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Siloxanes - Consumption, Toxicity and Alternatives

4 Environmental fate and effects

• 4.1 Initial screening for decamethylcyclopentasiloxane (D5)
• 4.2 PBT profiler screening
• 4.3 Aquatic toxicity data for octamethylcyclosiloxane and PDMS

It is beyond the scope of this project to prepare a comprehensive review of environmental effects of the siloxanes, but some data on persistence, bioaccumulation and toxicity are summarised below.

4.1 Initial screening for decamethylcyclopentasiloxane (D5)

Information about environmental properties and toxicity of decamethylcyclopentasiloxane (D5) was initially retrieved from the databases Aquire, CambridgeSoft Corporation database, HSDB database, IUCLID-CD, PHYSPROP DEMO-database, SPIN database, DART Special (RTECS) and ToxLine. The screening result for decamethylcyclopentasiloxane is shown in Annex 6. No information on environmental toxicity was found and it was decided not to go further on with similar database screenings for the other substances.

4.2 PBT profiler screening

In order to make a first comparison between the substances as to persistence, bioaccumulation and toxicity, the substances were screened using the PBT profiler developed by U.S. EPA (U.S. EPA 2003).

The profiler uses a procedure to predict persistence, bioaccumulation, and toxicity of organic chemicals on the basis of the chemical structure and physical parameters of the substances combined with experimental parameters for substance with a similar structure, using a QSAR approach. For more information see U.S. EPA (2003).

The results for six members of the siloxane family (Table 4.1) predict the highest bioconcentration factors for the two phenyl siloxanes, one order of magnitudes higher than the values for the cyclic siloxanes and two orders of magnitudes higher than the values for the small linear methyl siloxanes. The predicted toxicity is as well significantly higher (lowest ChV values - see description in table notes) for the phenyl siloxanes. The predicted half-life is nearly the same for all substances.

Using U.S. EPA's criteria, the screening indicates that all substances are of high concern as to environmental toxicity, and that the phenyl siloxanes are considered very bioaccumulative.

Table 4.1 PBT profiler results for selected siloxanes (based on U.S. EPA 2003)

CvH: Chronic Value (ChV) is the same as the chronic NEC (No effect concentration). US EPA uses the following criteria for Fish ChV (mg/l):
> 10 mg/l: Low Concern
0.1 - 10 mg/l: Moderate Concern
< 0.1 mg/l: High Concern

4.3 Aquatic toxicity data for octamethylcyclosiloxane and PDMS

The environmental fate and effects of volatile methylsiloxanes (mainly cyclosiloxanes) and polydimethylsiloxane (PDMS) have been reviewed by Hobson et al. (1997) and Fendinger et al. (1997), respectively.

A summary of aquatic toxicity data for octamethylcyclosiloxane is shown in Table 4.2 whereas toxicity data for PDMS is shown in Table 4.3.

Table 4.2 Summary of octamethylcyclosiloxane aquatic toxicity data (Hobson et al. 1997)

* This concentration is the mean value measured in the highest exposure level.

Table 4.3 Soil and sediment testing results used for PDMS risk screening (Fendinger et al. 1997)

* Indicates highest dose tested with no effects observed in test.
** Indicates nominal concentration.
*** Indicates acute test.

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Version 1.0 September 2005, © Danish Environmental Protection Agency