Sophorolipids: fermentation products of glucose and rapeseed-oil fatty acids methyl esters with yeast Candida Bombicola

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Deviations:

not specified

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

The sludge was taken from the activation basin of the domestic sewage treatment plant in D-67480 Edenboken. It was filtrated, washed with tap water twice, then washed with and resuspended in test medium. It was then aerated. The dry matter was determined with 4040 mg suspended solids/liter

Duration of test (contact time):

ca. 29 d

Initial conc.:

ca. 20 mg/L

Based on:

COD

Parameter followed for biodegradation estimation:

inorg. C analysis

Reference substance:

aniline

Parameter:

other: % biodegradation

Value:

ca. 19.4

Sampling time:

4 d

Remarks on result:

other: mean

Parameter:

other: % biodegradation

Value:

ca. 46.8

Sampling time:

9 d

Remarks on result:

other: mean

Parameter:

other: % biodegradation

Value:

ca. 60.3

Sampling time:

11 d

Remarks on result:

other: mean

Parameter:

other: % biodegradation

Value:

ca. 72.5

Sampling time:

15 d

Remarks on result:

other: mean

Parameter:

other: % biodegradation

Value:

ca. 76.6

Sampling time:

29 d

Remarks on result:

other: mean

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The test item SOPHOROLIPIDS is considered as "readily biodegradable",
The degree of biodegradation reached 76.6 % after 28days,
The 10 days window began on day 3, at its end; 68 % were reached surpassing the pass level of 60% given in the OECD guideline,
The abiotic degradation was <2%

Description of key information

Sophorolipids underwent 76.6% biodegradation after 28 days in an OECD 301B ready biodegradability study. The 10-day window criterion was also fulfilled. Therefore the registered substance and its underlying constituents are considered readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

The aerobic ready biodegradability of Sophorolipids has been determined in the CO2 Evolution Test following OECD 301B and EU-Method C.4-C using a test item concentration of nominally 20mg organic carbon/l (corresponding to 54.7 mg Sophorolipids /L). Aniline was chosen as positive control. Activated sludge was used as inoculum (concentration 25mg dry matter /L). The test duration was 28 days. All validity criteria were met. The degradation of the positive control was 63% after nine days.

The following data were determined for the test item SOPHOROLIPIDS:

10 day window: day 3-13

Degradation at the end of the 10 day window: 68%

Degradation at the end of the test: 77%

Pass level: 60% at the end of the 10 day window

Therefore, it was concluded that Sophorolipids is readily biodegradable following OECD 301B/EU C.4-C.

 

The registered substance is a UVCB substance. ECHA guidance on PBT assessment (Chapter R.11) notes that it is difficult to assess persistence of complex substances containing many constituents using biodegradation methods that measure summary parameters (such as evolution of carbon dioxide or theoretical oxygen demand). In the case of multi-constituent and UVCB substances, the following general strategy is suggested for P assessment (R.11.1.4.2). If the substance consists of homologous structures and is shown to meet the stringent ultimate ready biodegradation test criterion (>60% in 28 days), it can be concluded that the underlying constituents comprising the complex substances are not expected to be persistent.

 

The registered substance, Sophorolipids, is the fermentation products of glucose and rapeseed-oil fatty acids methyl esters. The identified constituents are shown in attached figure 1. These include lactone A (CAS 141304-59-8, 15-40% w/w concentration range), lactone A’ (CAS 1400527-63-0, ≤10% w/w), the corresponding “ring-opened” methyl esters (Product B, 10-40% and Product C, 5-25%) and the corresponded “ring-opened” carboxylic acid (Product D, 5-25%). Oleic acid (CAS 112-80-1, ≤15% w/w) and linoleic acid (CAS 60-33-3, ≤3% w/w) may also be present.

 

Constituents A, A’, B, C and D are closely related structural analogues that are expected to undergo similar biodegradation pathways. The most likely biodegradation pathway for lactones and esters is hydrolysis to give the corresponding hydroxycarboxylate and alcohol + carboxylate. This would result in a common degradation product for constituents A, B and D (i.e. degradation product 1, figure 2). Similarly, A’ and C would produce the related degradation product 2 (Figure 2). It is expected that these degradation products would undergo further degradation, most likely via beta-oxidation of the fatty acid chain resulting in a disaccharide-type moiety.  Bacteria produce a large number of enzymes for breaking down polysaccharides / disaccharides with these substances generally recognised as readily biodegradable (DID No. 2551, reference 1). Fatty acids, such as oleic acid and linoleic acid that may be present in the registered substance, are also readily biodegradable (DID No.2520, reference 1). The high percentage of mineralisation observed in the OECD301B study (77% after 28 days) for the tested Sophorolipids, supports the ready biodegradation of its underlying constituents.

 

To conclude, the registered substance and its underlying constituents are considered readily biodegradable and not persistent.

 

References

1. Detergents Ingredients Database (DID-list) Part A. List of ingredients 2016.
   https://ec.europa.eu/environment/ecolabel/documents/DID%20List%20PART%20A%202016%20FINAL.pdf