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Toxicological information

Carcinogenicity

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Description of key information

Animal carcinogenicity studies demonstrated that carbon black of respirable size could produce lung tumours in rats of both sexes, but not in mice or hamsters. Increases in the incidence of benign and malignant lung tumours were seen at the lowest concentration tested (2.5 mg/m3, 16 hrs/day, 2 years). The lung tumours occurred under conditions that resulted in impaired lung clearance (“overload”). There is also evidence that inflammation and cell proliferation may have contributed to the development of rat lung tumours. 
Skin painting studies in mice using a variety of commercial carbon blacks did not induce signs of skin cancer development. Limited lifetime oral studies showed no evidence of carcinogenicity in rats and mice.
Studies of the carcinogenic potential of carbon black in workers generally suffered from limitations, and are considered not to reveal evidence for a causal role of carbon black in the development of human cancers.
In relation to lung cancer, various cohort and case-control studies in the US did not show any increases in lung cancer risk in carbon black production workers. Cohort mortality studies of workers exposed to carbon black in the UK found an excess of lung cancer in some, but not all factories included in the study, and there was no association between duration of carbon black exposure and lung cancer mortality, nor were possible confounders such as smoking or past occupational histories taken into account.
A number of cases of skin cancer were identified in carbon black production workers in the US, whilst in a UK cohort of carbon black workers no excesses of skin cancer were found. Also, a study in the rubber and tyre manufacturing industry did not reveal an increased risk of squamous cell skin cancer in workers exposed to carbon black contaminated materials.
An excess number of bladder cancer cases were recently reported in dock workers with a history of manually unloading shipments of carbon black. As there is no information on...

Key value for chemical safety assessment

Carcinogenicity: via oral route

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed

Carcinogenicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEC
1 mg/m³

Additional information

Studies conducted in rats have demonstrated that chronic inhalation of high doses of carbon black results in increased pulmonary inflammation, adenomas and carcinomas in the peripheral rat lung. This response is generally referred to as an overload response or threshold effect. The hypothesis that a threshold effect is relevant to the tumor response in rats is supported by data from numerous studies indicating that at exposure levels below that which causes a persistent inflammatory response, tumors are not produced. Substantial data also indicates the involvement of secondary processes, such as inflammation and inflammatory-induced oxidative stress, as possible mechanisms for the rat lung tumor response. Furthermore, recent studies have highlighted the impact of particle size and surface area on these processes.


Carcinogenicity: via inhalation route (target organ): respiratory: lung

Justification for classification or non-classification

Not classifiable according to the criteria as laid down in CLP regulation