RESEARCH IN ENVIRONMENTAL EPIDEMIOLOGY - SELECTED METHODOLOGICAL ASPECTS

Research in environmental epidemiology deals with physical, chemical a nd biological agents whose presence - or relative absence - within the different media coming into contact with human beings (air, water, so il, food, etc...) may be harmful to human health. Some ((major,, envir onmental risk factors are well known. In a number of situations, howev er, environment-disease associations are ''weak''. This does no rule o ut the possibility that the exposures involved have a significant impa ct on human health, considering their prevalence which is frequently h igh. However, this complicates their study owing to the potential impo rtance of biases as well as that of sampling fluctuations. Although in creasing study size is of crucial importance, it is not sufficient to establish a clearcut distinction between ''weak'' associations and ''d iluted'' ones. To improve our knowledge of health risks which are asso ciated with environmental exposures, the basic methodological principl es of epidemiological research - to define and adequately measure expo sures, health outcomes, confounders and effect modifiers - may be very valuable to approach the study of ''weak'' associations : I) identify ing and quantifying the presence of the agents of interest in the envi ronment, studying the distribution of environmental exposures among in dividuals and its determinants, taking into account the whole history of personal exposures and integrating adequately the short term time v ariability of exposures, giving special attention to the type and inte nsity of exposures may help in the definition and measurement of expos ures; 2) carefully analyzing the interactions which may exist between the physical, chemical and biological agents of interest and the human body may greatly help in the elaboration, measurement and validation of relevant health outcomes (exposures to the target organs, early les ions and health impairments) ; 3) this same approach may also greatly contribute to the identification of constitutional or acquired individ ual characteristics which may interact with environmental agents in th e development of diseases. While there is no guarantee that such appro aches will successfully discriminate between ''weak'' and ''diluted'' associations, it is likely that inconclusive epidemiological evidence will be very difficult to avoid if such approaches are neglected by en vironmental epidemiologists.