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EC number: 231-130-8
CAS number: 7440-21-3
The low solubility of silicon may be the reason that the number of
studies can be found regarding the aquatic toxicity of Si/silica is
limited. No studies on acute or chronic aquatic effect of elemental
silicon have been located. More often it is the impurities of commercial
substances which may raise some concern over Si-based industrial
products rather than the Si-element itself. For sparingly soluble
substances such as metals and metalloids, environmental hazard
assessments can be performed using data on particle dissolution and
metal release by using the OECD T/Dp (transformation/dissolution)
protocol (OECD 2001). The principle of the T/D protocol is to determine
the concentration of metal elements that are released from sparingly
water soluble substances. These data are then compared with data that
are already available for each of the elements to determine if the
concentration released is above the concentration expected to cause an
effect in the environment. Information on the different elements and
their potential effects to the environment is discussed in the following
Information regarding solubility of
Silicon powder dissolves relatively sparingly in distilled water,
but dissolves to much higher extent in natural waters (e.g. in brackish
and sea water). Technically aquatic reliable and valid tests for silicon
(applying dissolved material) can be carried out.
The solubility of silicon for particles sized less than 0.05 mm of
Si HG, Si LG and PCS after 168 hours of exposure at 100 mg/l load were
tested and results, as dissolved %, are as follows:
Silicon HG 12 % ± 0.7 % (at pH 7.2)
Silicon LG 3.2 % ± 0.2 % (at pH 7.2)
Silicon PCS 32 % ± 1 % (at pH 7.2)
Normally, the dissolved fraction in ecotoxicity tests
refers to the fraction that passes through a filter of 0.45 μm. It
should be noted, however, that this definition may not necessarily refer
to the metals/elements in solution. In the range of 0.01- 0.45 μm
colloid inert particles remain suspended.
Soluble amorphous silica or sparingly soluble forms of silica have
been studied on aquatic species, fish, daphnia and algae in few studies.
These results can be used partly as a read across/Weight of Evidence
approach (WoE) material in support of the silicon hazard assessment.
Performing ecotoxicity tests on sparingly water soluble
substances, and in particular metals and metalloids, can be problematic.
Therefore, the Transformation/Dissolution (T/D) protocol is recommended
as a first tier for assessing testing requirements (OECD 2001). The T/D
protocol has been performed on Silicon (low grade) for a period of 7 and
28 days representing potential acute and chronic effects respectively.
The T/D protocol is a relevant approach particularly for sparingly water
soluble metals. The 7 day test is only representative of acute toxicity,
and for substances which are produced/imported at high tonnage, chronic
data may be required which can be obtained from the full 28 day
transformation/ dissolution protocol.
The T/D test protocols were performed (7 and
28 days) according to the methods presented in section 220.127.116.11
(Lillicrap et al, 2011). In addition, the results from the T/Dp tests
are also presented in section 18.104.22.168 and are summarised below in Table
Table A10. 7 day transformation/dissolution data.
Si low grade (7 day)
DWC (28 day)
Si low grade (28 day)
Comparing the data from the 7 and 28 day T/Dp tests with the
limits recommended in the EU Risk Assessment Reports (RAR) as shown in
Lillicrap et al. (2010), the data indicate that the impurities present
in the silicon (low grade) should not cause an effect to aquatic
organisms and hence these substances should require no further testing
and silicon does not require environmental hazard classification.
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