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

Endpoint summary

Description of key information

Reliable short-term toxicity tests results are available for freshwater fish (Pimephales promelas) with the registration substance.

Data for fish, invertebrates (Daphnia magna) and algae are read across from the structural analogues dodecamethylpentasiloxane (L5, CAS 141-63-9), decamethyltetrasiloxane (L4, CAS 141-62-8) and 3-hexyl heptamethyltrisiloxane (CAS 1873-90-1).

The relevant short-term values are:

 

Fish: LC₅₀ (96 h): >110 mg/l. 

Invertebrates: EC₅₀ (48 h): >41 μg/l (read across from 3-hexyl heptamethyltrisiloxane (CAS 1873-90-1)).

Algae: EC₅₀ (72 h): >2.2 μg/l; NOEC of ≥2.2 μg/l (read across from decamethyltetrasiloxane (L4, CAS 141-62-8)).

 

The relevant long-term values are:

Daphnia: EC₅₀ (48 h): >47 ng/l (read across from dodecamethylpentasiloxane (L5, CAS 141-63-9)).

Fish: 60-d post-hatch NOEC ≥7.9 µg/l , hatching, larval survival, abnormal appearance and behaviour in Oncorhynchus mykiss (read-across from decamethyltetrasiloxane (L4, CAS 141-62-8). 

An activated sludge respiration inhibition 3 hour EC₅₀value of >1000 mg/l was determined in a reliable study (read across from 3-hexyl heptamethyltrisiloxane (CAS 1873-90-1).

Additional information

Data are available for short-term toxicity of the registered substance to fish. A 96-hour LC₅₀ value of >110 mg/l has been empirically estimated for effects on mortality of fathead minnow (Pimephales promelas) based on nominal concentrations of the substance in a flow-through test. The presence of undissolved test material in the toxicant delivery system and in the exposure solutions indicated that the concentration range tested exceeded the test material's limit of water solubility. Due to the limited water solubility of the test material under the maintained test conditions, further testing at higher concentrations to establish an LC₅₀ is not practical.

This acute toxicity result was supported by another study done with the same test item on zebra fish (Danio rerio) (limit test, OECD 203, GLP compliant) and for which a 96-hour NOEC value at a concentration of 100 mg/l has been reported.

In addition, short-term toxicity to fish results have been read across from 3-hexyl heptamethyltrisiloxane (CAS 1873 -90 -1) as supporting data.

No effects were observed in a 96-hour study. When the results are expressed using measured concentrations of the saturated solution a 96-hour EC₅₀ value of >49 μg/l was determined for the effects of the test substance on mortality of Lepomis machrochirus, based on geometric mean measured concentrations.

There are no short-term toxicity data with the registered substance for aquatic invertebrates and algae.

Short-term toxicity to invertebrates data are read-across from the structural analogue 3-hexyl heptamethyltrisiloxane (CAS 1873-90-1). No effects were observed in a 48-hour study conducted with Daphnia magna. When the results are expressed using measured concentrations of the WAF, a 48-hour EC₅₀ value of >41 μg/l was determined for the effects of the test substance on mobility of Daphnia magna, based on geometric mean measured concentrations.

 

Algal toxicity data are also read across from 3-hexyl heptamethyltrisiloxane (CAS 1873 -90 -1). A 72-hour ErC₅₀ value of >21.6 μg/l and NOEC of ≥21.6 μg/l (>LoS) (highest concentration tested) have been determined for the effects of 3-hexyl heptamethyltrisiloxane on growth rate of Selenastrum capricornutum, expressed relative to geometric mean measured concentrations.

 

Long-term toxicity to fish data are available with the structural analogue, decamethyltetrasiloxane (L4, CAS 141-62-8). A 60-d post-hatch NOEC of ≥7.9 µg/l (time weighted mean measured) has been determined for the effects of L4 on hatching, larval survival, abnormal appearance and behaviour of Oncorhynchus mykiss.

Long-term toxicity data for invertebrates have been read across from the structural analogue dodecamethylpentasiloxane (L5, CAS 141-63-9). No effects were seen in the long-term study, up to the limit of solubility: A 21-day EC₅₀ of >47 ng/l and NOEC of ≥47 ng/l (mean measured concentrations) have been determined for the effects of L5 on adult mortality, reproduction and growth of Daphnia magna.

 

There are no reliable data available for toxicity to microorganisms for the registration substance. A 3 hour EC₅₀value of >1000 mg/l (ASRI) is read-across from the structurally-related substance 3-hexyl heptamethyltrisiloxane (CAS 1873-90-1).