Silicic acid, aluminum magnesium sodium salt

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-09-15 - 2016-12-07

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

GLP compliance:

yes (incl. QA statement)

Remarks:

Rheinland-Pfalz Landesamt für Umwelt, Wasserwirtschaft und Gewerbeaufsicht

Specific details on test material used for the study:

Name Silicic acid Aluminium Magnesium Sodium Salt
Batch no. code # 1107274003
Appearance white powder
Composition Silic acid Aluminium Magnesium Sodium Salt
CAS No. 12040-43-6
EINECS-No. 234-919-5
Purity > 99 %
Homogeneity homogeneous
Vapour pressure not volatile
Stability stable at room temperature
Solubility poor soluble in water
Production date 2011
Expiry date 01. Nov. 2018
Storage room temperature (20 ± 5 °C), dry

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
Due to the poor solubility of the test item, the test item was weighed directly into the test vessels.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Source: The sludge was taken from the activation basin of the ESN (Stadtentsorgung Neustadt) sewage treatment plant D-67435 NW-Lachen-Speyerdorf.
- Pretreatment: Upon arrival in the test facility, the sludge was filtrated, washed with tap water and re-suspended in tap water. The activated sludge was aerated until usage in the test and fed daily with 50 ml/L synthetic sewage feed.
- Initial biomass concentration: The dry matter was determined as 2.62 g suspended solids/L, giving a concentration of 1.31 g suspended solids/L in the test.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Hardness:

1.08 mmol/L (Analysis of drinking water, Sep 2012)

Test temperature:

20.6 – 21.6 °C

Nominal and measured concentrations:

Nominal: 0, 1, 10, 100 and 1000 mg/L

Reference substance (positive control):

yes

Remarks:

3.5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

- Results with reference substance valid? yes

Results with reference substance (positive control):

3h-EC50 Positive Control: 8.8 mg/L
All values lie within the recommended range of 2 – 25 mg/L.

Reported statistics and error estimates:

For the estimation of the EC50 of the positive control, the fits showed good statistical correspondence of the data with the dose-response-equation. The positive control gave an EC50 of 8.8 mg/L which lie within the recommended range of 2 –25 mg/L. The coefficient of variation of oxygen uptake rate in control replicates was below 30 % at the end of the test. The oxygen uptake rate of the blank controls was above 20 mg O2 per gram activated sludge in 1 hour.
No observations were made which might cause doubts concerning the validity of the study outcome. The result of the test can be considered valid.

Table O2-Consumption, Inhibition

The values of the O2consumption (which is a measure for the viability of the bacteria) of control, test and positive control vessels and the calculated inhibition are presented in the following table. The measured pH at the end of the test is also stated.

Vessel No.	Content	Concentration in mg/L nominal	O2consump- tion in mg/(L*min)	O2consump- tion in mg/(L*h)	Inhibition in %	pH
1	Blank Control	0	0.6416	38.496	0	7.7
2	Blank Control	0	0.6158	36.950	0	7.8
3	Positive Control	5	0.4499	26.992	30.1	7.8
4	Positive Control	10	0.2788	16.726	56.7	7.8
5	Positive Control	20	0.1558	9.347	75.8	7.8
6	Positive Control	40	0.0870	5.222	86.5	7.9
7	Blank Con- trol	0	0.6484	38.904	0	7.7
8	Blank Con- trol	0	0.6317	37.902	0	7.7
9	Test Item	1000	0.6207	37.239	3.5	7.8
10	Test Item	1000	0.6370	38.219	1.0	7.8
11	Test Item	1000	0.6535	39.211	-1.6	7.8
12	Test Item	1000	0.6311	37.869	1.9	7.8
13	Test Item	1000	0.6579	39.477	-2.3	7.8
14	Test Item	100	0.6334	38.005	1.5	7.8
15	Test Item	10	0.6638	39.826	-3.2	7.7
16	Test Item	1	0.6747	40.481	-4.9	7.7
*17-32	*	*	*	*	*	*
33	Blank Con- trol	0	0.6639	39.832	0	7.7
34	Blank Con- trol	0	0.6575	39.449	0	7.7

Validity criteria fulfilled:

yes

Conclusions:

Silicic acid Aluminium Magnesium Sodium Salt did not inhibit respiration of activated sludge significantly.

Description of key information

Silicic acid Aluminium Magnesium Sodium Salt did not inhibit respiration of activated sludge significantly.

Key value for chemical safety assessment

EC50 for microorganisms:

1 000 mg/L

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

Toxicity to microorganisms is not relevant due to physical and chemical similarity of substance to silicates of natural origin resp. soil.

If released to the environment, silicic acid, aluminum magnesium sodium salt combines indistinguishably with the soil or sediment due to their similarity with inorganic soil and sediment matter, and will be subjected to natural processes under environmental conditions (cation exchange, dissolution, sedimentation). Furthermore the amounts released are negligible in comparison to the release by natural deposit or alteration.

Conclusion: Growth of plants is not affected by silica by-products. No hint for harm on soil mircroorganisms is given.