Registration Dossier

Environmental fate & pathways

Biodegradation in water: screening tests

Currently viewing:

Administrative data

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:
2016-04-04 to 2016-08-04
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
Remarks:
Study plan deviations are listed; a different batch of the reference item was used for the test but the study integrity was not adversely affected by these deviations
GLP compliance:
yes
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge: activated sludge freshly obtained from a municipal sewage treatment plant (Netherlands), receiving predominantly domestic sewage.
- Method of cultivation: The freshly obtained sludge was kept under continuous aeration until further treatment.
- Concentration of sludge: 3.4 g of suspended solids in 1 L of concentrated sludge
- Preparation of inoculum for exposure: the supernatant liquid was used as inoculum at the amount of 10 mL/L of mineral medium
- Storage length: the sludge was allowed to settle for 44 min before use
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
test mat.
Initial conc.:
12 mg/L
Based on:
TOC
Remarks:
based on the molecular formula
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS

- Composition of medium: test material, sludge inoculum and mineral media (mineral components and Milli-RO water). The day before the start of the test, mineral components, Milli-RO water (ca.80% of final volume) and inoculum (1% of final volume) were added to each bottle. This mixture was aerated with synthetic air overnight to purge the system of CO2. At the start of the test (day 0), weighted amounts of test and reference item (test item bottle A: 39.2 mg; test item bottle B: 40.4 mg and toxicity control bottle: 39.4 mg) were added to the bottles containing the microbial organisms and mineral components. The volumes of suspensions were made up to 2 litres with Milli-RO water. Three CO2-absorbers (bottles filled with 100 mL 0.0125 M Ba(OH)2) were connected in series to the exit air line of each test bottle.
The test solutions were continuously stirred during the test, to ensure optimal contact between the test item and the test organisms.
- Additional substrate: no
- Solubilising agent (type and concentration if used): no
- Test temperature: 21.4 to 22.9°C
- pH: 7.9 (before addition of concentrated HCL) - 7.6 in control blank and test bottles (Phenolphthalein (1% solution in ethanol, Merck) was used as pH-indicator.)
- pH adjusted: yes (using 1 M HCL)
- Continuous darkness: yes

TEST SYSTEM

- Culturing apparatus: 2L Glass brown coloured bottles
- Number of culture flasks/concentration: 2 bottles for the test suspension (test item and inoculum), 2 bottles for the inoculum blank, 1 bottle for the positive control (containing reference item and inoculum) and 1 bottle for the toxicity control (containing test item, reference item and inoculum).
- Measuring equipment: not specified (device for determination of carbon dioxide titrimetrically)
- Details of trap for CO2 and volatile organics if used: A mixture of oxygen (ca. 20%) and nitrogen (ca. 80%) was passed through a bottle, containing 0.5 - 1 litre 0.0125 M Ba(OH)2 solution to trap CO2 which might be present in small amounts. The synthetic air was sparged through the scrubbing solutions at a rate of approximately 1-2 bubbles per second (ca. 30-100 mL/min). The CO2 produced in each test bottle reacted with the barium hydroxide in the gas scrubbing bottle and precipitated out as barium carbonate.

SAMPLING

- Sampling frequency: every 2nd or 3rd day during the first 10 days and thereafter at least every fifth day until day 28 for the inoculum blank and test suspension.
- Sampling method: Each time the CO2-absorber nearest to the test bottle was removed for titration; each of the remaining two absorbers was moved one position in the direction of the test bottle. A new CO2-absorber was placed at the far end of the series. The amount of CO2 produced was determined by titrating the remaining Ba(OH)2 with 0.05 M standardized HCl.


CONTROL AND BLANK SYSTEM

- Inoculum blank: Yes. 2 bottles of 2L containing only inoculum.
- Reference control: Yes: Positive (reference and inoculum) and Toxicity control (test item, reference item and inoculum). 1001.0 mg of sodium acetate in Milli-RO water up to a total volume of 250 mL was prepared as stock solution. 20 mL of this stock solution were added to 2L of the test medium of the positive and the toxicity control bottles, resulting in a final concentration of 40 mg sodium acetate/L (12 mg TOC/L).
Reference substance:
other: sodium acetate
Key result
Parameter:
% degradation (CO2 evolution)
Remarks:
bottle A
Value:
30
Sampling time:
29 d
Remarks on result:
other: based on ThCO2
Key result
Parameter:
% degradation (CO2 evolution)
Remarks:
bottle B
Value:
39
Sampling time:
29 d
Remarks on result:
other: based on ThCO2
Results with reference substance:
The positive control item was biodegraded by at least 60% (61%) within 14 days (a first test has been disregarded because the positive control did not meet the acceptability criterion)

Table 1 : CO2 production and percentage biodegradation of the test item (bottle A)

 

 Day  HCL (0.05N) titrated (mL)   HCL (0.05N) titrated (mL) Produced CO2 (mL HCL)   Produced CO2 (mg)  Cumulative CO2 (mg) Biodegradation (%)* 
  Blank (mean)  Bottle A        
2 47.52 47.00  0.52

0.6

0.6 

1

 5

45.56

45.86

0.00

0.0

0.6

1

 7

45.46

45.66

0.00

0.0

0.6

1

 9

45.98

45.86

0.12

0.1

0.7 

1

 14

46.25

45.23

1.02

1.1

1.8

 19

44.12

38.23

5.89

6.5

8.3

10

 23

44.38

35.56

8.82

9.7

18.0

21

 27

 45.77

39.96

5.81

6.4

24.4

28

 29

45.15

43.68

1.47

1.6 

26.0

30

 29

 46.91

47.15

0.00

0.0 

26.0

30

 29  48.24 48.66 0.00 0.0 26.0 30

*= Calculated as the ratio between CO2 produced (cumulative) and the ThCO2 of the test item: 86.2 mg CO2/2L

Table 2 : CO2 production and percentage biodegradation of the test item (bottle B)

 Day  HCL (0.05N) titrated (mL)   HCL (0.05N) titrated (mL) Produced CO2 (mL HCL)   Produced CO2 (mg)  Cumulative CO2 (mg) Biodegradation (%)* 
  Blank (mean)  Bottle B        
2 47.52  47.56  0.00

0.0

0.0 

0

 5

45.56

45.45

0.11

0.1

0.1

0

 7

45.46

44.53

0.93

1.0

1.1

1

 9

45.98

45.93

0.05

0.1

1.2

1

 14

46.25

44.68

1.57

1.7

2.9

3

 19

 44.12

29.48

14.64

16.1

19.0

21

 23

44.38

37.28

7.10

7.8

26.8

30

 27

 45.77

41.41

4.36

4.8

31.6

36

 29

45.15

42.86

2.29

2.5

34.1

38

 29

46.91

46.76

0.15

0.2

34.3

39

 29 48.24 48.23 0.01 0.0 34.3 39

*Calculated as the ratio between CO2 produced (cumulative) and the ThCO2 of the test item: 88.9 mg CO2/2L

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
Ready biodegradation values of 30 and 39% were obtained for the test substance in 29 days using an appropriate test procedure. Since at least 60% biodegradation was not reached within 10 days immediately following the attainment of 10% biodegradation (10-day window), the criterion for ready biodegradability was not met. Thus, under the conditions of this test 1-methyl-N,N’,N’’-tris(1-methylpropyl)silantriamine was not readily biodegradable.

Description of key information

Biodegradation in water: screening tests: 30% and 39% in 29 days (OECD 301B), read-across from a structurally-related substance.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

There are no reliable ready biodegradation data available for the submission substance, 1-dimethyl-N,N'-bis(1-methylpropyl)silanediamine (CAS No. 93777-98-1), therefore good quality data for the structurally-related substance, 1-methyl-N,N',N''-tris(1-methylpropyl)silanetriamine (CAS No. 37697-65-7), have been read across. The read-across is based on structural similarities between the source and target substance and similarities in their physicochemical properties.

 

1-Methyl-N,N',N''-tris(1-methylpropyl)silanetriamine (CAS No. 37697-65-7) and 1-dimethyl-N,N'-bis(1-methylpropyl)silanediamine (CAS No. 93777-98-1) are structurally-similar substances. Both are silyl amines (Si-N) with 1-methylpropylamine and methyl groups bound to silicon. The difference between the two substances is that the target substance has two 1-methylpropylamine groups and two methyl groups bound to the silicon, whereas the source substance has three 1-methylpropylamine groups and one methyl group bound to the silicon.

 

The purity of both substances is similar, 97% and 98.9% for the source and target substance respectively. Both substances possess similar physicochemical properties including very rapid hydrolysis in contact with water.  The hydrolysis products for the target substance are sec-butylamine (1-methylpropylamine; 2 moles) and dimethylsilanediol (1 mole). The hydrolysis products for the source substance are sec-butylamine (1-methylpropylamine; 3 moles) and methylsilanetriol (1 mole). Therefore, the two substances have the same non-silicon hydrolysis product, but the target substance produces 2 moles per mole of parent substance and the source substance 3 moles. The silanol hydrolysis products are structurally similar.

 

The silanol hydrolysis products, dimethylsilanediol and methylsilanetriol, are both low molecular weight silanols with two or three silanol groups (Si-OH) and one or two methyl groups at the silicon centre. No significant biodegradation is expected for the silanol hydrolysis products, methylsilanetriol and dimethylsilanediol.

 

A comparison of the key physicochemical properties is presented in the table below.

 

Property

Source substance

Target substance

Silanol hydrolysis product source substance

Silanol hydrolysis product target substance

1-Methyl-N,N',N''-tris(1-methylpropyl)silanetriamine (CAS No. 37697-65-7)

1-Dimethyl-N,N'-bis(1-methylpropyl)silanediamine (CAS No. 93777-98-1)

Methylsianetriol

Dimethylsilanediol

Molecular weight (g/mol)

259.5

202.41

94.14

92.17

log Kow

Not relevant due to very rapid hydrolysis

Not relevant due to very rapid hydrolysis

-2.4

-0.4

Water solubility (mg/L)

Not relevant due to very rapid hydrolysis

Not relevant due to very rapid hydrolysis

1.0E+06 at 20°C

1.0E+06 at 20°C

Vapour pressure (Pa)

2.9 at 20°C

6 at 20°C

0.053 at 25°C

7 at 25°C

Hydrolysis half-life (25°C) and pH 7

<2 minutes

<2 minutes

Not relevant

Not relevant

 

In the study with 1-methyl-N,N',N''-tris(1-methylpropyl)silanetriamine (CAS No. 37697-65-7), 30% and 39% (OECD 301B) biodegradation was observed in 28 days. 1-Methyl-N,N',N''-tris(1-methylpropyl)silanetriamine (CAS No. 37697-65-7) hydrolyses within the timescale of the ready biodegradation study to form methylsilanetriol and sec-butylamine. The read-across substance has three amine groups (92% of the substance by number of carbons, 85% of the substance by weight), whereas the target substance has two amine groups (80% of the substance by number of carbons, 72% of the substance by weight). So less biodegradation is expected in a study with the target substance than is seen in the read-across study. The biodegradation observed in the study is attributable to the biodegradation of the sec-butylamine hydrolysis product. This is consistent with the expectation that significant biodegradation is not expected for the silanol hydrolysis product.

 

A 100 mg/L concentration of sec-butylamine was reported to attain >60% and 70% theoretical BOD after 10 and 28 days respectively in an aerobic screening study in the presence of activated sludge (Painter 1985).

 

Reference:

Painter HA, King EF; Assessment of Biodegradability of Chemicals in Water by Manometric Respirometry. Ring Test Program 1983-1984. Comm Eur Communities, Eur 9962, pp. 105 (1985)