1,3-bis(trimethylsilyl)urea

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:

08 Jul - 06 Aug 2019

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Version / remarks:

1992

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Version / remarks:

440/2008

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.3110 (Ready Biodegradability)

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum: Severn Trent Water Plc sewage treatment plant, Loughborough, Leicestershire, UK; final effluent stage (08 Jul 2019)
- Laboratory culture: No
- Pretreatment: Filtration through coarse filter paper (first approximate 200 mL discarded)
- Storage conditions: Aerated in a temperature controlled room at 21 °C
- Storage length: < 1 d (inoculum was obtained on same day as test start)

Duration of test (contact time):

28 d

Initial conc.:

100 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: Mineral medium according to OECD guidelines
- Solubilising agent: The test item was dissolved in dimethylformamide (auxiliary solvent) prior to adsorption onto filter paper (Whatman GF/A, 70 mm diameter). High shear mixing was applied to break up the filter paper to evenly distribute the test item and increase the surface area of test item exposed to the test organisms.
- Test temperature: 21 ± 1 °C (temperature controlled water bath)
- pH: 7.3 - 7.4 (Day 0) and 7.6 - 8.2 (Day 28)
- pH adjusted: No
- Continuous darkness: No, diffuse light
- Other: A filter paper (Whatman GF/A, 70 mm diameter) was added to each inoculum control vessel in order to maintain consistency between the test and control vessels.

TEST SYSTEM
- Culturing apparatus: Amber glass bottles containing a final volume of 500 mL
- Number of culture flasks/concentration: 3 (test item and inoculum control); 2 (procedure control and toxicity control)
- Method used to create aerobic conditions: The samples were stirred for the duration of the test with a magnetically coupled stirrer.
- Measuring equipment: CES Multi-Channel Aerobic Respirometer
- Test performed in closed vessels due to significant volatility of test substance: Yes
- Test performed in open system: No, the sample flasks were sealed by a sensor head/CO2 trap
- Details of trap for CO2: CO2 was absorbed into an ethanolamine solution (50% v/v) causing a net reduction in gas pressure within the sample flask. 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.
- Other: All vessels were inoculated with the prepared inoculum at a rate of 1% v/v.

SAMPLING
- Sampling frequency: Biological Oxygen Demand was measured daily.
- Sampling method: The data generated from the respirometer's own battery backed memory was collected on the hard drive of a non-dedicated computer.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Inoculated mineral medium + filter paper (3 replicates)
- Procedure control: Inoculated mineral medium + reference item (aniline) (2 replicates)
- Toxicity control: Inoculated mineral medium + test item on filter paper + reference item (2 replicates)
- Test item: Inoculated mineral medium + test item on filter paper (3 replicates)
- Other: A filter paper was added to each vessel in order to maintain consistency between the test and procedure control vessels. The solvent DMF (with and without test item) was dispensed onto each filter paper and evaporated to dryness for approximately 30 min.

STATISTICAL METHODS:
A Students t-test was performed on the Day 28 BOD values for the control and test item vessels. All analyses were performed using the SAS computer software package (SAS 1999 - 2001).

Reference substance:

aniline

Parameter:

% degradation (O2 consumption)

Remarks:

Biological Oxygen Demand

Value:

0

Sampling time:

28 d

Results with reference substance:

Aniline (procedure control) attained 63% biodegradation after 14 d in a 10-d window and 68% biodegradation after 28 d.

BIOLOGICAL RESULTS

Table 1. Biological Oxygen Demand Values

Day	BOD (mg O2/L)
	Inoculum Control		Procedure Control	Test Item		Toxicity Control
	R1	R2		R1	R2
0	0.00	0.00	0.00	0.00	0.00	0.00
1	1.50	1.38	1.92	2.16	2.00	2.16
2	2.20	2.54	2.92	3.24	3.16	3.04
3	3.24	3.88	4.74	4.16	4.08	4.24
4	5.08	5.24	16.46	5.54	5.42	5.74
5	5.54	5.74	72.30	6.00	5.88	15.16
6	7.16	7.46	132.28	7.12	7.28	95.46
7	7.84	8.28	179.38	7.70	7.88	160.02
8	8.24	8.74	187.68	7.96	8.20	171.80
9	8.92	9.46	192.46	8.70	8.96	176.68
10	10.04	10.62	196.30	9.96	10.12	180.42
11	10.04	10.70	198.38	9.96	10.16	182.22
12	10.46	11.42	202.58	10.74	11.00	185.60
13	11.16	11.96	204.80	11.00	11.38	187.34
14	11.50	12.24	208.04	11.38	11.70	189.96
15	12.28	12.54	210.00	11.54	11.88	195.64
16	12.82	13.28	213.12	12.42	12.66	198.08
17	13.42	13.54	214.84	12.50	12.82	199.18
18	14.16	14.50	217.58	13.78	13.78	201.50
19	15.04	15.62	219.66	14.96	14.86	203.42
20	16.08	16.58	221.36	15.82	15.82	204.92
21	17.24	17.62	222.62	16.74	16.78	206.12
22	17.24	17.62	223.20	17.08	16.78	207.00
23	17.36	18.04	224.42	17.90	17.24	208.12
24	17.70	18.50	225.40	18.54	17.74	208.88
25	18.20	19.16	226.54	19.28	18.36	209.80
26	18.28	19.16	226.86	19.32	18.36	210.16
27	18.74	19.90	228.20	20.12	19.12	211.34
28	19.90	21.04	229.78	21.20	20.28	212.74

VALIDITY CRITERIA

The validity criteria were met (Table 2).

Table 2: Validity criteria for OECD 301.

Criterion from the guideline	Outcome	Validity criterion fulfilled
Difference of extremes of replicate values of the removal of the test chemical at the end of the 10-d window is less than 20%.	The difference between extremes of replicate BOD values at the end of the 10-d window was < 20%.	Yes
Percentage degradation of the reference compound reached the pass level by day 14 (≥ 60%).	Aniline attained 63% biodegradation after 14 d in a 10-d window.	Yes
The toxicity control should degrade to at least 25% (based on ThOD or ThCO2) within 14 d.	The toxicity control attained 34% biodegradation after 14 d and 36% after 28 d thereby confirming that the test item was not toxic to the sewage treatment microorganisms used in the test.	Yes
The oxygen uptake of the inoculum blank is normally 20-30 mg O2/L and should not be greater than 60 mg/L in 28 days.	The mean BOD of the inoculated mineral medium (control) was 20.47 mg O2/L after 28 d.	Yes

Validity criteria fulfilled:

yes

Remarks:

See Table 2 in "Any other information on results incl. tables"

Interpretation of results:

not readily biodegradable

Description of key information

Not readily biodegradable (0% in 28 d, OECD 301 F)

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater

Additional information

One experimental study is available for the biodegradation of 1,3-bis(trimethylsilyl)urea (CAS No. 18297-63-7), which was conducted according to OECD guideline 301 F.

In a manometric respirometry test a nominal concentration of 100 mg/L test item was exposed to sewage treatment microorganisms in mineral medium and sealed culture vessels under diffuse light at 21 ± 1 °C for 28 d.

Due to the low solubility of the substance, the standard test item preparation method was modified following the recommendations of the International Standards Organisation (ISO 1995) and published literature (Handley et al., 2002). First, a solvent stock solution (1000 mg test item/10 mL) was prepared by dissolving 1000 mg test item in 10 mL dimethylformamide (DMF), with the aid of ultrasonication for approximately 15 min. Then, an aliquot (500 µL) of this solvent stock was dispensed onto a filter paper (Whatman GF/A, 70 mm diameter) and the solvent was allowed to evaporate to dryness for approximately 30 min. The filter paper was dispersed in approximately 350 mL of mineral medium with the aid of high shear mixing (approximately 7500 rpm, 15 min) prior to addition of inoculum (5 mL). The volume was than adjusted to 500 mL to give the final concentration of 100 mg/L. This method allowed for an even distribution of the test item throughout the test medium and increased the surface area of test item exposed to the test organisms, thereby increasing the potential for biodegradation. No analysis was conducted to determine the homogeneity, concentration or stability of the test item as it was not a requirement of the test guidelines.

An inoculum, procedure and toxicity control were run in parallel. All vessels were inoculated at a rate of 1% v/v. A filter paper (with or without test item, as applicable) was added to each vessel in order to maintain consistency between the experimental setups.

Biodegradation was assessed by the measurement of the daily oxygen consumption for 28 d using a CES Multi-Channel Aerobic Respirometer. Temperature and pH values were recorded daily.

After 28 d, the test item attained 0% biodegradation. The procedure control confirmed the suitability of the test and the study fulfilled the validity criteria, as defined by the guideline. The toxicity control resulted in 34% biodegradation after 14 d and 36% biodegradation after 28 d, indicating that the test item was not toxic to the sewage treatment microorganisms used in the test.

In conclusion, the obtained result likely reflects the biodegradability of the silanol hydrolysis product trimethylsilanol rather than the biodegradability of the registered (parent) substance 1,3-bis(trimethylsilyl)urea (CAS No. 18297-63-7) itself since the registered substance hydrolyses rapidly (DT50 < 10 min, OECD 111) and the second hydrolysis product, urea, is known to be ultimately biodegradable (OECD SIDS, 2002). Therefore, it is concluded that the silanol hydrolysis product trimethylsilanol is not readily biodegradable according to OECD guideline 301 F.