Kieselguhr, soda ash flux-calcined

Toxicological Summary

Workers - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

0.05 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

1

Acute/short term exposure

Hazard assessment conclusion:

no-threshold effect and/or no dose-response information available

DNEL related information

Local effects

Acute/short term exposure

Hazard assessment conclusion:

no-threshold effect and/or no dose-response information available

DNEL related information

Workers - Hazard via dermal route

Systemic effects

Acute/short term exposure

DNEL related information

Local effects

Long term exposure

Hazard assessment conclusion:

no-threshold effect and/or no dose-response information available

Acute/short term exposure

Hazard assessment conclusion:

no-threshold effect and/or no dose-response information available

Additional information - workers

Kieselguhr soda ash flux-calcined is a UVCB substance, the main constituents of which are amorphous silica and crystalline silica, principally in the form of cristobalite. The percentages of each type of silica may vary between 20-70 %w/w and 4-80%w/w, respectively, for the amorphous and crystalline forms.

In a 28-day repeat dose inhalation study performed according to OECD TG 412 under GLP, kieselguhr soda ash flux-calcined was administered to Wistar rats (20 animals/sex/dose) by nose-only, flow-past inhalation for a period of 5 days/week (6 hours/day) for 4 consecutive weeks at aerosol concentrations of 0.044, 0.207 and 0.700 mg/L air [Schuler 2011]. The initial sample used contained 45% of cristobalite (i.e. a crystalline silica polymorph) and approximately 55% of amorphous silica. The respirable fraction was 3.8% including 1.8% crystalline silica. In order to be compliant with the OECD TG 412 (which recommends the generation of aerosols with mass median aerodynamic diameters ranging from 1 to 3 μm), the test material was micronized for its use in the 28-day study to allow that the majority of material/particles could reach the deep lung (alveoli). The test method of processing of the material resulted in the content of respirable crystalline silica being increased from 1.8% to approximately 45%, which is approximately double the worse-case level found in commercially produced material. Under these conditions, the toxicity observed in the study material reflects and confirms the health hazards of extremely high concentrations of crystalline silica. However, as stated above, the study material is not reflective of the toxicity of, or risk factor associated with, the much lower concentration of crystalline silica contained in commercially available product, the registered substance. Furthermore, as it was not possible to define an NOAEL from this study a DNEL cannot be derived with any degree of confidence.

As already mentioned, Kieselguhr soda ash flux-calcined is a UVCB substance. Hence it should be possible to derive a DNEL based on the toxicity of its constituents. For amorphous silica, the DNEL is reported as 4 mg/m3 in the disseminated dossier for synthetic amorphous silica (http://apps.echa.europa.eu/registered/data/dossiers/DISS-76fd35e0-69c4-29a3-e044-00144f26965e/DISS-76fd35e0-69c4-29a3-e044-00144f26965e_DISS-76fd35e0-69c4-29a3-e044-00144f26965e.html). It is clear from the available studies on amorphous and crystalline silica that crystalline silica presents the more severe long-term hazard compared to amorphous silica. In addition, in industrial settings, it is the level of respirable crystalline silica present in the atmosphere that is monitored and of importance from a health perspective. Therefore, it is sensible to derive a DNEL based on respirable crystalline silica so that it can be compared directly with the predicted or measured exposure level in the workplace and the true health risk.

The Scientific Committee on Occupational Exposure Limits have reviewed the information available on respirable crystalline silica (RCS) and in 2003 produced a draft recommendation of a SCOEL of 0.05 mg RCS/m³[SCOEL/SUM/94]. This value is at the low end of the range of national OELs within the EU (0.05 – 0.3 mg/m³) for quartz, cristobalite and tridymite. Therefore, it is proposed to adopt 0.05 mg RCS/m³as the DNEL for use in the risk assessment for Kieselguhr soda ash flux-calcined.

General Population - Hazard via inhalation route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

0.05 mg/m³

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

1

Acute/short term exposure

DNEL related information

Local effects

Acute/short term exposure

DNEL related information

General Population - Hazard via dermal route

Systemic effects

Acute/short term exposure

DNEL related information

General Population - Hazard via oral route

Systemic effects

Long term exposure

Hazard assessment conclusion:

DNEL (Derived No Effect Level)

Value:

18.7 mg/kg bw/day

Most sensitive endpoint:

repeated dose toxicity

DNEL related information

Overall assessment factor (AF):

200

Modified dose descriptor starting point:

NOAEL

Acute/short term exposure

DNEL related information

Additional information - General Population

Kieselguhr soda ash flux-calcined is a UVCB substance, the main constituents of which are amorphous silica and crystalline silica, principally in the form of cristobalite. The percentages of each type of silica may vary between 20-70 %w/w and 4-80%w/w, respectively, for the amorphous and crystalline forms.

In a 28-day repeat dose inhalation study performed according to OECD TG 412 under GLP, kieselguhr soda ash flux-calcined was administered to Wistar rats (20 animals/sex/dose) by nose-only, flow-past inhalation for a period of 5 days/week (6 hours/day) for 4 consecutive weeks at aerosol concentrations of 0.044, 0.207 and 0.700 mg/L air [Schuler 2011]. The initial sample used contained 45% of cristobalite (i. e. a crystalline silica polymorph) and approximately 55% of amorphous silica. The respirable fraction was 3.8% including 1.8% crystalline silica. In order to be compliant with the OECD TG 412 (which recommends the generation of aerosols with mass median aerodynamic diameters ranging from 1 to 3 μm), the test material was micronized for its use in the 28-day study to allow that the majority of material/particles could reach the deep lung (alveoli). The test method of processing of the material resulted in the content of respirable crystalline silica being increased from 1.8% to approximately 45%, which is approximately double the worse-case level found in commercially produced material. Under these conditions, the toxicity observed in the study material reflects and confirms the health hazards of extremely high concentrations of crystalline silica. However, as stated above, the study material is not reflective of the toxicity of, or risk factor associated with, the much lower concentration of crystalline silica contained in commercially available product, the registered substance. Furthermore, as it was not possible to define an NOAEL from this study a DNEL cannot be derived with any degree of confidence.

As already mentioned, Kieselguhr soda ash flux-calcined is a UVCB substance. Hence it should be possible to derive a DNEL based on the toxicity of its constituents. For amorphous silica, the DNEL is reported as 4 mg/m3 in the disseminated dossier for synthetic amorphous silica (http: //apps. echa. europa. eu/registered/data/dossiers/DISS-76fd35e0-69c4-29a3-e044-00144f26965e/DISS-76fd35e0-69c4-29a3-e044-00144f26965e_DISS-76fd35e0-69c4-29a3-e044-00144f26965e. html). It is clear from the available studies on amorphous and crystalline silica that crystalline silica presents the more severe long-term hazard compared to amorphous silica. In addition, in industrial settings, it is the level of respirable crystalline silica present in the atmosphere that is monitored and of importance from a health perspective. Therefore, it is sensible to derive a DNEL based on respirable crystalline silica so that it can be compared directly with the predicted or measured exposure level in the workplace and the true health risk.

The Scientific Committee on Occupational Exposure Limits have reviewed the information available on respirable crystalline silica (RCS) and in 2003 produced a draft recommendation of a SCOEL of 0.05 mg RCS/m³[SCOEL/SUM/94]. This value is at the low end of the range of national OELs within the EU (0.05 – 0.3 mg/m³) for quartz, cristobalite and tridymite. Therefore, it is proposed to adopt 0.05 mg RCS/m³as the DNEL for use in the risk assessment for Kieselguhr soda ash flux-calcined for the general population as this is considered to be protective taking into account the reduced frequency and duration of exposure compared to workers.