Decamethylcyclopentasiloxane

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

1.2 µg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.12 µg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

10 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

11 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

1.1 mg/kg sediment dw

Assessment factor:

100

Extrapolation method:

assessment factor

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

2.54 mg/kg soil dw

Assessment factor:

50

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

16 mg/kg food

Assessment factor:

90

Additional information

The hydrolysis half-life of decamethylcyclopentasiloxane is 73.4 d at pH 7 and 25°C. The water solubility of the substance is low (17 µg/l at 23°C) and the log K_ow is high (8.07). It is therefore likely that, under the flow-through exposure conditions of the aquatic toxicity tests reported in the following sections, that the test organisms will have been predominantly exposed to very low concentrations of the registered parent substance.

Conclusion on classification

It is proposed that D5 should not be classified in the EU for environmental hazards. The substance was found to be non-toxic at its functional water solubility limit in short- and long-term studies with fish, Daphnia and algae.

To add further certainty “to assess likelihood or severity of an event occurring due to physicochemical properties of the substance” as defined in the REACH requirements, a new risk analysis method that applies thermodynamic principles of ‘fugacity’ and ‘activity’ to express the results of field monitoring and laboratory bioaccumulation and toxicity studies in a comprehensive risk analysis was conducted on D5 (Gobas et al., 2015). Fugacity (f) or activity (a) is the chemical potential of a substance in a given media or phase.

 

The use of fugacity/activity to describe the degree of saturation (or solubility) achieved by a compound in a given media is particularly useful for substances that display a narcosis mode-of-action in aquatic organisms, e.g., the cVMS substances (Redman et al., 2012), as chemical activities may provide valuable estimates of the proximity of measured concentrations to potentially toxic levels (Arnot and Mackay, 2011). Gobas et al. (2015) examined the available field data on D5 and concluded that:

 

“Fugacity and activity ratios of D5 derived from bioaccumulation measures indicate that D5 does not biomagnify in food-webs, likely due to biotransformation. The fugacity and activity analysis further demonstrates that reported no-observed effect concentrations of D5 normally cannot occur in the environment. Observed fugacities and activities in the environment are, without exception, far below those corresponding with no observed effects, in many cases by several orders of magnitude. This analysis supports the conclusion of the Canadian Board of Review and the Minister of the Environment that D5 does not pose a danger to the environment.”

 

D5 does not reach concentrations in surface water or sediment that cause toxicity to pelagic or benthic organisms. Analysis of chemical activity and fugacity shows that concentrations of D5 measured in biota, including plankton, invertebrates, fish, birds, and terrestrial and marine mammals are three to nine orders of magnitude below the maximum activity of one and below all NOEC levels.