2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane

Short-term toxicity to fish

Description of key information

Short-term toxicity to fish: 96 hr LL50: >1000 mg/l loading rate (WAFs) (highest concentration tested) (OECD Guideline 203 (Fish, Acute Toxicity Test)), equivalent to >7.3 mg/l measured initial concentration, mortality Cyprinodon variegatus. The values are above limit of solubility of the substance in water.

Short-term toxicity to fish: 14-day NOEC: 0.0044 mg/l, mortality Oncorhynchus mykiss (EPA OTS 797.1400 (Fish Acute Toxicity Test)), read-across from CAS 556-67-2. 

Additional information

A 96-h LL₅₀ value of >1000 mg/l loading rate (WAFs), equivalent to >7.3 mg/l measured concentration (initial) (highest concentration tested), has been determined in a reliability 1 study conducted with the registration substance using the salt water fish Cyprinodon variegatus. A NOELR value of 560 mg/l loading rate (WAFs), equivalent to 0.16 mg/l measured concentration (initial), has also been determined based on one mortality after 48 h at the 1000 mg/l loading rate and an equivalent result being achieved during the range finding test. The LL₅₀ and NOELR are above the water solubility limit of the substance (LoS: 0.0073 – 0.0088 mg/l at 23°C), therefore the LL₅₀ and NOELR are >LoS. For monoconstituent substances it would not normally be appropriate to test at concentrations above the solubility limit. However, the results as reported do provide strong evidence of the absence of toxicity at the solubility limit of the substance following short-term exposures.

A 14 -day NOEC of 0.0044 mg/l (mean measured concentration) has also been determined for effects of the structurally-analogous read-across substance, octamethylcyclotetrasiloxane (D4, CAS 556-67-2) on mortality of the freshwater fish, Oncorhynchus mykiss.

A 96-hour LC₅₀ value of 191 mg/l (nominal concentration) has been determined for the effects of trimethoxy(vinyl)silane (CAS 2768-02-7) on mortality of Oncorhynchus mykiss. The data indicate that the vinyl side chain is unlikely to contribute significant excess ecotoxicity to the substance.

The data above are supported by read-across evidence relevant to the impurities. The registration substance has an average purity of >80% Vi4-D4, with <15% 2,4,6,8,10-pentamethyl-2,4,6,8,10-pentavinylcyclopentasiloxane Vi5-D5 (CAS 17704-22-2; Impurity 1) and <10% 2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane Vi3-D3 (CAS 3901-77-7; Impurity 2) present as impurities. After due consideration of the properties, the presence of these impurities is not expected to affect the overall hazard profile of the substance. Read-across studies are in place as supporting studies, to consider the properties of the impurities. Data for Vi5-D5 are read-across from decamethylcyclopentasiloxane D5 (CAS 541-02-6), data for Vi3-D3 are read-across from hexamethyltrisiloxane D3 (CAS 541-05-9). These siloxanesbelong to the structural class of siloxanes (alkyl, vinyl, aryl or hydrogen substituted) and are expected tohave similar properties with regard to aquatic ecotoxicity.

A reliable short-term fish study is available for the siloxane D5 (CAS 541-02-6) and is read-across to Impurity 1. This study (14-d, flow through test with Oncorhynchus mykiss) gave a result 96-h LC₅₀>16 µg/l and 14-d LC₅₀>16 µg/l. LC₅₀was not reached within the limit of solubility in test media.

A reliable short-term fish study is available for the siloxane D3 (CAS 541-05-9) and is read-across to Impurity 2. This study (96-h, flow through test with Oncorhynchus mykiss) gave a result 96-h LC₅₀>1.6 mg/l. LC₅₀was not reached within the limit of solubility in test media.

 

Further information is given in a supporting report (PFA, 2017) attached in Section 13 of the IUCLID 6 dossier.