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Water: Water Quality Standards Academy

Basic Course: Supplemental Topics - Health (s)

Toxicological Parameter for Cancer Effects (Nonlinear): POD/UF

Human Health Ambient Water Quality Criteria

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The following equation is used for deriving nonlinear cancer human health AWQC (mg/L):

formula8

The nonlinear approach is only an option if the mode-of-action information supports a zero slope at a dose of zero. In other words, there are some doses where there is no risk.

In such an instance, a Point of Departure or an estimate of a dose near the bottom of the dose-response curve for tumors or a precursor effect is selected and divided by an Uncertainty Factor to arrive at the value that will be used for the calculation. The POD/UF term in the equation for a carcinogen with a nonlinear response to dose is analogous to the RfD in the noncancer human health AWQC equation except that it applies to a tumor precursor event or tumor incidence as the POD. Cytotoxicity and regenerative hyperplasia are examples of precursor events that can serve as a POD for a carcinogen with a nonlinear response to dose.

key point
Key Point. A mode of action is an experimentally documented sequence of key events starting with the interaction of an agent with a cell, proceeding through functional and anatomical changes, and resulting in cancer formation. In other words, there is no cancer risk at doses below those that cause the precursor cellular events.

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

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