Step 1.5 Using Comparison Values

ATSDR Values

ATSDR's comparison values are based on chemical-specific toxicologic information derived from human and animal studies, and on the conservative assumption that a person will come in contact with the chemical every day throughout the exposure period.

Here are some available comparison values.

ATSDR has developed an environmental media evaluation guide, called the EMEG, and a cancer risk evaluation guide, the CREG.

Comparison values available from EPA include maximum contaminant levels, MCLs; reference dose media evaluation guides, RMEGs; health advisories for drinking water; EPA Region 3 Risk-Based Concentration Tables; soil screening levels; and national ambient air quality standards.

Other comparison values have been developed by the Food and Drug Administration (advisories), and state and local agencies have established state and local standards.

Following is an example of a comparison value calculation for Aroclor 1254 for an adult exposure.

To calculate the environmental media evaluation guide, you must multiply the minimum risk level by the body weight and divide the product by the intake rate.

In this case, multiply 0.00002 milligrams of chemical per kilogram per day by seventy kilograms (which is the assumed body weight for an adult) and divide the number by the intake rate.

The intake rate is the soil ingestion rate in kilograms per day. Often the intake rate is provided in milligrams per day. You must convert milligrams per day to kilograms per day. To do this, multiply one hundred milligrams of soil per day by 0.000001 kilograms of soil per milligram of soil. Then divide the numerator by the denominator to calculate the environmental media evaluation guide for Aroclor 1254 for an adult exposed to the soil containing the chemical.

The answer is fourteen milligrams of chemical per kilogram of soil.

Round to one significant figure. The final answer is ten milligrams of chemical per kilogram of soil.

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