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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:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
Please refer to the Read-across statement attached under section 13.

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
This Read-Across is based on the hypothesis that the target and the source substances have similar environmental fate and (eco)toxicological properties because both substances have the same common compound octyl sulfonate while another main constituent of the target substance octyl disulfonate is considered to have similar level of toxicity as octyl sulfonate. Other non-common compounds represented by impurities are considered not to influence the read-across validity because they are either structurally identical in the target and in the source substances or, if different, do not contribute to the toxicity effects because they are also anionic sulfonates with the same functional groups and their content is very low.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Please refer to the Read-across statement attached under section 13.

3. ANALOGUE APPROACH JUSTIFICATION
Microorganisms mineralize all sub-categories of ANS including PAS. All members of this category are considered to be readily biodegradable, although the rate of biodegradability is inversely dependent on alkyl chain length. Since all sulfonate containing constituents of the source substance are octyl derivatives, they are all expected to biodegrade to a similar degree. The minor amounts of hexadecyl sulfonate moiety seems not to influence the biodegradation rate of the source substance.
The target substance is considered to follow similar biodegradation pattern as the source substance because it has the same structural features. Moreover, there is sufficient weight of evidence that the entire range of substances of ANS category including the source substance biodegrade rapidly, it is therefore a high probability that the target substance is also readily biodegradable. There are no other structural alerts in the sulfonate containing constituents of the target substance pointing to a different from the source substance biodegradation pattern. The second main constituent octyl disulfonate is a linear alkyl sulfonate possessing two sulfonate groups is expected to biodegrade to the same degree following the same pathway as the common compound octyl sulfonate: i.e “via a keto-bisulfite intermediate, which is further hydrolysed into bisulfite (HSO3-) and the corresponding aldehyde, which is then oxidised to the carboxylic acid. Bisulfite is chemically oxidised to sulfate in the environment. From this point onwards the biodegradation pathway is the same as for the alkyl sulfates (Painter, 1992, cited in SIDS, 2007)”. Benzoic acid is also a biodegradable substance (SIDS, 2001; SCCP, 2005). Although tert-butyl alcohol is resistant to biodegradation (EPA, 2014), it will not influence biodegradation of the target substance due to its minor amounts. The sulfinate moiety of the octyl sulfinosulfonate was reported to be slowly but spontaneously oxidised to the sulfonate moiety (see previous section).
Therefore, it is predicted that the target substance would possess the same biodegration rate as the source substance if it was tested in a biodegradation study.

4. DATA MATRIX
Please refer to the Read-across statement attached under section 13.
Reason / purpose:
read-across source
Preliminary study:
N/A
Test performance:
The test satisfied all validation criteria as indicated below:
- The IC content in the test vessel was less than 5 % of the TOC introduced with the test item.
- The CO2 evolution in the inoculum blank at the end of the test was below 40 mg/L.
- The difference of extremes of replicate values of the test item at the end of the 10-d window and at the end of the test was less than 20%.
- The biodegradation of the reference compound reached the pass level of 60 % ThCO2 by day 4.
- The degradation extent in the toxicity control was above 25 % in 14 days based on ThCO2.

However, the temperature was outwith the recommended range for this test between days 15-20. Although this is a slight deviation from the guideline it did not impact the quality of the results or the study.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
90.7
Sampling time:
28 d
Remarks on result:
other: predicted result from the source substance
Details on results:
Although temperature was below that defined in the guidelines (19.2 °C vs a low of 20 °C), this did not effect the qulaity or integrity of the results. The degradation of the test item at the end of the test was 90.7% (28 d after acidification, mean of three replicates). The test item reached the criteria for ready biodegradability. 60% of ThCO2 was reached within a 10-d after reaching 10 % within the test system. Therefore, the test item also satisfies the acceptance criteria for ready biodegradability with regards to the 10-d window.

The degradation of the toxicity control after 14 days was 77.8%. The test item had no inhibitory effect on the inoculum according to the criterion of the guideline.
Results with reference substance:
The reference compound sodium benzoate reached the pass levels for ready biodegradability within 4 days.

Table 1 Biodegradation at day x as % ThCO2

reactor

day

0

4

7

11

14

21

28

29

 

 

 %

 %

 %

 %

 %

 %

7

Test flasks

0

59.4

77.2

83.7

85.7

88.2

90.6

90.5

8

 

0

56.5

74.9

82.5

85.0

87.3

89.1

87.7

9

 

0

66.7

79.7

86.7

88.0

94.9

95.3

94.0

MW

0.0

60.9

77.3

84.3

86.2

90.1

91.7

90.7

SD

0.0

4.3

2.0

1.7

1.3

3.4

2.6

2.6

4

reference flasks

0

75.4

86.3

88.4

89.5

90.6

93.1

96.8

5

 

0

77.7

82.7

84.7

87.1

86.0

90.4

94.6

6

 

0

72.8

80.7

86.7

87.8

87.6

88.9

91.8

MW

0.0

75.3

83.2

86.6

88.1

88.1

90.8

94.4

SD

0.0

2.0

2.3

1.5

1.0

1.9

1.7

2.0

 

Toxicity control

 

 

 

 

 

 

 

 

10

Test item

0

38.6

65.2

74.2

77.8

80.7

82.2

83.9

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The same result is predicted for the target substance.
An OECD 301B CO2 Evolution Test (1992) was conducted with the test item. This was to assess the ready biodegradability of the substance. The test met all guideline validity criteria.
The test item had no inhibitory effect on the inoculum according to the criterion of the guideline. The degradation of the test item was 90.7 % after 28 days and the criteria of the 10-d-window was met.
The test item reached the criteria for ready biodegradability.
Executive summary:

A study was performed to assess the ready biodegradability of the source substance in an aerobic aqueous medium. The study was in concordance with OECD (1992) 301B, "Ready Biodegradability; CO2 Evolution Test" referenced as Method C.4-C of Commission Regulation (EC) No. 440/2008 and US EPA Fate, Transport, and Transformation Test Guidelines OPPTS 835.3110 (Paragraph (M)).

The test item was added to activated sludge from a municipal wastewater treatment plant (sewage sludge contained 30 mg/L of dry solids). The test item was applied to the system at a concentration of ~20 mg TOC/L and left for 28 days in diffuse light at approximately 19.2-22.3 °C. Although the temperature was marignally below that defined within the guideline it did not affect the quality or integrity of the study or the results.

The degradation of the test item was assessed by the determination of carbon dioxide produced. Control solutions with inoculum and the reference item (sodium benzoate), together with a toxicity control (reference item and test item), were used for validation purposes.

On day 4 the degradation extent was 60.87 %.  The degradation of the test item is therefore higher than 60 % within 10 days of 10 % degradation being reached. Thus, the 10-d window criterion was fulfilled.

The test item reached the criteria for ready biodegradability according to the OECD criteria (≥ 60% ThCO2 and fulfilment of 10-d window).

Based on this data on the source substance, the registered substance is alco considered to be readily biodegradable.

Description of key information

Read-across: OECD 301B, GLP, readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

A study was performed to assess the ready biodegradability of the test item in an aerobic aqueous medium. The study was in concordance with OECD (1992) 301B, "Ready Biodegradability; CO2 Evolution Test" referenced as Method C.4-C of Commission Regulation (EC) No 440/2008 and US EPA Fate, Transport, and Transformation Test Guidelines OPPTS 835.3110 (Paragraph (M)).

The test item was added to activated sludge from a municipal wastewater treatment plant (sewage sludge contained 30 mg/L of dry solids). The test item was applied to the system at a concentration of ~20 mg TOC/L and left for 28 days in diffuse light at approximately 19.2-22.3 °C. Although the temperature was marignally below that defined within the guideline it did not affect the quality or integrity of the study or the results.

The degradation of the test item was assessed by the determination of carbon dioxide produced. Control solutions with inoculum and the reference item (sodium benzoate), together with a toxicity control (reference item and test item), were used for validation purposes.

On day 4 the degradation extent was 60.87 %.  The degradation of the test item is therefore higher than 60 % within 10 days of 10 % degradation being reached. Thus, the 10-d window criterion was fulfilled.

The test item reached the criteria for ready biodegradability according to the OECD criteria (≥ 60% ThCO2 and fulfilment of 10-d window).

Based on this data on the source substance, the registered substance is alco considered to be readily biodegradable.