Silicon

Ecotoxicological Summary

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Standard AF assessment method is not suitable for aquatic PNEC derivation of silicon/silica. On the other hand the dataset is too scarce for statistical assessment method. Long term effects data is currently not available for dissolved silicon/silica.

PNEC derivation for fresh water and marine sediment has not been carried out for silicon (powders/granules) and PNEC derivation has not been seen relevant.PNEC derivation for soil is not regarded very important since the composition of most soils is normally rich in silicon based minerals.

PNEC derivation for soil is not regarded important since the composition of most soils is normally rich in silicon based minerals.

Conclusion on classification

A summary of comparison of the available information with the criteria for environmental classification in Directive 67/548/EEC according to the relevant parts of Section 1 of Annex I and the criteria inCLP Regulation 1272/2008 (EC)is documented here below.

 

Silicon– HG – LG - PCS

Solubility: Water solubility values for silicon and different grades of silicon are relatively low, of the order of few micrograms per liter to some tens of milligrams per litre. Values are quite variable, highly dependent on grade, test media, method, loading rate and test duration. Specific and detailed studies on the speciation of (freshly) dissolved form of elemental Si is not available. However, the soluble form in dilute solutions, after oxidation of silicon, is known to be Si(OH)₄.

Three representative commercial Silicon qualities (Si‐HG, Si‐LG, PCS) were investigated in the physical chemical test. Materials were:

Silicon HG: (99.1 % wt), Silicon LG: (98.6), Silicon PCS: (ca. 100%)

For particle sizes less than 0.05 mm of Si HG, Si LG and PCS after168 hours of exposure (at pH 7.2 buffer solution):

Silicon HG‐(168 hr) -          dissolved fraction of Si at 100 mg/l load was                  12 % ± 0.7 % (at pH 7.2)

Silicon LG (168 hr)-           dissolved fraction of Si at 100 mg/l load was                  3.2 % ± 0.2 % (at pH 7.2)

Silicon PCS (168 hr)-        dissolved fraction of Si at 100 mg/l load was                  32 % ± 1 % (at pH 7.2)

The dissolution water was pH 7.2 buffered media (PBS media)

Solubility in dissolved water seems to be extremely low. At initial 100 mg/l load in the OECD T/D dissolution screening test only 61 µg/l of Si was dissolved at maximum.

Si-impurities, (HG, LG, PCS)

The dissolved impurities were as follows:

Si HG: (Si, Fe, Mn, Ba, Cu, Al)

Si LG: (Si, Fe, Mn, Ba, Cu, Al)

PCS: (Si, Al, Mn#, Ba, Mo#) # from foreign particles, sample contamination

The dissolution of impurity metals of all tested grades may be regarded low. At initial 100 mg/l load in the OECD T/D dissolution screening test 32 µg/l of Fe and less than 10 µg/l of any other impurity was dissolved during the 24 hr screening test period.

Effects:All known L(E)C₅₀values of soluble Si(OH)₄are >> 100 mg/l. All dissolved SiO₂concentrations are << 100 mg/l. All dissolved concentrations of impurity elements of Si (HG, LG, PCS), independent on pH, were in all cases significantly below the L(E)C₅₀levels of their corresponding water soluble salts.

In addition, the data from the 7 and 28 day T/Dp tests compared with the limits recommended in the EU Risk Assessment Reports (RAR) as shown in Lillicrap et al. (2010), indicated 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 doesnot require environmental hazard classification.

 

 

Proposed classificationSilicon– High grade, Low grade, PCS (impurities included):

Classification	Toxicity	Degradation	Bioaccumulation	Escape clause
No environmental classification	Solubility < L(E)C50	No evidence of rapid partitioning from the water column	Not relevant	Not relevant