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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1997-01-23 to 1997-02-10
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: EC Guideline: 88/302/EC (30.5.1988)
GLP compliance:
yes
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Activated sludge from Marl-West (Lippeverband) sewage treatment plant. Suspended solids: 2.75 g/l activated sludge
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Test temperature:
At the beginning of incubation 18 - 19.5 °C

During the determination of oxygen content 19.2 - 20 °C
Nominal and measured concentrations:
Nominal concentrations: 180, 240, 300, 360, 420 mg/L
Details on test conditions:
Test substance, synthetic sewage (16 mL), inoculum (200 mL). Total volume 500 ml.
Reference substance (positive control):
yes
Remarks:
3, 5, Dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
400 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Key result
Duration:
3 h
Dose descriptor:
EC10
Effect conc.:
197 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration

Table 1 % inhibition

Substance ID / Conc.

Time period of O2 measurement (minutes)

Start value mg O2/L

End value mg O2/L

Mg O2/L*h

% Inhibition

pH before O2 Measurement

CPMDCS

480 mg/L

7.5

8.21

7.17

8.32

69.2

6.3

CPMDCS 360 mg/L

7

6.92

5.1

15.6

42.2

7

CPMDCS 300 mg/L

8

7.21

4.43

20.85

22.8

7.3

CPMDCS 240 mg/L

8

6.91

3.9

22.58

16.4

7.4

CPMDCS 180 mg/L

7

7.01

4.14

24.6

8.9

7.7

DCP 5 mg/L

8

7.87

5.89

14.85

45

8.5

DCP 15 mg/L

7.5

8.41

7.29

8.96

66.8

8.5

DCP 30 mg/L

7.5

8.72

8.03

5.52

79.6

8.5

Control RC1

6.5

7.67

4.83

26.22

8.4

Control RC2

6.5

7.63

4.62

27.78

8.3

Sum RC1+ RC2

54

 

Validity criteria fulfilled:
yes
Conclusions:
An activated sludge respiration inhibition 3hr EC50 value of 400 mg/L and EC10 value of 197 mg/L were determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

REVIEWER’S ATTENTION

The study available currently is based on a 5 hour Putida test data which has used an emulsifier and shorter test period compared to that stated in the guidance. To complete this endpoint, interim read-across has been made from CAS 7787-93-1 as an interim measure. It has been proposed to conduct a reliable ASRI study using the triethoxy analogue, CAS 5089-70-3. Therefore, this endpoint will be revisited when the result of that study becomes available.

Toxicity to microorganisms: ASRI 3 hour EC50 400 mg/L and EC10 197 mg/L (ASRI), read-across from an analogous substance.

Key value for chemical safety assessment

EC50 for microorganisms:
400 mg/L
EC10 or NOEC for microorganisms:
197 mg/L

Additional information

An activated sludge respiration inhibition 5 hour EC10 value of 1.1 ml/L (equivalent to 1.2 g/L based on a density of 1.05 g/cm3, Pseudomonas putida) based on oxygen consumption/respiration inhibition was determined for the substance using a relevant test method and in compliance with GLP (Schoberl 1993). The result is considered to be reliable but is not used as key study because (i) the study is a 5 hour study instead of the recommended 16 hour growth inhibition type test recommended in ISO 10712 Test Method (ii) the study uses an emulsifier - nonylphenol ethoxylate to improve solubility of the test substance and (iii) no reference substance was used during the study.

A second result is available for the registered substance in a secondary source to which reliability cannot be assigned; a bacterial respiration inhibition value of >1000 mg/L was reported for the substance (Dow Corning Corporation, year not reported).

Therefore good quality data for the analogous substance dichloro(3-chloropropyl)methylsilane (CAS 7787-93-1), have been read across. The submission substance, (3-chloropropyl)trimethoxysilane, hydrolyses rapidly in contact with water to form (3-chloropropyl)silanetriol and methanol. The read-across substance, dichloro(3-chloropropyl)methylsilane hydrolyses very rapidly in contact with water to form 3-chloropropyl(methyl)silanediol and hydrochloric acid. Both substances hydrolyse rapidly and share a similar silanol hydrolysis product; (3-chloropropyl)silanetriol and 3-chloropropyl(methyl)silanediol. In view of the rapid hydrolysis of the registered substance, it is the silanol hydrolysis product that is relevant for environmental risk assessment.

Methanol does not have adverse effects on microorganisms (OECD 2004).

Hydrochloric acid is not expected to have adverse effects on microorganisms in a sewage treatment plant, where the pH is maintained within a favourable range.

(3-Chloropropyl)trimethoxysilane and dichloro(3-chloropropyl)methylsilane are within an analogue group of substances that exhibit some evidence of toxicity to microorganisms.

This group consists of substances containing a number of different functional groups but specific read-across is between substances with similar functionality. (3-Chloropropyl)trimethoxysilane and dichloro(3-chloropropyl)methylsilane are members of this group.

The table below presents microorganism toxicity data for substances relevant to (3-chloropropyl)trimethoxysilane (CAS 2530-87-2).

It is considered valid to read-across the results for dichloro(3-chloropropyl)methylsilane (CAS 7787-93-1) to fill the data gap for the registered substance since the source and target substances generate similar silanol hydrolysis product. Additional information is given in a supporting report (PFA 2013j) attached in IUCLID Section 13.

Table: Microorganism toxicity data for relevant substances

CAS

Name

Result: E(I)C50 (mg/L)

Result: NOEC (or EC10/ EC20) (mg/L)

Guideline Number

Test method

Species

Duration (hours)

Reliability

7787-93-1

Dichloro(3-chloropropyl)methylsilane

400

 

88/302/EC

ASRI

 

3

1

2530-87-2

3-Chloropropyl(trimethoxy)silane

 

EC10 1.1 ml/l
Note: WS predicted 14000

Huls method

oxygen consumption

P. putida

5

2

5089-70-3

3-Chloropropyl(triethoxy)silane

 

EC10 >2 ml/l

Huls method

oxygen consumption

P putida

5

2

15267-95-5

3-Chloromethyl(triethoxy)silane

>1000

≥1000 mg/l

OECD 209

ASRI

 

3

1

In the study with dichloro(3-chloropropyl)methylsilane (CAS 7787-93-1), an activated sludge respiration inhibition 3 hour EC50 value of 400 mg/L and EC10 value of 197 mg/L were obtained.

References:

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1

PFA (2013j). Peter Fisk Associates, STP Microorganism toxicity Main Analogue Group report, PFA.300.003.006