A contaminant can enter the body and exert its toxic effect through inhalation, ingestion, or absorption through the skin. As mentioned above, external sources of radioactive contaminants can also be harmful. This section is concerned with quantification of contaminant intake through inhalation, ingestion, and skin absorption. Throughout the discussion, default and typical values are given. However, a complete exposure assessment requires a more accurate estimation of the uptake rates for the population actually exposed, along with the uncertainty and variability in these estimates. Default values are useful primarily for screening and should not be taken as representative of the exposed population without further verification. Detailed guidance on exposure assessment and exposure factors is provided in EPA documents (EPA 1992, 1997, 2004).
Contaminant intake rate is the mass or activity of contaminant entering the body per unit time,
where ï is the rate at which the contaminant enters the body [M/T for chemicals or activity/T for radionuclides] and CR is the contact rate with the contaminated medium [L3/T for inhalation, L3/T for ingestion of water, M/T for ingestion of food, L3/T for skin absorption from water, and M(s)/T for skin absorption from soil]. For ingestion and inhalation, the contact rate is sometimes called the uptake rate.
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