Introduction High aspect ratio nanoparticles (HARNs) represent a growth area in nanotechnology. Best known of all HARNs are carbon nanotubes (CNTs). These nanomaterials have found applications in several production fields with subsequent potential for occupational exposure during industrial manufacture, use and disposal. Concerns regarding possible adverse health effects on workers who are routinely exposed to CNTs have been motivated by their resemblance to asbestos fibres, as well as by the International Agency for Research on Cancer classification of one type of multi-walled, CNTs-7, as ‘possibly carcinogenic to humans’. Therefore, aim of this work is to point out critical topics that should be addressed in industrial hygiene contexts for a suitable CNT risk assessment and precautionary management.

Methods Available literature was analysed to extrapolate priorities of research concerning toxicological issues, risk assessment and management strategies for CNT exposed workers.

Results Toxicological in vitro and in vivo research may be helpful in identifying and characterising CNT hazards, particularly in defining what are the properties that may dictate fibre pathogenicity including carcinogenicity, i.e. width, length, bio-persistence. Additionally, environmental monitoring strategies should be developed to assess not only airborne CNT concentrations, but also other metric parameters, i.e. fibre number and surface area, which may better represent the effective dose for adverse health effects. In this scenario, innovative field-portable, near real-time instruments, and personal samplers can meaningfully provide more timely and accurate aerosol characterisation.

Discussion The extrapolation of definite evidence for CNT risk characterisation seem a challenging issue due to great heterogeneity of these materials. Suitable toxicity models able to predict fiber-type pathogenic effects according to specific physico-chemical characteristics and doses of exposure should be pursued for a suitable risk assessment process. These may be important also for the definition of appropriate occupational exposure limits to manage the exposure and protect workers’ health.