Biopersistence, fiber length, and cancer risk assessment for inhaled fibers

We briefly review the evidence that the carcinogenic risk posed by inhaled fibers depends principally on the lung burden of long fibers. We use a deposition clearance model to generate time-dependent lung burdens in rats of a dozen long fibers for various exposure concentrations. Together with a previously estimated potency factor for long fibers, we use the generated lung burdens to estimate risks of lung cancer associated with inhaled fibers in rats. Over a broad range of exposure concentrations, excess risk is a linear function of exposure concentration. Excess risk of lung cancer is also a linear function of weighted half-life for fibers for which the weighted half-life is short compared to the life span of the rat. We propose an approach to estimating human lung cancer risk associated with inhaled fibers from animal studies.