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EC number: 244-182-1 | CAS number: 21056-98-4
Endpoint summary
Administrative data
Link to relevant study record(s)
Description of key information
No toxicokinetic or metabolism studies are available for phosphonic acid, calcium salt. Its assessment can be mabe by read across with data available for phosphonic acid.
Background
Phosphonic acid (phorphorous acid) is a mono-constituent substance of high purity (>98,5%). Its main impurity is phosphoric acid (= 1,5%). Phosphonic acid is described by the formula H3PO3.
No studies on toxicokinetics are available for phosphonic acid. The available toxicity studies provide little information on absorption, distribution, metabolism and excretion of phosphonic acid. The blood levels of inorganic phosphate were not affected in male rats and were lower rather than higher with increasing doses after repeated oral application of phosphonic acid in female rats, as reported in the 28-day repeated dose toxicity and reproduction/developmental screening study.
Therefore, the assessment is primarily based on physicochemical properties, supported by some toxicological indications.
Physical/chemical properties:
The physical/chemical properties that are of importance to assess the toxicokinetic behaviour of phosphoric acid are:
· Water solubility > 1067 g/L
· Molecular weight: 82 g/mol
· Log Kow: not relevant for inorganic substances
· Vapour pressure: 0.000011 mmHg or 1,47 x 10-3Pa (20°C)
Absorption
Phosphonic acid is hydrophilic (based on the high water solubility) and relatively small (low molecular weight; Mw = 82). Therefore oral/GI-absorption by passive diffusion is expected to be high. In a 28-day repeated dose oral toxicity and reproduction/developmental study (Peter, B., 2013), phosphonic acid was found to cause a treatment-related microscopical change in the spleen at the highest dose level of 500 mg/kg bwt/day. This finding indicates that oral absorption had occurred.
Respiratory exposure to phosphonic acid is unlikely to occur on a large scale, due to the very low vapour pressure of the substance (<0.5 kPa). However, when phosphonic acid occurs as an aerosol, some respiratory exposure may occur. Any inhaled phosphonic acid may be absorbed through the inhalation tract to the same extent and for the same reasons as for oral absorption.
After dermal exposure, dermal absorption is indicated due to the liquid state of formulations of phosphonic acid and the low vapour pressure. The molecular weight (Mw<100) is also favourable for dermal uptake. Based on the hydrophilic nature of phosphonic acid, uptake into the stratum corneum will be low. The water solubility of the compound is high, indicating that the substance may readily partition from the stratum corneum into the epidermis. Moreover, phosphoric acid is classified as corrosive to skin, indicating that systemic dermal absorption after exposure to corrosive concentrations of phosphonic acid may also be favoured by skin abrasion.
Distribution
The low molecular weight and high water solubility of phosphonic acid favour its distribution throughout the body, especially into the extracellular spaces. Due to its highly hydrophilic character it is anticipated that it will tend to partition readily to aqueous compartments/tissues. It is less likely that it will partition to the adipose tissues and lipophilic layers like the stratum corneum.
Metabolism and excretion
No studies on metabolism and excretion are available. The low molecular weight (Mw<300) and high water solubility of phosphonic acid will favour rapid excretion via the urine.
Conclusions
Although no study addressing the toxicokinetic properties of phosphonic acid is available, it is assumed that, based on its physicochemical properties, it can readily be absorbed via the oral, dermal and inhalation route and will readily distribute throughout the aqueous compartments of the body.
However for risk assessment, oral and dermal absorption are assumed to be similar (50%). In absence of information on the inhalation route, 100% absorption is applied in order that a default absorption of twice the inhalation absorption is assumed for oral absorption, in accordance with ECHA Guidance R.8.
Key value for chemical safety assessment
- Bioaccumulation potential:
- no bioaccumulation potential
- Absorption rate - oral (%):
- 50
- Absorption rate - dermal (%):
- 50
- Absorption rate - inhalation (%):
- 100
Additional information
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