Under residential land use, residents are assumed to be exposed to contaminated media on a daily basis over a lifetime. For equations for consumption of farm products, please see agricultural land use . For equations for consumption of fish, please see recreational land use .
Exceptions are tritium and radon.
Tritium is considered because it may exist as either hydrogen gas in water or replace one of the hydrogens found in the water molecule. Radon is considered because groundwater that is in contact with rock or soil containing radium will pick up radon-222 and release it to the atmosphere when the water is used. For the soil and sediment pathway, it is assumed that there is an unlimited potential for surface erosion and the production of particulates and vapor emissions. Because the rate of incidental ingestion of soil and sediment in relation to body weight varies significantly between children and adults, the calculation of the PRG based on carcinogenic risk due to incidental ingestion of soil is calculated using an age-adjusted ingestion factor. Additional information concerning these calculations can be found at the links listed below.