Boron carbide

Endpoint summary

Description of key information

No studies are available for the Sensitisation endpoint with boron carbide. Due to the inherent physical-chemical properties of boron carbide (practically insoluble in water, not bioavailable, no structural alerts) and long-term experience in manufacturing, handling and use, no skin sensitisation is to be expected from boron carbide and further testing for sensitisation is considered scientifically unnecessary.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vitro

Data waiving:

study technically not feasible

Justification for data waiving:

other:

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

A sensitizer is an agent that is able to cause an allergic response in susceptible individuals. Following exposure via the skin by the allergen, the characteristic adverse health effects of allergic contact dermatitis or atopic dermatitis may be provoked. According to ECHA Guidance on information requirements and chemical safety assessment, the skin sensitisation potential of a chemical is related to its ability to react with skin proteins to form covalently linked conjugates and recognition of these by the immune system. In the vast majority of cases, this is dependent on electrophilic reactivity of the skin sensitizer or a derivative produced (usually by oxidation) in vivo or abiotically. Among the key steps required for a chemical to induce sensitisation via skin contact are gaining access to the viable epidermis, protein binding, metabolic activation (if required), internalization and processing by Langerhans cells (LC), transport of antigen by LC to draining lymph nodes, and presentation to and recognition by T lymphocytes. Epidermal bioavailability and chemical reactivity are key factors which may indicate the sensitising effect of a substance. Skin penetration is a prerequisite for skin sensitisation.  

Boron Carbide („Black Diamond“), a covalent non-metallic carbide, is an inorganic solid with a high chemical inertness. With a hardness of 9.3 on the mohs scale, it is one of the hardest materials known, behind cubic boron nitride and diamond. It does not noticeably react with chlorine or oxygen below 1,000 °C, is completely inert against hydrogen fluoride and hot nitric acid and is practically insoluble in water (see section 4.8 of the IUCLID dossier) and organic solvents [1]. Due to its inherent properties (insoluble, no lipophilic characteristics), boron carbide does not cross biological membranes, is not bioavailable and does not have skin penetration properties. Therefore, boron carbide does not have any potential of being a skin sensitizer. The majority of chemical allergens is electrophilic and reacts with nucleophilic amino acids. Boron carbide does not contain any electrophilic structural elements or electrophilic reactive groups being able to react with amino acids or to build covalently linked conjugates.  B2O3 is the only Boron containing impurity of B4C soluble in water (see section 4.8 of the IUCLID dossier). B2O3 forms boric acid when getting in contact with water. However, boric acid itself is neither a skin nor a respiratory sensitizer [2].  Furthermore, companies involved in the elaboration of the registration dossier confirmed by certificates of their company doctors that in up to 23 years of manufacturing, handling and use of B4C no cases of skin sensitisation or respiratory sensitisation occurred due to exposure of workers to B4C. For details see attached company declarations on observations of skin and eye irritation/corrosion and sensitising effects related to handling and use of boron carbide.  

Conclusion: Due to the inherent physical-chemical properties of boron carbide (practically insoluble in water, not bioavailable, no structural alerts) and long-term experience in manufacturing, handling and use, no skin sensitisation is to be expected from boron carbide. Against this background and in conformity with ECHAs principle of avoiding unnecessary animal testing, it is considered unnecessary to perform a skin sensitisation study.      

Literature:  

[1] Hollemann A.F., Wiberg E., Lehrbuch der anorganischen Chemie, 101. Auflage, Walter de Gruyter, New York 1995.  

[2] Transitional annex XV dossier on boric acid submitted by Austria. http://echa.europa.eu/chem_data/transit_measures/annex_xv_trans_reports_en.asp  

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on data describing the inherent physical-chemical properties of Boron Carbide (sand-like, granulated, solid particles insoluble in water, showing no acidity) and long-term experience in manufacture, handling and use of the substance, it is not considered likely that boron carbide will cause sensitisation to the skin and respiratory tract.

Therefore, classification according to the criteria set out in Annex I of Regulation (EC) No. 1272/2008 (CLP criteria) is not warranted.