Environmental epidemiology: Challenges and opportunities

Epidemiology is struggling increasingly with problems with correlated expos ures and small relative risks. As a consequence, some scholars have strongl y emphasized molecular epidemiology, whereas others have argued for the imp ortance of the population context and the reintegration of epidemiology int o public health. Environmental epidemiology has several unique features tha t make these debates especially pertinent to it. The very large number of e nvironmental exposures require prioritization, and the relative risks are u sually very low. Furthermore, many environmental exposures can be addressed only by comparing populations rather than individuals, and the disruption of both local and global ecosystems requires us to develop new methods of s tudy design. The population context is also very important to consider in r isk management decisions because of the involuntary nature of most environm ental exposures and the diversity of possible outcomes, both health- and no nhealth-related. Studies at the individual or molecular level tend to focus the research hypotheses and subsequent interventions at that level, even w hen research and interventions at other levels may be more appropriate. Thu s, only by starting from the population and ecosystem levels can we ensure that these are given appropriate consideration. Although better research is needed at all levels, it is crucially important to choose the most appropr iate level, or levels, of research for a particular problem. Only by conduc ting research at all these levels and by developing further methods to comb ine evidence from these different levels can we hope to address the challen ges facing environmental epidemiology today. Key words: environmental healt h, epidemiology, methodology.