Tetraethyl orthosilicate

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:

From 1992-10-27 to 1993-11-24

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.4-A (Determination of the "Ready" Biodegradability - Dissolved Organic Carbon (DOC) Die-Away Test)

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Details on inoculum:

- Source of inoculum/activated sludge: Living slime from a primarily communal sewage treatment plant (Marl - East). Collected 10/27/92.

- Preparation of inoculum for exposure: Washed, re-suspended in mineral medium

- Initial cell/biomass concentration: 5.17 g dry weight per litre

Duration of test (contact time):

28 d

Initial conc.:

9.6 mg/L

Based on:

DOC

Initial conc.:

1 000 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

DOC removal

Details on study design:

TEST CONDITIONS
- Test temperature: 21.8 - 22.1°C

- Suspended solids concentration: 25.9 g/ml

- Continuous darkness: yes



TEST SYSTEM
- Culturing apparatus: 2000 ml Erlenmeyer flasks with loose closure of aluminium foil.

- Number of culture flasks/concentration: Two test substance (9.6 mg DOC/l); Two control (9.71 mg DOC/l)


SAMPLING
- Sampling frequency: 0, 7, 14, 21, 27 and 28 d.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

% degradation (DOC removal)

Value:

98

Sampling time:

28 d

Details on results:

The degree of biodegradation exceeded 70% within a 10 day window.

The positive control substance, sodium benzoate, achieved a biodegradation rate of 99% within 28 days.

Table 1: Dissolved organic carbon levels (mg/l) and calculated % DOC reduction

Type of suspension	0		7		14		21		27		28
	DOC (mg/l)	DOC reduction (%)	DOC (mg/l)	DOC reduction (%)	DOC (mg/l)	DOC reduction (%)	DOC (mg/l)	DOC reduction (%)	DOC (mg/l)	DOC reduction (%)	DOC (mg/l)	DOC reduction (%)
Test sample Replicate 1	10.32	0	1.37	94	0.80	98	0.76	96	0.82	98	0.72	98
Test sample Replicate 2	9.85	0	1.40	93	0.66	99	0.84	95	0.77	98	0.68	98
Median value		0		93		98		96		98		98
Blank Replicate 1	0.53		0.76		0.57		0.41		0.62		0.50
Reference substance Replicate 1	10.06	0	0.91	98	0.75	98	0.95	94	0.73	99	0.64	98
Reference substance Replicate 2	10.42	0	0.86	99	0.52	101	0.86	95	0.68	99	0.61	99

 

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

A biodegradation rate of 98% was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP. The substance may be considered readily biodegradable.

Description of key information

Biodegradation in water: screening tests: 98% degradation (DOC removal) in 28 days (EU C.4-A); biodegradation is not relevant for silicic acid being inorganic. Ethanol is readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

A biodegradation of 98% in 28 days (DOC removal) was determined for the submission substance in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP (EU C.4-A) (Evonik 1993).

Tetraethyl orthosilicate (CAS 78-10-4; EC No. 201-083-8) hydrolyses rapidly (t_1/2 = 4.4 h at pH 7 and 25°C) in contact with water to form monosilicic acid (CAS 10193-36-9; EC No. 233-477-0) and ethanol (CAS 64-17-5; EC No. 200-578-6).

The biodegradation observed in the study is attributable to the biodegradation of the ethanol hydrolysis product which is readily biodegradable.

Biodegradation is not relevant for silicic acid as it is inorganic. Monosilicic acid exists only in dilute aqueous solutions and readily condenses at concentrations above approximately 100-150 mg/L as SiO₂ to give a dynamic equilibrium between monomer, oligomers and insoluble polysilicic acid. These are naturally-occurring inorganic substances and degradation studies are not relevant. The silanol hydrolysis products will enter the natural biogeochemical cycle for silicon.

Ethanol is readily biodegradable (OECD 2004).

Reference:

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.