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Environmental Epidemiology

1. Epidemiologic methods developed for use in the study of other chronic diseases are applicable to the field of environmental epidemiology.
2. Study designs range from experimental studies (most conclusive) to case series and cluster investigation (least conclusive).
3. 1. An experimental study design is rarely applied to environmental exposure based on the fact that it is unethical to intentionally expose individuals or communities to environmental hazards.
   2. Analytic designs, cohort and case control studies, are frequently the design of choice in environmental health studies of the cause of human health effects in relation to environmental exposures.
   3. Cluster investigations are often used to respond to community concerns about an excess of cancer or birth defects.
   4. 1. Cluster investigations usually render negative or equivocal results.
      2. Cluster investigations are most convincing when the disease in question is rare and very specific for the putative etiologic exposure as is the case in asbestos causing mesothelioma.
   5. Limitations inherent in environmental epidemiology include the following.
   6. 1. Exposures are often poorly defined and measured.  There is insufficient health effect information for over 90% of the 70,000 chemicals used in the US. 
      2. A very limited understanding of the health effects of mixed exposures makes studying the most common type of environmental exposure situations particularly challenging.
      3. Often a relatively small number of individuals (e.g. a community) constitute the study populations yielding limited statistical power to detect an association between the exposure(s) of concern and health effects.
      4. A lack of understanding of the variability in the susceptibility of segments of the populations (e.g. the poor, children, elderly) is a challenge to any epidemiologic study of a heterogeneous population and limits our ability to compare finding across studies.
      5. The long latency between many environmental exposures and the evidence of chronic disease, in particular cancer, creates additional challenges to exposure assessment.