Human and Ecological Risk Assessment - Earthjustice

Section 3.0Analysisa per kilogram body weight basis. Doses were then summed over the exposure duration,resulting in an ADD received from ingestion exposure. The ADD was used to assess noncancerrisk from ingestion exposures and is defined aswhereADD C ×= IR(3-2)C = average concentration (mass/volume or mass/mass)IR = intake rate (mass/body weight mass/time, or volume/body weightmass/time).Contaminant concentration represents the concentration of a chemical in a medium thatcontacts the body. The ADD was calculated from concentrations averaged over the exposureduration for each receptor.For cancer effects, where the biological response is described in terms of lifetimeprobabilities even though exposure may not occur over the entire lifetime, dose is presented as aLADD. The LADD was used to assess cancer risks from each exposure route (i.e., ingestion) andis defined asLADDC IR ED ×××EF= (3-3)AT × 365whereC = average concentration (mass/mass or mass/volume)IR = intake rate (mass/body weight mass/time, or volume/body weightmass/time)ED = exposure duration (yr)EF = exposure frequency (d/yr)AT = averaging time (yr)365 = units conversion factor (d/yr).As with the ADD, contaminant concentration represents the concentration of a chemicalin a medium that contacts the body. Intake rate depends on the route of exposure; for example, itmight be an inhalation rate or an ingestion rate. Exposure frequency is the number of days peryear the receptor is exposed to the contaminated source during the exposure duration.For cancer effects, biological responses are described in terms of lifetime probabilities,even though exposure may not be lifelong; consequently, the exposure duration (the length oftime of contact with a contaminant) was used to average the ADD over a lifetime (70 years). Themedia concentrations used were averaged over the duration of exposure.3.9 Risk EstimationThe final step of the risk assessment process is to estimate the risk posed to human andecological receptors (e.g., residents, fishers; aquatic organisms). In this step, estimates of toxicityApril 2010–Draft EPA document. 3-44