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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.

Click on the headings below  to see what comparison values are and are not.

Comparison values are

	checkmark Doses of concentrations set well below levels known to result in adverse health affects

	checkmark Media-specific concentrations of chemicals considered safe for human contact

	checkmark Used to select chemicals for further evaluation

	checkmark Conservative values, with safety factors added to protect human health

	checkmark Suitable for use at any site

Comparison values are not

	cross mark Clean-up levels

	cross mark Indications that exposure above the values will be harmful

	cross mark Intended to be used in evaluating or predicting health effects from exposure

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