Model-based assessment for human inhalation exposure risk to airborne nano/fine titanium dioxide particles.

This paper proposed a model-based approach to assess inhalation risk levels to manufacturing workers in titanium dioxide (TiO2) production factories. The risk level-based analytical schemes were present for investigations of job-related airborne nano/fine TiO2 dust exposures. A Hill model was used to reconstruct dose-response function based on data from rats exposed by chronic inhalation to poorly soluble fine and nanosized particles. A physiologically based lung model was used to predict surface area-based TiO2 burdens in alveolar surface and interstitial granuloma, respectively. The exposure effect was characterized by polymorphonuclear leukocytes (PMN) elevation effect on lung surface and lung tumor proportion on interstitium. Combining laboratory, field, and modeling results, two major findings were proposed to the current epidemiological studies: (i) the estimated median effective surface area-based TiO2 lung burden (EC50) for PMN elevation effect is 0.11 m2 g(-1) lung (95% CI: 0.04-0.2) and EC50 for lung tumor proportion is 1.15 m2 g(-1) lung (95% CI: 0.65-1.89) and (ii) the estimates of risk curves are the pivotal results for public policy. The results demonstrate that packers in US factories have approximately 85.77 fold (95% CI: 63.84-94.33) of standard PMN counts of 10(6), whereas 86.97 fold (95% CI: 66.72-94.54) for surface treatment workers in EU factories at risk of 0.5. The lung had approximately 45% (95% CI: 15%-54%) tumor proportion for packers in US factories, whereas 48.19% (95% CI: 20-53.79%) for surface treatment workers in EU factories at risk of 0.5. The findings point out that dry/wet treatment and ore handlers in US and maintenance mechanics in EU factories were unlikely to pose substantial lung cancer risks.