Using Intake Fraction to Define Source to Dose Relationships

Deborah H. Bennett

University of California, Davis

     Abstract Number: 477
     Last modified: January 20, 2010

Abstract
Activities such as comparative risk analysis, life-cycle assessment, emissions trading and sustainable development are creating a growing demand for information about the potential exposure and adverse effects of the thousands of chemicals released to the environment. This demand has fostered measurement and modeling efforts that link emissions to effects for the release of substances from a wide range of human products and activities, such as consumer goods, cooking, smoking, energy conversion, industrial production, and agricultural activities. A source-to-intake metric is useful, allowing researchers to compare the intake resulting from various sources in a clear, straightforward manner. As a result, researchers see a need for, and have proposed, various terms to express source-to-intake relationships. The first known articulation of the source-to-intake relationship was in the field of radiation protection by the ICRP in 1982. In the following years, the idea was expanded resulting in many examples of calculations relating the inhaled intake of a substance to the amount emitted to air, particularly to contrast releases to the outdoor and indoor environments. There were also efforts to estimate multimedia intake by a population relative to a specified release (to air, water, or soil), in these cases contrasting the difference between various chemicals. These examples point out two of the critical attributes in a soure-to-intake relationship, specifically, differences in the emission scenario and differences between compounds. The diversity of fields of inquiry between the investigators, often with a lack of intersection, led to a lack of consistency, particularly with regard to units and calculation boundaries. To promote consistency, a working group formed with the goal of developing a consistent definition and terminology for this idea. The group proposed the term intake fraction (iF) as the primary label for quantifying the source-to-intake relationship. The intake fraction is defined as the integrated incremental intake of a pollutant, summed over all exposed individuals, and occurring at any time, released from a specified source or source class, per unit of pollutant emitted. Work on indoor sources as well as toxic air pollutants continues, by researchers such as Smith, Evans, Guinee, Hertwich, Jolliet, Huijbregts, Nazaroff, Bennett and their colleagues. There have been increased efforts looking at emission of criteria air pollutants from specific source categories. Applications include work on power plant emissions by Levy and colleagues as well as Nazaroff and colleagues. Recent studies by researchers such as Levy and colleagues and Marshall and colleagues have focused on near road exposures, critical for understanding the impacts of a significant emission source for many of the criteria air pollutants. The concept has taken hold internationally, with researchers such as Li in China and Jantunen in Europe conducting studies using this concept. In this talk, the concept of intake fraction will be discussed and relevant works for air pollution by various authors will be highlighted.