Exposure Assessment

• Example of an Intake Equation for Ingestion of Drinking Water

Intake (mg/kg-day) =

CW x IR x EF x ED

BW x AT

CW = Concentration in water of chemical of concern (mg/l)

IR = Ingestion Rate (l/day)

EF = Exposure Frequency (days/yr)

ED = Exposure Duration (yr)

BW = Body Weight (kg)

AT = Averaging Time (period over which exposure is averaged) (days)

For noncarcinogens: AT = ED * 365 days per year and intake is called Chronic Daily Intake (CDI).

For carcinogens: AT = Lifetime (70 years) * 365 days per year and intake is called Lifetime Average Daily Dose (LADD).

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Intake is mg of chemical per kg of body weight per day.

Averaging time is different for non-carcinogens and carcinogens. The carcinogenic intake is a prorated cumulative dose over a lifetime and the non-carcinogenic intake is averaged only over the exposure duration. The difference is based on the understanding of the different mechanisms for cancer and non-cancer effects. For cancer the idea is all of the exposures add up - manifests its self any time in your lifetime. For non-cancer effects the idea is the effect happens during the exposure