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Environmental fate & pathways

Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
other information
Study period:
Experimental starting date: 10th July 2014 Experimental completion date: 29th September 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Study conducted in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EPA OPPTS 835.3110 (Ready Biodegradability)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Remarks:
E
Inoculum or test system:
sewage, domestic, non-adapted
Details on inoculum:
Test System
A mixed population of sewage treatment micro-organisms was obtained on 20 August 2014 from the final effluent stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.


Preparation of Inoculum
The sample of effluent was filtered through coarse filter paper (first approximate 200 mL discarded) and maintained on aeration in a temperature controlled room at 21 ± 1 ºC prior to use.

FOR A DESCRIPTION OF THE MINERAL MEDIUM, PLEASE REFER TO THE ATTACHED APPENDIX 1


Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Remarks:
Daily oxygen consumption
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
Experimental Preparation
Test Item
For the purpose of the test, due to the volatile nature of the test item, at the request of the Sponsor, the test item was added directly to the test vessels using a gas tight syringe.

An amount of test item (70 µL, equivalent to 50 mg of test item determined by preliminary weighings) was dispensed into mineral medium (495 mL) and inoculum (5 mL) to give the test concentration of 100 mg/L. Due to the volatile nature of the test item each vessel was placed immediately on the respirometer after the addition of the inoculum.

A test concentration of 100 mg/L was selected for use in the study following the recommendations of the Test Guideline.

Inoculum control vessels were prepared containing mineral medium (495 mL) and inoculum (5 mL).

Reference Item
A reference item, aniline (C6H5NH2), was used to prepare the procedure control vessels. An initial stock solution of 1000 mg/L was prepared by dissolving the reference item directly in mineral medium with the aid of ultrasonication for approximately 10 minutes. An aliquot (50 mL) of this stock solution was diluted with mineral medium (445 mL) and the inoculum
(5 mL), to give the test concentration of 100 mg/L. The volumetric flask containing the stock solution was inverted several times to ensure homogeneity.

Toxicity Control
A toxicity control, containing the test item and aniline, was prepared in order to assess any toxic effect of the test item on the sewage treatment micro-organisms used in the test.

An amount of test item (70 µL, equivalent to 50 mg of test item determined by preliminary weighings) was dispensed into mineral medium (445 mL) and an aliquot (50 mL) of the
1000 mg/L aniline stock solution (see Section 3.5.1.2) and inoculum (5 mL) to give the test concentration of 100 mg test item/L and 100 mg aniline/L. Due to the volatile nature of the test item each vessel was immediately placed on the respirometer after the addition of the inoculum.

Abiotic Test
A nominal amount of sodium azide (10.00 g) was dissolved in mineral medium with the aid of ultrasonication for approximately 10 minutes and the volume adjusted to 500 mL to give a
20 g/L stock solution.

An amount of test item (70 µL, equivalent to 50 mg of test item determined by preliminary weighings) was dispensed into mineral medium (445 mL) with an aliquot (50 mL) of the 20 g/L sodium azide stock solution and inoculum (5 mL) to give the test concentration of 100 mg test item/L and 2000 mg sodium azide/L. Due to the volatile nature of the test item each vessel was immediately placed on the respirometer after the addition of the inoculum


Preparation of Test System
The following test preparations were prepared and inoculated in 500 mL bottles:

a) Five replicate bottles containing inoculated mineral medium to act as the inoculum control.
b) Two replicate bottles containing inoculated mineral medium and the reference item, aniline, at a concentration of 100 mg/L.
c) Five replicate bottles containing inoculated mineral medium and the test item at a concentration of 100 mg/L.
d) Two replicate bottles containing inoculated mineral medium the reference item, aniline, at a concentration of 100 mg/L and the test item at a concentration of 100 mg/L to act as toxicity control vessels.
e) Four replicates bottles containing the test item at a concentration of 100 mg/L and sodium azide at a concentration of 2000 mg/L to act as abiotic test vessels.

Data from the inoculum control and procedure control vessels was shared with similar concurrent studies.

All vessels were inoculated with the prepared inoculum at a rate of 1% v/v.

On Day 0 the reference item and sodium azide was added (where appropriate) and the pH of all vessels measured using a Hach HQ40d Flexi handheld meter prior to the addition of test item (where appropriate). If necessary the pH values were adjusted to pH 7.4 ± 0.2 using diluted hydrochloric acid or sodium hydroxide solution prior to the addition of the inoculum and test item.

Two of the five inoculum control and test item vessels and two of the four abiotic test vessels were sacrificed for immediate chemical analysis (see Appendix 3). All remaining inoculum control, test item, procedure control, toxicity control and abiotic test vessels were placed in a CES Multi-Channel Aerobic Respirometer.

The system consists of a sample flask sealed by a sensor head/CO2 trap immersed in a temperature controlled water bath. The samples were stirred for the duration of the test with a magnetically coupled stirrer.

As biodegradation progresses, the micro-organisms convert oxygen to carbon dioxide which is absorbed into the ethanolamine solution (50% v/v) causing a net reduction in gas pressure within the sample flask (see Figure 1). The pressure reduction triggers the electrolytic process, generating oxygen and restoring the pressure in the sample flask. The magnitude of the electrolyzing current and the duration of the current is proportional to the amount of oxygen supplied to the micro-organisms. The data generated from the respirometer’s own battery backed memory was collected on the hard disk drive of a non-dedicated computer.

The test was conducted in diffuse light at temperatures of between 23 and 24 ºC.

On Day 28 an assessment of the biological oxygen demand data was made and the most consistent vessels (two inoculum control, one procedure control, two test item, one toxicity control and two abiotic test vessels) chosen for calculating and reporting purposes. The remaining vessels were discarded and are not reported.

The remaining vessels which were not sampled were discarded and are not reported. Additional replicate vessels were prepared and incubated in order that in the event of a leak in the test system a replicate vessel could be discarded without jeopardizing the integrity of the test.

Evaluations
Oxygen Consumption Measurements
The daily Biological Oxygen Demand (BOD) values for the inoculum control, test item, procedure control and the toxicity control are given Table 1.

Physico-chemical Measurements
The temperature of the water bath was recorded daily.

pH Measurements
On Day 0 the pH of each of the test vessels was determined prior to the addition of the inoculum and, where appropriate, the addition of the test item using a Hach HQ40d Flexi handheld meter. The pH values were adjusted where necessary to pH 7.4 ± 0.2 using diluted hydrochloric acid. The required quantity of inoculum and test item, where appropriate, was then added to each vessel.

On Day 28 the pH of the inoculum control and procedure control vessels was determined. Due to the volatile and oily nature of the test item it was considered inappropriate to determine the pH of the vessels containing test item.

Total Viable Counts
In order to confirm that abiotic conditions were present in the abiotic test vessels at the end of the test, total viable counts were performed. An aliquot (100 µL) of sample was dispensed onto a Tryptone Soya Agar (TSA) plate and spread over the plate prior to incubation at approximately 25 ºC for approximately 2 days. After the incubation period, the number of colony forming units (cfu) were determined by direct counting of the colonies on each agar plate.

Compound Specific Analysis
On Day 0, two inoculum control, two abiotic test and two test item vessels were sacrificed for compound specific analysis. On Day 28 chemical analysis of the two inoculum control, two abiotic test and two test item vessels from which the oxygen consumption values were taken was performed.

Data Evaluation
Calculation of Theoretical Oxygen Demand
The Theoretical Oxygen Demand (ThOD) for a compound CcHhClclNnPpSsOoNana was calculated by:

ThOD (NO3)(mgO2/,g) = (16(2c+0.5(h-cl) + 5/2p + 3s + 1/2 na-o))/molecular weight

Percentage Biodegradation
The percentage biodegradation in terms of oxygen consumption was calculated as follows:

% degradation = (BOD B/ThOD) x 100

Where:
BOD = Biological Oxygen Demand of the test item or reference item (mgO2/L)
B = Oxygen consumption in basal mineral medium to which inoculum is added (control) (mgO2/L)
ThOD = Theoretical oxygen demand to completely oxidize the reference and/or test item (mgO2/L)
Reference substance:
aniline
Preliminary study:
Not applicable
Test performance:
Validation Criteria
The mean BOD of the inoculated mineral medium (control) was 53.48 mg O2/L after 28 days and therefore satisfied the validation criterion given in the OECD Test Guidelines.

The difference between extremes of replicate BOD values at the end of the test was less than 20% and therefore satisfied the validation criterion given in the OECD Test Guidelines.

Total Viable Counts
The total viable counts from the abiotic test vessels confirmed that abiotic conditions had been present as the number of total viable counts were very low.
Parameter:
% degradation (O2 consumption)
Value:
73
Sampling time:
28 d
Details on results:
The test item attained 73% biodegradation after 28 days and can therefore be considered to be readily biodegradable. The test item failed to meet the 10-Day window validation criterion, whereby 60% biodegradation must be attained within 10 days of the biodegradation exceeding 10%. However, in accordance with the Revised Introduction to the OECD Guidelines for Testing of Chemicals, (2006), if testing on a complex mixture is performed, and it is anticipated that a sequential biodegradation of the individual structures takes place, then the 10-Day window should not be applied to interpret the results of the test.

The toxicity control attained 69% biodegradation after 14 days and 76% biodegradation after 28 days thereby confirming that the test item was not toxic to the sewage treatment micro-organisms used in the test.
Aniline (procedure control) attained 74% biodegradation after 14 days and 76% biodegradation after 28 days thereby confirming the suitability of the inoculum and test conditions.

Chemical analysis of the 100 mg/L test preparation at 0 hours showed a mean measured concentration of 92% of nominal was obtained. A decline in measured test concentration was observed on Day 28 to less than the limit of quantification (LOQ) of the analytical method employed, which was determined to be 0.26 mg/L (100% loss over the test duration assuming 100% recovery on Day 0).

The losses observed by chemical analysis were higher than those observed by oxygen consumption. This was considered to be due to a combination of volatility of the test item and incorporation of the test item, or degradation products of the test item, into the microbial biomass. In such cases the micro-organisms present utilize carbon originating from the test item to increase their biomass by incorporation the carbon into new cells. This effectively removes the test item from the aqueous phase and hence reduces the apparent biodegradation of the test item as measured by oxygen consumption.

Chemical analysis of the abiotic test vessels on Day 0 showed a mean measured concentration of 90% of nominal was obtained with analysis on Day 28 showed a mean measured concentration of 6% of nominal was obtained. Given the low total viable counts from the abiotic test vessels on Day 28 and the low biological oxygen consumption values from these vessels it was considered that this 93% loss of test item measured by chemical analysis on Day 28 occurred due to the volatile nature of the test item.
Results with reference substance:
Aniline (procedure control) attained 74% biodegradation after 14 days and 76% biodegradation after 28 days thereby confirming the suitability of the inoculum and test conditions.

Definitive Test - Validation of the Analytical Method

Specificity

The biological control samples and an analyzed analytical blank showed no significant interfering response at the retention time of the test item. The standard solutions contained a peak specific for the test item whose area changed accordingly with known concentration, hence the specificity of the method by retention time was confirmed. 

 

 Linearity

The data was found to have a linear correlation within the calibration range of 0 to 265 mg/L. The R² fit of the calibration curve to the data was 0.9987, and was considered to be acceptable.

 

Accuracy (Recovery) and Precision

A set of recovery samples accurately fortified at a relevant concentration of test item was prepared five-fold and analyzed. 

 

The method was considered to be sufficiently accurate and precise for the purposes of this test. The test sample results were not corrected for recovery. 

Limit of Quantification (LOQ)

The limit of quantification (LOQ) was determined by calculating the sample concentration that gave a peak equivalent to ten times the baseline noise. Using this method the LOQ was determined to be 0.26 mg/L.

 

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test item attained 73% biodegradation after 28 days and can therefore be considered to be readily biodegradable.
Executive summary:

SUMMARY


Introduction

The study was performed to assess the ready biodegradability of the test item in an aerobic aqueous media. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (1992) No. 301F, “Ready Biodegradability; Manometric Respirometry Test” referenced as method C.4-D of Commission Regulation (EC) No. 440/2008 and US EPA Fate, Transport, and Transformation Test Guidelines OCSPP 835.3110 (Paragraph (q)).

 

Methods…….

The test item at a concentration of 100 mg/L was exposed to sewage treatment micro-organisms with mineral medium in sealed culture vessels in diffuse light at temperatures of between 23 and 24 ºC for 28 days. 

 

The biodegradation of the test item was assessed by the measurement of daily oxygen consumption values and compound specific analyses on Days 0 to 28. Control solutions with inoculum and the reference item, aniline, together with a toxicity control were used for validation purposes.

 

Results…….

The test item attained 73% biodegradation after 28 days and can therefore be considered to be readily biodegradable. 

Chemical analysis of the 100 mg/L test preparation at 0 hours showed a mean measured concentration of 92% of nominal was obtained. A decline in measured test concentration was observed on Day 28 to less than the limit of quantification (LOQ) of the analytical method employed, which was determined to be 0.26 mg/L (100% loss over the test duration assuming 100% recovery on Day 0). 

 

The losses observed by chemical analysis were higher than those observed by oxygen consumption. This was considered to be due to a combination of volatility of the test item and incorporation of the test item, or degradation products of the test item, into the microbial biomass. In such cases the micro-organisms present utilize carbon originating from the test item to increase their biomass by incorporation the carbon into new cells. This effectively removes the test item from the aqueous phase and hence reduces the apparent biodegradation of the test item as measured by oxygen consumption.

 

Chemical analysis of the abiotic test vessels on Day 0 showed a mean measured concentration of 90% of nominal was obtained with analysis on Day 28 showed a mean measured concentration of 6% of nominal was obtained. Given the low total viable counts from the abiotic test vessels on Day 28 and the low biological oxygen consumption values from these vessels it was considered that this 93% loss of test item measured by chemical analysis on Day 28 occurred due to the volatile nature of the test item. 

 

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2013-10-16 to 2013-11-16
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
The study was conducted according to a standard guideline without deviations from the protocol, and was conducted under GLP guidelines.
Reason / purpose for cross-reference:
reference to same study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
yes
Remarks:
pH readings of test substance on day 28 was not taking due to the volatile and oily nature of test substance. This deviation was considered have had no adverse effect on the outcome of the test given the >60% degradation was achieved.
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
yes
Remarks:
pH readings of test substance on day 28 was not taking due to the volatile and oily nature of test substance. This deviation was considered have had no adverse effect on the outcome of the test given the >60% degradation was achieved.
Qualifier:
according to guideline
Guideline:
EPA OPPTS 835.3110 (Ready Biodegradability)
Deviations:
yes
Remarks:
pH readings of test substane on day 28 was not taking due to the volatile and oily nature of test substance. This deviation was considered have had no adverse effect on the outcome of the test given the >60% degradation was achieved.
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
A mixed population of sewage treatment micro-organisms was obtained on 11 October 2013 from the final effluent stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK. The site treats predominantly domestic sewage. Sample of the inoculum was filtered through a coarse filter paper (first approximate 200 ml discarded) and maintained on aeration in a temperature controlled room at 21±1°C before use.
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Reference substance:
aniline
Preliminary study:
Preliminary solubility/dispersibility study was performed in order to determine the most suitable method of preparation.
Parameter:
% degradation (O2 consumption)
Value:
17
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
29
Sampling time:
10 d
Parameter:
% degradation (O2 consumption)
Value:
41
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
63
St. dev.:
6
Sampling time:
20 d
Parameter:
% degradation (O2 consumption)
Value:
80
Sampling time:
28 d
Details on results:
The test substance exhibited rapid biodegradation and assessed as readily biodegradable. By Day 28, the average percent biodegradation of the test substance was 80%. The test substance reached 13% biodegradation on approximately Day 6 and 49% biodegradation on approximately Day 16.

Biodegradation was based on oxygen consumption and the theoretical oxygen demand of the test substance was calculated using results of an elemental analysis of the test substance.
Results with reference substance:
The reference substance biodegraded to an extent of 79% at Day 28. At Day 14, 63% biodegradation was observed, at Day 20, the biodegradation was 77%.

Results:

Daily BOD values for the test substance, procedure control, toxicity control and inoculum control vessels are in Table 1. The percentage biodegradation values of the test and reference substance and toxicity controls are shown in Table 3 below. The pH results are in Table 2.

Table 3: Biodegradation values

Day

Procedure control

Test item

 

Toxicity control

 

 

R1

R2

Mean

 

0

0

0

0

0

0

1

0

0

0

0

0

2

0

0

0

0

0

3

0

1

1

1

0

4

0

6

4

5

0

5

1

11

7

9

2

6

1

15

11

13

9

7

1

20

14

17

22

8

1

25

17

21

33

9

1

29

21

25

37

10

1

33

24

29

42

11

4

36

27

32

50

12

20

39

30

35

58

13

49

42

33

38

64

14

63

45

37

41

67

15

68

49

41

45

70

16

71

53

45

49

71

17

73

57

48

53

73

18

75

60

52

56

74

19

76

63

55

59

76

20

77

66

60

63

77

21

77

68

63

66

77

22

78

70

67

69

78

23

78

71

70

71

79

24

78

73

73

73

79

25

78

74

76

75

80

26

79

76

78

77

80

27

79

77

79

78

81

28

79

78

81

80

81

R1, R2= Replicates 1 and 2

Validation criteria:

The mean BOD of the inoculated mineral medium (control) was 33.72 mg O2/L after 28 days and therefore satisfied the validation criterion of the test guideline.

The difference between extremes of replicate BOD values at the end of the test and at the end of the 10-day window was <20% and therefore satisfied the validation criterion of the test guideline.

Biodegradation:

The test item achieved 80% biodegradation after 28 days and is therefore considered readily biodegradable.

The toxicity control attained 67% biodegradation after 14 days and 81% biodegradation after 28 days, thereby confirming that the test item was not toxic to the sewage treatment micro-organisms used during the study.

Aniline (procedure control) attained 63% biodegradation after 14 days and 79% biodegradation after 28 days thereby confirming the suitability of the inoculum and test conditions.

Chemical analysis of the 100 mg/l test preparation at 0 hours, showed that a mean measured concentration of 97% of nominal was obtained. A decline in measured test concentration was observed at day 28 to less than the limit of quantification (LOQ) of the analytical method used which was determined to be 0.47 mg/l.

The losses observed by chemical analysis were higher that those observed by oxygen consumption, this was considered to be due to possible losses of the test substance due to its volatility during sampling and analytical procedures.

Another factor in the apparent reduced biodegradation value based on oxygen consumption values compared to losses calculated from the chemical analysis conducted may be due to incorporation of the test substance or degradation products of the test substance into the microbial biomass. In such cases, the micro-organisms present utilise carbon originating from the test substance to increase their biomass by incorporating the carbon into new cells. This effectively removes the test substance from the aqueous phase and hence reduces the apparent biodegradation of the test item by oxygen consumption.

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
A ready biodegradation value of 80% after 28 days was observed for the substance in accordance with OECD 301F and in compliance with GLP. The result is considered reliable.
Executive summary:

The test substance biodegraded to an extent of 80% after 28 days. The data support characterizing the test substance as readily biodegradable, not expected to persist in the environment under aerobic conditions. Although it did not meet the 10 -day window requirement, it is characterized as readily biodegradable because the criterium is not applied to multi-component substances when assessing their ready biodegradability.

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
1. Hypothesis for the analogue approach:
The hypothesis for the analogue approach is that both the registration substance, Hydrocarbons, C9-C11, n-alkanes, isoalkanes, <2% aromatics (target substance), and the test substances, Hydrocarbons, C8-C11, n-alkanes, isoalkanes, <2% aromatics (source substance) and Hydrocarbons, C9-C12, n-alkanes, isoalkanes, <2% aromatics (source substance), are produced from the same Fischer-Tropsch substance, GTL Gasoil, by fractional distillation.

The source substances contain the all of the constituents of the target substance. The substances have constituents that are part of the same homologous series and have many constituents in common. The substances therefore have qualitatively similar properties (RAAF Scenario 2 applies).
2. Source and target chemical(s)
The source substance Hydrocarbons, C8-C11, n-alkanes, isoalkanes, <2% aromatics (GS 160) is composed of linear, branched and cyclic hydrocarbons of chain length C8-C11
The source substance Hydrocarbons, C9-C12, n-alkanes, isoalkanes, <2% aromatics, (GS 170) is composed of linear, branched and cyclic hydrocarbons of chain length C9-C12
The target substance, Hydrocarbons, C9-C11, n-alkanes, isoalkanes, <2% aromatics, (GS 180) is composed of linear, branched and cyclic hydrocarbons of chain length C9-C11.
3. Analogue approach justification
The constituents of the source and target substances are all hydrocarbons. Identical constituents have identical biodegradation profiles. There is evidence for ready biodegradability in the studies on the source substance which covers the full carbon chain length of the target substance.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Parameter:
% degradation (O2 consumption)
Value:
17
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
29
Sampling time:
10 d
Parameter:
% degradation (O2 consumption)
Value:
41
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
63
St. dev.:
6
Sampling time:
20 d
Parameter:
% degradation (O2 consumption)
Value:
80
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
ca. 10
Sampling time:
5 d
Parameter:
% degradation (O2 consumption)
Value:
ca. 50
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
ca. 52
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
ca. 61
Sampling time:
20 d
Parameter:
% degradation (O2 consumption)
Value:
80
St. dev.:
6
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
73
Sampling time:
28 d

Description of key information

Hydrocarbons, C9-C11, n-alkanes, isoalkanes, <2% aromatics is considered readily biodegradable based on read-across from structural analouges

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

No measured biodegradation data are available for the registration substance itself. However, reliable data are available for related substances in the relevant carbon number range, including a study on two similar Fischer-Tropsch process-derived material (GTL Solvent GS160 and GTL Solvent GS170).

In an OECD 301F manometric respirometry test conducted in compliance with GLP, Hydrocarbons, C9-C12, n-alkanes, isoalkanes, <2% aromatics (GTL Solvent GS170) attained 80% degradation in 28 days (Vryenhoef, 2014a). The 10-day window criterion is not applicable for complex substances where sequential degradation of the constituents takes place ( REACH guidance R.7b ECHA, 2017). The substance was therefore concluded to be readily biodegradable.

Hydrocarbons, C8-C11, n-alkanes, isoalkanes, <2% aromatics (GTL Solvent GS160) has been tested in an OECD 301F (manometric respirometry) test conducted in compliance with GLP (Best, 2014). The test substance attained 73% biodegradation in 28 days and was therefore considered to be readily biodegradable.

These studies are considered to be reliable and are used as weight of evidence that Hydrocarbons, C9-C11, n-alkanes, isoalkanes, <2% aromatics is readily biodegradable.

In a supporting study, Hydrocarbons, C9-C11, n-alkanes, isoalkanes, cyclics, <2% aromatics, biodegraded 80% after 28 days under the conditions of the study and is readily biodegradable.

The available data cover the entire carbon number range relevant to the registration substance and the test materials contain similar chemical structures. The results are therefore read across to Hydrocarbons, C9-C11, n-alkanes, isoalkanes, <2% aromatics. Both tested substances demonstrated significant biodegradation and it can therefore be concluded that the registration substance is readily biodegradable.