The concept of cause in epidemiology has multiple implications because modern science is universally predicated upon the cause and effect relationships. Differences between traditional, infection-oriented and present, ecology–oriented epidemiology show major difficulties in identifying causality of non-specific diseases that are attributed to environmental factors. While epidemiology remains primarily a set of techniques tightly bound to other biomedical sciences and operates in a widely open area of population health, variables such as complex interactions and numerous confounding or ethical constrains frequently render causal interpretation of the observed increases in disease rates virtually impossible. In the specific case of air pollution by solid particles, large differences exist between exposures determined by stationary sampling sites and personal monitoring, between the outdoor and indoor exposures (people spend more time indoors than outdoors) and between the total inhaled dust and respirable portions retained in the lung. Biological monitoring can be of substantial help for more accurate exposure assessment. Similarly, principles developed for establishing causality in community studies show that general consensus exists in the scientific community concerning factors required for conversion of the observed associations into causal relationships. However, evidence from published reports suggests that community studies comply only with a fraction of required conditions for attributing causality to a single factor i.e. inhaled particles. No plausible mechanisms exist that would explain the role of daily fluctuations in ambient particles on mortality or morbidity rates across communities that vary in pollutant sources, climate and geography. More information is needed before inhaled particles can be ultimately declared as the factor responsible for the observed effects. Unless a better explanation of the mechanisms of particle effects is provided and major uncertainties in assessing actual exposures are removed, the divergence of opinion in the scientific community will remain unresolved.

        Key words: air pollution, solid particles, exposure assessment