Hazardous substance assessment - Phosphoric acid

Identification

Chemical name:

Phosphoric acid

CAS #:

7664-38-2

Chemical composition:

H₃PO₄

Synonyms:

Orthophosphoric acid; o-Phosphoric acid; Phosphoric acid, ortho-.

UN #:

1805

Pictogram(s):

Figure 1 - Text Description

The symbol within the pictogram shows a container dripping liquid onto a piece of metal and another container dripping liquid onto a hand. This symbol indicates that hazardous products with this pictogram can:

• damage or destroy metal
• cause irreversible damage to the skin (for example, burns, blisters, scarring)
• produce tissue damage in the eye or vision loss that is irreversible or not fully reversible within 21 days

WHMIS classification

Health hazards:

Skin Corrosion – Category 1

Serious Eye Damage – Category 1

Physical hazards:

Phosphoric acid does not meet the criteria for classification.

Health hazards

Acute Toxicity (Oral):

Does not meet criteria 

Median lethal dose (LD₅₀): 3,500 mg/kg (rat)^{Footnote 1}.

The available data do not meet the classification criteria for Acute Toxicity (Oral).

Acute Toxicity (Dermal):

Does not meet criteria

LD₅₀: 2,740 mg/kg (rabbit) (based on study summary^{Footnote 2} ).

The available data do not meet the classification criteria for Acute Toxicity (Dermal).

Acute Toxicity (Inhalation – Gases):

Not applicable

Phosphoric acid is not a gas. The classification criteria for Acute Toxicity (Inhalation – Gases) do not apply to this substance.

Acute Toxicity (Inhalation – Vapours):

No data available

Acute Toxicity (Inhalation – Dusts and Mists):

No data available

Skin Corrosion / Irritation:

Category 1

In a United States (US) Department of Transportation (DOT) skin corrosion study, 0.5 mL of commercial preparations of phosphoric acid of varying concentrations were applied under semi-occlusive dressings to the clipped, intact skin of albino rabbits (number of animals not specified) for 4 hours followed by a 7-day observation period ^{Footnote 1}. Skin responses were scored in accordance with the Classification of Corrosive Hazards – US DOT method. Solutions of 75% and 80% phosphoric acid were non-corrosive to rabbit skin. A solution of 85% phosphoric acid was corrosive to rabbit skin, which meets the classification criteria for Skin Corrosion – Category 1C [HPR 8.2.2(2)]. However, since shorter durations of exposure had not been tested, sub-categorization is not possible given that Category 1A or 1B cannot be excluded.

In an experimental study based on Globally Harmonized System of Classification and Labelling of Chemicals (GHS) criteria, 6 male white rabbits exposed to an 80% solution of phosphoric acid for 24 hours showed edema and mild necrosis at 24 hours for all animals, with edema in 3 animals and deep tissue necrosis in the other 3 animals at the 72-hour time point (based on study summary ^{Footnote 2}).

Following the US Federal Hazardous Substances Act scoring regime for skin corrosion, 0.5 mL of commercial preparations of phosphoric acid of varying concentrations were applied under semi-occlusive dressings to the clipped skin of New Zealand albino rabbits for 24 hours ^{Footnote 1}. A 7-day observation period followed application. Solutions of 75% to 85% phosphoric acid were corrosive to skin.

The available data meet the classification criteria for Skin Corrosion – Category 1 [HPR 8.2.2(2)].

Serious Eye Damage / Eye Irritation:

Category 1

Following the US Federal Hazardous Substances Act scoring regime for eye response, 0.1 mL of commercial preparations of phosphoric acid of varying concentrations were placed into the conjunctival sac of New Zealand albino rabbits ^{Footnote 1}. Solutions of 75% to 85% phosphoric acid were corrosive to rabbit eyes.

In a study following the US Code of Federal Regulations, section 1500.42, 6 white rabbits exposed to an 85% solution of phosphoric acid developed severe eye irritation at all 3 observation time points (24-, 48-, and 72-hours), which was not fully reversible within 7 days of observation (based on study summary ^{Footnote 2}).

The available data meet the classification criteria for Serious Eye Damage – Category 1 [HPR 8.3.2(1)].

Respiratory Sensitization:

No data available

Skin Sensitization:

No data available

Germ Cell Mutagenicity:

Does not meet criteria

In vivo: No data available

In Vitro: Negative results were obtained in bacterial and mammalian cell systems in the presence and absence of metabolic activation ^{Footnote 3Footnote 4Footnote 2}.

The available data do not meet the classification criteria for Germ Cell Mutagenicity.

Carcinogenicity:

No data available

Phosphoric acid has not been reviewed by the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), or the American Conference of Governmental Industrial Hygienists (ACGIH).

No carcinogenicity studies were available.

Reproductive Toxicity:

Does not meet criteria

No reproductive or developmental effects were observed in animals in an Organisation for Economic Co-operation and Development Test Guideline (OECD TG) 422 study ^{Footnote 2Footnote 5}. In a non-standard reproductive toxicity study, rats (13 per sex per dose) were gavaged with 0, 125, 250, or 500 mg/kg/day of phosphoric acid. Males were treated daily for a total of 6 weeks (2 weeks prior, 2 weeks during and 2 weeks after mating). Female rats were treated daily from 2 weeks before mating to day 4 post-partum (approximately 54 days)^{Footnote 6}. No reproductive effects, treatment-related changes in neonatal survival or external abnormalities were noted.

The available data do not meet the classification criteria for Reproductive Toxicity.

Specific Target Organ Toxicity – Single Exposure:

Does not meet criteria

Oral Route of Exposure: Human ingestion of phosphoric acid by a single individual resulted in necrosis of the stomach, duodenum, jejunum, and pancreas ^{Footnote 7}. The patient experienced spontaneous gastric perforation and died 19 days after being admitted to hospital. The effects, resulting from exposure to the substance, led directly to lethality and therefore are not applicable to classification in this hazard class.

Dermal Route of Exposure: The available acute animal studies do not provide information on toxic effects other than those that lead to lethality and therefore are not applicable to classification in this hazard class ^{Footnote 2}.

Inhalation Route of Exposure: No data available

The available data do not meet the classification criteria for Specific Target Organ Toxicity – Single Exposure.

Specific Target Organ Toxicity – Repeated Exposure:

Does not meet criteria

Oral Route of Exposure: In an OECD TG 422 study, rats were dosed with 0, 125, 250, or 500 mg/kg/day of phosphoric acid for 54 days, with no clinical signs observed in any animals in any treatment group ^{Footnote 6}. Two females in the 500 mg/kg/day group died, with a resulting no-observed-adverse-effect level (NOAEL) of 250 mg/kg/day ^{Footnote 2Footnote 5}.

Dermal Route of Exposure: No data available

Inhalation Route of Exposure: No data available

The available data do not meet the classification criteria for Specific Target Organ Toxicity – Repeated Exposure.

Aspiration Hazard:

No data available

No human data are available for phosphoric acid. This substance is not a liquid hydrocarbon.

Biohazardous Infectious Materials:

Not applicable

Phosphoric acid is not a microorganism, protein, or nucleic acid.

Physical hazards

Explosives:

Not Evaluated*

* Explosives are excluded from the HPA and its regulations. Explosives are regulated under the Explosives Act. For more information, visit Natural Resources Canada.

Flammable Gases:

Not applicable

Phosphoric acid is not a gas. The classification criteria for Flammable Gases do not apply to this substance.

(Flammable) Aerosols:

Not evaluated

Classification of a hazardous product in the Flammable Aerosols or Aerosols hazard class is product dependent.

Oxidizing Gases:

Not applicable

Phosphoric acid is not a gas. The classification criteria for Oxidizing Gases do not apply to this substance.

Gases Under Pressure:

Not applicable

Phosphoric acid is not a gas. The classification criteria for Gases Under Pressure do not apply to this substance.

Flammable Liquids:

Not applicable

Pure phosphoric acid is not a liquid as defined in subsection 1(1) of the HPR. The classification criteria for Flammable Liquids do not apply to the pure substance.

Flammable Solids:

Does not meet criteria

Phosphoric acid is non-combustible and non-flammable ^Footnote 2. 

Phosphoric acid esters are used as flame retardants. The phosphonate esters break down to phosphoric acid from the heat. The acid reacts and forms pyro phosphoric acid, which acts as a heat transfer barrier in the condensed phase ^{Footnote 8Footnote 9Footnote 10Footnote 11}.

The available data do not meet the classification criteria for Flammable Solids.

Self-Reactive Substances and Mixtures:

Does not meet criteria

Phosphoric acid is a non-combustible and non-flammable weak acid ^Footnote 2.

Phosphoric acid esters are used as flame retardants. The phosphonate esters break down to phosphoric acid from the heat. The acid reacts and forms pyro phosphoric acid, which acts as a heat transfer barrier in the condensed phase^{Footnote 8Footnote 9Footnote 10Footnote 11}.

The available data do not meet the classification criteria for Self-reactive Substances and Mixtures.

Pyrophoric Liquids:

Not applicable

Pure phosphoric acid is not a liquid as defined in subsection 1(1) of the HPR. The classification criteria for Pyrophoric Liquids do not apply to the pure substance.

Pyrophoric Solids:

Does not meet criteria

Phosphoric acid is a non-combustible and non-flammable solid^Footnote 2.

Phosphoric acid esters are used as flame retardants. The phosphonate esters break down to phosphoric acid from the heat. The acid reacts and forms pyro phosphoric acid, which acts as a heat transfer barrier in the condensed phase^{Footnote 8Footnote 9Footnote 10Footnote 11}.

The available data do not meet the classification criteria for Pyrophoric Solids.

Self-Heating Substances and Mixtures:

Does not meet criteria

Phosphoric acid is non-combustible and non-flammable (based on study summary ^{Footnote 2}). 

Phosphoric acid esters are used as flame retardants. The phosphonate esters break down to phosphoric acid from the heat. The acid reacts and forms pyro phosphoric acid, which acts as a heat transfer barrier in the condensed phase^{Footnote 8Footnote 9Footnote 10Footnote 11}.

The available data do not meet the classification criteria for Self-heating Substances and Mixtures.

Substances and Mixtures which, in Contact with Water, Emit Flammable Gasses:

Not applicable

Phosphoric acid is a weak acid that does not contain metals or metalloids and is, therefore, excluded from classification [HPR 7.12.1(1)].

Oxidizing Liquids:

Not applicable

Pure phosphoric acid is not a liquid as defined in subsection 1(1) of the HPR. The classification criteria for Oxidizing Liquids do not apply to the pure substance.

Oxidizing Solids:

Does not meet criteria

Phosphoric acid is a weak acid, composed only of chemically bonded phosphorus, oxygen and hydrogen; however, while it is not an oxidant, at high concentrations and density, it can produce a large exothermic reaction upon neutralization ^{Footnote 12}.

The available data do not meet the classification criteria for Oxidizing Solids.

Organic Peroxides:

Not applicable

Phosphoric acid is not an organic peroxide. The classification criteria for Organic Peroxides do not apply to this substance.

Corrosive to Metals:

No data available

Phosphoric acid has been known to be corrosive to metals, including carbon steel and aluminum^{Footnote 12}. The degree of corrosivity is largely dependent upon the type of metal, the concentration of the acid, and the temperature at which the metal comes in contact with the acid ^{Footnote 13}. Phosphoric acid solutions (concentration 50-85%) are corrosive at normal temperatures (20-25 °C) to type 1100 and 3003 aluminum alloys, type 1020 carbon steel, some stainless steels (400 series), and unalloyed cast irons and copper alloys, like brass and bronze^{Footnote 14}.

Phosphoric acid solutions are reported to be corrosive to aluminum at a rate of >50 mils per year (>1.27 mm/yr) at 15°C^{Footnote 15}. At room temperature, phosphoric acid was tested for corrosion to aluminum using 5% and 85% aqueous solutions^{Footnote 16}. The corrosion rate is reported as 100 mils per year (2.54 mm/yr.) and 1200 mils per year (30.5 mm/yr.).

Phosphoric acid solutions (concentration 50-85%) are not corrosive at normal temperatures (20-25 deg C) to most stainless steels (300 series, Carpenter 20Cb-3), to high-nickel and high silicon cast irons, to copper and some copper alloys, like copper-nickel, and to nickel and nickel-base alloys, like Hastelloy^{Footnote 14}.

The temperatures used in the above studies are not those required by the test method prescribed in section 7.16.1 of the HPR (55°C). As such, no data are available that are suitable to determine whether phosphoric acid meets the classification criteria for Corrosive to Metals.

Combustible Dusts:

No data available

While phosphoric acid is a solid in pure form at room temperature, it has not been reported in the literature to form a combustible dust.

No data are available to determine whether the substance meets the classification criteria for Combustible Dusts.

Simple Asphyxiants:

Not applicable

Phosphoric acid is not a gas. The classification criteria for Simple Asphyxiants do not apply to this substance.

Pyrophoric Gases:

Not applicable

Phosphoric acid is not a gas. The classification criteria for Pyrophoric Gases do not apply to this substance.

Chemicals Under Pressure:

Not evaluated

Classification of a hazardous product in the Chemicals Under Pressure hazard class is product dependent.

Regulatory and other information

Regulatory information:

Hazardous substance assessments are prepared by Health Canada as educational and information resources. Under the HPA, suppliers of hazardous products must, upon the sale or importation of a hazardous product, provide a label and safety data sheet that meet the requirements set out in the HPR.

Other information:

The information and classifications contained in these hazardous substance assessments are based on publicly available sources, such as peer-reviewed literature or reports by international bodies. New information, including proprietary information, could have an impact on the classification of substances or hazardous products containing them. It is the responsibility of the supplier to ensure the accuracy, sufficiency, and reliability of their hazardous product classifications.

Last updated:

2022

Prepared by:

Workplace Hazardous Materials Bureau, Health Canada