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Sediment toxicity

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Description of key information

A 28-d EC50 value of >130 mg/kg sediment dry weight  and a NOEC of 130 mg/kg sediment dry weight  have been determined for effects on growth rate of Hyalella azteca. The results are read-across from decamethylcyclopentasiloxne (D5) CAS 541-02-6.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:
130 mg/kg sediment dw

Additional information

A result for effects in natual sediment on the invertebrate amphipod Hyallela azteca is read across from decamethylcyclopentasiloxane (D5), CAS 541 -02 -6. The result from that test is a 28 d EC50 value of > 130 mg/kg sediment dry weight for growth rate and a NOEC of 130 mg/kg sediment dry weight for growth rate.

The following results have been obtained in two tests performed with the registered substance (D6) using natural sediment:

A 28 -d EC50value of >420 mg/kg dry weight and a NOEC of ≥420 mg/kg dry weight have been determined for effects on numbers and biomass of Lumbriculus variegatus. A 28-d EC50value of >620 mg/kg dry weight and a NOEC of ≥620 mg/kg dry weight have been determined for effects on emergence and development rate of Chironomus riparius.

A test with Chiromomus riparius exposed via artificial sediment gave a 28 -Day EC50value of 37 mg/kg dry weight for the effects of the registered substance (D6) on mortality and a NOEC of <22 mg/kg dry weight for effects on development rate and development time. However, the result is disregarded because a result for the same species is available from a test with natural sediment.

The results of all tests are expressed relative to mean measured exposure concentrations in the treated sediment.

A NOEC value of 130mg/kg dw sediment for effects on Hyalella azteca is used as the key value for the CSA.

A total of twenty-one sediment toxicity studies for siloxanes are available and sixteen results from studies of standard duration in standard test species have been reviewed in detail. There is a general trend for studies using natural sediment, which all have pH <~8, to show no effects, or higher NOECs than those with artificial sediment. No significant toxicity (NOEC <100 mg/kg) in any organism is found at pH near 7 with natural sediment. The data suggest that it is possible to read across sediment toxicity data between different siloxane structures, especially where natural sediment data are available, given that the sound studies show relatively minimal effects across the dataset. In the use of the data set for hazard assessment and derivation of predicted no-effect concentration (PNEC), the following approaches are used:

- Where the hydrolysis half-life is >48 hours, the chemical safety assessment will focus on the parent form.

- Where data are available for a substance with natural sediment and with artificial sediment for the same species, the natural sediment data will be give preference over data obtained with artificial sediment.

- PNEC will be determined on a weight-of-evidence basis for each substance, including use of read-across. Equilibrium partitioning calculations will be used if necessary.

     

REFERENCE:

Peter Fisk Associates (2015i), Peter Fisk Associates. Siloxane analogue report. PFA.404.005.008.R2