There the particles need to be cleared by cells of the immune system, a process which takes months or years. Some of the tiny particles are never cleared from the body, but instead accumulate in the lungs and the lymph nodes. 44 Autopsy studies of people living in urban areas show significant blackening of the lungs due to accumulation of fine particles. The small particles which come from diesel exhaust are particularly dangerous because they are coated with a mixture of chemicals such as polycyclic aromatic hydrocarbons, nitroaromatics, benzene, dioxins, and other toxicants. The particles act like a special delivery system which places these toxic chemicals deep within our bodies.
Some asthma medications use the principle of delivering a beneficial drug in a fine inhaled aerosol.
Diesel exhaust is like a perversion of a drug delivery system which delivers hazardous toxicants into our lungs. The particles are retained in the body along with the toxic chemical hitchhikers which would otherwise be quickly eliminated. Thus the particles lengthen our exposures to the toxicants in diesel exhaust. Human Respiratory Tract Model for Radiological Protection, ICRP Publication 66, Elsevier Science Inc., Tarrytown, N. Y 11. Gross, Marilyn, and Richard N. Feldman.