A new approach to evaluation of the fraction of airborne particles that is responsible for adverse health effects has been developed. In this approach a two-fraction concept for the adverse health effects is proposed. This concept considers aerosol particles in the air, the fraction of particles deposited in the respiratory system (captured by the system) and the fraction of particle accumulated in the body (captured by the body). The latter fraction of airborne particles actually causes the adverse health effects and associated with the health risk. The approach has been applied to workers in crystal glass industry exposed to lead. A size resolved sampling technique was employed to characterize nanoparticles at work places at several plants involved in lead processing. Lead aerosol size distributions were obtained across the entire aerosol particle size range from 1 nm to 30 μm (diameter). Size distributions were used to calculate the total lead intake due to particle deposition in the respiratory system of workers. A bio-kinetic model was employed to evaluate various size fraction contributions to the total blood lead level in workers. A comparison was made between calculated blood lead levels and actual measurements of blood lead levels of workers exposed to atmospheres containing lead. It was found that nanoparticles cause the major health risk due to high deposition efficiency and low clearance rate by the mucociliary escalator.