2.0 EXPOSURE PATHWAY MODELS

    This section describes details of the exposure pathway models used in MEPAS. The pathway descriptions are organized by intake route (ingestion, dermal contact, inhalation, and external radiation exposure) and by purpose of transport medium usage (domestic water, aquatic foods, etc.).

    Ingestion pathways include ingestion of drinking water, ingestion of water while showering, ingestion of agricultural products (leafy vegetables, other vegetables, meat, and milk), ingestion of aquatic foods (fin fish and shellfish), ingestion of water or sediment while participating in aquatic recreational activities (swimming, boating, or shoreline use), ingestion of soil, and ingestion of special foods (for which measured pollutant concentrations are available). Dermal exposure pathways include contact with soil, shoreline sediments, and water (while swimming or showering). Inhalation exposure pathways include inhalation of air transported from the release site to the exposure location, inhalation of resuspended particulate material from soil, and inhalation of volatile pollutants released from shower water or other domestic water uses. External exposure may occur from proximity of individuals to radionuclides on ground (deposited from air, deposited onto shoreline sediment, or for measured soil concentrations), in water (swimming and boating), or in air (submersion in a passing plume). The direct radiation dose rate measurement pathway is also an external exposure route.

    Six major transport pathways are considered in MEPAS including special pathways for handling exposure to measured pollutant levels in soils and foods, and measurement of direct radiation fields. These transport pathways and their associated exposure pathways are listed in Table 2.1. This table also indicates the transport medium, the exposure medium, and the intake or exposure route for each exposure pathway.

    The subsections that follow describe the models used for each of the exposure pathways. The discussion for a given exposure pathway defines the

TABLE 2.1. Transport and Exposure Pathway Summary

Transport Pathway		Contaminated Medium		Exposure Route		Exposure Pathways
Ground Water		Water at well location     Water at intake for agricultural production		Ingestion Ingestion Dermal Inhalation Ingestion Ingestion Ingestion Ingestion		Drinking water Water while showering Shower water contact  Air while showering Leafy vegetable Other vegetables Meat Milk
Surface Water		Water at domestic intake location     Water at recreational use location         Water at intake for agricultural production     Water at aquatic food production location		Ingestion Ingestion Dermal Inhalation Ingestion Ingestion Dermal Dermal External External External Ingestion Ingestion Ingestion Ingestion     Ingestion Ingestion		Drinking water Water while showering Shower water contact Air while showering Water while swimming Sediment from shoreline Swimming water contact Shoreline sediment contact Water while swimming Water while boating Shoreline sediment Leafy vegetable Other vegetables Meat Milk     Fin fish Shellfish
Atmospheric		Air at location of people   Soil at location of people		Inhalation External Ingestion Dermal Inhalation External		Air Submersion in air Soil Soil contact Soil resuspension Soil
Ground Water		Water at well location     Air at location of agricultural production   Soil at location of agricultural production		Ingestion Ingestion Dermal Inhalation Ingestion  Ingestion Ingestion Ingestion Ingestion  Ingestion Ingestion Ingestion		Drinking water Water while showering Shower water contact  Air while showering Leafy vegetable Other vegetables Meat Milk Leafy vegetable Other vegetables Meat Milk
Measured Soil		Soil at location of people     Soil at location of agricultural production		Ingestion Dermal Inhalation External Ingestion Ingestion Ingestion Ingestion		Soil Soil contact Soil suspension Soil Leafy vegetables Other vegetables Meat Milk
Measured Foods		Food eaten by people		Ingestion		Food
Direct Radiation		Radiation dose rate at location of people		External		Radiation exposure

transport pathways leading to the exposure pathway, the special transfers and processes considered in determining the pollutant concentration in the exposure medium, and the exposure model used to estimate the average daily dose or lifetime radiation dose. The estimation of health impacts from the average daily dose is described in Section 3.0.