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Environmental fate & pathways

Hydrolysis

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Description of key information

It can be concluded that a study on the hydrolysis as a function of pH is not required based the rapid biodegradability of the test substance in the environment. For information, evidence of hydrolysis is included based on hydrolysis as a function of pH testing of DMDMH and its breakdown product.

Key value for chemical safety assessment

Additional information

In Annex VIII 9.2.2.1 column 2 of the REACH Regulation, it is stated that a study on the "Hydrolysis as function of pH" does not need to be conducted if the “substance is readily biodegradable". As can be seen in section 5.2, areliable study by Mead (2001) determined that DMDMH was degraded 78% within the 10-day window and the test substance can be considered readily biodegradable. Additional studies with the degradation product showed that DMH is also readily biodegradable. Therefore, a study on the "Hydrolysis as function of pH" does not have to be conducted for DMDMH.

 

For information, data are available on hydrolysis of DMDMH. There is also reliable hydrolysis study available for the hydrolysis product, DMH.   Due to the rapid hydrolysis of DMDMH to DMH studies conducted with the hydrolysis product, DMH, are considered relevant for environmental fate and ecotoxicology and are considered in this dossier.

 

White & Mulee (2007) conducted a reliable (Klimisch 1) GLP compliant study following Method C7 of Commission Directive 92/69/EEC. Samples of DMDMH were prepared in stoppered glass flasks at nominal concentration of 0.40 g/l in the three buffer solutions.It was observed that the rate of hydrolysis increases with an increase in pH. At pH 4, less than or equal to 10% hydrolysis occurred after 5 days at 50°C, equivalent to a half-life greater than 1 year at 25°C. At pH 7, greater than 50% hydrolysis occurred after 2.4 hours at 50°C equivalent to a half-life less than 1 day at 25°C. At pH 9 greater than 50% hydrolysis occurred after 2.4 hours at 50°C equivalent to a half-life less than 1 day at 25°C. Therefore, DT50 at pH 4 is > 1 year, at pH 7 is < 1 day, and at pH 9 is <1 day.

 

Haner (2007) conducted a reliable (Klimisch 2) partially meeting the requirements of OECD 111 method. The objective of the study was to determine the hydrolysis of DMDMH to DMH under simulated dirty dish washing conditions (diluted synthetic sewage according to OECD 209) and in tap water.DMDMH was shown to hydrolyse rapidly with half-lives < 1 h under all conditions employed in this study. Significant differences in half-lives at an initial DMDMH concentration of 2.5 mg/l were observed at simulated dirty dish washing conditions (0.69 h) and in tap water (0.85 h) respectively. No significant differences in half-lives were observed at an initial DMDMH concentration of 10 mg/l (0.84 h at simulated dirty dish washing conditions and 0.76 h in tap water, respectively).

 

Schmidt & Stansbrey (1992) conducted a reliable (Klimisch 1) GLP compliant study following U.S. EPA FIFRA N 161-1 40 CFR Sec. 158.130 methods. The objectives of this study were to determine the effect of pH on the hydrolysis rate constants and half-lives of 14C-DMH and characterize major (>10% of the initial concentration of DMH) hydrolysis products of 14C-DMH. Hydrolysis half-lives of 3194 days and 1715 days were calculated for the pH 7 (TRIS) and pH 7 (HEPES) buffer systems, respectively.

  

Junghans (2009) conducted a reliable (Klimisch 1) GLP compliant study following OECD 111 methods. A significant pH-dependence of the DMDMH hydrolysis was observed: at a temperature of 35 ± 2 °C DMDMH was shown to hydrolyze rapidly at pH 9 with a half -life of < 1 h, moderately at pH 7 with a half-life of 10.7 h. At pH 4 no hydrolysis was observed.

 

It can be concluded that a study on the hydrolysis as a function of pH is not required based the rapid biodegradability of the test substance in the environment. For information, evidence of hydrolysis is included based on hydrolysis as a function of pH testing of DMDMH and its breakdown product.