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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Biodegradation in water: screening tests: 3.7% biodegradation in 29 days (OECD Guideline 310)

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

A result of 3.7% biodegradation in 29 days was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

A biochemical oxygen demand study (Dow Corning 1976) is also available, which indicated no significant biodegradation in water over 5 days at 500 mg/l.

Biodegradation was observed to occur with sludge taken from WWTPs which had been acclimated to nitrogenous wastes (Wolfgang and Rast 1995).Complex silanols were tentatively identified as the degradation products. This reaction appeared to be linked

with the formation of nitrous oxide by the oxidation of ammonia or via denitrification.

The results of these two studies were taken from secondary literature, the original references were not available for review and no further information (in particular relating to the precautions taken to avoid loss from volatilisation) is available. The reliability of these results is therefore not assignable.

A study using radio-labelled substance at 30µg/L in a sediment and water system over a period of 42 days ( Springborn Smithers Laboratories1991) found no evidence of any biodegradation. However, a number of shortcomings with this study have been identified:

 

  • The mass balance was often poor and variable
  • The amount of 14C measured in the sediment was very variable in replicates for the same time point
  • The paper assumed that hydrolysis occurred in the volatiles trap because of backflow into the trap of potassium hydroxide from the CO2 trap. Although it was shown that a similar product could be formed from D4 under basic hydrolysis conditions, and that this product of basic hydrolysis was of low volatility and so unlikely to be purged from the test chamber into the trap during the study, it is still possible that a genuine degradation product was actually detected in the trap.

 

Therefore, it is difficult to draw firm conclusions on whether or not degradation of D4 occurred in this study as the variability and uncertainty in the results is too high.