Step 2.1 Estimating Exposure Doses

Example of an Ingestion Dose for Evaluating Noncancer Health Effects

The following example involves the calculation of a noncancer dose and a cancer dose for a gardener exposed to arsenic in surface soil for 35 years where the following assumptions are made.

The arsenic concentration is eleven milligrams of chemical per one kilogram of soil.

The intake rate for incidental ingestion is one hundred milligrams of soil per day.

The exposure factor is based on five days per week, twenty-six weeks per year, for thirty-five years.

The body weight is seventy kilograms.

To calculate the noncancer exposure factor, multiply five days per week by twenty-six weeks per year by thirty-five years. Then divide the product by three hundred sixty-five days per year times thirty-five years. The noncancer exposure factor equals 0.36. Then divide the numerator by the denominator.

Note: if the exposures are daily, then the exposure factor is one.

To calculate the site-specific dose, multiply eleven milligrams of chemical per kilogram of soil by 100 milligrams of soil per day by 0.000001 kilograms of soil per milligram of soil by the exposure factor of 0.36. Then divide the product by seventy kilograms, which is the body weight.

The 0.000001 kilograms of soil per milligram of soil is used to convert the arsenic level from milligrams of chemical per kilogram of soil to milligrams of chemical per milligram of soil.

Using this calculation, the dose is equal to 0.000006 milligrams of chemical per kilogram of body weight per day.