Sub-module 2B, Page 1

 Sub-module 2B  Begin fate and persistence, Pathways - qualitative - conceptual site models (CSMs). Environmental media.

Learning Goals:

Introduce Exposure Assessment


Unlike laboratory animals where exposures are deliberate and carefully controlled, exposure to chemicals in the environment vary from location to location and over time. Analyzing the dose to the human receptor requires an analysis of the fate and transport of the contaminant. Here is a figure from RAGS, Chapter 6, that says a lot.

Note some things:

1. The Primary Source is the drum field. The contaminant is released from the drums. This sudden spill or gradual leak is the "release mechanism" for the contaminant.

2. The soil is now contaminated under the drums. This soil will remain contaminated after the drums are removed. This soil is now a "source" as contaminants continue to leach out of the soil and/or are volatilized from it.

3. There are three "mediums" that are contaminated, but since the contaminant is moving in or through two of the mediums, we think of these as transport media, rather than "sources." Soil might be a transport media, if it is blown by wind or moved by water runoff.

4. There are three different "receptors," one is a worker at the site, the other is a person in their home, and the peripatetic third, perhaps he is a trespasser.

5. The contaminant that leaches from the soil enters the groundwater, then is carried by the groundwater flow to a drinking water well.

6. The occupant of the building is exposed by drinking the water. She might also be exposed via inhalation, if the contaminant is volatilized from the water in the shower or by cooking.


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