Diammonium dihydrogenpyrophosphate

Endpoint summary

Description of key information

No specific data on the ADME of diammonium dihydrogenpyrophosphate is available.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

100

Absorption rate - inhalation (%):

100

Additional information

In the absence of specific data regarding the ADME of diammonium dihydrogenpyrophosphate its physicochemical properties and relevant toxicity data (where available) were assessed for insights into likely ADME characteristics. Diammonium dihydrogenpyrophosphate has a molecular weight of ca. 212 and is considered to be soluble in water; Therefore, absorption via the dermal route is possible. Due to the high water solubility; the substance will readily dissolve in biological fluids and therefore absorption via the inhalation and oral routes is anticipated. A default value of 100% absorption is considered appropriate for all routes of exposure as a worst-case. There are no substance-specific data regarding distribution and metabolism but the body is likely to handle any absorbed material in the same way that it normally deals with ammonium and phosphate compounds. Following ingestion, any absorbed diammonium dihydrogenpyrophosphate will be absorbed as ammonium and phosphate ions. Ammonium ions absorbed from the gastrointestinal tract travels via the hepatic portal vein directly to the liver, where in healthy individuals, most of it is converted to urea and glutamine.

Phosphate may be present as diphosphate or orthophosphate. The diphosphate/pyrophosphate ion is the simplest form of a condensed phosphate group. A condensed phosphate anion has one or several P-O-P bonds. As the group contains only two phosphate groups, both of the phosphorus ions are classified as “terminal phosphorus”. The diphosphate can undergo ionisation with loss of H+ from each of the two –OH groups on each P and therefore can occur in the -1, -2 -3 or -4 state. The degree of ionisation is dependent upon the associated cations and the ambient pH (if in solution).

The polymer chains do undergo hydrolysis (increased in acidic conditions) to form shorter polymers and ultimately orthophosphoric acid (P2O5). Biotic hydrolysis is fast through ubiquitous alkaline phosphatase activity in micro- and macroorganisms.

It is anticipated that phosphate will be primarily absorbed in the orthophosphate form.  

ABSORPTION

Oral

No data were found specifically regarding the oral absorption of diammonium dihydrogenpyrophosphate. Given the water solubility and the low molecular weight absorption via aqueous pores is anticipated. Therefore, it is assumed that diammonium dihydrogenpyrophosphate is systemically available. As such, oral absorption is anticipated to be 100%.

Dermal

According to ECHA guidance, a molecule with a MW of ca. 212 may be absorbed through the skin (ECHA, 2012). For a compound to penetrate the stratum corneum, it must be sufficiently water soluble i.e. above 1 mg/L (ECHA, 2012). Although, the substance is soluble it is likely to be absorbed in the highly ionised form which reduces drastically the potential to penetrate the lipid rich environment of the striatum corneum. Therefore, dermal uptake of diphosphate will probably be minimal. In addition, as a result of binding to skin components, the uptake of ammonium ions will be slowed.

Due to the uncertainty regarding dermal exposure, a default worst-case value of 100% absorption is considered. 

Inhalation

A default value of 100% inhalation absorption is usually applied. In general, very hydrophilic substances might be absorbed through aqueous pores (MW <200) or be retained in the mucous and transported out of the respiratory tract, and subsequently swallowed (ECHA, 2012). In the case of diammonium dihydrogenpyrophosphate absorption via the respiratory tract is likely.

DISTRIBUTION and METABOLISM

No data are available regarding the distribution and metabolism for diammonium dihydrogenpyrophosphate. Since the substance is highly soluble and has a molecular weight of 212 the substance may be able to diffuse through aqueous channels and pores (ECHA, 2012). Presumably, any absorbed material will be handled in the same way as other absorbed ammonium and phosphate compounds. Following ingestion, any absorbed diammonium dihydrogenpyrophosphate will be absorbed as ammonium and phosphate ions. Ammonium ion absorbed from the gastrointestinal tract travels via the hepatic portal vein directly to the liver, where in healthy individuals, most of it is converted to urea and glutamine.

 

EXCRETION

It is anticipated that excretion will mainly occur via the urine. Due to the presence of the ammonium ion, excretion via the bile is considered to be low.

References

 

ECHA (2012). Guidance on information requirements and chemical safety assessment. Chapter R.7c: Endpoint specific guidance. November 2012 (version 1.1).