The European Chemicals Agency (ECHA) has published a proposal submitted by Norway to classify Octamethyltrisiloxane (EC Number: 203-497-4, CAS Number: 107-51-7) as a Substance of Very High Concern (SVHC) under the REACH regulation due to its very persistent and very bioaccumulative (vPvB) properties.
Background on Octamethyltrisiloxane
Octamethyltrisiloxane, also known by its chemical name 2,2,4,4,6,6-hexamethyl-3,5-dioxa-2,4,6-trisilaheptane, is a colourless liquid that is widely used in various industries. It serves as a chemical intermediate and is a key ingredient in the formulation of personal care products, such as hair conditioners and skin lotions, where it acts as a conditioning agent and emollient. The substance is also utilised in industrial applications, including the manufacturing of silicone polymers, sealants, and as a spreading agent in agricultural products.
Norway, acting as the proposing authority, has based its proposal on Article 57(e) of the REACH Regulation, which covers substances that are very persistent and very bioaccumulative. The proposal is grounded in a comprehensive Annex XV report that assesses the environmental and health impacts of Octamethyltrisiloxane, highlighting concerns over its long-term persistence in aquatic environments and significant potential to accumulate in living organisms.
Key Findings from the Annex XV Report
The Annex XV report, prepared in line with REACH requirements, presents a weight-of-evidence approach indicating that Octamethyltrisiloxane does not readily degrade in the environment. Experimental data show that the substance has a hydrolysis half-life of up to 61 days under certain conditions and is highly adsorptive to organic matter in sediments and soils. These characteristics suggest a slow degradation rate, leading to prolonged environmental presence.
Moreover, the report identifies a high bioconcentration factor (BCF) in aquatic species, with values significantly exceeding the threshold of 5,000 L/kg for classification as very bioaccumulative. The data indicates that Octamethyltrisiloxane can persist in both fresh and marine water environments, potentially impacting a range of biota.
Uses of Octamethyltrisiloxane
Octamethyltrisiloxane is used across a variety of sectors due to its chemical properties. In the personal care industry, it is valued for its ability to provide a silky texture and improve the spreadability of lotions and creams. In the industrial sector, it is used in the production of silicone-based products due to its stability and effectiveness as a spreading agent. Additionally, its role in agricultural products helps to ensure an even application of pesticides and other chemicals.
Implications and Next Steps
If classified as an SVHC, Octamethyltrisiloxane could be subject to further regulatory measures under REACH, including restrictions or authorisations aimed at controlling its use and mitigating environmental and health risks. Stakeholders, including manufacturers, importers, and downstream users, are encouraged to review the proposal and provide comments.
ECHA has opened a public consultation on the proposal, with a deadline for submitting comments set for 14 October 2024. Interested parties can access the full Annex XV report and submit their feedback through the ECHA website.
