Differences in chemical and crystalline composition, fiber dimension, aerodynamic characteristics and biodurability are among the critical factors that define the toxicological and pathological consequences of asbestos exposure. Specifically, fiber dimension can impact whether the fiber is respired, whether and how deeply it is deposited in the lung, and how efficiently and rapidly it may be cleared. This paper provides a current, comprehensive evaluation of the weight of evidence regarding the relationship between asbestos fiber length and disease potency (for malignant and nonmalignant endpoints). In vitro studies, animal exposure studies and epidemiology data were reviewed. We found that the data reported over the last several decades consistently support the conclusions that exposure to fibers longer than 10 µm and perhaps 20 µm are required to significantly increase the risk of developing asbestos-related disease in humans and that there is very little, if any, risk associated with exposure to fibers shorter than 5 µm. Fiber length as a predictor of potency has been evaluated by several federal agencies in the U.S. and could significantly influence future regulatory decisions for elongated mineral particles (EMPs) and high-aspect ratio nanoparticles (HARNs).
Keywords: Asbestos; fiber length; fibrosis; lung cancer; mesothelioma; risk assessment; short fiber.