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EC number: 217-496-1
CAS number: 1873-88-7
There are no reliable data describing the long-term toxicity of the
registered substance to soil macroorganisms.
Stability study using the related substance octamethyltrisiloxane
(L3) under OECD TG 222 conditions without test organisms:
A stability/recovery test was conducted in preparation for terrestrial
ecotoxicology studies with the related substance L3. H-L3 and L3 are
members of the Siloxane Category of compounds and have high vapour
pressures (850 Pa and 530 Pa), high log Kow (6.2 and 6.60),
high log Koc (3.8 and 4.3) and low water solubility (0.02
mg/l and 0.034 mg/l). In addition, the substances have a slow hydrolysis
rate relative to the time-scale of ecotoxicity testing (t1/2 =
53 h and 329 hours at pH 7 and 25°C). In the context of terrestrial
toxicity, both L3 and H-L3 are expected to have similar stability in
soil and prior to volatilisation, any exposure is likely to be to the
parent substance during the terrestrial toxicity studies. Therefore, it
is considered valid to read-across the results of the soil stability
study with L3.
The study demonstrated a method of introducing neat 14C-octamethyltrisiloxane
(14C-L3) into natural soil with subsequent
mixing to distribute the test article throughout the soil uniformly.
The second phase of the study investigated the stability of 14C-L3
in the same soil under conditions representative of those used for the
OECD TG 222 Earthworm Acute Toxicity and Reproduction Test. The system
was partially open to allow for respiration during a planned future
Effect of headspace on loss of test material during dosing of soil was
examined. The main experiment test vessel was selected in order to
minimise headspace as much as possible, while still allowing for enough
tumbling to ensure homogeneity. However, even the container with the
best recovery only observed an average recovery of 69.7% (or 22.9 mg/kg
Measures were taken to avoid loss of test substance through
volatilisation during the homogeneity experiment. These included:
- fitting the test vessel jar with a polytetrafluoroethylene (PTFE)
lined lid and covering the threads of the jar with PTFE tape;
- spiking the soil with a calibrated gastight syringe;
- spiking with a concentration 34% above the saturation concentration,
to attempt to account for test substance losses;
- taping the lid closed to avoid inadvertent opening.
The stability experiment was then carried out using the spiked soil from
the homogeneity experiment, which was divided into five beakers. Each
beaker had 10 mL of headspace and was covered with plastic film having
five small holes (approximately 3 mm in diameter) to allow for air
exchange. The plastic film was secured with rubber bands.
By day 3 in the stability experiment, only 6.3% of the initially
observed radioactivity was detected, and sampling was stopped. However,
the average of the homogeneity determination was taken as the initial
concentration for each beaker in the stability test. The soil was not
analysed again after dividing into the beakers, therefore the potential
loss from moving the test soil from the container used in the
homogeneity experiment to the 5 test beakers used in the stability study
was not determined.
A single peak was observed consistent with14C-L3,
showing that the primary mechanism of loss in the initial recovery
experiment was volatilisation.
The absence of degradation products in the vast majority of samples,
coupled with the rapid loss of 14C activity,
shows that the primary mechanism of test article loss was volatilisation
of 14C-L3 from the simulated OECD TG 222 test
H-L3 is more volatile and also more rapidly degradable than L3, meaning
that similar losses from the test system would be expected under
equivalent test conditions. Additionally, in an OECD TG 216 (Soil
Microorganisms: Nitrogen Transformation Test) study for the effects of
the related substances HMDS and L3 on nitrate formation rate of soil
microflora, analysis of the test substance concentrations show that test
material was lost by day three of the test (see Section 6.3.4). Based on
these experimental findings, the registrants believe it is not
technically feasible to conduct an OECD TG 222 test for the registration
substance on the basis that the test substance is too volatile to
maintain adequate concentrations in the test system.
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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