Carbon nanotube risk assessment: implications for exposure and medical monitoring.

OBJECTIVE: Quantitative risk estimates using toxicology data provide information for risk management to protect workers with potential exposure to carbon nanotubes (CNTs). METHODS: Dose-response data from subchronic inhalation studies in rats were used in benchmark dose modeling. Dose was airborne mass concentration of multiwalled CNTs. Responses included pulmonary inflammation, lipoproteinosis, and fibrosis. RESULTS: Estimated human-equivalent concentrations to the rat lowest observed adverse effect levels were similar to some workplace airborne concentrations of CNTs. Working lifetime risk estimates of early-stage adverse lung effects were more than 10% at the limit of quantification (7 µg/m³) of the National Institute for Occupational Safety and Health analytical method for measuring CNT airborne concentrations. CONCLUSIONS: Exposure monitoring and control are the primary occupational health measures to protect workers from potential exposure to CNT. Medical monitoring for early detection of occupational respiratory diseases may also be warranted.