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Water: Water Quality Standards Academy

Basic Course: Supplemental Topics - Health (n)

Toxicological Parameter for Cancer Effects (Linear): RSD

Human Health Ambient Water Quality Criteria

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The following equation is used for deriving linear cancer human health AWQC (mg/L). Note that the exposure and BAF terms in the equation have not changed except that this equation does not include an RSC.

formula7

The linear cancer toxicological parameter needed for this calculation is the Risk Specific Dose (RSD) (mg/kg-day), which equals the acceptable risk level divided by the Cancer Slope Factor (CSF).

EPA recommends using the RSD for a one-in-a-million extra risk (10-6 risk), but also accepts a one-in-a-hundred-thousand risk (10-5 risk) as long as the risk for highly exposed individuals does not exceed a one-in-ten-thousand (10-4) risk. The “extra” term in the definition of the RSD refers to a risk from environmental exposure to the chemical of interest above the background risk that is always present.

The RSD is derived by dividing the risk of interest (i.e., one-in-a-million) by the cancer slope factor (CSF or Q1* —note, however, that the Q1* abbreviation for the slope factor is gradually falling out of use):

Equation: RSD = 1/1,000,000 divided by CSF = 0.000001 divided by CSF.

Resource. The CSF (Q1*) values for individual chemicals can be located in their files in EPA’s IRIS database.


Disclaimer:
For informational purposes only–Not official statements of EPA policy.

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