D4, D5 and D6: Substances of Very High Concern

D4, D5, D6

Back on November 9, 2023 the European Court of Justice, after a long legal battle against Global Silicones and others (the list is long: Dow Silicones UK Ltd, Evonik Operations GmbH, Shin-Etsu Silicones Europe BV, just to name a few) confirmed the classification of D4, D5 and D6 as substances of very high concern (SVHC), confirming the previous restrictions enforced by ECHA in 2018. This judgment is final, and no further appeal is available.

But first, let’s take a step back: what are D4, D5 and D6?

Cyclotetrasiloxane, also known as D4, CAS No. 556-67-2; Cyclopentasiloxane, also known as D5, CAS No. 541-02-6 and Cyclohexasiloxane also known as D6, CAS No. 540-97-6 are all cyclic compounds of low molecular weight, volatile, and belonging to siloxanes and silicon family. In particular, cyclic siloxanes are used as precursors in the production of polymers, such as polydimethylsiloxane but are also used as substances on their own or in mixtures. There are four production sites in the EU, producing up to 200,000 tonnes per annum (tpa) of D4, 50,000 tpa of D5 and 6,000 tpa of D6.

All three have a similar chemical structure (as we can appreciate in the pictures below) and hazard profile, as they were all identified as very persistent and very bioaccumulative (vPvB) substances. In particular, D4 was identified as persistent, bioaccumulative and toxic (PBT) and vPvB substance, while D5 and D6 were identified as vPvB substances, but were also considered to be PBT substances where the concentration of D4 (as a constituent) exceeded a concentration limit of 0.1 % (w/w).

According to regulation (EU) No. 253/2011, “A substance fulfils the bioaccumulation criterion (B) when the bioconcentration factor in aquatic species is higher than 2,000” and “A substance fulfils the “very bioaccumulative” criterion (vB) when the bioconcentration factor in aquatic species is higher than 5,000”. Substanced classified either as PBT or vPvB are worrying since their effects are unpredictable in the long-term and are difficult to reverse even when releases cease. That’s why their risk cannot be adequately assessed even with the derivation of risk characterization ratios. The total releases to the environment from the uses of D4, D5 and D6 have been estimated to be approximately 18,000 tpa.

Toxicologically speaking, all concerned chemicals are well characterized, as numerous safety reviews and studies have been published since 1991. They exert low acute toxicity in oral, dermal and inhalation administration routes, not mutagenic, not sentisisers or irritants. However, some studies demonstrated that D4 has the possibility to be a reproductive toxicant and a carcinogen via inhalation route of exposure in rats, and that’s why it was classified also as PBT, while the others are not.

Let’s take a look at their regulatory dispute:

It all started when, in 2014, ECHA director requested ECHA Member State Committee (MCS) to prepare an opinion on the persistence and bioaccumulation of D4 and D5 against the criteria in Annex XIII of REACH. Subsequently, in 2015, the UK proposed a REACH restriction on the use of D4 and D5 in wash-off cosmetic products, based on Annex XV of REACH. This proposal was later approved by ECHA’s scientific committees for risk (RAC) and socio-economic analysis (SEAC) in 2016, and in January 2018 the European Commission (EC) published a decision amending Annex XVII of REACH, adopting the proposed restriction on wash-off cosmetic products that should have been entered into effect from 31 January, 2020.

In December 2016, the European Commission requested ECHA to prepare a further Annex XV restriction proposal on uses of D4 and D5 in leave-on cosmetic products and in other consumer or professional products that were not covered by the original UK’s proposal. Moreover, the EC requested ECHA to include uses of D6, including in wash-off cosmetic products, in the scope of the proposal in February 2018.

Fast forward to June, 2018: ECHA, pursuant to Article 59(8) of the REACH Regulation, adopted Decision ED/61/2018 regarding the inclusion of D4, D5 and D6 in the Candidate List for eventual inclusion in Annex XIV to Regulation No 1907/2006 on the ground that they had been identified as PBT and vPvB substances.

After this implementation, the aforementioned companies pleaded to override this decision, in whole or in part on September 2018. In support of their action, the appellants relied on two pleas in law. In particular, the first plea alleged manifest error of assessment on the part of ECHA in its assessment of the B properties of D4, D5 and D6 and in its assessment of the T properties of D5 and D6, that it exceeded its powers and infringed Article 59 of the REACH Regulation; while the second plea alleged breach of the principle of proportionality. Finlly, on 30 June 2021, the General Court of EU dismissed the action in its entirety.

Not happy with this result, the same companies appealed again, seeking to set aside the previous 2021 judgment and annul the decision. This time, the appealers relied on four grounds of appeal. Nonetheless, this time too, the appeal was be dismissed in its entirety on November 9, 2023, confirming the classification of D4, D5 and D6 as substances of high concern, and warranting the 2018 restriction.

What does the restriction says?

According to the confirmed RAC and SEAC Opinion, D4, D5 and D6 are to be restricted in consumer and professional products following these conditions:

D4, D5 and D6 shall not be placed on the market:

  • As substances;
  • As constituents of other substances (except polymers as defined under the REACH Regulation (EC) No 1907/2006), in a concentration equal to or greater than 0.1% w/w;
  • As constituents in mixtures in a concentration equal to or greater than 0.1% w/w.

D4, D5 and D6 shall not be used:

  • As a solvent for the dry cleaning of textiles,leather and fur.

However, derogations were also mentioned. In particular paragraph 1 shall not apply to placing on the market of D4, D5 and D6 for the following uses:

  • Industrial use as a monomer in the production of silicone polymer;
  • Industrial use as an intermediate in the production of other organosilicon substances;
  • Industrial use as a monomer in emulsion polymerization;
  • Industrial use in formulation and/or (re-)packing of mixtures;
  • Industrial production of articles;
  • Industrial use in non-metal surface treatment;
  • Industrial use as laboratory reagent in Research & Development activities;
  • Placing on the market of D5 and D6 for use as medical devices, as defined in Directive 93/42/EEC or in the Regulation (EU) 2017/745, for the (i) treatment/care of scars and wounds, (ii) prevention of wounds, and iii) care of stoma;
  • Placing on the market of D5 for professional use in the cleaning or restoration of art and antiques.

In addition, by way of derogation, paragraph 1 shall not apply to the placing on the market of mixtures that contain silicone polymers with residues of:

  • D4 or D5 or D6 in a concentration equal to or less than 1% w/w, for use in adhesion, sealing, glueing and casting
  • D5 in a concentration equal to or less than 0.3% w/w or D6 in a concentration equal to or less than 1% w/w, for use as medical devices (as defined in Directive 93/42/EEC or in the Regulation (EU) 2017/745) for dental impression.
  • D4 in a concentration equal to or less than 0.5% w/w, or D5 or D6 in a concentration equal to or less than 0.3 % w/w for use as protective coatings (including marine coatings).
  • D5 in a concentration equal to or less than 1% w/w or D6 in a concentration equal to or less than 3% w/w, for (i) rapid prototyping and mould making, and (ii) high performance uses stabilised by quartz filler.
  • D4 or D5 or D6 in a concentration equal to or less than 0.2% w/w, for use as medical devices as defined in Directive 93/42/EEC or in the classification rule 21 set in Annex VIII to the Regulation (EU) 2017/745.
  • D4 in a concentration equal to or less than 0.2% w/w, or D5 or D6 in a concentration equal to or less than 1 % w/w for use as silicone insoles for horses, or as horseshoes.
  • D4 or D5 or D6 in a concentration equal to or less than 0.5 % w/w, for use as adhesion promoters.
  • D6 in a concentration equal to or less than 1 % w/w, for professional use in the cleaning or
  • restoration of art and antiques.
  • D5 or D6 in a concentration equal to or less than 1 % w/w, for use in pad printing, or manufacturing of printing pads.
  • D4, or D5, or D6 in a concentration equal to or less than 1 % w/w, for use in 3D-printing.

By way of derogation, paragraphs 1 and 2 shall not apply to:

  • Use of D5 in strictly controlled closed dry cleaning systems for textile, leather and fur where the cleaning solvent is recycled or incinerated.

The original restriction, approved in 2018, had a 5-year transitional period. According to ECHA dossier, alternatives to D4, D5 and D6 are available and economically feasible, and there are already alternatives on the marked for cosmetics and mixtures that are free of concerned chemicals. Moreover, ECHA reiterates that industrial uses and articles are out of scope of this restriction.

In conclusion, the proposed restriction not only safeguards human health but also contributes to environmental well-being, marking a positive step towards sustainable practices in the industry.

Article issued by Chiara Gazerro

 

References:

https://echa.europa.eu/documents/10162/f148d6f2-4284-a3c1-fd08-8cdaddf73978

https://echa.europa.eu/documents/10162/a3e8195a-23d3-5859-6fdc-7805a3148b46

https://echa.europa.eu/it/registry-of-restriction-intentions/-/dislist/details/0b0236e181a55ade