Silicic acid, aluminum sodium salt

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Jan, 20 - Oct. 13, 2011; experimental phase: Jan. 26 - May 3, 2011

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2011

Report date:

2011

Materials and methods

Objective of study:

absorption

distribution

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

This study is a further investigation of an OECD-guideline (407) repated dose oral one. It was performed for the chemical analysis of
silicon concentration (blood analysis) and the transmission of silicon particles in organ samples examined by electron microscopy.

GLP compliance:

no

Remarks:

The main study was performed under GLP conditions except for the chemical analysis of silicon concentration and the transmission electron microscopy of silicon particles in organ samples documented in this endpoint.

Test material

Test material information

Constituent 1

Reference substance name:

Silicon dioxide

EC Number:

231-545-4

EC Name:

Silicon dioxide

Cas Number:

7631-86-9

Molecular formula:

O2Si

IUPAC Name:

Silicon dioxide

Test material form:

solid: particulate/powder

Remarks:

amorphous

Specific details on test material used for the study:

SAS (Synthetic Amorphous Silica PR-A-02 ): NM-200
supplied by JRC, Ispra, on behalf of the sponsor, CEFIC, The European Chemical Industry Council

Radiolabelling:

no

Test animals

Species:

rat

Strain:

Wistar

Details on species / strain selection:

purchased from: Charles River Deutschland, Sulzfeld, Germany

Sex:

male

Details on test animals or test system and environmental conditions:

Animals were housed in groups of 5 per cage in Makrolon Type IV cages in animal room T1.044 in the conventional area. Absorbent softwood was used as bedding material in the cages (Lignocel BK 8-15, ssniff GmbH, Soest, Germany). Drinking water from the Hannover city water supplier was offered fresh weekly, in Makrolon bottles (approximately 300 ml), ad libitum. Food was offered ad libitum fresh weekly. The diet used (ssniff R/M-H) was supplied by ssniff GmbH, Soest, Germany. The temperature in the animal room was set at 22 ± 2oC and the rel. humidity at 30 - 70%. The animal room lighting was a 12-hour light/dark cycle controlled by an automatic timing device.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

other:

Duration and frequency of treatment / exposure:

28 d, daily exposure

Doses / concentrations

Dose / conc.:

1 000 mg/kg bw/day (nominal)

No. of animals per sex per dose / concentration:

5

Control animals:

yes, concurrent vehicle

Details on study design:

s. below

Statistics:

Differences between groups were considered case by case as statistically significant for p<0.05. Data were analyzed using analysis of variance. If the group means differed significantly according to the analysis of variance, the means of the treatment groups were compared with the means of the control group, using DUNNETT's modification of the t-test. Kruskal-Wallis ANOVA and Mann-Whitney U-test were applied in the case of non-homogeneous data. The statistical evaluation of the histopathological findings was done with the two-tailed FISHER test using the PROVANTIS system. For comparisons of semiquantitative data, the Chi-square test was used.

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Transmission electron microscopy (non-GLP) found electron dense structures composed of irregular homogenous to fine granular material in the cytoplasm of mesenteric lymph nodes cells, liver cells and kidney cells of all animals from the control and from the high dose group. The granular structures measured only few nanometer. However, these structures did not have the shape or appearance of amorphous material such as amorphous silica.

Details on distribution in tissues:

Determination of Silicon Ion Concentration
The results of the chemical analysis of silicon ion concentration are presented in Table 19. In summary, the ion concentrations in kidney, liver and blood were comparable in control animals (group 1) and high dose animals (group 4) and no treatment related changes were observed.

Determination of Silicon Particles
For electron microscopical investigation two samples per organ of the mesenteric lymph nodes, kidney as well as liver of all high dose group animals (group 4) were used. Vehicle treated animals served as controls (group 1).
To achieve better visibility of possible nanoparticles in comparison to the biological background composed of the organic structure, ultrathin sections have not been contrasted using uranyl acetate and lead citrate.

Mesenteric lymph node: Occasionally, cells of the mesenteric lymph node of all animals of the untreated group (group 1) and of the amorphous silica treated group (group 4) showed electron dense structures. Theses electron dense structures were found intracytoplasmatically in vacuoles and were characterized by irregular homogenous to fine granular material.
Liver: Occasionally, liver cells of all animals of the untreated group (group 1) and of all animals of the amorphous silica treated group (group 4) showed electron dense structures. Theses electron dense structures were found intracytoplasmatically in vacuoles and were characterized by irregular homogenous to fine granular material.
Kidney: Occasionally, kidney cells of all animals of the untreated group (group 1) and of all animals of the amorphous silica treated group (group 4) showed electron dense structures. Theses electron dense structures were found intracytoplasmatically in vacuoles and were characterized by irregular homogenous to fine granular material.

Applicant's summary and conclusion

Conclusions:

Toxicological analysis of silica ion concentrations in blood, kidney and liver tissue did not reveal differences between the control and the dose group. This result is most likely due to the naturally occurring high background values of silica.

Executive summary:

This is a toxicokinetic examination of an oral 28-day study in rats. It showed, that silicon is naturally absorbed by the body, as shown by its presence in blood, kidneys and liver of treated as well as untreated animals.