Tetradecamethylhexasiloxane

Endpoint summary

Additional information

There are no reliable aquatic toxicity data available for tetradecamethylhexasiloxane (L6, CAS 107-52-8) therefore good quality data for the structurally-related substances decamethyltetrasiloxane (L4, CAS 141-62-8) and dodecamethylpentasiloxane (L5, CAS 141-63-9) have been read across.

Reliable short-term toxicity test results are available for freshwater fish (Oncorhynchus mykiss) read across from dodecamethylpentasiloxane (L5, CAS 141-63-9) and decamethyltetrasiloxane (L4, 141-62-8). The relevant short-term values are:

KEY: Fish: LC₅₀ (96 h): >75 ng/l (0.000075 mg/l); NOEC ≥75 ng/l (0.000075 mg/l) based on geometric mean measured concentrations, read across from L5.

Supporting: Fish: LC₅₀ (96 h): >6.3 μg/l (>0.0063 mg/l) and NOEC of ≥6.3 μg/L (>= 0.0063 mg/l) based on geometric mean measured concentrations, read across from L4.

The requirement for conducting a short-term test with Daphnia has been waived on the basis that there are reliable read-across long-term toxicity data available with invertebrates.

A reliable toxicity test result is available for algae (Pseudokirchneriella subcapitata) read-across from decamethyltetrasiloxane (L4, CAS 141-62-8). The relevant short-term values are:

Algae: EC₅₀ (72 h): >2.2 μg/l (>0.0022 mg/l); NOEC: ≥2.2 μg/l (≥0.0022 mg/l) determined for the effects of decamethyltetrasiloxane on growth rate of the freshwater algae Pseudokirchneriella subcapitata, based on geometric mean measured concentrations.

A reliable long-term toxicity test result is available for freshwater fish (Oncorhynchus mykiss) read across from decamethyltetrasiloxane (L4, CAS 141-62-8) . The relevant long-term value is:

Fish: NOEC (60 d): ≥79 µg/l (≥0.0079 mg/l) determined for the effects of L4 (CAS 141-62-8) on hatching, larval survival, abnormal appearance and behaviour of Oncorhynchus mykiss, based on time weighted mean measured concentrations.

A reliable long-term toxicity test results is available for freshwater invertebrates (Daphnia magna) read across from dodecamethylpentasiloxane (L5, CAS 141-63-9). The relevant long-term value is:

Invertebrates: EC₅₀ (21 d): >47 ng/l (0.000047 mg/l) and NOEC of ≥47 ng/l (0.000047 mg/l) have been determined for the effects of L5 on adult mortality, reproduction and growth of Daphnia magna. The data have been obtained in flow-through tests and are expressed relative to mean measured concentrations of the substance.

These concentrations were measured in test media prepared at a nominal concentration that corresponded with the water solubility of the substance (70 ng/l). It is thought that the low water solubility and high log K_owof siloxanes with slow hydrolysis limits the bioavailability in aquatic studies and toxicity is not expressed. The studies with the majority of the substances indicate that no effects at the limit of solubility are detectable.

There are no reliable data available for toxicity to microorganisms.

An activated sludge respiration inhibition 3hr EC₅₀ value of >100 mg/l (nominal) was determined in a reliable study read across from decamethyltetrasiloxane, L4, (CAS 141 -62 -8).

There are no reliable data with the test substance available for toxicity to sediment organisms. Data have been read across from a structural analogue: A 28-d EC₅₀ of >68 mg/kg sediment dw and NOEC of >=68 mg/kg sediment dw have been determined for the effects of decamethyltetrasiloxane (L4; CAS 141-6-8) on survival and growth of Hyalella azteca.

In all cases these studies indicate no effects at the highest concentration tested, which in the case of the aquatic studies represents the limit of solubility of the tested substances. These data are read across as evidence that the registration substance would not be expected to exhibit toxic effects at its limit of solubility in test medium, which is similar to or lower than these read-across substances.

Refer to IUCLID Section 6 endpoint summary (CSR Section 7.0) for further discussion of the approach to chemical safety assessment and justification for read across.