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Environmental fate & pathways

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Biodegradation

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.

 

Adsorption/Desorption

The adsorption coefficient (KOC) on soil and on sewage sludge using high performance liquid chromatography (HPLC) according to OECD Guideline No. 121 (2001) and Council Regulation (EC) No. 440/2008 Method C.19 for the test item Hostanox SE 10 P (batch DEG4139435) could

not be determined. The reason is that the in the guidelines recommended mobile phases for the chromatographic system could not be used due to incompatibility (insolubility of test item Hostanox SE 10 P).

Hydrolysis

Prior to the testing of hydrolysis as function of pH of Hostanox SE 10 P solubility testing was performed. Based on the analytical method development a minimum test concentration of 10 mg/L has to be used in order to realize sufficient analytical sensitivity for analyses down to 10 % of the applied test item concentration, as required by the guideline.

Therefore solubility testing with water solvent mixtures was performed in order to determine a suitable mixture which supports the analytical and test design related requirements for the hydrolysis testing. Stock solutions of Hostanox SE 10 P were prepared in 2-Propanole and Tetrahydrofuran at a concentration of 100 mg/L and were diluted to 10 mg/L with the respective water solvent mixtures to reach final solvent concentrations from 10 to 70 % (in 10 % steps).

Additionally during these experiments it was recognized that Hostanox SE 10 P is not sufficiently soluble in Acetonitrile or Methanol to serve as solvents for the desired purpose. All prepared water solvent mixtures of up to 70 % solvent content showed a positive Tyndall-effect indicating colloidal dispersed Hostanox SE 10 P. According to the guideline hydrolysis studies should be performed at a maximum co-solvent content of up to 10%, for the test items with low water solubility.

As Hostanox SE 10 P could not be dissolved, at the necessary concentration in water solvent mixtures of up to 70 % solvent content, it was concluded that hydrolysis testing is not feasible for Hostanox SE 10 P as test item.

 

Bioaccumulation

Due to molecular weight (MG: 571), structure and the physico-chemical properties it can be assumed that the substance has low potential to cross biological membranes.Calculation of log Ko/w using KOWWIN v1.68 reveals a log Ko/w value of 18.57. The aquatic BCF of a substance is probably lower than 2000 L/Kg if the calculated log Ko/w is higher than 10 (Chapter 11 PBT Assessment R 11.1.3.2.).

Since the calculated value is far above this threshold it can be concluded that the substances has only low potential for bioaccumulation and a bioaccumulation study is not warranted.

 

The BCF/BAFs calculated with theBCFBAF v3.01 model which is included in EPI Suite 4.1 developed by the USEPA are as follows:

  Log BCF from regression-based method = 0.500 (BCF = 3.162 L/kg wet-wt)

  Log BCF Arnot-Gobas method (upper trophic) = -0.049 (BCF = 0.893)

  Log BAF Arnot-Gobas method (upper trophic) = -0.049 (BAF = 0.8941)

 

These data additionally support the conclusion that the substance has only low potential for bioaccumulation.

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