Bronopol

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

The study as such was conducted according to OECD 111 and no investigation on metabolites was done. However, Challis BC and Yousaf TI (1991; see order 2) reported very reliable data on degradation products and -pathways of bronopol in water in their publication (Chem. Soc.Perkin Trans. 2: 283-286) and the test substance they used was from Boots Microcheck. These data can be seen as complementory to the results of the study performed by Lewis C (1996).

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

GLP compliance:

no

Analytical monitoring:

yes

Details on test conditions:

- Test concentrations: solutions of Bronopol were prepared in three buffer systems (pH 4, 7 and 9) at concentrations of 1000, 100, 25 and 10 ppm (also 2 ppm for pH 4 only), with one replicate per test concentration.
- Test vessels: 100 ml conical sterile flasks with stoppers (sterile cotton wool bungs) and covered in foil to prevent photolytic interference.
- Handling of solutions: solutions were maintained at 50°C in a covered water bath, and the bronopol concentration was monitored over the test period.
- Test duration: from 5 to 7 days:
- 5 days: 100 and 2 ppm
- 6 days: 1000 and 25 ppm
- 7 days: 10 ppm

Number of replicates:

One replicate per test concentration

Transformation products:

no

pH:

4

Temp.:

25 °C

DT50:

120 h

pH:

7

Temp.:

25 °C

DT50:

2.4 h

pH:

9

Temp.:

25 °C

DT50:

2.4 h

Details on results:

At bronopol concentrations of 10 to 100 ppm the half-life was reached well within the OECD criteria of 2.4 hours at both pH 7 and 9, i.e. t1/2 less than one day at 25 °C. For all concentrations of Bronopol at pH 4, there was greater than 10 % hydrolysis at 120 hours, i.e. t1/2 less than one year at 25 °C (but greater than one day). The initial rate of Bronopol hydrolysis is rapid and concentration dependent at pH 7 and 9 but at pH 4 the pattern of hydrolysis is slower although there is still clear evidence of concentration dependence.

Description of key information

In contact with water bronopol will hydrolyse rapidly.

Key value for chemical safety assessment

Half-life for hydrolysis:

2.4 h

at the temperature of:

25 °C

Additional information

In Annex VIII of Regulation (EC) no. 1907/2006 it is laid down that the study on hydrolysis does not need to be conducted if the substance is readily biodegradable. Although bronopol is readily biodegradable, the hydrolysing potential of the test substance has been investigated in a guideline study according to OECD 111 (preliminary test) at pH 4, 7 and 9 at 50°C in sterile buffer solutions [Knoll MicroCheck, 1996].

In water and at environmental relevant pH values, hydrolysis of Bronopol takes place very rapidly, with a significant pH and concentration dependency displaying an accelerated rate of hydrolysis at lower concentrations and elevated pH.

Decomposition of Bronopol in water results in the formation of tris(hydroxymethyl)-nitromethane, glycolic acid, formic acid, methanol (all <5%, 24 h) and 2,2-nitroethanol (<1%) which is shown in a supporting publication conducted by Challis and Yousaf, 1991. Four concurrent degradation pathways resulting in the production of these degradation products have to be considered, with 3 of them involving 2-bromo-2-nitroethanol as reactive intermediate. It could be shown that at pH 8.98 and 25°C, 2-bromo-2-nitroethanol is formed from Bronopol and increases in concentration over about 30 min following pseudo first-order kinetics. Thereafter, the concentration of 2-bromo-2-nitroethanol remained constant in equilibrium with the parent compound Bronopol. Moreover, Challis and Yousaf confirmed the fact that the degradation of Bronopol accelerates with increasing pH.