Cyclic methylsiloxanes with persistent, bioaccumulative and toxic properties in the environment

The three organosiloxane compounds D4 (octamethylcyclotetrasiloxane, CAS no. 556-67-2), D5 (decamethylcyclopentasiloxane, CAS no. 541-02-6) and D6 (dodecamethylcyclohexasiloxane, CAS no. 540-97-6) are grouped as cyclic volatile methylsiloxanes (cVMS). cVMS are widely applied in different applications. In Europe, cVMS are imported or manufactured in large amounts: annually 10,000 - 100,000 metric tons D4 and D5, and 1000 - 10,000 metric tons D6. Large amounts of cVMS are used as intermediates in the production of silicone polymers. For D5, further industrial usages in electronics and coatings are known. But cVMS are also used in household products (for example, car cleaning products).

cVMS are known to be persistent, bioaccumulative in aquatic organisms, and have potential for long-range transport in the atmosphere. In some investigations, a biomagnification in aquatic food webs was observed. cVMS were already detected in freshwater fish from several countries, e.g., Norway Sweden or Canada. Generally, it is assumed that sewage treatment plant effluents are important sources of cVMS to water bodies. In 2018, the European Union (EU) classified cVMS as Substances of Very High Concern (s) under the REACH chemicals regulation. D4 fulfils the criteria for persistent, bioaccumulative and toxic (PBT) compounds as well as for very persistent and very bioaccumulative (vPvB) chemicals. D5 and D6 were assessed as vPvB substances. Based on these findings, measures were implemented to restrict the use of cVMS. The application of D5 in wash-off cosmetic products, which accounts for the majority of D5 emitted to wastewater, was largely restricted in the EU. Since February 2020 only product concentrations lower than 0.1% are allowed.


  • Octamethylcyclotetrasiloxane (D4)
    Persistent, bioaccumulative and toxic compound (PBT) and very persistent, very bioaccumulative (vPvB) compound
  • Decamethylcyclopentasiloxane (D5)
    Very persistent, very bioaccumulative compound (vPvB)
  • Dodecamethylcyclohexasiloxane (D6)
    Very persistent, very bioaccumulative compound (vPvB)


  • Bioindicator in rivers and lakes
  • As the only viviparous fish in German nearshore waters, it is a bioindicator in nearshore coastal marine ecosystems.

Sampling area

Sampling period

1995 - 2018

Extended information