CDI and its role in risk assessment.

• A. CDI stands for Chronic Daily Intake and is used in HQ and ILCR calculations; HQ = CDI/RfD; ILCR = CDI × CSF.
• B. CDI stands for Chronic Dose Index and is not used in risk assessment.
• C. CDI is the immediate dose received per event and is used for acute risk.
• D. CDI is only used for non-cancer risk and not ILCR.

Answer: (A)

Chronic Daily Intake is the amount of contaminant a person is exposed to on average each day over a defined period, expressed in mg/kg-day. This single metric links how much someone accumulates over time to the risk they may face. In non-cancer risk assessment, the Hazard Quotient uses CDI divided by the reference dose (RfD); when CDI exceeds the RfD, there’s concern for non-cancer effects. For cancer risk, the same chronic exposure estimate is used but combined with the cancer slope factor: Incremental Lifetime Cancer Risk equals CDI multiplied by CSF, giving a probability of developing cancer over a lifetime due to that exposure. So CDI is central to both non-cancer risk calculations (via HQ) and cancer risk calculations (via ILCR). The other descriptions misdefine CDI or limit its use: it’s not a “Chronic Dose Index,” not the immediate dose per event (that reflects acute exposure), and it’s applicable to ILCR as well as non-cancer risk.