1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane

Toxicity to microorganisms

Description of key information

Toxicity to microorganisms: EC50 >1000 mg/l (ASRI), read-across from a structurally-related substance.

Additional information

There are no reliable microorganism toxicity data available for 1,1,1,3,5,5,5-heptamethyl-3-octyltrisiloxane, therefore good quality data for the structurally-related substance, 3-hexyl heptamethyltrisiloxane (CAS 1873-90-1) have been read-across as key data.

A category approach is applied to this endpoint and is detailed in the Siloxane Category report (PFA, 2017at). The hypothesis for read-across is that siloxane substances exhibit no evidence of significant toxicity to sewage treatment plant microorganisms. This is consistent with a non-polar narcosis mode of action.

1,1,1,3,5,5,5 -Heptamethyl-3-octyltrisiloxane and 3-hexyl heptamethyltrisiloxane are members of the Reconsile Siloxanes Category within which, in general, the substances exhibit no evidence of significant toxicity to microorganisms.

The table below presents microorganism toxicity data available for substances within the Siloxanes Category.

It is therefore considered valid to read-across the results for 3-hexyl heptamethyltrisiloxane to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2017at) attached in Section 13.

Table: Microorganism toxicity data for substances within the Reconsile Siloxanes Category

CAS	Name	Result: E(I)C50	Result: NOEC (or EC10/ EC20)	Guideline Number	Duration	Reliability
540-97-6	Dodecamethylcyclohexasiloxane	>100 mg/l		OECD 209	3hr	1
541-05-9	Hexamethylcyclotrisiloxane	>100 mg/l	>100 mg/l	OECD 209	3hr	1
541-02-6	Decamethylcyclopentasiloxane	>2000 mg/l		C11	3hr	1
556-67-2	Octamethylcyclotetrasiloxane	>10 000 mg/l		ISO 8192 (Test for Inhibition of Oxygen Consumption by Activated Sludge)	3hr	4 (WOE)
556-67-2	Octamethylcyclotetrasiloxane	little or no toxicity (24 h): 0.1 g/g solution test mat. based on: reduction in number of viable bacteria		Toxicity toEscherichia coliandStaphylococcus aureusat 37°C for 24 hours	24hr	4 (WOE)
107-46-0	Hexamethyldisiloxane	>100 mg/l	≥100 mg/l	OECD 209	3hr	1
141-62-8	Decamethyltetrasiloxane	>100 mg/l		OECD 209	3hr	1
352230-22-9	Siloxanes and Silicones, di-Ph, Ph (trimethylsilyl)oxy	>1000 mg/l	≥1000 mg/l	OECD 209	3hr	1
2627-95-4	1,1,3,3 -Tetramethyl-1,3-divinyldisiloxane	>1000 mg/l	≥1000 mg/l Nitrification control indicated no heterotrophic inhibition of respiration rate	OECD 209	3hr	1
2554-06-5	2,4,6,8 -Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane	>1000 mg/l	≥1000 mg/l Nitrification control indicated no heterotrophic inhibition of respiration rate	OECD 209	3hr	1
70131-69-0	Silsesquioxanes, Phenyl	>1000 mg/l	≥1000 mg/l Nitrification control indicated no heterotrophic inhibition of respiration rate	OECD 209	3 h	1
99363-37-8	Dimethyl, methyl(3-aminopropyl) siloxane, trimethylsiloxy-terminated	> water soluble fraction	≥ water soluble fraction	OECD 209	3hr	1
71750-79-3	Dimethyl, (aminoethylaminopropyl)methyl siloxane, trimethylsiloxy-terminated	> water soluble fraction	≥ water soluble fraction	OECD 209	3hr	1
1873 -90 -1	3 -hexyl heptamethyltrisiloxane	>1000 mg/l		OECD 209	3 hr	1

In the study with 3-hexyl heptamethyltrisiloxane, an activated sludge respiration inhibition 3h EC₅₀ value of >1000 mg/l was reported.

Reference:

Peter Fisk Associates (2017at), Peter Fisk Associates. Siloxane Category Report for Environmental Endpoints. Owner company: Reconsile. Report number: 404.114.001. Report date: 2017-06-02