Sub-module 5A, page 1

Exposure Assessment

In order to determine the risk of adverse health effects, we need to know the amount of the contaminant that enters the body of the receptor. We start with the amount that is presented to the skin, lungs or GI tract of the receptor's body. We could also say "amount entering the microenvironment of the receptor." After we know that amount, the analysis of toxicity begins with toxicokinetics, specifically issues about absorption.

We have been discussing the source of contaminants, and their chemical fate in the environment. In module 2B you learned some of the basic terminology about contaminants in the environment. Then in 3B and 4A you learned how you might estimate "where the chemicals are going.""Fate" could apply to the area around the source only, or the chemical as it is transported through the environment towards a receptor that may be distant from the source. This transport is likely by the air or water. (Let's ignore regulatory issues about purposely transporting contaminants.) Transport by surface water is fairly straightforward, and you already have some mathematical tools to describe that. Transportation by groundwater is incredibly complex. One needs two or three graduate-level courses in hydrology plus some numerical analysis and computer skills to really have a handle on the transport of contaminants in groundwater. Regarding groundwater transport we will examine some of the complexities, then use a computer program that performs some simple analyses and computations. Air transport is midway in complexity, and we will learn one approximation that is commonly used.

Air transport and use of the model are several lessons away. In this sub-module you will learn a systematic process for defining the pathways that a chemical takes from the source to the receptor, and how to characterize receptors. In Module 6 we will learn how to Quantitate Exposures.

Here is a Department of Energy web site that you should look at in order to get an overview of exposure assessment. Note that the entire RAIS is useful, although they use slightly different terminology than we do, the concepts are the same. There is no need to download the SCEM program, unless you want to. DoE Tutorial. Then go to MODULE #3: DEVELOPING A SITE CONCEPTUAL MODEL. Read that section and look at the three examples of CSMs, all three are in common use and all have value: the first for public information, the second for analysis, and the third for reporting. (Be sure to look at all three CSM's from that page.)


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