Exposure to carbon black: a cancer risk?

Our plain-English summary of Exposure to carbon black: a cancer risk?, by M. Brockmann, M. Fischer, K.M. Müller (International Archives of Occupational and Environmental Health, 1998).

The study

• Authors: M. Brockmann, M. Fischer, K.M. Müller
• Journal: International Archives of Occupational and Environmental Health
• Published: 1998;71(2):85-99
• Type of article: Review
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Lung cancer is one of the most serious health problems in the industrial nations and is therefore of great public and scientific interest. Although inhalative cigarette smoking is without doubt the main cause for the increasing frequency of lung cancer, during recent years there has been more and more public interest in other substances in the environment or at the work place that are assumed to be potentially carcinogenic especially due to experiences with fibrous particles such as asbestos and their effects. Enhanced attention is also directed to inert or nuisance dusts such as carbon black. Evaluation of the possibly increased risk for humans should first be based on exact epidemiology data. In the absence of those data--as in the case of carbon black--experimental data in animals serve as the point of orientation, especially results gained in rats in long-term inhalation studies. Pathologic anatomy investigations of human lungs under similar exposure conditions, however, render results quite different from those obtained in rats and, thus, preclude ready interpretation of animal results to human risk assessment. This is particularly true for the development of lung tumors in rats under overload conditions as well as for certain tumor types not observed in human lung tissues. It is therefore quite understandable that many researchers propose to interpret the changes observed in rat lung tissues after inhalation of carbon black as rat-specific reaction mechanisms that cannot be applied to human tissues, which in the past have led to the wrong conclusions regarding human risk assessment due, among other factors, to incorrect experimental design and inaccurate nomenclature of tumorous lesions in rats.

In plain English

This article was a review, not a new study. It was written by pathologists at the Mesothelioma Register in Bochum, Germany, and asked whether carbon black, a finely dispersed carbon powder used in tires, printing inks and plastics, poses a cancer risk. The authors compared published clinical and epidemiology studies of carbon black workers with animal experiments, mainly in rats. They also compared rat lung tissue with lung changes in coal miners and arc welders. Asbestos was mentioned only in passing. As the authors summarized them, Western worker studies found no increased tumor rate, though bronchitic complaints increased with exposure. Eastern European studies reported dust levels up to more than 900 mg/m3 but described no malignant tumors of the lungs. Rats developed lung tumors under heavy 'overload' exposure, but mice, hamsters, guinea pigs and monkeys did not. The authors concluded that the epidemiology studies showed no increase in tumor risk, and that the later changes seen in rats had no equivalent in human tissue. They noted that most worker studies could be compared only to a very limited extent and that not all accounted for smoking.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Review of published human clinical and epidemiology studies and animal experiments on carbon black, with the authors' own comparative pathology of rat and human lung tissue
• Who was studied: Published studies of carbon black workers in the United States, Western Europe and Eastern Europe (literature from 1935 onward), and animal experiments, mainly in rats. For comparison, the authors used rat lung preparations supplied by the Fraunhofer Institute in Hanover and human lungs with dust diseases. The figures show a 72-year-old and a 54-year-old former miner and a 46-year-old welder. The number of human lungs examined is not stated.
• Exposure: Carbon black: more than 96% finely dispersed carbon, with primary particles of 10 to 500 nm, used for example as a filler in tires, in printing inks and in plastics. For comparison: coal dust (anthracosilicosis, anthracosis, 'black hole lung') and arc-welding dust (mainly iron oxide).
• Main results:
  • As the authors summarized Western studies of carbon black workers: no increased tumor rate overall, but an increase in bronchitic complaints.
  • Eastern European studies described very poor working conditions, with dust concentrations up to more than 900 mg/m3. Despite this, none of these papers described a malignant tumor of the lower respiratory tract or the lungs.
  • In a reviewed US retrospective cohort (Robertson and Ingalls 1980), the authors' table reports the following for 4 US carbon black producers with 34,739 person-years at risk: 29 observed versus 41 expected deaths from malignant tumors, and 13 observed versus 14.7 expected deaths from lung cancer.
  • Rats developed lung tumors in carbon black experiments. Other species (mouse, hamster, guinea pig, monkey) did not develop tumors after inhaling carbon black particles.
  • In the authors' comparison, human dust-related lung disease resembled rat lungs in the build-up of dust-loaded macrophages. It differed in other respects, including the early activation of pneumocytes seen in rats.
  • The authors stated that coal miners do not have a generally increased cancer risk.
  • The authors stated that arc welders, whose lung changes most resemble those of rats exposed to carbon black, generally do not have an increased lung cancer risk.
  • The authors attributed increased lung cancer frequency seen in individual welder studies partly to cigarette smoking and partly to other causes. In shipbuilding, these other causes frequently included simultaneous bystander exposure to asbestos.
• The authors' conclusion: The authors concluded that relevant epidemiology studies show no increase in tumor risk after carbon black exposure. They also concluded that the later changes seen in rat experiments have no equivalent in human tissue, so the rat tumor findings are not apparently relevant to human risk.
• Limitations the authors state:
  • Most of the available epidemiology studies can be compared with one another only to a very limited extent.
  • Not all worker studies took account of confounding factors such as cigarette smoking.
  • No pathologic examinations of lungs from people exposed to carbon black had been carried out, so the authors compared rat findings with other human dust diseases instead.
  • In almost all of the animal studies, the maximum tolerated dose was clearly exceeded.
  • The review did not claim to include all the literature in the field.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Carcinogenic, Epidemiology.

Related studies

• Effects of asbetos, iron oxide, silica, and carbon black on the microsomal availability of benzo[a]pyrene — J.R. Lakowicz, D.R. Bevan (1979)
• Exposure to nitrosamines, carbon black, asbestos, and talc and mortality from stomach, lung, and laryngeal cancer in a cohort of rubber workers — K. Straif, U. Keil, et al. (2000)
• Cytotoxicity and reactive oxygen species generation from aggregated carbon and carbonaceous nanoparticulate materials — K.M. Garza, K.F. Soto, et al. (2008)
• Comparative proteomics and pulmonary toxicity of instilled single-walled carbon nanotubes, crocidolite asbestos, and ultrafine carbon black in mice — J.G. Teeguarden, B.J. Webb-Robertson, et al. (2011)
• In vitro cytotoxicity and transforming potential of industrial carbon dust (fibers and particles) in syrian hamster embryo (SHE) cells — C. Darne, F. Terzetti, et al. (2010)
• Genotoxicity and carcinogenicity risk of carbon nanotubes — S. Toyokuni (2013)

Browse more research in International Archives of Occupational and Environmental Health, or return to medical research.