A Case for Changing I-131 Transfer Factors Based on Changes in Dairy Industry Practices

Abstract

Following a large-scale radioactive release, transfer factors (TF) are used to estimate the amount of radioactive material retained by an organism. These values are based on the concentration of the consumed radionuclide and where it is deposited in the biological system. TFs exist for several radionuclides but special attention is paid to isotopes which might enter our food chain following a radiological event. Iodine-131 is one of these radionuclides and if ingested by a cow, it will pass through the animal and concentrate in its milk. The milk can subsequently be ingested by humans, with infants being the sensitive pathway. TFs for the grass-cow-milk-infant pathway that are used to assess radiation doses to the public are based on research performed in the 1960s and 1970s. However, the dairy industry has changed drastically in the past 40 years. Dairy cows are now capable of producing more milk due to genetic advancements and administration of hormones. In fact, this increase in production is 5-fold: from 5,000 to nearly 25,000 lbs of milk per cow per year. By examining food intake and other production factors, a sensitivity analysis of the TFs was performed. This preliminary work indicates that TFs used to calculate public dose may no longer be valid and may significantly overestimate potential doses to the public.