferred Identification Name)	diarsenic trioxide
IUPAC name	diarsenic trioxide
CAS name	arsenic oxide
Other status information	PAB Bad Actor Chemical
Relevant Environmental Water Quality Standards	-
Physical state	Colourless crystalline solid

Formulations

Property	Product	Manufacturer	Authorisation Route	Legal Class (GB/UK)
Example products (past and present) using this active	-	-	-	-
Formulation and application details	-

ENVIRONMENTAL FATE

Property		Value	Source; quality score; and other information	Interpretation
Solubility - In water at 20 °C (mg l⁻¹)		17000	L3 L = Pesticide manuals and hard copy reference books / other sources 3 = Unverified data of known source	High
Solubility - In organic solvents at 20 °C (mg l⁻¹)		Insoluble	L3 L = Pesticide manuals and hard copy reference books / other sources 3 = Unverified data of known source Chloroform	-
		Insoluble	L3 L = Pesticide manuals and hard copy reference books / other sources 3 = Unverified data of known source Diethyl ether	-
		Insoluble	L3 L = Pesticide manuals and hard copy reference books / other sources 3 = Unverified data of known source Ethanol	-
Melting point (°C)		272	L3 L = Pesticide manuals and hard copy reference books / other sources 3 = Unverified data of known source	-
Boiling point (°C)		465	Q3 Q = Miscellaneous data from online sources 3 = Unverified data of known source	-
Degradation point (°C)		-	-	-
Flashpoint (°C)		-	-	-
Octanol-water partition coefficient at pH 7, 20 °C	P	-	-	-
	Log P	-	-	-
Fat solubility of residues	Solubility	-	-	-
	Data type	-	-	-
Density (g ml⁻¹)		-	-	-
Dissociation constant pKa) at 25 °C		-	-	-
		-
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)		-	-	-
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	Kd (mL g⁻¹)	-	-	-
	Koc (mL g⁻¹)	-
	Notes and range	-
Freundlich	Kf (mL g⁻¹)	-	-	-
	Kfoc (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)		20	L3 L = Pesticide manuals and hard copy reference books / other sources 3 = Unverified data of known source 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)		-	-	-
Birds - Short term dietary (LC₅₀/LD₅₀)		-	-	-
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)		> 18.1	F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment ) 4 = Verified data Oncorhynchus mykiss	Moderate
Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)		2.65	P3 P = Other non-EU, UK or US Governments and Regulators 3 = Unverified data of known source Oncorhynchus mykiss 10 day	Moderate
Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)		> 12.9	F4 F = U.S. EPA ECOTOX database / U.S. EPA pesticide fate database / Miscellaneous WHO documents / FAO data, IPCS INCHEM data (US EPA Databases Related to Pesticide Risk Assessment ) 4 = Verified data Danio rerio	Moderate
Temperate Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)		> 3.85	P4 P = Other non-EU, UK or US Governments and Regulators 4 = Verified data Daphnia magna	Moderate
Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)		1.85	P4 P = Other non-EU, UK or US Governments and Regulators 4 = Verified data 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 - Acute 7 day EC₅₀, biomass (mg l⁻¹)		10	L3 L = Pesticide manuals and hard copy reference books / other sources 3 = Unverified data of known source Lemna paucicostata	Moderate
Algae - Acute 72 hour EC₅₀, growth (mg l⁻¹)		-	-	-
Algae - Chronic 96 hour NOEC, growth (mg l⁻¹)		-	-	-
Mesocosm study data	NOEAEC mg l⁻¹	-	-	-
	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)		20	L3 L = Pesticide manuals and hard copy reference books / other sources 3 = Unverified data of known source Rat	High
Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)		-	-	-
Mammals - Inhalation LC₅₀ (mg l⁻¹)		-	-	-
Other Mammal toxicity endpoints		Intraperitoneal LD₅₀ = 871 mg kg⁻¹	Q3 Q = Miscellaneous data from online sources 3 = Unverified data of known source Rat	-
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	Highly toxic - PPE/PPC essential
Mammalian dose elimination route and rate		Eliminated in urine	Q3 Q = Miscellaneous data from online sources 3 = Unverified data of known source	-

Health issues

Specific human health issues		Carcinogen Genotoxic Endocrine disruptor ✓Yes, known to cause a problem A0 A = Chromosome aberration (EFSA database) 0 = No data ; B0 B = DNA damage/repair (EFSA database) 0 = No data ; C0 C = Gene mutation (EFSA database) 0 = No data ; D0 D = Genome mutation (EFSA database) 0 = No data ; E2 E = Unspecified genotoxicity type (miscellaneous data source) 2 = Mixed/ambiguous results XNo, known not to cause a problem Reproduction / development effects Acetyl cholinesterase inhibitor Neurotoxicant ✓Yes, known to cause a problem XNo, known not to cause a problem ?Possibly, status not identified Respiratory tract irritant Skin irritant Skin sensitiser ✓Yes, known to cause a problem ✓Yes, known to cause a problem No data found Eye irritant Phototoxicant   ✓Yes, known to cause a problem No data found
General human health issues		Extremely toxic IARC Group 1 carcinogen Will cause a number of severe symptoms if ingested including chest pains, dizziness, breathing problems and weakness

Handling issues

Property	Value and interpretation
General	Dissolves in alkali to form toxic arsenites Corrosive
CLP classification 2013	-
WHO Classification	Ia (Extremely hazardous)
UN Number	-
Waste disposal & packaging	-
Shelf-life, storage, stability and reactivity	-

TRANSLATIONS

Language	Name
English	arsenous oxide
French	oxyde arsenieux
German	-
Danish	-
Italian	-
Spanish	-
Greek	-
Polish	-
Swedish	-
Hungarian	-
Dutch	-
Norwegian	-

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Record last updated:	22/08/2024
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