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Sediment toxicity

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Description of key information

Sediment toxicity: NOEC 130 mg/kg dw (135 mg/kg dwt normalised to 5% OC)

Key value for chemical safety assessment

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

Additional information

No sediment toxicity data are available for the registration substance ViM4Q.

A category approach is applied to this endpoint and is detailed in the Siloxane Category report (PFA, 2017). The hypothesis for read-across of sediment ecotoxicity evidence within the Siloxanes Category is that no structure-based or property-based pattern is evident from the category dataset of existing studies, although patterns are identifiable associated with extrinsic aspects of test design to which effects may be attributed. The approach will be revisited in the event that reliable new data become available. With this in mind, a single overall interpretation is made across the category. To fulfil the requirements of REACH, a conservative approach is made by reading across on a nearest-neighbour basis the reliable data within the category.

In the context of the RAAF, Scenario 6 is expected to apply to this endpoint. It is considered that effects observed in benthic organisms are associated primarily with extrinsic factors associated with test design and not to structural similarities as such.

 

A total of twenty-four sediment toxicity studies for siloxanes and nineteen 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 corresponding studies 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 studies which are not suspected to be confounded by extrinsic factors show relatively minimal effects across the dataset.

READ-ACROSS JUSTIFICATION

No data are available for the effects of the registration substance on sediment organisms. Data are read-across from low functionality siloxanes of a similar molecular weight, D5 (CAS 541-02-6) and D6 (540-97-6).

The registered substance (ViM4Q) and read-across substancesD5 (CAS 541-02-6) and D6 (540-97-6)are members of the Reconsile Siloxanes Category. They are methylated siloxanes containing Si atoms linked by oxygen.The registration substance, ViM4Q, is a quaternary-branched structure of five Si atoms, with four terminal Si atoms linked to a central Si atom by Si-O-Si bonds. Each of the four terminal Si atoms is substituted by one vinyl and two methyl groups.The registration and read-across substances have similar physicochemical properties (low water solubility, high log Kowand slow hydrolysis rates), are not readily biodegradable and have high potential for adsorption to sediment.

A result for effects in natural sediment on the invertebrate amphipodHyalella aztecais 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 (135 mg/kg dw normalised to 5% OC) for growth rate.

The following results are read-across from dodecamethylcyclohexasiloxane (D6) in studies using natural sediment:

A 28 -d EC50value of >420 mg/kg dry weight and a NOEC of ≥420 mg/kg dry weight (≥656 mg/kg dw normalised to 5% OC) have been determined for effects on numbers and biomass ofLumbriculus variegatus. A 28-d EC50value of >620 mg/kg dry weight and a NOEC of ≥620 mg/kg dry weight (≥969 mg/kg dw normalised to 5% OC) have been determined for effects on emergence and development rate ofChironomus riparius.

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

A NOEC value of 130 mg/kg dw sediment for effects onHyalella aztecais used as the key value for the CSA.