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Environmental fate & pathways

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The ready biodegradability of the test item Hostanox SE 10 P was determined with non adapted activated sludge in the Manometric Respirometry Test for a period of 28 days. The study was conducted according to OECD guideline 301. The test item concentrations selected as appropriate were 20 mg/L.

In order to check the activity of the test system sodium benzoate was used as functional control. The pass level > 60 % was reached after 2 days. The biodegradation rate came to a maximum of 98 % on day 26.

In the toxicity control containing both test and reference item 59 % degradation occurred within 14 days. After 28 days the biodegradation came to 67 %. The degradation of the reference item was not inhibited by the test item.

The 1sttest item replicate reached the 10 % level (beginning of biodegradation) after 11 days, and the 2ndtest item replicate after 9 days. The 60 % pass level was not reached within 28 days. After 28 days the mean biodegradation was 32 %.

 

To confirm the potential for biodegradability of the test item Hostanox SE10 P a second enhanced Manometric Respirometry Test with non-adapted activated sludge was conducted for a period of 60 days. The study was conducted according to OECD guideline 301 F. The test item concentration selected as appropriate was 15 mg/L.

In order to check the activity of the test system aniline was used as functional control. The pass level > 60 % was reached after 14 days. The biodegradation reached a maximum of 96 % degradation on day 43.

The mean of all three test item replicates reached the 10 % level (beginning of biodegradation) within 30 days. The 60 % pass level was not reached. After 60 days the mean biodegradation was 20 %.

 

In the second study conducted form November 2012 to January 2013it was confirmed that the test item Hostanox SE 10 P has a potential for degradation, but the biodegradation progresses only slowly.

It is assumed that the degradation is decelerated by the low water solubility and the resulting low bioavailability of the test item in the test solution. Furthermore the biodegradation might be influenced by the number of competent degraders present in the activated sludge inoculum. 

 

In comparison with the study on ready biodegradability conducted in September 2011 (acc. to OECD 301F standard test), the biodegradation was slower as expected. In the study on ready biodegradability a mean biodegradation of 32 % was reached after 28 days. It is assumed that the lower biodegradation in the current study was due to a lower concentration of competent degraders in the activated sludge used for inoculation.

 

The composition of the bacterial population of activated sludge is subjected to natural fluctuations, mainly caused by variations in the sewage flow and seasonal changes. From experience it is known that during drier periods with little rain, as it often takes place in summer and early autumn, the sewage flow is lower and the biodegradation potential and microbial diversity of the activated sludge increases. This effect influences mainly the biodegradation results of substances which show a certain biodegradation but are not readily biodegradable. It is assumed that under these conditions the microbial adaptation to degradation of not readily biodegradable substances is enlarged.

 

In conclusion, the substance is not readily biodegradable but the potential for biodegradation is confirmed.