Silicic acid (H4SiO4), tetraethyl ester, reaction products with bis(acetyloxy)dioctylstannane

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:

08 Dec 2011

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 (Carbon and Ammonium Oxidation))

Version / remarks:

July 2010

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

May 2008

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Version / remarks:

2007

GLP compliance:

yes (incl. QA statement)

Remarks:

Food and Consumer Product Safety Authority (VWA), Utrecht, The Netherlands

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: The test substance was not completely soluble in test medium at the loading rates initially prepared. Therefore, 1 L test bottles were filled with 200 mL of test substance mixtures in Milli-RO water (tap water purified by reverse osmosis) with initial loading rates of 2.5 times the final loading rate. These mixtures were stirred in closed dark brown bottles for 25.5 h. Subsequently, 16 mL synthetic sewage feed, 250 mL sludge and Milli-RO water up to 500 mL were added resulting in the required loading rates. Optimal contact between the test substance and test organisms was ensured applying continuous aeration and stirring.
- Eluate: no
- Differential loading: yes
- Controls: yes, test medium control

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Laboratory culture: no
- Name and location of sewage treatment plant where inoculum was collected: Municipal sewage treatment plant "Waterschap Aa en Maas", 's-Hertogenbosch, The Netherlands
- Pretreatment: The sludge was coarsely sieved, washed and diluted with ISO-medium. A small amount of the sludge was weighed and dried overnight at ca. 105 °C to determine the amount of suspended solids (3.0 g/L of sludge, as used for the test). The pH was 7.6 on the day of testing. The batch of sludge was used one day after collection; therefore 50 mL of synthetic sewage feed was added per liter of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

19.2 - 20.8 °C

pH:

7.5 - 7.8 (start of exposure)
7.6 - 8.5 (end of exposure)

Dissolved oxygen:

approx. 7.9 - 9.0 mg O2/L

Nominal and measured concentrations:

nominal: 10, 100, 1000 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: All-glass bottles
- Material, size, headspace, fill volume: all-glass, 1 L, headspace: 750 mL, fill volume: 500 mL
- Aeration: yes, clean oil-free air
- No. of vessels per concentration (replicates): 1 (10 and 100 mg/L), 3 (1000 mg/L)
- No. of vessels per control (replicates): 6
- No. of vessels per abiotic control (replicates): 1
- No. of vessels per procedure control (reference substance): 3
- Sludge concentration (weight of dry solids per volume): 1.5 g/L
- Nutrients provided for bacteria: synthetic sewage
- Nitrification inhibitor used: yes, N-allylthiourea
- Test set-up: The synthetic sewage feed (16 mL) and an adequate amount of the test substance loading were mixed and made up to 250 mL with Milli-RO water in a 1 L bottle. Thereafter 250 mL activated sludge was added.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Tap-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges.

OTHER TEST CONDITIONS
- Adjustment of pH: no

EFFECT PARAMETERS MEASURED
- Respiration rate. After the 3 h contact time, the oxygen consumption was recorded for a period of 10 to 18 min. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10

Reference substance (positive control):

yes

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

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

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: EC50 (3 h): 8.2 mg/L

Reported statistics and error estimates:

Two Sample t-Test, alpha=0.05, Toxstat.

In the combined limit/range-finding test no statistically significant inhibition of the respiration rate of the sludge was recorded at a loading rate of 1000 mg/L. Furthermore, there was no oxygen uptake from abiotic processes and no inhibition of the respiration rate was observed at a loading rate of 1000 mg/L with a nitrification inhibitor.

Table 1: Respiration rate and inhibition of respiration

Flask	Loading rate [mg/L]	Respiration rate [mg O2/L h]	% inhibition of respiration rate relative to the control (mean value)
C1	0	43
C2	0	40
C3	0	45
C4	0	45
C5	0	42
C6	0	46
Mean		44
SD		2
CV [%]		5
CN (+ATU)	0	26
R1	5.0	26	40
R2	12	19	56
R3	30	8	82
T1	10	37	15
T2	100	39	10
T3a	1000	54	-24
T3b	1000	51	-17
T3c	1000	53	-22
T3 mean		53	-21
TA (abiotic)	1000	0	100
TN (+ATU)	1000	43	-65¹

C: Blank Control

CN: Nitrification control

R: Reference substance, 3,5-dichlorophenol

T: Test substance

CV: Coefficient of variation

ATU: N-allylthiourea

TA: Abiotic control of test substance.

TN: Test substance with ATU.

¹ Relative to CN

Validity criteria fulfilled:

yes

Description of key information

NOEC (3 h) ≥ 1000 mg/L (nominal, OECD 209)

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

One experimental study is available investigating the effects of the substance to activated sludge microorganisms. The study was performed according to OECD 209 (GLP). Activated sludge from a predominantly domestic sewage treatment plant was exposed to the test substance at concentrations of 10, 100 and 1000 mg/L. No inhibition of total respiration was recorded after 3 h resulting in a NOEC (3 h) of ≥ 1000 mg/L. Thus, the degradation process in sewage treatment plants is not considered to be inhibited by the substance.