Measurement of human exposure to biologically relevant fractions of inhaled aerosols

Aerosol sampling has evolved with changes in technology and lour understand ing of the importance of assessing the biologically relevant fractions of t he total aerosol. During the past decade there has been international agree ment on the definitions for the inhalable, thoracic, and respirable fractio ns and instruments have been developed to collect samples according to thes e conventions. These measurement techniques are now well established in the workplace and are increasingly being applied to assessments of nonoccupati onal exposure, as the practical difficulties in obtaining samples over 24 h ours have been solved. It is argued that multiple aerosol size fractions sh ould be measured for hazardous substances-such as inorganic lead-in which i nhaled material may either be absorbed in the alveoli (respirable) or clear ed from the ciliated airways in the lung to the gut and then absorbed (thor acic and extrathoracic). Such measurements should improve the evaluation of the risk for inhaled lead, particularly for non-occupational exposure of c hildren. Also, passive aerosol sampling techniques may enable measurements of non-occupational exposure to be made over several weeks and this would a lso help improve the reliability of the risk evaluation for aerosol toxican ts with a long biological half life. However, further development of these techniques is required if they are to be practicable and biologically relev ant.