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Toxicological information

Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable, well-documented publication which meets basic scientific principles
Cross-reference
Reason / purpose:
reference to other study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2009
Report Date:
2009

Materials and methods

Objective of study:
other: dissolution kinetics
Principles of method if other than guideline:
Solubility of pyrogenic silica was studied by loading 100 mg of substance to different biological solutions (phosphate buffer (PBS); Gamble's solution, (GMB); artifical sweat (ASW); artificial lysosomal fluid (ALF); artifical gastric fluid (GST)). Concentration of dissolved silica was measured after 2, 4, 8, 24 and 168 h. In addition, in screening test the release of impurities present in pyrogenic silica was also evaluated in PBS and artificial gastric fluid during 1 week incubation.
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): fumed silica (synthetic amorphous silica)
- tradename: Aerosil Ox50
- specific surface area: 43 m2/g

Administration / exposure

Details on study design:
Dissolution of synthetic pyrogenic silica was studied by loading 100 mg of substance to different biological solutions (phosphate buffer, PBS; Gamble's solution, GMB; artifical sweat, ASW; artificial lysosomal fluid, ALF; artifical gastric fluid, GST). Concentration of dissolved silica was measured after 2, 4, 8, 24 and 168 h as a measure of bioaccessibility. In addition, the release of impurities present in silica fume was evaluated in PBS and artificial gastric fluid after 1 week incubation.
Statistics:
not done

Results and discussion

Preliminary studies:
The dissolution of pyrogenic silica (Aerosil Ox50) was 5 to 19% at 24 h and 49-71% at 168 h. This is somewhat higher than that of silica fume in similar experimental conditions; the proportion of dissolved silicon dioxide from the same amount of silica fume ranged from 1.4 to 6.4% at 24 h and from 11 to 35% at 168 h incubation. This can be, at least partly, explained by the lower specific surface area of the silica fume samples (19 m2/g) in comparison to pyrogenic silica samples. The main metallic impurities that were released from pyrogenic silica included aluminium, calcium, iron (in GST) and magnesium (in GST). The released amount was 112-253 μg/l for calcium, 5.1-128 μg/l for aluminium, ND-116 μg/l for iron and 2.5-109 μg/l for magnesium. The release of arsenic, barium, copper, lithium, manganese, sulfur, strontium and titanium ions was very low. Also other metals were screened but remained below the detection limits.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): other: pyrogenic silica is dissolved in physiological media
This in vitro dissolution data on pyrogenic silica shows that pyrogenic silica is dissolved in neutral physiological solutions. pH affects the dissolution of silicon ion from silica (lower pH=>lower dissolution). Dissolution in physiological media can be used to predict bioaccessibility of the compound and for the comparison between different silicon-based compounds to support read-across.
Executive summary:

Herting et al (2009) studied the dissolution of silicon from pyrogenic silica particles (Aerosil Ox50 with specific surface area 43 m2/g). The results show that the dissolution of pyrogenic silica (Aerosil Ox50) is 15 to 19% at 24 h and 49-71% at 168 h. Also the release of different metallic impurities from pyrogenic silica was evaluated in PBS and artificial gastric fluid after 1 week incubation. The main metallic impurities that were released from pyrogenic silica (Aerosil particles) included aluminium, calcium, iron (in GST) and magnesium (in GST). The release of calcium was 112-253 μg/l. Iron release varied from ND-116 μg/l. The release of arsenic, barium, copper, lithium, manganese, sulfur, strontium and titanium ions was very low. Also other metals were screened but remained below the detection limits. The release of magnesium was 2.5-109 μg/l. Lead was not released at measurable levels from Aerosil particles. Aerosil released only very minor or non-detectable levels of zinc.