Epidemiology is the study of how disease is distributed in populations and the factors that influence or determine this distribution. The are five objectives of epidemiology used to address each environmental hazard;
•    Identify the etiology and the risk factors,
•    Determine the extent of the disease found in the community;
•    Study of the natural history and prognosis;
•    Evaluate both existing and new preventative  measures;
•    Provide foundation for developing public policy and regulatory decisions relating to environmental problems such as natural or manmade toxins, water quality, chemical or biological exposure.