Radioactive Iodine-131

The means by which radioactive materials can be transmitted to humans include ingestion of surface and ground water, fish and wildlife, and dairy products - primarily milk - passed through cows which have fed on crops exposed to airborne contaminants. Exposure to radioactive Iodine-131 released from Hanford has largely been in the latter form. Between 1944 and 1951 approximately 730,000 curies of radioactive Iodine-131 were released from the Hanford reactors, most of it in 19451.


Once consumed by humans, the thyroid gland receives the highest concentration of radioactive iodine. As a result, the question of thyroid related medical problems, hypothyroidism in particular, continues to be studied among Hanford downwinders and those exposed to the release of radioactive Iodine-131 around the world.

Wind can come from any direction at Hanford. Open the Hanford Map and close all but the Hanford & Nearby Weather Stations and Oregon & Washington layers. Zoom in on the Hanford area. Clicking on any of the weather station sites opens a popup window containing a wind rose depicting wind speed and direction information from June 2010 thru May 2011.


Use the information from each weather station to complete the following table:



Wind Predominately From

Normal Wind Speed



Mill Creek




Saddle Mt.


Columbia National Wildlife Refuge


Juniper Dunes





Turn on the Iodine Radiation layer in the map. The layer shows zones of decreasing dispersal of radioactive Iodine-131 from Hanford out. Click in any zone to see the approximate cummulative dose from 1944 thru 1960 in that region for a child consuming locally processed dairy products and produce.1

To Start You Thinking

1) Describe the predominate wind pattern in the area around Hanford using the results from the table you completed above. Now add a layer to the map from the National Oceanic & Atmospheric Administration (NOAA) showing the current wind speed. Describe how today's wind flow compares with the typical pattern.

Click to Modify Map and Add Content ( Add File ) from ArcGIS Online.

Enter the search term NOAA Wind Speed

Add the USDOC NOAA Global Surface Wind Observations layer


Zoom in to the Hanford area.

When you click on one of the arrows keep in mind that Wind Direction is a 0 - 360 degree compass value giving you the direction the wind is from. For example, a value of 270 indicates wind from the west.

2) There is radiation exposure in our day-to-day lives. Do some research and identify at least five different common sources of radiation that we may be exposed to over a year. Discuss how much exposure this is compared to the cumulative doses of Iodine-131 experienced around Hanford.

3) The Hypothyroidism layer in the map shows the rate per 100,000 population of cases of hypothyroidism reported by individuals who were children in the Hanford region from 1944 to 1960.2

Change Style and map the of Rate of Hypothyroidism. Describe how the pattern of rates of hypothyroidism compares with the dispersal of Iodine-131 from Hanford.

4) The hypothyroidism data in your map comes from a small study conducted by doctors and researchers working for the Northwest Radiation Health Alliance, a group of downwinders and volunteers interested in studying the health related effects of radiation releases from Hanford. A larger scale study recently completed by the Centers for Disease Control released its conclusions in 2009. Read the Overview of the study. Compare and contrast their findings with your conclusions from analyzing the data in your map.


1The Technical Steering Panel of the Hanford Environmental Dose Reconstruction Project, Summary: Radiation Dose Estimates from Hanford Radioactive Material Releases to the Air and the Columbia River, April 21,1994, p 31.

2John R. Goldsmith, et. al, Juvenile Hypothyroidism among Two Populations Exposed to Radioiodine, Environmental Health Perspectives, Volume 107, Number 4, April 1999, 303-308.

Last modified in August, 2019 by Rick Thomas