DOSE PREDICTION OF DIESEL EXHAUST PARTICULATES IN THE LUNGS (DEPOSITION, AEROSOL)

Diesel powered vehicles have unique advantages over spark-ignition gasoline engines in fuel savings and produce less carbon monoxide and hydrocarbons. However, diesel exhaust particulates (DEP) are potentially hazardous when they are inhaled into the respiratory system. For a reliable assessment of the health impact due to exposure to diesel exhaust emissions, the knowledge of lung burden is ultimately vital.; This study is directed towards developing a model for predicting the dose commitment and retention of diesel exhaust particulates in the lungs under various exposure conditions. To this end, a particle model is first developed to describe the dynamic characteristics of DEP, which are usually in the form of clustered aggregates. Based upon the existing data on lung geometries, deposition calculations are performed for humans as well as for laboratory animals (rats, hamsters, guinea pigs) using parametric analysis and species analogy.; It has been found that deposition of DEP in lungs is diffusion dominated. Over the relevant range of particle sizes, deposition of DEP is quite insensitive to variations in particle physical characteristics, respiratory mechanics, and lung anatomy. Under normal breathing conditions, the percentage of deposition in the alveolar region in human adults was found to be between 7% and 14% with the average value of 10%. The deposition pattern of DEP in humans was found to be similar for all ages; however, with the exception of alveolar deposition at very early ages (before the age of two years), total and regional deposition of DEP in children was always higher than adults under identical exposure conditions. Deposition predictions involving laboratory animals (rats) compared favorably with the available data, and showed similarities to those of humans.; Modeling the retention of DEP in the respiratory tract has also been attempted. Tentative results from the retention model agree well with experimental data obtained from rats. However, care must be taken when quantitively extrapolating animal deposition data to humans since the long term clearance of DEP seems to be dose level related and varies with different species.