Trichromium dicarbide

Endpoint summary

Description of key information

The NOAEL for oral repeated dose toxicity was obtained from a study in which rats were fed chromium(III) oxide baked in bread for 90 days. No signs of toxicity were observed even at the highest dose.

The LOAEC for inhalation was derived from a guideline subchronic inhalation study with chromium(III) oxide. At the lowest concentration slight inflammation was observed in the lungs.

Due to the low bioavailability of chromium, the dermal route is not relevant for repeated dose toxicity.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEL

1 368 mg/kg bw/day

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

LOAEC

3 mg/m³

Additional information

No data were available on repeated dose toxicity tests with trichromium dicarbide, and therefore the read-across approach was used. Dissolution studies utilizing various synthetic body fluids have shown similar release profiles for chromium carbide and chromium metal and chromium(III) oxide.

No signs of toxicity were observed in an oral rat study with chromium(III) oxide, although the doses used were relatively high. The results are obviously due to the water-insolubility and poor oral bioavailability of chromium(III)oxide. The NOAEL 1368 mg Cr(III)/kg/bw obtained with chromium(III) oxide can be directly adopted for trichromium dicarbide.

Mild inflammatory reactions were observed with chromium(III) oxide in male and female rats in a 13 -week subchronic inhalation study at all exposure levels. These slight inflammatory changes are likely to be a reflection of a non-specific lung response caused by particle overload, rather than being a response of intrinsic toxicity of trivalent chromium. According to these studies the LOAEC for chromium(III) oxide is 4.4 mg/m3 (corresponding to 3 mg Cr(III) /m3), which is in fact most likely not much higher than the NOAEC for chromium(III) oxide in rats, as the severity and frequency of inflammatory changes in the lungs were minimal. No systemic adverse effects were observed in the inhalation study. The LOAEC of 3 mg Cr(III) /m3 can be used for chromium metal, as its surface is always auto-oxidized to chromium(III) oxide and therefore, in the case of fine chromium dusts, a large proportion of the chromium is in the form of chromium(III)oxide.

No studies were available on the repeated dose toxicity of chromium carbide, chromium metal or trivalent chromium compounds via the dermal route. As trichromium dicarbide is practically insoluble in various synthetic biological fluids, it does not pass through the skin or enter the systemic circulation, and repeated dose toxic effects via the skin are therefore not expected.

Repeated dose toxicity: inhalation - systemic effects (target organ) respiratory: lung

Justification for classification or non-classification

Repeated exposures of chromium(III) oxide via the oral or inhalation routes have not resulted in any signs of systemic toxicity. Dissolution studies have shown similar release profiles for chromium carbide, chromium metal and chromium(III) oxide. Therefore the results obtained with chromium(III) oxide can directly be adopted for trichromium dicarbide.

Mild local effects were observed in rats after repeated inhalation of chromium(III) oxide. These slight effects were most likely non-specific, caused by accumulation of insoluble particles. Rat lungs are known to be sensitive to particle overload, and inflammation is an expected outcome of rat inhalation studies with insoluble particles.

A DNEL for local effects caused by inhalation was derived, but there is no need to suggest classification for this endpoint.