Carbon monoxide

Endpoint summary

Description of key information

Acute oral toxicity - waiver

Acute dermal toxicity - waiver

Acute inhalation toxicity: Bowden, A (2005) VAB001; Author unknown (1970) HL 96-70; Rose et al., (1970).

Key value for chemical safety assessment

Acute toxicity: via inhalation route

Endpoint conclusion

Dose descriptor:

LC50

Value:

1 489 mg/m³ air

Additional information

As carbon monoxide is a gas the oral and dermal routes of exposure are not considered relevant.

Of the first two rat acute inhalation toxicity studies submitted, one study (HL 96 -70) determined a 4 -hour LC₅₀ of 1300 ppm (equivalent to 1489 mg/m³ [1ppm = 1.145 mg/m³, WHO, 2000]). The design for this study consisted of a single 4 hour exposure (in accordance with the guideline requirements), and therefore was considered the most relevant dose descriptor for this endpoint.

 

The remaining study confirmed deaths at 1987 ppm (2275 mg/m^3;Author unknown, 1970), with the maximum tolerated dose being the mid-high dose tested in the Bowden (2005) study following a 2 -hour exposure.

 

Whilst no LC₅₀ value was determined in the latter study, the results obtained from a single 2 hour exposure provide support for the LC₅₀ value obtained in the initial study discussed.

 

Whilst no LC₅₀ value was determined in the latter study, the results obtained from a single 2 hour exposure provides support for the LC₅₀ value obtained in the initial study discussed.

 

The final study, conducted by Rose et al., (1970) confirmed the LC₅₀of 2070 mg/m³(1807 ppm according to the conversion factor listed above) following a 4hr exposure, with surviving animals sacrificed immediately post exposure. This paper has been directly cited by the ISO 10298 International standards document for the Determination of toxicity of a gas or gas mixture. Following time adjustment a 1hr LC₅₀ value of 3760 ppm was derived.

 

References:

International standard ISO 10298 (1995). Determination of toxicity of a gas or gas mixture. Reference number ISO 10298:1995(E).

Justification for classification or non-classification

Whilst acute inhalation studies with carbon monoxide confirm an LC₅₀of 1489 mg/m³, acute exposure in humans ranging from headaches through to coma and death at high levels of carbon monoxide have been reported. To reflect this, the EU IOELV STEL value for carbon monoxide has been set at 117 mg/m³(15 minutes). Based on the animal data, carbon monoxide has been classified as ‘H331- Toxic if inhaled (Acutely toxic (inhalation) [Hazard Category 3])’,according to the new CLP classification (EC 1272/2008).