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EC number: 451-620-7 | CAS number: 352230-22-9
Table 1. Mean percent survival and mean dry weight during the 28-day static-renewal exposure of freshwater amphipods (Hyalella azteca) to D5 applied to sediment.
Test Day 28
Mean Dry Weight
Per Larvae in mg (SD)
aSD = Standard Deviation.
bSignificantly reduced compared to the negative control, based on Dunnett’s Test. However, due to the lack of statistical significance at the higher treatment levels tested (i.e., 62 and 130 mg a.i./kg), this effect was not considered to be biologically relevant.
cSignificantly reduced compared to the negative control, based on Steel’s Many-One Rank Test.
dThis treatment level was excluded from statistical analysis for growth due to the survival effect observed.
Table 2. Concentrations of D5 measured in sediment samples during the 28‑day static-renewal exposure of freshwater amphipods (Hyalella azteca) to D5 applied to sediment.
Measured Sediment Concentration (mg a.i./kg)
aAnalytical samples were removed from replicate I.
bAnalytical samples were removed from replicate J.
cAnalytical samples were removed from replicate K.
dMean measured and percent recovery values were calculated using the actual analytical results and not the rounded values (two significant figures) presented in this table.
eConcentrations expressed as less than values were below the limit of quantitation (LOQ). The LOQ for this analysis was set at 2.0 mg a.i./kg, the lowest validated concentration.
fNA = Not Applicable.
gQC = Quality Control sample. Percent of nominal is presented in parentheses below the measured results.
hPercent recovery for this QC sample is outside of the acceptable range (i.e., 70.0 to 120%,Appendix 2).
Table 1. Results of analysis of sediment for exposure concentrations of the test substance.
Measured Concentration(mg/kg dw)
Percent of Nominald
a Analytical samples were removed from replicate E, with the exception of the control and solvent control which were removed from replicate G.
b Analytical samples were removed from replicate F, with the exception of the control and solvent control which were removed from replicate H.
c Analytical samples were removed from replicate G, with the exception of the control and solvent control which were removed from replicate I.
d Mean measured and percent recovery values were calculated using the actual analytical results and not the rounded values (two significant figures) presented in this table.
e NA = Not Applicable.
Table 2. Test results
Mean measured sediment concentration (mg/kg dw)
Mean number of oligochaetes per replicate (SD)
Mean biomass per replicate per concentration in mg (SD)
Table 1. Results of analysis of test sediments
(mg/kg dry weight)
Measured Concentration(mg/kg dry weight)
a Analytical samples were removed from replicate E of the additional exposure vessels.
b Analytical samples were removed from replicate F of the additional exposure vessels.
c Analytical samples were removed from replicate G of the additional exposure vessels.
d Mean, standard deviation and percent of nominal were calculated using the original unrounded results and not the rounded (two significant figures) presented in this table.
Mean Measured Sediment
Mean % emerged
Mean Male/Female Combined
28-day NOEC: 130 mg/kg dw (135 mg/kg dwt normalised to 5% OC), Hyalella azteca
Long-term sediment toxicity studies are not required for Annex VIII substances under the REACH Regulation. However, due to the high sediment adsorption potential of the substance and the potential for persistence in the sediment, the compartment has been assessed.
No sediment toxicity data are available for the registration substance, Reaction Mass of 3,3-diphenylhexamethyltrisiloxane and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (CAS 352230-22-9).
A category approach is applied to this endpoint and is detailed in the Siloxane Category report (PFA, 2017at). 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.
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, decamethylcyclopentasiloxane (D5, CAS 541-02-6) and dodecamethylcyclohexasiloxane (D6, CAS 540-97-6).
The registered substance, (Reaction Mass of 3,3-diphenylhexamethyltrisiloxane and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (CAS 352230-22-9)) and read-across substances decamethylcyclopentasiloxane (D5, CAS 541-02-6) and dodecamethylcyclohexasiloxane (D6, CAS 540-97-6) are members of the Reconsile Siloxanes Category.
D5 is a cyclic siloxane with 5 silicon atoms with methyl branches and alternated by oxygen. D6 has 6 silicon atoms with methyl branches and alternated by oxygen. The registration substance is a multi-constituent substance containing two main constituents 3,3-diphenylhexamethyltrisiloxane (55-70%) and 3,3,5,5-tetraphenylhexamethyltetrasiloxane (15-25%). The main constituent has three silicon atoms with 2 phenyl groups and 6 methyl groups. The second constituent has 4 silicon atoms, with 4 phenyl groups and 6 methyl groups. The registration and read-across substances have similar physicochemical properties (low water solubility, high log Kow and slow hydrolysis rates), are not readily biodegradable and have high potential for adsorption to sediment.
See IUCLID Section 6.0, CSR Section 7.0, Ecotoxicological Information for further discussion and justification of read-across.
A result for effects in natural sediment on the invertebrate amphipod Hyalella azteca is read across from D5. 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 D6 in studies using natural sediment:
A 28-d EC50 value 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 of Lumbriculus variegatus. A 28-d EC50 value 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 of Chironomus 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 on Hyalella azteca is used as the key value for the CSA, normalised to 135 mg/kg dw.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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