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Description of key information

7.2.1 Acute toxicity oral

For acute oral toxicity assessment, the data base compiles 42 studies performed between 1958 and 2014. They used test substances of synthetic amorphous silica forms produced by different processes including untreated and surface-treated test material with the specific surface area (BET) ranging from 45-349 m2/g. 17 of these studies meet the criteria for Klimisch score 1 and 23 studies met the criteria for Klimisch score 2 performed according to OECD guidelines 401, 420 or 423 in rats or mice. Mortality or significant toxicity were absent in all these studies. LD50values exceeded the top doses tested.

LD50values of >2000 mg/kg bw or >5000 mg/kg bw have thereby been established.

 

7.2.2 Acute toxicity inhalation:

For the acute inhalation toxicity assessment of untreated SAS, 6 studies performed between 1972 and 1983 are available and a new one recently conducted in 2019. Different forms of untreated SAS were tested with the specific surface (BET) ranging from 170-420 m2/g. The majority of the studies were conducted before the release of OECD guideline 403 (1981). Different test set-ups, not comparable, were used, i.e. most studies used the whole-body exposure, while nose-only has now become the preferred route of exposure.The latest study with a precipitated SAS according to OECD 436 is the only one which achieved a characterized aerosol of 5 mg/L and resulted in a LD50 > 5.01 mg/L air (Vivotecnia, 2019).

All early/former studies have technical deficiencies and do not entirely fulfill the criteria laid down in OECD 403. Due to the limited particle size information and the expected agglomeration of the tested SAS forms after atmosphere generation in the test chamber, the real exposure conditions of the animals in the older tests was not verified. Only one of these studies (Toxicogenics Inc., 1981) fulfills the technical conditions of OECD 403 in a sufficient way to provide a Klimisch rating of 2.

No mortality or significant toxicity was observed in 6 of the 7 studies (only 1 over 10 animal dead in a single study). For all these studies LC50 values are above the maximum achievable concentration or the highest concentration tested. The achievable test concentrations varied over 3 orders of magnitude (>0.139 mg/L and >207 mg/L) and based on the limited data available it is not possible to conclude on any reason for these differences. Maximum concentrations required by guideline were in the past not achievable due to technical limitations and possibly materials properties. However, the recent study (30 years later than the previous one) demonstrated the absence of mortality even under a stable 5 mg/L characterized aerosol, as confirmed by particle size distribution measurements.

  

7.2.3 Acute toxicity dermal:

The assessment of acute dermal toxicity is based on 9 studies performed between the years 1976 and 2000. Different forms of synthetic amorphous silica with the specific surface area (BET) ranging from 80-347 m2/g produced by different processes including untreated and surface-treated material were used as test substances. Three studies meet the criteria for Klimisch score 1 and were performed according to OECD guideline 402 in rats. The other studies meet the criteria for Klimisch score 2. Mortality or significant toxicity were absent in all studies. LD50values exceeded the top doses tested.

LD50values of >2000 mg/kg bodyweight have thereby been established.

Key value for chemical safety assessment

Additional information

Justification for classification or non-classification

Synthetic amorphous silicas did not induce toxicity or lethality by any route of exposure.

According to Annex I of the Regulation (EC) 1272/2008 and GHS (Globally Harmonized Classification System), the test substance requires no classification and has no mandatory label requirement.