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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From May 28, 2003 to June 11, 2003
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
yes
Buffers:
- pH: 1.2
- Composition of buffer:
Hydrochloric acid: 0.0065 mol/dm3
Potassium chloride: 0.005 mol/dm3

- pH: 4
- Composition of buffer:
Potassium hydrogen phthalate: 0.005 mol/dm3

- pH: 7
- Composition of buffer:
Disodium hydrogen orthophosphate (anhydrous): 0.003 mol/dm3
Potassium dihydrogen orthophosphate: 0.002 mol/dm3
Sodium chloride: 0.002 mol/dm3

- pH: 9
- Composition of buffer:
Disodium tetraborate: 0.001 mol/dm3
Sodium chloride: 0.002 mol/dm3

Details on test conditions:
TEST SYSTEM
- Type of test flasks: Stoppered glass flasks
- Lighting: Solutions were shielded from the light
TEST MEDIUM
- Preparation of samples: Prepared in stoppered glass flasks at a nominal concentration of 0.001 g/L in the four buffer solutions
- Identity and concentration of co-solvent: Acetonitrile (1 %)
Duration:
24 h
pH:
1.2
Initial conc. measured:
0.032 mg/L
Duration:
0.5 h
pH:
4
Initial conc. measured:
0.917 mg/L
Duration:
1 h
pH:
7
Initial conc. measured:
0.99 mg/L
Duration:
1 h
pH:
9
Initial conc. measured:
0.555 mg/L
Number of replicates:
Two
Positive controls:
no
Negative controls:
no
Statistical methods:
Not applicable
Preliminary study:
- Estimated half life at pH 4, 7 and 9 at 25 °C: < 1 d
- Hydrolysis after 2.4 h: > 50 %
- Results indicated the need of definitive test to estimate the rate constant and t1/2

Test performance:
Not applicable
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
Not applicable
% Recovery:
>= 45.9 - <= 51.5
pH:
4
Temp.:
25 °C
Duration:
0.5 h
% Recovery:
>= 64 - <= 69.5
pH:
7
Temp.:
25 °C
Duration:
1 h
% Recovery:
>= 49 - <= 55.2
pH:
9
Temp.:
25 °C
Duration:
1 h
Key result
pH:
4
Temp.:
25 °C
Hydrolysis rate constant:
1.69 h-1
DT50:
0.41 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
7
Temp.:
25 °C
Hydrolysis rate constant:
1.9 h-1
DT50:
0.36 h
Type:
(pseudo-)first order (= half-life)
Key result
pH:
9
Temp.:
25 °C
Hydrolysis rate constant:
2.07 h-1
DT50:
0.34 h
Type:
(pseudo-)first order (= half-life)
Details on results:
TEST CONDITIONS
- pH, sterility, temperature and other experimental conditions maintained throughout the study: Yes
Validity criteria fulfilled:
yes
Conclusions:
Under the study conditions, rate constant and estimated half-life were found to be 1.692 h-1 and 0.410 h (at pH 4), 1.9044 h-1 and 0.364 h (at pH 7), and 2.0664 h-1 and 0.336 h (at pH 9), respectively. Under physiologically important conditions (pH 1.2, 37°C), the test substance was found to degrade almost instantaneously in the media, with only 3.45% of the fortified concentration remaining at the time zero initial analysis.
Executive summary:

A study was performed to assess the hydrolytic stability of the test substance according to OECD Guideline 111, in compliance with GLP. Based on the results of a preliminary study, the test was conducted at pH 4, 7 and 9 at 25 ± 0.5°C, and at pH 1.2 at 37 ± 0.5°C for 24 h. Under the study conditions, rate constant and estimated half-life were found to be 1.692 h-1 and 0.410 h (at pH 4), 1.9044 h-1 and 0.364 h (at pH 7), and 2.0664 h-1 and 0.336 h (at pH 9), respectively. Under physiologically important conditions (pH 1.2, 37°C), the test substance was found to degrade almost instantaneously in the media, with only 3.45% of the fortified concentration remaining at the time zero initial analysis (Woolley and Mullee, 2003).

Description of key information

Key value for chemical safety assessment

Half-life for hydrolysis:
0.4 h
at the temperature of:
25 °C

Additional information

A study was performed to assess the hydrolytic stability of the test substance according to OECD Guideline 111, in compliance with GLP. Based on the results of a preliminary study, the test was conducted at pH 4, 7 and 9 at 25 ± 0.5°C, and at pH 1.2 at 37 ± 0.5°C for 24 h. Under the study conditions, rate constant and estimated half-life were found to be 1.692 h-1 and 0.410 h (at pH 4), 1.9044 h-1 and 0.364 h (at pH 7), and 2.0664 h-1 and 0.336 h (at pH 9), respectively. Under physiologically important conditions (pH 1.2, 37°C), the test substance was found to degrade almost instantaneously in the media, with only 3.45% of the fortified concentration remaining at the time zero initial analysis (Woolley and Mullee, 2003).

The hydrolysis products of m-TMXDI are comparable to those of other aliphatic and aromatic diisocyanates. Under environmentally relevant conditions (i.e. low concentrations of m-TMXDI, pH = 7), an insoluble urea and possibly also polyurea are formed (Allnex, pers. comm.; Pemberton and Tury, 2004; Heimbachet al., 1996; Yakabeet al., 1999; Turyet al., 2003; cited in Environment Canada/Health Canada, 2008). In specific cases (i.e. high dispersion combined with low concentrations), tetramethyl-m-xylene diamine may also be produced (Sopac and Boltromejuk, 1974; cited in Environment Canada/Health Canada, 2008).


The structure of the urea and polyurea are presented in Figure 1.

Figure 1: Structure of the urea and possible polyurea formed by hydrolysis of m-TMXDI
under environmentally relevant conditions

The structure of tetramethyl-m-xylene diamine is presented in Figure 2.

Figure 2: Structure of tetramethyl-m-xylene diamine potentially formed by hydrolysis of m-TMXDI under specific conditions (i.e. high dispersion combined with low concentrations)

 

References

Environment Canada/Health(2008). Screening assessment for the challenge. Benzene, 1,3-bis(1-isocyanato-1-methylethyl)-(tetramethyl-m-xylylene diisocyanate). Chemical Abstracts Service Registry Number 2778-42-9.https://www.ec.gc.ca/ese-ees/9C2F9934-38D3-4940-A472-5DD238B6076D/batch2_2778-42-9_en.pdf.

Heimbach F, Jaeger K and Sporenberg W (1996).Fate and biological effects of polymeric MDI (4,4-diphenylmethane diisocyanate and homologues) in small artificial ponds. Ecotox Environ. Safety 33:143-153.

Pemberton D and Tury B (2004). TDI industry risk assessment: sections on physico-chemical properties, environmental exposures and environmental effects. GIL report 2004/E.

Sopac ED and Boltromejuk LP (1974). Gig. Sanit. 7:10-13.

Tury B, Pemberton D and Bailey RE (2003). Fate and potential environmental effects of methylenediphenyl diisocyanate and toluene diisocyanate released into the atmosphere. J. Air and Waste Manage. Assoc. 53:61-66.

Yakabe Y, Henderson KM, Thompson WCet al.(1999). Fate of methylenediphenyl diisocyanate and toluene diisocyanate in the aquatic environment. Environ. Sci. Technol. 33(15):2579-2583.