a b s t r a c tInhaled aerosol dose models play critical roles in medicine, the regulation of air pollutants and basic research. The models fall into several categories: traditional, computational fluid dynamical (CFD), physiologically based pharmacokinetic (PBPK), empirical, semi-empirical, and "reference". Each type of model has its strengths and weaknesses, so multiple models are commonly used for practical applications. Aerosol dose models combine information on aerosol behavior and the anatomy and physiology of exposed human and laboratory animal subjects. Similar models are used for in-vitro studies. Several notable advances have been made in aerosol dose modeling in the past 80 years. The pioneers include Walter Findeisen, who in 1935 published the first traditional model and established the structure of modern models. His model combined aerosol behavior with simplified respiratory tract structures. Ewald Weibel established morphometric techniques for the lung in 1963 that are still used to develop data for modeling today. Advances in scanning techniques have similarly contributed to the knowledge of respiratory tract structure and its use in aerosol dose modeling. Several scientists and research groups have developed and advanced traditional, CFD, and PBPK models. Current issues under study include understanding individual and species differences; examining localized particle deposition; modeling non-ideal aerosols and nanoparticle behavior; linking the regions of the respiratory tract airways from nasal-oral to alveolar; and developing sophisticated supporting software. Although a complete history of inhaled aerosol dose modeling is far too extensive to cover here, selected highlights are described in this paper.

The Chernobyl accident was probably the worst possible catastrophe of a nuclear power station. It was the only such catastrophe since the advent of nuclear power 55 years ago. It resulted in a total meltdown of the reactor core, a vast emission of radionuclides, and early deaths of only 31 persons. Its enormous political, economic, social and psychological impact was mainly due to deeply rooted fear of radiation induced by the linear non-threshold hypothesis (LNT) assumption. It was a historic event that provided invaluable lessons for nuclear industry and risk philosophy. One of them is demonstration that counted per electricity units produced, early Chernobyl fatalities amounted to 0.86 death/GWe-year), and they were 47 times lower than from hydroelectric stations ( approximately 40 deaths/GWe-year). The accident demonstrated that using the LNT assumption as a basis for protection measures and radiation dose limitations was counterproductive, and lead to sufferings and pauperization of millions of inhabitants of contaminated areas. The projections of thousands of late cancer deaths based on LNT, are in conflict with observations that in comparison with general population of Russia, a 15% to 30% deficit of solid cancer mortality was found among the Russian emergency workers, and a 5% deficit solid cancer incidence among the population of most contaminated areas.

The established worldwide practice of protecting people from radiation costs hundreds of billions of dollars a year to implement and may well determine the world's future energy system. But is it right? The psychosomatic disorders observed in the 15 million people in Belarus, Ukraine, and Russia 1 who were affected by the April 1986 Chernobyl accident are probably the accident's most important effect on public health. 2 These disorders could not be attributed to the ionizing radiation, but were assumed to be linked to the popular belief that any amount of man-made radiation-even minuscule, close to zero doses-can cause harm, an assumption that gained wide currency when it was accepted in the 1950s, arbitrarily, as the basis for regulations on radiation and nuclear safety.

Personal reflections on radiation hormesis for the past 50 years are presented. The causes of ignoring and rejections of this phenomenon by international and national bodies and by radiation protection establishment are analyzed. The opposition against nuclear weapons and preparations for nuclear war was probably the main factor in inducing the concern for adverse effects of low doses of ionizing radiation, a byproduct of activism against the nuclear weapon tests. UNSCEAR was deeply involved in preparation of the scientific basis for cessation of nuclear test, and contributed to elaboration of the LNT assumption, which is in contradiction with the hormetic phenomenon. However, this authoritative body recognized also the existence of radiation hormesis, termed as ‘adaptive response.’ The political and vested interests behind exclusion of hormesis from the current risk assessment methodology are discussed.

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