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Step 1.5 Using Comparison Values


Comparison values are doses (termed health guidelines) or substance concentrations (termed environmental guidelines) set well below levels that are known or anticipated to result in adverse health effects. Comparison values are derived from scientific studies and modified by safety factors to be more protective of human health.

ATSDR's comparison values are developed for a specific chemical in each of three environmental media: air, soil, and drinking water. If a chemical is found at a level above the comparison value and people can contact the chemical, the health assessor selects the chemical for further evaluation. Also, if a chemical is found that people can contact, but there is no comparison value for that chemical, it is selected for further evaluation. Chemicals found at levels below comparison values are not selected.

Health assessors must keep in mind that comparison values are media-specific doses or concentrations of chemicals considered safe for human contact and that they are used to select chemicals for further evaluation. Comparison values are conservative values, with safety factors added to protect human health, and they are suitable for use at any site.

Health assessors must also keep in mind that comparison values are not clean-up levels and they are not indications that exposure above the values will be harmful. Comparison values are not intended to be used in evaluating or predicting health effects from exposure.

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