Question

An adult male, 150 pounds, consumes water contaminated with 1 milligrams of DDT per liter for three years at a rate of two liters per day. Assuming the man does not receive any does of DDT other than this, by how much is this amount (the average daily intake accumulated in those three years) above the life-time safety exposure limit of 0.02mg/kg body weight?

Also, given this scenario would the ADI life-time safety exposure limit be an appropriate measure of this man's risk? Why or why not?

Answer 1

Acceptable daily intake or ADI is a measure of the amount of a specific substance (originally applied for a food additive, later also for a residue of a veterinary drug or pesticide) in food or drinking water that can be ingested (orally) on a daily basis over a lifetime without an appreciable health risk.ADIs are expressed usually in milligrams (of the substance) per kilograms of body weight per day.

ADIs are based on NOAELs (no-observed-adverse-effect-level), but are not considered an absolute physiological threshold; they are based on safety factors that reflect variations in the population. Therefore, values for ADIs are significantly lower than values of corresponding NOAELs .

Reference doses (RfDs) are a regulatory parameter also based on NOAELs. The RfD is used by the EPA(Environmental Protection Agency) in place of the ADI (which sometimes results in lower values for acceptable intakes). Safety factors are used in the derivation of RfDs to account for hypersensitivity reactions. RfDs usually incorporate two safety factors: (i) a factor of 10 for variation among individuals and (ii) another factor of 10 for extrapolation from experimental animal data to humans. Another safety factor that may be used with the RfD is a “modifying factor” ranging from 1 to 10, which is based on professional judgment. The procedure for establishing RfDs is somewhat more detailed than for ADI development, and includes use of the most sensitive species, the appropriate route of exposure, and the most sensitive end point. RfDs have become a widely used indicator of chronic toxicity, and have been established for oral and inhalation routes.

The reference dose (RfD) for DDT is 5×10^-4mg/kg/day