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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study, nonGLP.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
GLP compliance:
no
Remarks:
The study was conducted in accordance with the OECD 301F guideline. Based on the result (no degradation observed), the result is considered adequate to fill this endpoint.
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Escatawpa Wastewater Treatment Plant, Mississipi, US
- Laboratory culture: not applicable
- Method of cultivation: not applicable
- Storage conditions: not applicable
- Storage length: None
- Preparation of inoculum for exposure: Settled and decanted (3x)
- Pretreatment: None
- Concentration of sludge:25-30 mg/l of suspended solids
Duration of test (contact time):
28 d
Initial conc.:
42.7 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium
- Additional substrate: No
- Solubilising agent (type and concentration if used): 500 mg silica gel per test bottle
- Test temperature: 22 +/- 1 °C
- pH adjusted: No
- Aeration of dilution water: Yes
- Suspended solids concentration: < 30 mg/l
- Continuous darkness: yes (dark bottles)


TEST SYSTEM
- Culturing apparatus: 1-L test vessels in water bath
- Number of culture flasks/concentration: 3
- Method used to create aerobic conditions: aeration/
- Method used to create anaerobic conditions: not applicable
- Measuring equipment: Electrolytic Respirometer


SAMPLING
- Sampling method: Online measurement of O2 depletion via pressure change


CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes
- Abiotic sterile control: No
- Toxicity control: No
- Positive control: Yes (sodium benzoate)

Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
1.48
St. dev.:
0.51
Sampling time:
28 d
Details on results:
All validity criteria fulfilled.
Results with reference substance:
79.85 % biodegradation (Std. = 3.42%) in 28 days
Validity criteria fulfilled:
yes
Interpretation of results:
not inherently biodegradable
Conclusions:
The test substance 2,2-bis[[(2-hexyl-1-oxodecyl)oxy]methyl]-1,3-propanediyl bis(2-hexyldecanoate) cannot be considered readily or inherently biodegradable, as little or no biodegradation was observed in the underlying study.
Executive summary:

The biodegradability of 2,2-bis[[(2-hexyl-1-oxodecyl)oxy]methyl]-1,3-propanediyl bis(2-hexyldecanoate) was assessed in an non-GLP OECD 301 F guideline study. The purpose of this study is to establish the ready biodegradability of the test substance as an indication of its environmental fate.

Sodium benzoate was tested in parallel as reference substance.

The biodegradation ws followed via O2 consumption over the test period, the incolum is was derived from a municipal waste water treatment plant and was used instantly after sampling.

The validity of the biodegradation test was confirmed by meeting the following criteria as specified in the OECD 301 F Test Guidelines:

-The delta of the max./min. of replicate %ThOD (COD) values at the plateau of the data, at the end of the test or at the end of the 10-day window, as appropriate, is less than 20%.

- The extent of biodegradation of the benzoate reference compound has reached the pass level of 60% ThOD (COD) on or before day 10-day window.

- The total O2 consumption in the inoculate standard blanks containing silica gel only did not exceed 60 mg/L in 28 days. The maximum O2 consumed was < 40 mg/l.

The test substance 2,2-bis[[(2-hexyl-1-oxodecyl)oxy]methyl]-1,3-propanediyl bis(2-hexyldecanoate) cannot be considered readily or inherently biodegradable, as little or no biodegradation was observed in the underlying study.cannot be considered readily or inherently biodegradable, as little or no biodegradation was observed in the underlying study.

Description of key information

The biodegradability of 2,2-bis[[(2-hexyl-1-oxodecyl)oxy]methyl]-1,3-propanediyl bis(2-hexyldecanoate) was assessed in an non-GLP OECD 301 F guideline study.

The substance cannot be considered readily or inherently biodegradable, as little or no biodegradation was observed in the underlying study.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information

The above mentioned findings are supported by the additional experimental study with the registered substance (Muckle, 2009; ~5% biodegradation in 28 days). This study was conducted according to the OECD 301B guideline.

In contradiction to the negligible degradation found for 2,2-bis[[(2-hexyl-1-oxodecyl)oxy]methyl]-1,3-propanediyl bis(2-hexyldecanoate), the available RA data for CAS 68604-44-4 reports 90.7 % degradation in an OECD 301 B study. And the biodegradation prediction for the registered substance based on the available models (BIOWIN 1-7) is ready biodegradability.

A known shortcoming of these predictions is the fact that BIOWIN does not consider steric factors or low solubility, which might limit an enzyme’s ability to access otherwise labile bonds. Since the underlying structure has a high molecular weight and a low water solubility, and steric hindrance is likely, the biodegradation potential could be overestimated. Nevertheless, the predictions indicate that the 2,2-bis[[(2-hexyl-1-oxodecyl)oxy]methyl]-1,3-propanediyl bis(2-hexyldecanoate) based on its fragments can undergo degradation.

The BIOWIN predicted biodegradation potential can be considered as an indication of potential degradation and as supporting information for the purpose of the risk assessment.

Considering all the available information, no clear conclusion on the biodegradation potential can be drawn for the registered substance. Due to the low solubility and therefore limited bioavailability, it is highly likely that the available studies underestimate the biodegradation potential.