Reaction mass of methyl dihydrogen phosphate and orthophosphoric acid and dimethyl hydrogen phosphate

Endpoint summary

Description of key information

From a toxicokinetic study performed with a structural analogue (Phosphoric acid, 2-Ethylhexyl ester) it appears that Phosphoric acid, esters are efficiently absorbed, metabolised and excreted quantitatively by the body. Hydrolysis of the ester linkage  provides an adequate degradation mechanism. There was no sign of accumulation.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Assessment of the Toxicokinetic Behaviour

 

Reaction mass of dimethyl hydrogen phosphate and methyl dihydrogen phosphate and orthophosphoric acid (EC-No. 908-996-7)

 

There are no studies available in which the toxicokinetic properties of the substance were investigated.

 

The substance, a clear viscous liquid, is the reaction mass of Methyl dihydrogen phosphate and Orthophosphoric acid and Dimethyl hydrogen phosphate. The substance is miscible with water at every ratio (see chapter 4.8). The octanol water partition coefficient (Log P_ow) value was determined to be -1.15 (see chapter 4.7). Due to the relative low Log P_owof -1.15 in combination with the high water solubility and the assumed hydrolysis of the ester binding to form phosphoric acid and the alcohol components (see chapter 7.1.1) no potential of bioaccumulation is assumed.

 

Absorption

With reference to its physical state (liquid), the Log P_owof -1.15, and the very high water solubility the absorption of the substance might be assumed to take place in considerable amounts. In addition a passage through aqueous pores is possible (please refer to Guidance on information requirements and chemical assessment, Chapter R.7c, Table R.7.12-1, p. 152). On the other site, the substance contains several hydroxyl functions which might be ionisable.Ionisation does not contribute to a ready diffusion across biological membranes (please refer to Guidance on information requirements and chemical assessment, Chapter R.7c, p. 150). Therefore, an excessive-scale absorption of the substance might be excluded. This assumption is strengthened by the results of the acute oral toxicity studies in rats (LD₅₀2690 mg/kg bw) that indicate a low acute toxicity.

 

Distribution

The substance is a veryhydrophilic substance that contains relatively small molecular components. Therefore, it will be distributed widely and tend to migrate via aqueous channels and pores (please refer to Guidance on information requirements and chemical assessment, Chapter R.7c, pp. 159-160).

 

Metabolism

Anavailable toxicokinetic study performed with Phosphoric acid, 2-ethylhexyl ester (please refer to Chapter 7.1.1) resulted a complete hydrolysis of the ester and the subsequent excretion via urine. The characteristic and functional active center of both substances (Phosphoric acid, 2-ethylhexyl ester and the ester components of the substance) is the ester binding between the alcoholic compound and Phosphate. With reference to the occurrence of endogenous esterases which take part in the mammalian phase I metabolism it can be assumed that both Phosphoric acid ester types are hydrolysed independent from the constitution of the alcoholic part. Studies on genotoxicity performed with the substance (Ames-Test; Chromosome aberration test (human lymphocytes) and HPRT test) were negative, i.e. there is no indication of a reactivity of the substance under the test conditions.

Excretion

With reference to the lowLog P_ow, the good water solubility and the molecular weight the urinary excretion is considered to be the most favorable excretion route (please refer to Guidance on information requirements and chemical assessment, Chapter R.7c, p. 162).