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EC number: 231-130-8 | CAS number: 7440-21-3
Based on the available data on synthetic amorphous silica, silicon has low toxicological activity after repeated oral exposure; even doses up to 2,500 mg/kg bw/day (in rats) and 10,000 mg/kg bw/day (in mice) did not cause any effects attributable to silicon in one chronic study with silica gel. Because of the low toxicological activity of silicon ion after ingestion, no oral DNEL is set. Also dermal DNEL is not considered relevant.
Although silicon is mainly handled in the form of lumps, inhalable and respirable silicon may be formed in some uses. Respirable dust is more important when considering the lung or lower respiratory tract effects.
Based on a subchronic inhalation study in rats, silicon particles in the respiratory size range (MMAD 2.6 µm) caused only very mild, local inflammatory effects in the lungs of the exposed animals. On the basis of the outcome of that study, a DNEL-value of 0.3 mg/m3 was derived for worker exposure to respirable silicon particles.
For the inhalable fraction of silicon there is no substance specific data available in relation to adverse effects after repeated exposure. However, it is relevant to set a long-term inhalation DNEL for workers also for that fraction. For inhalable silicon it is thus justified to follow the currently lowest occupational exposure limit value for inert dust (poorly soluble inert particles) in Europe, which is the German value (DFG 1997, 2014) of 4 mg/m3.
The recent epidemiological data from the silicon/ferrosilicon manufacturing have shown only effects attributable to general dust exposure. It has been shown in different industries that dust exposure may increase the risk of chronic bronchitis or COPD. In the recent study in Norwegian ferroalloy industry (Johnsen et al. 2010), an annual additional decline in lung function resembling the decline caused by smoking (6.4 ml fora non-smoking employee of average heightestimated on the basis of linear mixed effects model) was suggested at median exposure level of 2.3 mg/m3of general dust (representing thoracic fraction).This is close to the current view that occupational exposure to dust in general results in an extra decline in FEV1 of 7 to 8 ml/year (Toren and Balmes, 2007). For an exposure level of 1 mg/m3 Johnsen and co-workers (2010) calculated an additional decline of 2.7 ml for non-smokers. However, when the absolute annual decline in FEV1was examined by exposure groups (tertiles of exposure level: <1, 1.1 to 3.0 and >3.1 mg/m3) and controlled by age the values at the two lowest exposure group were close to the predicted, physiological annual decline of FEV1. Thus, this study suggests that 1 mg/m3 (thoracic fraction) can be regarded as a NOAEChumanfor the effects of dust exposure at FeSi/Si industry.According to the data from 7 of these FeSi/Si plants, the median levels of respirable dust in this industry varied between 0.4-2.1 mg/m3 (Elkem 2005), being highest at furnace department. Median levels of respirable amorphous silica (representing silica fume) were ~0.1-1.3 mg/m3. No signs of fibrosis in workers were seen in these studies. However, since silicon particles are only a minor component of these dusts present in silicon/ferrosilicon factories no firm conclusions on the inhalation toxicity and dose-response of silicon can be made.
Conclusion: Because of the low toxicological activity of silicon ion after ingestion, no oral DNEL is set. Also dermal DNEL is not considered relevant. For inhalation, the DNEL for respirable silicon is set at 0.3 mg/m3, and for inhalable silicon set at 4 mg/m3.
A detailed justification paper discussing the interpretation of the 90-day inhalation study results and DNEL derivation is attached in Section 13 of the Iuclid dossier.
As there is no consumer exposure to metallurgical silicon, no DNEL for the general public is derived.
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