| monosodium methylarsonate |
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SUMMARY
Monosodium methylarsonate is a herbicide that is not widely approved for use in the developed world due to its toxicity. As well as being highly toxic it is also a known skin, eye and inhalation irritant. It is highly soluble in water and considerd to be persistent in soils. Monosodium methylarsonate is moderately toxic to fish, algae and honeybees and slightly less toxic to birds. GENERAL INFORMATION 
for monosodium methylarsonate
Description: A non-food herbicide applied post-emergence and used to control weeds mostly in non-food areas
Example pests controlled: Grassy weeds; Sedges; Broad-leaved weeds
Example applications: Cotton; Turf grass
Efficacy & activity: -
Availability status: Current
Introduction & key dates: -
EC Regulation 1107/2009 (repealing 91/414):
| Status | Not approved |
| Dossier rapporteur/co-rapporteur | Not applicable |
| Date inclusion expires | Not applicable |
| EU Candidate for substitution (CfS) | Not applicable |
| Listed in EU database | No |
Approved for use (
) or known to be used (
) in the following European countries: 
AT |
BE |
BG |
CY |
CZ |
DE |
DK |
EE |
EL |
ES |
FI |
FR |
HR |
HU |
IE |
IT |
LT |
LU |
LV |
MT |
NL |
PL |
PT |
RO |
SE |
SI |
SK |
UK |
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Also used in: USA
Chemical structure:
| Isomerism | - |
| Chemical formula | CH4AsNaO3 |
| Canonical SMILES | C[As](=O)(O)[O-].[Na+] |
| Isomeric SMILES | No data |
| International Chemical Identifier key (InChIKey) | JITOKQVGRJSHHA-UHFFFAOYSA-M |
| International Chemical Identifier (InChI) | InChI=1S/CH5AsO3.Na/c1-2(3,4)5;/h1H3,(H2,3,4,5);/q;+1/p-1 |
| 2D structure diagram/image available? | Yes |
General status:
| Pesticide type | Herbicide | |||
| Substance group | Organometal | |||
| Minimum active substance purity | - | |||
| Known relevant impurities | - | |||
| Substance origin | Synthetic | |||
| Mode of action | Selective, contact herbicide, phytotoxic | |||
| CAS RN | 2163-80-6 | |||
| EC number | 218-495-9 | |||
| CIPAC number | 286 | |||
| US EPA chemical code | 013803 | |||
| PubChem CID | 23664719 | |||
| Molecular mass (g mol-1) | 161.95 | |||
| PIN (Preferred Identification Name) | - | |||
| IUPAC name | sodium hydrogen methylarsonate | |||
| CAS name | monosodium methylarsonate | |||
| Other status information | - | |||
| Relevant Environmental Water Quality Standards | - | |||
| Herbicide Resistance Classification (HRAC) | Z | |||
| Herbicide Resistance Classification (WSSA) | - | |||
| Insecticide Resistance Classification (IRAC) | Not applicable | |||
| Fungicide Resistance Classification (FRAC) | Not applicable | |||
| Examples of recorded resistance | - | |||
| Physical state | Technical form is a pale yellow liquid | |||
| Related substances & organisms | - | |||
Formulations:
| Property |
Value | |||
| Example manufacturers & suppliers of products using this active now or historically | - | |||
| Example products using this active | - | |||
| UK LERAP status | No UK approval for use as a pesticide under EC Regulation 1107/2009 | |||
| Formulation and application details | - | |||
ENVIRONMENTAL FATE
for monosodium methylarsonate
| Property |
Value | Source/Quality Score/Other Information |
Interpretation |
|
| Solubility - In water at 20oC (mg l-1) | 580000 | Q3 | High | |
| Solubility - In organic solvents at 20oC (mg l-1) | - | - | - | |
| Melting point (oC) | - | V3 | - | |
| Boiling point (oC) | - | - | - | |
| Degradation point (oC) | - | - | - | |
| Flashpoint (oC) | - | - | - | |
| Octanol-water partition coefficient at pH 7, 20oC | P | 7.94 X 10-04 | Calculated | - |
| Log P | -3.1 | V3 | Low | |
| Bulk density (g ml-1)/Specific gravity | - | - | - | |
| Dissociation constant (pKa) at 25oC | 9.02 | Q3 | - | |
| Note: Weak acid | ||||
| Vapour pressure at 20oC (mPa) | - | - | - | |
| Henry's law constant at 25oC (Pa m3 mol-1) | - | - | - | |
GUS leaching potential index  |
- | - | - | |
| SCI-GROW groundwater index (μg l-1) for a 1 kg ha-1 or 1 l ha-1 application rate |
Value | - | - | - |
| Note | - | |||
| Potential for particle bound transport index |
- | - | - | |
| Maximum UV-vis absorption L mol-1 cm-1 | - | - | - | |
| Surface tension (mN m-1) | - | - | - | |
Degradation:
| Property |
Value | Source/Quality Score/Other Information |
Interpretation |
General biodegradability | - |
| Soil degradation (days) (aerobic) | DT50 (typical) | 200 | F3 | Persistent |
| DT50 (lab at 20oC) | - | - | - | |
| DT50 (field) | - | - | - | |
| DT90 (lab at 20oC) | - | - | - | |
| DT90 (field) | - | - | - | |
| DT50 modelling endpoint | - | - | - | |
| Note | Arsenic is environmentally stable | |||
| Dissipation rate RL50 on plant matrix | Value | 2.54 | R3 | - |
| Note | Peanut leaves, n=1 | |||
| Dissipation rate RL50 on and in plant matrix | Value | - | - | - |
| Note | - | |||
| Aqueous photolysis DT50 (days) at pH 7 | Value | Stable | F3 | - |
| Note | - | |||
| Aqueous hydrolysis DT50 (days) at 20oC and pH 7 | Value | Stable | F3 | - |
| Note | - | |||
| Water-sediment DT50 (days) | - | - | - | |
| Water phase only DT50 (days) | - | - | - | |
Soil adsorption and mobility:
| Property |
Value | Source/Quality Score/Other Information |
Interpretation |
|
| Linear | Kd | - | - | - |
| Koc | - | |||
| Notes and range | - | |||
| Freundlich | Kf | - | - | - |
| Kfoc | - | |||
| 1/n | - | |||
| Notes and range | - | |||
| pH sensitivity | - | |||
ECOTOXICOLOGY
for monosodium methylarsonate
| Property |
Value | Source/Quality Score/Other Information |
Interpretation |
|
| Bio-concentration factor | BCF (l kg-1) | Low risk | Q3 Based on LogP < 3 | Low potential |
| CT50 (days) | - | - | ||
| Mammals - Acute oral LD50 (mg kg-1) | 2449 | F3 Rat | Low | |
| Mammals - Short term dietary NOEL | (mg kg-1) | - | - | - |
| (ppm diet) | - | - | ||
| Birds - Acute LD50 (mg kg-1) | 3269 | F4 Colinus virginianus | Low | |
| Birds - Short term dietary (LC50/LD50) | - | - | - | |
| Fish - Acute 96 hour LC50 (mg l-1) | 100.0 | F4 Oncorhynchus mykiss | Moderate | |
| Fish - Chronic 21 day NOEC (mg l-1) | - | - | - | |
| Aquatic invertebrates - Acute 48 hour EC50 (mg l-1) | 58.0 | F4 Daphnia magna | Moderate | |
| Aquatic invertebrates - Chronic 21 day NOEC (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) | 93.0 | F4 Lemna gibba | Low | |
| Non-target plants | - | - | - | |
| - | - | - | ||
| Algae - Acute 72 hour EC50, growth (mg l-1) | 1.8 | F4 Pseudokirchneriella subcapitata | Moderate | |
| Algae - Chronic 96 hour NOEC, growth (mg l-1) | - | - | - | |
| Honeybees (Apis spp.) | Contact acute LD50 (worst case from 24 , 48 and 72 hour values - μg bee-1) | 24.0 | F4 | Moderate |
| 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) | - | - | - | |
| 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 pollinators (1) | Acute LD50 (worst case from 24 , 48 and 72 hour values - μg insect-1) | - | - | - |
| Mode of exposure | - | |||
| Other pollinators (2) | Acute LD50 (worst case from 24 , 48 and 72 hour values - μg insect-1) | - | - | - |
| Mode of exposure | - | |||
| Earthworms - Acute 14 day LC50 (mg kg-1) | - | - | - | |
| Earthworms - Chronic NOEC, reproduction (mg kg-1) | - | - | - | |
| Other soil macro-organisms | Acute LC50 (mg kg-1) | - | - | - | Chronic NOEC (mg kg-1) | - | - | - |
| Other arthropod (1) | LR50 g ha-1 | - | - | - |
| % Effect | - | - | - | |
| Other arthropod (2) | LR50 g ha-1 | - | - | - |
| % Effect | - | - | - | |
| Soil micro-organisms | - | - | - | |
| Mesocosm study data | NOEAEC mg l-1 | - | - | - |
| NOEAEC mg l-1 | - | - | - | |
HUMAN HEALTH AND PROTECTION
for monosodium methylarsonate
General:
| Property |
Value | Source/Quality Score/Other Information |
Interpretation |
|
| Threshold of Toxicological Concern (Cramer Class) |
High (class III) | - | - | |
| Mammals - Acute oral LD50 (mg kg-1) | 2449 | F3 Rat | Low | |
| Mammals - Dermal LD50 (mg kg-1 body weight) | > 2000 | F3 Rabbit | - | |
| Mammals - Inhalation LC50 (mg l-1) | 2.2 | F3 Rat | - | |
| Other Mammal toxicity endpoints | - | - | ||
| ADI - Acceptable Daily Intake (mg kg-1bw day-1) | - | - | - | |
| ARfD - Acute Reference Dose (mg kg-1bw day-1) | 0.1 | F3 (USA) | - | |
| AAOEL - Acute Acceptable Operator Exposure Level (mg kg-1 bw day-1) | - | - | - | |
| AOEL - Acceptable Operator Exposure Level - Systemic (mg kg-1bw day-1) | - | - | - | |
| Dermal penetration studies (%) | - | - | - | |
| Dangerous Substances Directive 76/464 | - | - | - | |
| Exposure Routes | Public | Potential exposures to individuals in residential settings from residues on treated lawns | ||
| Occupational | Occupational handlers can be exposed via mixing, loading and application | |||
| European MRLs | Click here for the EU MRL pesticide database | |||
| Drinking Water Standards | - | - | - | |
| Drinking Water MAC (μg l-1) | - | - | - | |
Health issues:
| Carcinogen | Genotoxic | Endocrine disrupter | Reproduction / development effects | Cholinesterase inhibitor | Neurotoxicant | |||
|
A0; B0; C0; D0; E0 | - |
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| Respiratory tract irritant | Skin irritant | Skin sensitiser | Eye irritant | Phototoxicant | ||||
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| General human health issues | Harmful if swallowed or inhaled Liver and kidney toxicant Inorganic arsenic is a known carcinogen |
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| Key: Genotoxicity A: Chromosome aberration (EFSA database) B: DNA damage/repair (EFSA database) C: Gene mutation (EFSA database) D: Genome mutation (EFSA database) E: Unspecified genotoxicity type (miscellaneous data source) 0: No data 1: Positive 2: Mixed/ambiguous results 3: Negative |
Key: Other : Yes, known to cause a problem  : No, known not to cause a problem  : Possibly, status not identified - : No data found |
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Handling issues:
| Property |
Value | Source/Quality Score/Other Information |
Interpretation |
|
| General |
No information available | |||
| CLP classification 2013 | - | |||
| EC Risk Classification |
Xn - Harmful: R22 Xi - Irritant: R36/37/38 N - Dangerous for the environment: R55 |
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| EC Safety Classification |
- | |||
| WHO Classification | III | - | Slightly hazardous | |
| UN Number | - | |||
| Waste disposal & packaging |
- | |||
TRANSLATIONS
for monosodium methylarsonate
| Language | Name |
| English | monosodium methylarsonate |
| French | methylarsonate de sodium |
| German | Natriummethylarsonat |
| Danish | - |
| Italian | - |
| Spanish | metilarsonato de sodio |
| Greek | - |
| Slovenian | - |
| Polish | - |
| Swedish | - |
| Hungarian | - |
| Dutch | - |
Record last updated: Friday 25 May 2018
Contact: aeru@herts.ac.uk