When carcinogens are considered, the EPA generally takes which approach?

• A. Takes a zero-tolerance approach
• B. Assumes that a threshold exists
• C. Takes a zero-close, zero-response approach
• D. Assumes that high levels can be tolerated if exposure is brief

Answer: (C)

Carcinogens are treated as non-threshold hazards: there is no safe level of exposure. Any amount can contribute to cancer risk, and that risk increases with the dose. In practice, the EPA uses a linear no-threshold approach, meaning there’s no dose low enough to guarantee zero cancer risk and risk is estimated to rise in proportion to exposure. This concept is captured by describing the approach as one that assumes no safe dose (zero risk only at zero exposure, but any positive exposure carries some risk). The other ideas—zero tolerance of any exposure, a defined threshold below which there’s no risk, or tolerating brief high exposures—do not align with how carcinogens are evaluated, since the default expectation is that there is some risk at any nonzero level of exposure.