Nanoparticles exhibit properties different from those of the same bulk materials leading to unknown toxicological implications that have evoked concern for (1) occupational, (2) consumer and (3) environmental safety.The current work utilizes epidemiological and toxicological data for screening level assessment of these risks using various suggested health relevant dose metrics (mass, particle number and surface area) to (i) quantify the potential risk levels and to (ii) compare the properties of these alternative risk assessment methods.