Dibutyl hydrogen phosphate

Endpoint summary

Description of key information

Short description of key information on bioaccumulation potential result:
In an in vivo study on rats the metabolism of dibutyl hydrogen phosphate was investigated:
Male Wistar rats (180-210 g) were given a single intraperitoneal (ip) injection of dibutyl hydrogen phosphate or tributyl phosphate dissolved 10% in corn oil at a dosage of 250 mg/kg bw. Urinary metabolites were investigated on day 1-3 after application (Suzuki et al., 1984).
When rats were dosed with dibutyl hydrogen phosphate, the majority (47.6%) was recovered intact, and only small amounts of the carboxylated (0.1%) or hydroxylated (0.08%) (in the butyl side chain) derivates were formed, as well as some butyl dihydrogen phosphate (0.03%) was found. After a single intraperitoneal dose of tributyl phosphate at 250 mg/kg bw, the major metabolite were dibutyl hydrogen phosphate, butyl dihydrogen phosphate and butyl bis(3-hydroxybutyl) phosphate.

In an in-vitro study the metabolism of dibutyl hydrogen phosphate by rat liver homogenate was investigated. The incubation mixture consisted of 2 ml of liver homogenate (700 g supernatant, equivalent to 500 mg of liver), 0.5 ml of NADPH generating system (NADPplus 1 µmol), substrate (ethanol solution) 75 nmol and 10 ml of Tris-HCl buffer (pH 8.3). Dibutyl hydrogen phosphate was not decomposed at all by the rat liver homogenate (Sasaki et al., 1984).

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

In the in vivo study dibutyl hydrogen phosphate was only metabolised to a small extend after intraperitoneal (ip) injection in rats- the majority of the applied dibutyl hydrogen phosphate was recovered intact after 1-3 days. In the in-vitro study no degradation was observed.

Dibutyl hydrogen phosphate is the main metabolite of tributyl phosphate. Tributyl phosphate undergoes a rapid metabolisation to dibutyl hydrogen phosphate by the microsomal enzyme complex in the liver. The elimination occurs independently from the application form through the urine (50-70%), followed by exhalation (7-10%) and the faeces (4-6%) (BUA Report No. 108; GDCh Advisory Committee on Existing Chemicals).

Therefore a read across with tributyl phosphate (CAS No. 126-73-8) as a surrogate for dibutyl hydrogen phosphate (CAS No. 107-66-4) is justified for some endpoints.

  

Due to the corrosive properties of dibutyl hydrogen phosphate (tributyl phosphate is not corrosive) only endpoints where systemic effects dominate can be considered for read across.

Mathematical model calculations of skin permeation of dibutyl hydrogen phosphate revealed a for a one-hour exposition of hands and forearms an adsorption rate of 10.7 to 14.4 mg (ca. 0.2 mg/kg bw/day).