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Chemical Regulation

Tight EU regulation of three siloxanes recommended

D4, D5, and D6 are persistent, bioaccumulative, and toxic, European Chemicals Agency says

by Cheryl Hogue
April 15, 2021

Drawing shows the chemical structure of D4, also known as octamethylcyclotetrasiloxane or cyclomethicone.

All uses of the cyclic methyl siloxanes D4, D5, and D6 should be tightly regulated, the European Chemicals Agency (ECHA) says in an April 14 recommendation.

The three chemicals are environmentally persistent, bioaccumulative, and toxic, ECHA says. They are produced in high volumes and widely used, it adds.

Drawing shows the chemical structure of D5, also known as cyclomethicone or decamethylcyclopentasiloxane

Some uses of the three siloxanes, formerly ingredients in personal care and cleaning items, are already restricted in consumer products in the European Union. But some commercial applications of these substances remain, including use in the production of electronics and in closed dry cleaning systems, ECHA says.

Drawing shows chemical structure of D6, also known as dodecamethylcyclohexasiloxane.

Next, the European Commission—the EU’s executive branch of government—along with the European Parliament and EU member states will consider the ECHA’s recommendation. If they adopt it, D4, D5, and D6 will be added to the authorization list under the EU Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) law. After that, companies would have to seek official authorization from the ECHA to use any of the compounds.

The industry group CES-Silicones Europe argues that ECHA’s recommended action is unnecessary. “It needlessly duplicates existing regulation to no clear policy benefit,” Ralf Maecker, chairman of CES-Silicones Europe, says in a statement provided to C&EN. “REACH restrictions for D4, D5, and D6 already cover most of the uses and almost all the emissions that could be subject to authorisation.”

Besides the three siloxanes, ECHA recommends adding four other chemicals to the REACH authorization list.

Three are harmful to human health, according to the agency. Dicyclohexyl phthalate and disodium octaborate can interfere with reproduction, the agency says, and trimellitic anhydride can cause respiratory sensitization. ECHA says it wants to prevent use of these molecules as substitutes for other regulated chemicals. “They may be used to replace substances with similar chemical structures and uses that have already been recommended [for] or included in the authorisation list,” the agency says.

The final substance is hydrogenated terphenyl. It is used as a heat-transfer fluid primarily in industrial settings as well as in adhesives, sealants, coatings, inks, and paints. The material, which is very persistent and very bioaccumulative, is also found in some plastic items, the agency says.



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