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EC number: 273-761-1 | CAS number: 69012-64-2 Amorphous silicon dioxide particles from the volatilization and vaporization of furnace feed materials in the manufacture of ferrosilicon and silicon.
Toxicological Summary
Administrative data
Workers - Hazard via inhalation route
Systemic effects
Long term exposure
- Hazard assessment conclusion:
- no hazard identified
Acute/short term exposure
- Hazard assessment conclusion:
- no hazard identified
DNEL related information
Local effects
Long term exposure
- Hazard assessment conclusion:
- DNEL (Derived No Effect Level)
- Value:
- 0.3 mg/m³
- Most sensitive endpoint:
- repeated dose toxicity
DNEL related information
- DNEL derivation method:
- other: ECHA REACH guidance and ECETOC recommendations
- Overall assessment factor (AF):
- 3
- Dose descriptor:
- NOAEC
- Value:
- 1 mg/m³
- AF for dose response relationship:
- 1
- Justification:
- NOAEC used as starting point
- AF for differences in duration of exposure:
- 2
- Justification:
- Default AF for extrapolation from subchronic to chronic exposure.
- AF for interspecies differences (allometric scaling):
- 1
- Justification:
- No allometric scaling needed in the case of inhalation exposure.
- AF for other interspecies differences:
- 1
- Justification:
- The rat is considered sensitive towards local lung effects caused by particles. Humans are not considered more sensitive than rats.
- AF for intraspecies differences:
- 3
- Justification:
- Local inflammatory effects, justified to use a lower AF.
- AF for the quality of the whole database:
- 1
- AF for remaining uncertainties:
- 1
- Justification:
- No remaining uncertainties.
Acute/short term exposure
- Hazard assessment conclusion:
- no hazard identified
DNEL related information
Workers - Hazard via dermal route
Systemic effects
Long term exposure
- Hazard assessment conclusion:
- no hazard identified
Acute/short term exposure
- Hazard assessment conclusion:
- no hazard identified
DNEL related information
Local effects
Long term exposure
- Hazard assessment conclusion:
- no hazard identified
Acute/short term exposure
- Hazard assessment conclusion:
- no hazard identified
Workers - Hazard for the eyes
Local effects
- Hazard assessment conclusion:
- no hazard identified
Additional information - workers
DNEL for repeated dose toxicity of silica fume is based on lung effects, which are considered to be the critical effects of silica fume. In animal experiments with synthetic amorphous silicas, reversible lung effects, such as inflammation, granulomatous lesions and interstitial fibrosis, have been seen at exposures to 5-9 mg/m3of respirable (<5 microns-10) particles with the lowest NOAEL of 1.3 mg/m3. The small particle size and high surface area of these particles are likely to play a role in the generation of these effects. The pyrogenic silica studied by Reuzel et al. contained approximately 50 times more respirable material than the pyrogenic silica to which humans are exposed. Thus, the NOAEL for commercial synthetic amorphous silica is likely to be fiftyfold higher than 1.3 mg/m3. Amorphous silicon dioxide has not been classified as hazardous through inhalation, and a limit value of 4 mg/m3during an eight-hour shift for the inhalable dust has been derived for synthetic amorphous silica by the German MAK commission (DFG 1991).
A NOAEL of 1 mg/m3(representing respirable particles) identified in animal tests with synthetic amorphous silicas is taken as a starting point for the derivation of DNEL for silica fume. No allometric scaling between humans and rats is needed in the case of local effects, but the value should be corrected for differences in respiratory rates between rats and humans (1.3 mg/m3*6.7/10). This results in a starting point of 0.9 mg/m3. ECETOC has suggested that an assessment factor of one be used for interapecies differences and a factor of three for inter-individual differences in the case of local respiratory tract effects (ECETOC 2003). Application of these factors (1*3) to 0.9 mg/m3results in a DNELof 0.3 mg/m3for respirable fraction.
Based on epidemiological data on the ferrosilicon/silicon industries, a DNEL of 0.3 mg/m3for the respirable dust derived above is likely to be well on the safe side. Epidemiological data from different industries show that the occupational exposure to occupational dust and fumes may increase the risk of chronic bronchitis/COPD. This also seems to be the critical effect in humans in the ferrosilicon/silicon metal industry. In 1997, the MAK commission set a MAK value of 1.5 mg/m3for respirable dust and 4 mg/m3for inhalable dust to decrease the risk of general dust induced chronic bronchitis (DFG 1997). This represents currently the lowest OEL for general dust in. However, in the most recent study in a Norwegian ferroalloy industry (Johnsen et al. 2010), an annual additional decline in lung function resembling the decline caused by smoking was seen in the Si/FeSi industry at a median exposure level of 2.3 mg/m3of general dust (representingthoracicfraction). According to the data from seven of these FeSi/Si plants, the median levels ofrespirabledust in this industry varied between 0.4 and 2.1 mg/m3depending on the department/operations (Elkem 2005). The median levels of respirable amorphous silica were ~0.1-1.3 mg/m3. No signs of fibrosis in workers were seen in these studies. Thus, based on these studies, at these SiO2and total dust levels only effects attributable to general dust exposure were seen. This data supports the DNEL of 0.3 mg/m3(as respirable dust) for silica fume/silicon. However, commercial silica fume forms agglomerates whose size is based mostly on an inhalable fraction with only a 1-3 wt% in respiratory fraction. Thus, there is only limited exposure to respirable particles, and DNEL for inhalable silica fume should be derived. Since <5% of commercial silica fume is within a respirable size range, the ratio between inhalable and respirable fraction is >20. This means that a proposed DNEL of 0.3 mg/m3as respirable particles corresponds to >6 mg/m3as inhalable particles of commercial silica fume. It is, however, recommended that inhalable dust levels are controlled below 4 mg/m3, which is the recommendation by the German MAK commission (DFG 1997) for inhalable general dust and which currently represents the lowest OEL for general dust in. It is also the value given for synthetic amorphous silica by the German MAK commission (DFG 1991).
A DNEL of 4 mg/m3(inhalable fraction) and 0.3 mg/m3(respirable fraction)is recommended for commercial silica fume in occupational exposure.
As the data on SAS does not indicate systemic effects after oral ingestion of high doses of silica, no oral DNEL is set. Also, dermal DNEL is irrelevant.
General Population - Hazard via inhalation route
Systemic effects
Long term exposure
- Hazard assessment conclusion:
- hazard unknown but no further hazard information necessary as no exposure expected
Acute/short term exposure
- Hazard assessment conclusion:
- exposure based waiving
DNEL related information
Local effects
Long term exposure
- Hazard assessment conclusion:
- hazard unknown but no further hazard information necessary as no exposure expected
Acute/short term exposure
- Hazard assessment conclusion:
- hazard unknown but no further hazard information necessary as no exposure expected
DNEL related information
General Population - Hazard via dermal route
Systemic effects
Long term exposure
- Hazard assessment conclusion:
- hazard unknown but no further hazard information necessary as no exposure expected
Acute/short term exposure
- Hazard assessment conclusion:
- hazard unknown but no further hazard information necessary as no exposure expected
DNEL related information
Local effects
Long term exposure
- Hazard assessment conclusion:
- hazard unknown but no further hazard information necessary as no exposure expected
Acute/short term exposure
- Hazard assessment conclusion:
- hazard unknown but no further hazard information necessary as no exposure expected
General Population - Hazard via oral route
Systemic effects
Long term exposure
- Hazard assessment conclusion:
- hazard unknown but no further hazard information necessary as no exposure expected
Acute/short term exposure
- Hazard assessment conclusion:
- hazard unknown but no further hazard information necessary as no exposure expected
DNEL related information
General Population - Hazard for the eyes
Local effects
- Hazard assessment conclusion:
- no hazard identified
Additional information - General Population
Since there is no consumer/general population exposure to silica fume, no DNEL for consumers/general population is needed.
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