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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2018-02-20 to 2018-11-21
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
requested from ECHA final decision on substance evaluation
Qualifier:
according to
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)
Version / remarks:
corrected September 2014
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Municipal sewage treatment plant, 31137 Hildesheim, Germany
- Preparation of inoculum for exposure: The activated sludge was washed twice with chlorine free tap water. After the second washing the settled sludge was resuspended in mineral salts medium and was maintained in an aerobic condition by aeration for 2 hours Thereafter the sludge was homogenized with a blender. After sedimentation the supernatant was decanted and was maintained in an aerobic condition by aeration with CO2-free air for 2 days until test start.
- Pretreatment:
- Concentration of sludge: 10 mL/L were used to initiate inoculation. 80 mL mineral salts medium acc. to OECD 310 + inoculum was used in the test vessels
- Initial cell/biomass concentration: E+05 to E+08 CFU/L
Duration of test (contact time):
60 d
Initial conc.:
15.5 mg/L
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
inorg. C analysis
Remarks:
of CO2 produced
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium according to OECD guideline 310
- Test temperature: 20 ± 1 °C
- pH: not reported
- Aeration of dilution water: Mineral medium was aerated before exposure

TEST SYSTEM
- Number of culture flasks/concentration: 3
- Method used to create aerobic conditions: Before exposure the sludge was homogenized with a blender. After sedimentation the supernatant was decanted and was maintained in an aerobic condition by aeration with CO2-free air for 2 days until test start.
- Measuring equipment: Carbon analyser, Multi N/C 3100, ANALYTIK JEN
- Details of trap for CO2 and volatile organics if used: Determination of CO2 was carried out by IC analysis with a carbon analyser according to DIN EN 1484. Sampling was carried out at test start (day 0) of all replicates and at approx. 11 further sampling points of the test item and inoculum control replicates. The blank replicates were sampled on at least 4 further sampling points. The functional control was sampled on at least 3 further sampling points and the toxicity control replicates were sampled on at least 2 further sampling points. Sodium hydroxide solution (0.74 mL of 7 mol/L solution to 80 mL medium) was injected to each vessel sampled.
The TIC of the sodium hydroxide solution (blind value) was determined at each sampling time.


SAMPLING
- Sampling frequency: Sampling was carried out at test start (day 0) of all replicates and at approx. 11 further sampling points of the test item and inoculum control replicates. The blank replicates were sampled on at least 4 further sampling points. The functional control was sampled on at least 3 further sampling points and the toxicity control replicates were sampled on at least 2 further sampling points.
- Sample storage before analysis: The vessels were shaken on an overhead shaker (approximately 100 rpm) for 1 h at test temperature and analysed.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Mineral salts medium + inoculum. Triplicates (after 28 days and at test end 5 replicates). Humic acid was placed first in the test vessel (approx. 5 mg / test vessel, corresponding to approx. 62.5 mg / L)
- Blank: Test item in test concentration in ultrapure water. Triplicates (after 28 days and at test end 5 replicates).
- Toxicity control: Test and reference item in test concentration. Triplicates (after 28 days 5 replicates). Humic acid was placed first in the test vessel (approx. 5 mg/test vessel, corresponding to approx. 62.5 mg / L), then the test item will was pipetted onto the humic acid.
- Other: Reference item: Sodium benzoate (SIGMA ALDRICH). Triplicates (test end 5 replicates). Test concentration 17.5 mg/L. Humic acid was placed first in the test vessel (approx. 5 mg / test vessel, corresponding to approx. 62.5 mg / L).
Reference substance:
benzoic acid, sodium salt
Preliminary study:
A preliminary test (non GLP) was carried out with the test item HH-2014-548 (batch number: SR 08021) with non-adapted activated sludge over a period of 21 days.


Test performance:
Application Once at test start, directly pipetted into the measuring flask
Headspace to liquid ratio 1:2
Test vessels / volume Headspace flasks / 120 mL
Test medium / volume Mineral salts medium acc. to OECD 310 / 80 mL and inoculum
Agitation Shaker (150 - 200 rpm)
Temperature 20 ± 1 °C
Photoperiod Low light conditions
Dry sludge concentration 30 mg/L
Test Item HH-2014-548 in test concentration
Replicates Duplicates
Test concentration 640 µL test item dispersion / L
Carbon content 20.1 mg C / L
in the vessel
Abiotic test item control Test item in test concentration, mineral salts medium and HgCl2
Replicates Duplicates
Inoculum Control Mineral salts medium + inoculum
Replicates Duplicates
Toxicity Control Test item (20.1 mg C/L) and reference item (17.5 mg C/L)
Replicates Duplicates
Key result
Parameter:
% degradation (inorg. C analysis)
Remarks:
test item
Value:
10
Sampling time:
35 d
Key result
Parameter:
% degradation (inorg. C analysis)
Remarks:
test item
Value:
26
Sampling time:
60 d
Key result
Parameter:
% degradation (inorg. C analysis)
Remarks:
toxicity control
Value:
46
Sampling time:
14 d
Remarks on result:
other:
Remarks:
no inhibition at 15.5mg/L TS A.I.
Key result
Parameter:
% degradation (inorg. C analysis)
Remarks:
toxicity control
Value:
50
Sampling time:
28 d
Remarks on result:
other:
Remarks:
no inhibition at 15.5mg/L TS A.I.
Key result
Parameter:
% degradation (inorg. C analysis)
Remarks:
reference item
Value:
> 10
Sampling time:
7 d
Key result
Parameter:
% degradation (inorg. C analysis)
Remarks:
reference item
Value:
101
Sampling time:
28 d
Details on results:
In the toxicity control, containing test and reference item, a biodegradation of 46 % was determined after 14 days and 50% after 28 days. The biodegradation of the reference item was not inhibited by the test item in the toxicity control. The 95 % confidence interval on day 28 was 50 - 51%.
The test item replicates reached the 10% level (beginning of biodegradation) within 35 days. The biodegradation came to 7% after 28 days and to 26 % after 60 days. The 95 % confidence interval on day 28 was 6 – 8% and on day 60 25 – 28%.
In the Blank Sampels no CO2 - production was observed.
Results with reference substance:
The adaptation phase of the functional control changed within 7 days to the degradation phase (degradation > 10%). The course of the degradation phase was rapid and the pass level of 96 % was reached within 7 days. The biodegradation came to a maximum of 101% after 28 days. The validity criterion degradation > 60% after 14 d was fulfilled. The 95% confidence interval on day 28 was 98 – 104%.

 CO2-Production and Biodegradation in the Test Item Samples

 

CO2-Production in mg C/L

Day

P1

P2

P3

P4

P5

MP

Net MP

Degr. [%]

0

2.08

2.01

2.10

 

0.76

--

1

1.92

1.94

1.93

0.80

0.04

0

4

2.53

2.48

2.43

1.48

0.29

3

7

2.66

2.80

2.84

1.73

0.40

4

11

2.88

3.03

3.02

1.94

0.43

4

14

3.24

3.28

3.23

2.22

0.32

3

21

3.58

3.69

3.64

2.47

0.52

5

28

3.83

3.82

3.89

3.94

4.01

2.61

0.79

7

35

4.60

4.75

4.46

 

3.28

1.37

12

42

4.92

4.98

5.36

3.58

1.65

15

49

5.06

5.88

5.97

4.32

2.42

21

56

6.40

6.87

6.25

4.79

2.86

25

60

6.28

5.92

6.02

5.99

6.19

4.86

2.98

26

 

MP         = mean values (NaOH corrected)
NetMP   = netto mean production (corrected for inoculum control values)
Degr.
      = degradation

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The test item is classified as not readily biodegradable within the 60 day period of the present study.
Executive summary:

The study was performed according to guidelines OECD 310 and GLP principles.

The validity criteria were fulfilled according to the guidelines:

·   The degradation of the functional control reached the pass level of 60% within 7 days (validity criterion: > 60% after 14 days).

·   The maximum amount of TIC present in the inoculum controls ( C1 - C5) on day 28 was 1.06 mg C/L and 1.12 mg C/L on day 60 (validity criterion: TIC < 3 mg C/L).

The test item is classified as not readily biodegradable within the 60 day period of the present study.

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
11.12.1997-09.01.1998
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Qualifier:
according to
Guideline:
EPA OTS 796.3260 (Ready Biodegradability: Modified Sturm Test)
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Activated sludge collected from the Prospect Bay Wastewater Treatment Facility in Grasonville, Maryland. The facility treated wastes from primarily domestic sources.
- Laboratory culture: no
- Storage conditions: no data
- Storage length: no data
- Preparation of inoculum for exposure: The sludge was sieved through a 2 mm screen to remove debris and then aerated overnight. After the aeration period, the sludge was blended at medium speed for ca. 2 minutes and then allowed to settle for ca. 30 minutes. The supernatant above the settled solids was decanted, filtered using glass wool, and blended at medium speed for ca. 2 minutes. The following was added to each test chamber: 2943 mL of Nanopure water, 3 mL of ammonium sulfate solution (4.0%), 3 mL calcium chloride solution (2.75%), 12 mL of ferric chloride solution (0.025%), 3 mL magnesium sulfate solution (2.25%), 6 mL of phosphate buffer (pH 7.2), and 30 mL activated sludge inoculum. Then the chambers were aerated with CO2-free air for 24 h at a rate of 50 to 100 mL/min to purge the systems of CO2. After the aeration period, the flow of CO2-free air was stopped and three CO2 traps each containing 100 mL of 0.5 N KOH were connected to the test chambers. Then reference and test substance were added to the test chambers by direct weight addition.
- Pretreatment: not reported
- Concentration of sludge: 30 mL/3000 mL
- Initial cell/biomass concentration: 2.05 x 10E6 CFU/mL
- Water filtered: no data
- Type and size of filter used, if any: no data
Duration of test (contact time):
28 d
Initial conc.:
10 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: The following was added to each test chamber: 2943 mL of Nanopure water, 3 mL of ammonium sulfate solution (4.0%), 3 mL calcium chloride solution (2.75%), 12 mL of ferric chloride solution (0.025%), 3 mL magnesium sulfate solution (2.25%), 6 mL of phosphate buffer (pH 7.2), and 30 mL activated sludge inoculum.
- Additional substrate: no
- Solubilising agent (type and concentration if used): no
- Test temperature: 20 +/- 3°C
- pH: 7.2 (pH of buffer solution), pH at test termination 6.84, 6.89, and 6.90, respectively
- pH adjusted: yes using phosphate buffer
- Aeration of dilution water: yes
- Suspended solids concentration: 2.05 x 10E6 CFU/mL (no further details stated)
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: darkened 4-liter bottles connected to CO2 traps, the contents was stirred via magnetic stir bars
- Number of culture flasks/concentration: 3 flasks per concentration (3 replicates)
- Method used to create aerobic conditions: aeration
- Measuring equipment: Shimadzu TOC-5000 carbon analyzer
- Details of trap for CO2 and volatile organics if used: Test chamber connected to three CO2 traps in line. Each trap contained 100 mL of 0.5 N KOH


SAMPLING
- Sampling frequency: Inorganic carbon was analysed at 3 to 4 day intervals over the test period
- Sampling method: The CO2 trap nearest to the chamber was removed and analysed via carbon analyzer. The two remaining traps were placed one position closer to the test chamber and a new trap was placed on the end of the series.
- Sample storage before analysis: no data

CONTROL AND BLANK SYSTEM
- Inoculum blank: performed
- Abiotic sterile control: no data
- Toxicity control: no data

STATISTICAL METHODS: -
Reference substance:
benzoic acid, sodium salt
Test performance:
The test was performed according to OECD Guideline 301B and US EPA Method 796.3260.
Parameter:
% degradation (CO2 evolution)
Value:
4.4 - 12.7
Sampling time:
28 d
Remarks on result:
other: not readily biodegradable
Details on results:
Results of the biodegradation study with the test substance conducted according to OECD Guideline 301 B and US EPA Method 796.3260

Day Test item Test item Test item
4 0 0 1.1
7 0.3 0 1.5
11 1.0 0.9 2.3
15 1.2 1.3 3.2
18 1.1 0.9 3.4
22 1.6 1.5 4.5
25 1.5 1.3 7.0
29 4.5 4.4 12.7
Results with reference substance:
Results of the biodegradation study with the reference substance conducted according to OECD Guideline 301 B and US EPA Method 796.3260

Day Sodium benzoat Sodium benzoate Sodium benzoate
4 29.3 32.8 26.5
7 32.4 63.8 61.8
11 82.8 91.1 97.2
15 96.2 97.7 101.4
18 97.5 98.4 101.9
22 98.5 99.2 102.5
25 98.8 99.5 102
29 99.0 98.7 102.6

Oleic-acid based IQAC, DMS quaternised proved to be not readily biodegradable (<= 12.7 % degradation after 28 d) in a test conducted according to OECD Guideline 301B and US EPA Method 796.3260.

Validity criteria fulfilled:
yes
Interpretation of results:
other: not readily biodegradable
Conclusions:
Oleic-acid based IQAC, DMS quaternised proved to be not readily biodegradable (<= 12.7 % degradation after 28 d) in a test conducted according to OECD Guideline 301B and US EPA Method 796.3260.
Executive summary:

Oleic-acid based IQAC, DMS quaternised proved to be not readily biodegradable (=12.7 % degradation after 28 d) in a test conducted according to OECD Guideline 301B and US EPA Method 796.3260.

Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: guideline study with some minor deficiencies in reporting
Qualifier:
according to
Guideline:
other: German Guideline DIN 38412, Part 25
Principles of method if other than guideline:
The study was conducted according to the German DIN 38412, Part 25 which corresponds to OECD Guideline 302 B (Inherent biodegradability: Zahn-Wellens/EMPA Test). The chemical oxygen demand was determined according to the German DIN 38 409 H 41.
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): The inoculum was obtained by mixing activated sludge samples collected at the waste water treatment plants of Bonn, Köln, Siegburg, Berg.-Gladbach (Germany).
- Laboratory culture: no
- Preparation of inoculum for exposure: Inoculum was separated by filtration
- Pretreatment: no
- Concentration of sludge: 1.2 g/L dw
- Water filtered: yes
- Type and size of filter used, if any: membrane filter: 0.2 µm pore width
Duration of test (contact time):
28
Initial conc.:
0.56 g/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: not reported
- Additional substrate: no
- Solubilising agent (type and concentration if used): no
- Test temperature: not reported
- pH: not reported
- pH adjusted: not reported
- Aeration of dilution water: not reported
- Suspended solids concentration: not reported
- Continuous darkness: not reported

TEST SYSTEM: not reported

SAMPLING
- Sampling frequency: sampling was performed at time 0 and after 2 h, 1 , 2, 5, 10, 15, 20, and 28 d
- Sampling method: not reported
- Sterility check if applicable: not reported
- Sample storage before analysis: not reported

CONTROL AND BLANK SYSTEM
- Inoculum blank: not reported
- Abiotic sterile control: not reported
- Toxicity control: not reported
- Other: functional/procedural control (reference substance) performed
Reference substance:
benzoic acid, sodium salt
Test performance:
The study was conducted according to the German DIN 38412, Part 25 which corresponds to OECD Guideline 302 B (Inherent biodegradability: Zahn-Wellens/EMPA Test).
Parameter:
% degradation (O2 consumption)
Value:
> 90
Sampling time:
28 d
Remarks on result:
other: test item proved to be inherently biodegradable
Details on results:
The following results were obtained

Time COD (mg/L)
0 h 250
2 h 240
1 d 190
2 d 150
5 d 110
10 d 70
15 d 45
20 d 25
28 d <15
The test item proved to be inherently biodegradable (>90% biodegradation after 28 d).
Results with reference substance:
The reference substance sodium benzoate was biodegraded by >95%.

The study was conducted according to the German DIN 38412, Part 25 which corresponds to OECD Guideline 302 B (Inherent biodegradability: Zahn-Wellens/EMPA Test). The following results were obtained

Time

COD (mg/L)

0 h

250

2 h

240

1 d

190

2 d

150

5 d

110

10 d

70

15 d

45

20 d

25

28 d

<15

The test item proved to be inherently biodegradable (>90% biodegradation after 28 d).

Validity criteria fulfilled:
not specified
Interpretation of results:
inherently biodegradable
Conclusions:
In a study conducted according to the German DIN 38412 Teil 25 which corresponds to OECD Guideline 302 B the test item proved to be inherently biodegradable (>90% biodegradation after 28 d).
Executive summary:

The ready biodegradation of the test substance was investigated in a study conducted according to German Guideline DIN 38412, Part 25, which corresponds to the OECD 301 B testover a period of 28 days and using predominantly domesticsewage sludge micro-organismsas inoculum. The biodegradation rate was determined by measurement of O2consumption. This study is regarded as reliable without restriction satisfies the guideline requirements for ready biodegradation. The test item proved to be inherently biodegradable. The functional control with sodium benzoate reached >95% degradation after 28 d.

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Study period:
17.10.1991-14.11.1991
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: guideline study, basic data given
Qualifier:
according to
Guideline:
OECD Guideline 301 E (Ready biodegradability: Modified OECD Screening Test)
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): effluent of the preliminary treatment of the municipal watewater treatment plant at Wiesbaden (Germany) was collected
- Laboratory culture: no
- Method of cultivation: -
- Storage conditions: not reported
- Preparation of inoculum for exposure: -
- Pretreatment: not reported
- Initial cell/biomass concentration: 1 mL sewage effluent/L medium were used
- Water filtered: not reported
Duration of test (contact time):
28 d
Initial conc.:
70 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
TEST CONDITIONS
- Composition of medium: mineral standard nutrient broth according to guideline
- Additional substrate: no
- Solubilising agent (type and concentration if used): not reported
- Test temperature: not reported
- pH: not reported
- pH adjusted: not reported
- Aeration of dilution water: the whole culturing apparatus was aerated
- Suspended solids concentration: 1 mL sewage effluent/L medium was used (not further specified)
- Continuous darkness: not reported

TEST SYSTEM
- Culturing apparatus: not reported
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: the whole culturing apparatus was aerated
- Measuring equipment: DOC measurement via UV-DOC apparatus (Fa. Maihak)
- Test performed in open system: yes

SAMPLING
- Sampling frequency: sampling was performed after 3 h, and 1, 4, 7, 11, 14, 18, 21, 25, and 28 d
- Sampling method: an aliquot was removed from the test vessels and filtered
- Sample storage before analysis: not reported

CONTROL AND BLANK SYSTEM
- Inoculum blank: performed
- Toxicity control: not reported
- Other: functional/procedural control (reference substance) performed
Reference substance:
ethylene glycol
Test performance:
The study was conducted according to OECD Guideline 301 E (Ready biodegradability: Modified OECD Screening Test).
Parameter:
% degradation (DOC removal)
Value:
63
Sampling time:
28 d
Details on results:
The following results were obtained in the study conducted according to OECD Guideline 301 E
Time Test substance Blank Elimination rate
DOC (mg/L) DOC (mg/L) (%)
3 h 62 2.1 14
1 d 59 1.1 17
4 d 27 2.4 65
7 d 19 2.5 76
11 d 27 2.2 65
14 d 21 1.6 72
18 d 24 3.7 71
21 d 27 4.3 68
25 d 24 4.8 73
28 d 32 5.8 63
Results with reference substance:
The reference substance ethylene glycol was biodegraded by 96% after 14 d.

In a study conducted according to OECD Guideline 301 E (Ready biodegradability: Modified OECD Screening Test) the following results were obtained

Time

Test substance

DOC (mg/L)

Blank

DOC (mg/L)

Elimination rate (%)

3 h

62

2.1

14

1 d

59

1.1

17

4 d

27

2.4

65

7 d

19

2.5

76

11 d

27

2.2

65

14 d

21

1.6

72

18 d

24

3.7

71

21 d

27

4.3

68

25 d

24

4.8

73

28 d

32

5.8

63

The test item proved to be readily biodegradable and fulfilling the 10 -d window criterion (76% degradation after 7 d).

Interpretation of results:
readily biodegradable
Conclusions:
In a study conducted according to OECD Guideline 301 E (Ready biodegradability: Modified OECD Screening Test) the test item proved to be readily biodegradable and fulfilling the 10 -d window criterion (76% degradation after 7 d).
Executive summary:

In a study conducted according to OECD Guideline 301 E (Ready biodegradability: Modified OECD Screening Test) the following results were obtained

Time

Test substance

DOC (mg/L)

Blank

DOC (mg/L)

Elimination rate (%)

3 h

62

2.1

14

1 d

59

1.1

17

4 d

27

2.4

65

7 d

19

2.5

76

11 d

27

2.2

65

14 d

21

1.6

72

18 d

24

3.7

71

21 d

27

4.3

68

25 d

24

4.8

73

28 d

32

5.8

63

The test item proved to be readily biodegradable and fulfilling the 10 -d window criterion (76% degradation after 7 d).

Description of key information

Oleic-acid based IQAC, DMS quaternised is not readily biodegradable, but inherently biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, fulfilling specific criteria

Additional information

Oleic-acid based IQAC, DMS quaternised was biodegraded under the strict conditions of a test conducted according to OECD Guideline 301B and US EPA Method 796.3260 (<=12.7% degradation after 28 d) and therefore did not meet the pass level for ready biodegradability.

In a test of the closely related partially unsaturated IQAC, DMS quaternised (CAS 86088-85-9) according to the German Guideline DIN 38412, Part 25, which corresponds to the OECD 302 B test, the read across substance proved to be inherently biodegradable, > 90% COD elimination after 28 d.

These findings are supported by another study on readily biodegradability according to OECD 301 E for the read across substance partially unsaturated IQAC, DMS quaternised (CAS 86088-85-9) resulting in 63% Biodegradation after 28 days.

In a weight of evidence approach with these three study resutls, Oleic-acid based IQAC, DMS quaternised, is regarded as inherently biodegradable.