nano sized particles and respiratory system

most nano -sized solid materials will easily enter the lungs and reach the alveoli these particles can be cleared from the lungs as long as the clearance mechanisms are not affected by the particles themselves or any other cause nano-sized particles are more likely to hamper the clearance resulting in a higher burden possibly amplifying any possible chronic effects causes by these particles it is also important to note that specific particle surface area is probably a better indication for maximum tolerated exposure level than total mass inhaled nano -fibres diameter smaller than 100 nm also can enter the alveoli and their clearing would in addition depend on the langth of the specific fiber