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EC number: 205-491-7 | CAS number: 141-62-8
Half-life in sediment: >192 d at 12 °C (based on read-across)
There is no sediment degradation data available for L4; an OECD 308 study is available with the analogous substance hexamethyldisiloxane (HMDS; CAS 107-46-0) and has been read across to the registration substance.L4 and HMDS are members of the Reconsile Siloxane Category are structurally similar substances. HMDS and L4 are linear siloxanes with two silicon atoms and one oxygen atom, and four silicon and three oxygen atoms, respectively. Each silicon atom is fully substituted with methyl groups. The physico-chemical properties of L4 are reasonably similar to those of HMDS, but the former should have greater stability in sediment: HMDS has a higher tendency to volatilise from sediment compared to L4, based on its higher vapour pressure (5500 Pa versus 73 Pa at 25°C) and lower tendency to partition to organic matter (log Koc3.0 versus 5.16) than L4. Substances that are highly absorbing are expected to have slow degradation rates in sediment. Available data indicate that degradation of siloxanes is predominantly abiotic, with the formation of hydrolytic products. Mineralisation rate is expected to be very slow. The degradation of L4 may be expected to be slower than HMDS, however since the degradation half-life for HMDS leads to a conclusion of ‘vP’ for the sediment compartment based on a worst-case half-life of 192 d at 12 °C, it is reasonable to read-across the conclusion of ‘vP’ in sediment for L4.
Reconsile Siloxane Category Simulation test data for degradation in water and sediment
Natural sediment (aerobic)
242 d in sediment at 24 °C (pH 7.9 after acclimation)
Dow Corning Corporation (2009b)
Natural sediment (anaerobic)
365 d in sediment at 24 °C (pH 7.9 after acclimation)
Dow Corning Corporation (2009c)
Natural sediment (aerobic and anaerobic)
1200 d in sediment at 24°C (Non-sterilised. Aerobic.)
2700 d in sediment at 24°C (Sterilised. Aerobic.)
Approximately 3100 d in sediment at 24°C (Non-sterilised. Anaerobic. (a good trend of degradation was not able to be established, so half-life is approximate))
800 d in sediment at 24°C (Sterilised.. Anaerobic.)
Dow Corning Corporation (2010b)
107 -46 -0
Natural sediment (aerobic)
Half-life (DT50): 192 d at 12°C (high %OC sediment); 53 d at 12°C (lower % OC sediment)
The Dow Chemical Company (2019)
The chemical safety assessment according to REACH Annex I indicates that it is not necessary to conduct the simulation test on ultimate degradation in surface water, because the risk characterisation ratios (RCRs) for the aquatic compartment, even with the assumption that the parent substance is not biodegradable, are <1.
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