Malathion (Ref: OMS 1)

Malathion (Ref: OMS 1)	Last updated: 21/08/2024
(Also known as: carbophos; maldison; mercaptothion; carbofos; ENT 17034)

SUMMARY

Malathion is a broad-spectrum insecticide. It is moderately soluble in water and readily soluble in many organic solvents. It is quite volatile and has a low potential for leaching to groundwater. Malathion is not usually persistent in soil or water systems. It is moderately toxic to mammals, a cholineserase inhibitor and a neurotoxin. Malathion is highly toxic to honeybees and aquatic species with the exception of algae. It is moderately toxic to birds and earthworms.

GENERAL INFORMATION

Description

An organophosphate insectide once used to control animal parasites

Availability status

Current

Introduction & key dates

1952, first reported

Examples of veterinary uses

Once used to control fleas, ticks, mites, lice and keds on a variety of animals

Examples of species treated

Cats; Dogs; Cattle; Sheep; Horses; Pigs

Approval status

VMR 2013/2033 approval status (GB/UK)

Not approved

EU Regulatory approval status

Not approved

Chemical structure

Isomerism

A chiral molecule existing as two enantiomers

Chemical formula

C₁₀H₁₉O₆PS₂

Canonical SMILES

CCOC(=O)CC(C(=O)OCC)SP(=S)(OC)OC

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

JXSJBGJIGXNWCI-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C10H19O6PS2/c1-5-15-9(11)7-8(10(12)16-6-2)19-17(18,13-3)14-4/h8H,5-7H2,1-4H3

2D structure diagram/image available?

Yes

General status

Veterinary substance type

Insecticide, Antiparasitic

Substance groups

Organophosphate insectide; Organophosphate acaricide; Organothiophosphate insecticide; Organothiophosphate acaricide

Minimum active substance purity

950 g kg⁻¹ (racemic mixture)

Known relevant impurities

EU dossier - malaoxon <1g kg⁻¹, isomalathion <2g kg⁻¹, MeOOSPS-triester <15g kg⁻¹, MeOOOPS-triester 5g kg⁻¹

Substance origin

Synthetic

Mode of action

Broad-spectrum, non-systemic with contact, stomach and respiratory action. Acetylcholinesterase (AChE) inhibitor.

Molecular targets

[Cholinesterase, Inhibitor]

CAS RN

121-75-5

EC number

204-497-7

CIPAC number

US EPA chemical code

057701

PubChem CID

4004

CLP index number

015-041-00-X

Therapeutic Class

Antiparasitic products, insecticides & repellents: Ectoparasiticides

ATCvet Code

QP53AF12

Controlled Drug?

Regulation 37/2010 MRL Classification

Molecular mass

330.36

PIN (Preferred Identification Name)

IUPAC name

diethyl (dimethoxyphosphinothioylthio)succinate

CAS name

diethyl ((dimethoxyphosphinothioyl)thio)butanedioate

Other status information

Marine Pollutant; Evidence of use in third world countries; Chemical subject to PIC regulations; Phytotoxic to some ornamentals including orchids, ferns and petunias

Relevant Environmental Water Quality Standards

UK statutory standard for the protection of aquatic life in inland waters and for surface water quality: 0.01 µg l⁻¹ as annual average conc.
UK statutory standard for the protection of aquatic life in coastal and territorial waters: 0.02 µg l⁻¹ as annual average conc.

Physical state

Clear to amber liquid

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)

148

Moderate

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

250000

Xylene

62000

Heptane

250000

Acetone

250000

Methanol

Melting point (°C)

-20

Boiling point (°C)

Decomposes before boiling

Degradation point (°C)

174

Flashpoint (°C)

173

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

5.62 X 10⁰²

Calculated

Log P

2.75

at 25 °C

Moderate

Fat solubility of residues

Solubility

Insoluble

Data type

Regulatory data

Density (g ml⁻¹)

1.23

Dissociation constant pKa) at 25 °C

Not applicable

No dissociation

Vapour pressure at 20 °C (mPa)

3.1

Low volatility. If applied directly to plants or soil, drift is a concern & mitigation is advisable

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

1.00 X 10^-03

Non-volatile

Volatilisation as max % of applied dose lost

From plant surface

16 day

From soil surface

6.0

16 day

Volatilisation is not considered critical for air pollution

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

No absorbance above 290nm

Surface tension (mN m⁻¹)

58.0

at 20°C

Refractive Index

Environmental release

Degradation

Property

Value

Source; quality score; and other information

Interpretation

Soil degradation (days) (aerobic)

DT₅₀ (typical)

0.17

Non-persistent

DT₅₀ (lab at 20 °C)

0.17

Non-persistent

DT₅₀ (field)

Non-persistent

DT₉₀ (lab at 20 °C)

0.63

Non-persistent

DT₉₀ (field)

Note

EU dossier lab studies range DT₅₀ 0.1-0.25 days, DT₉₀ range 0.3-0.84 days; Other sources: DT₅₀ 1.0 days (DW4)

Manure DT₅₀ (days)

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Stable

Note

DT₅₀ 156 days under test conditions - not natural light (A5)

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

Value

6.2

Non-persistent

Note

pH sensitive: DT₅₀ 107 days at pH 5, 0.49 days at pH 9, all at 25 °C

Water-sediment DT₅₀ (days)

0.4

Fast

Water phase only DT₅₀ (days)

0.4

Fast

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

[Wheat grain: 12 wks @ 30 DegC, 50% RH; Modelled data], [Malt: 1291 days @ 20-22 DegC, dark conditions; Field study], [Mushroom (Agaricus bisporus): 4.4 days @ 25 DegC; 8.9 days @ 4 DegC; 17.3 days @ -18 DegC; Lab study], [Maize grain: 27.3 wks, open basket storage, 37.3 wks, closed wooden box storage @ 23 DegC, Field study]. [Field beans: 37.0 wks, open basket storage, 57.9 wks, closed wooden box storage @ 23 DegC, Field study].

Soil adsorption and mobility

Property

Value

Source; quality score; and other information

Interpretation

Linear

K_d (mL g⁻¹)

Slightly mobile

K_oc (mL g⁻¹)

1800

Notes and range

Freundlich

K_f (mL g⁻¹)

1.58

Moderately mobile

K_foc (mL g⁻¹)

217

¹/_n

0.94

Notes and range

EU dossier kf range 0.83-2.47 mL g⁻¹, K_foc range 151-308 mL g⁻¹, ¹/_n range 0.904-0.978, Soils=5

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

0.00

Calculated

Low leachability

Bio-concentration factor

BCF (l kg⁻¹)

103

(Other literature Log BCF range 0-3.7 (R3))

Threshold for concern

CT₅₀ (days)

0.69

Known soil metabolites

Metabolite

Major/Minor fraction

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

Estimated maximum occurrence fraction

Notes

malathion monocarboxylic acid (Ref: MMCA)

Major fraction

0.250

malathion dicarboxylic acid

Major fraction

0.617

Known groundwater metabolites

None

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

diethyl (2RS)-2-[(dimethoxyphosphoryl)sulfanyl]butanedioate
Note: Considerably more toxic than malathion

Malaoxon

Plant; Animal

desmethyl malathion

DMM

Plant

malathion dicarboxylic acid

DCA

Human (Liver)

malathion monocarboxylic acid

DMA

Human (Liver)

isomalathion

On heating

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

1778

Rat

Moderate

Mammals - Short term dietary NOEL

(mg kg⁻¹)

34.4

Rat

High

(ppm diet)

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

Birds - Acute LD₅₀ (mg kg⁻¹)

359

Colinus virginianus

Moderate

Birds - Short term dietary (LC₅₀/LD₅₀)

554 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)

306

Eisenia foetida corr

Moderate

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

Soil micro-organisms

Nitrogen mineralisation: No significant adverse effect
Carbon mineralisation: No significant adverse effect

Dose: 6.3 kg ha⁻¹

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

> 1800

six species
Vegetative vigour, ER₅₀
as g ha⁻¹

Honeybees (Apis spp.)

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

0.16

Apis mellifera

High

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

0.40

Apis mellifera

High

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)

0.0005

Megachile rotundata

High

Mode of exposure

Contact

Other bee species (2)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

0.265

Trigona spinipes

High

Mode of exposure

Contact

Beneficial insects (Ladybirds)

Beneficial insects (Lacewings) as Mortality, Contact ppm

> 111.1

Chrysoperla carnea Larva

Beneficial insects (Parasitic wasps) as Mortality LR₅₀ g ha⁻¹ 48 hr

0.061

Aphidius rhopalosiphi

Beneficial insects (Predatory mites) as Mortality LR₅₀ g ha⁻¹ 7 day

85.4

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)

0.018

Oncorhynchus mykiss

High

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

0.091

Oncorhynchus mykiss

Moderate

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

> 0.027

Danio rerio Eggs

High

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

0.0007

Daphnia magna

High

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

0.00006

Daphnia magna

High

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

> 0.002

Ceriodaphnia dubia LC₅₀

High

Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)

0.0015

Americamysis bahia

High

Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)

0.0004

Chironomus riparius 1 day

High

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)

Raphidocelis subcapitata EU dossier EC₅₀ = 4.1 Unknown species

Low

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

Mesocosm study data

NOEAEC mg l⁻¹

0.030

Aquatic invertebrates

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)

1778

Rat

Moderate

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

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

> 5.0

Rat 4 hr

Other Mammal toxicity endpoints

Intraperitoneal LD₅₀ = 250 mg kg⁻¹

Rat

Intravenous LD₅₀ = 50 mg kg⁻¹

Rat

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

0.03

Rat SF=1000

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

0.3

Rat SF=100

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

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

0.03

Rat SF=1000

Dermal penetration studies (%)

5.0-15.0

concentration dependent

Dangerous Substances Directive 76/464

List I; List II

Exposure Routes

Public

Possible concerns for bystanders especially children should they enter a sprayed area

Occupational

Operators should use PPC/PPE at all times

Mammalian dose elimination route and rate

Mainly excreted as metabolites in the urine

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

Respiratory tract irritant

Skin irritant

Skin sensitiser

Eye irritant

Phototoxicant

No data found

General human health issues

Possible adrenal gland, thyroid and liver toxicant
Acetylcholinesterase inhibition
IARC group 2A carcinogen; US EPA - weak evidence to suggest possible human carcinogen
Endocrine issues - Inhibition of catecholamine secretion

Handling issues

Property

Value and interpretation

General

Prevent generation of mists
Store at low temperatures, do not heat
Not explosive or oxidising
IMDG Transport Hazard Class 6.1

CLP classification 2013

Health: H302, H317
Environment: H400, H410

WHO Classification

III (Slightly hazardous)

UN Number

UN3018

Waste disposal & packaging

Packaging Group II (moderate danger)

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

malathion

French

malathion

German

Malathion

Danish

malathion

Italian

malation

Spanish

malation

Greek

malathion

Polish

malation

Swedish

Hungarian

malathion

Dutch

malathion

Norwegian

Record last updated:	21/08/2024
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