Biomarkers are very useful in the world of exposure assessment when dealing with direct measurement methods. The use of biomarkers in exposure studies is also referred to as biomonitoring. They are chemicals, metabolites, susceptibility characteristics, or changes in the body that relate to the exposure of an organism to a chemical. Biomarkers have the ability to identify if an exposure has occurred, the route of exposure, the pathway of exposure, or the resulting effects of the exposure.