Answer to Question #9715 Submitted to "Ask the Experts"

Category: Radiation Basics

The following question was answered by an expert in the appropriate field:


I live in eastern Pennsylvania. Recently there has been email and talk about radioactivity from Japan in rainwater. One day it was raining while I went shopping. That day I purchased some spices and cleaning wipes—all in plastic containers. The plastic grocery bags had rain drops and perhaps a few drops migrated onto the merchandise. Does radioactivity remain after the rainwater dries? AND, I continue wearing my jeans and sweatshirt that got rained on—are they radioactive? Also, another worry—it may have transferred to my automobile seat. I'm upset about this. Regards and thank you for your advice and answer.


You are not alone in your concern regarding the significance of the radioactivity that has reached our shores. Unfortunately, there have been numerous reports of "radiation" from Fukushima, Japan, being detected here, and there have not always been sufficient meaningful explanations and/or perspectives given to alleviate undue concerns.

The "radiation" that we actually measure is radiation, such as gamma radiation, emitted by the radioactive material as it undergoes radioactive decay. The levels of radioactivity measured, radioactive iodine (131I) probably being the most notable, have been extremely small. The highest recorded level I have seen has been thousands of times less than any recommended limiting values that would elicit protective action on our part. The radiation levels attributable to this imported radioactivity have been thousands of times less than the natural background radiation levels that we abide on a continuous basis.

It is true that rain and other precipitation can carry radioactive airborne materials to the earth's surface, and this has happened in the case of some of the radioactivity transported from Japan. The concentrations of such radioactivity in rainwater and other media (milk, vegetation, etc.) have been insignificant from a radiation dose impact standpoint.

Any personal items saturated with rainwater would present no radiation hazard to the wearer or user of such items, whether they be wet or dry. In fact, neglecting any other possible contaminants that might have found their way into the rainwater, one could freely drink the rainwater with no concern for negative effects associated with the Fukushima-originated radioactivity.

As an aside, you might be interested to know that the rainfall typically washes out significant amounts of naturally occurring radon gas and some of the radioactive progeny produced by the radioactive decay of the radon. Some of these natural radioactive products in the water would greatly outweigh the amounts of radioactivity associated with the Japanese events, likely by factors of hundreds to thousands.

When rainwater contaminated with radioactive material, such as 131I, falls to the earth's surface and evaporates, some or all of the radioactive material may remain on the surfaces on which the rain fell. This could be a real concern in locations close to the reactor release points in Fukushima, but the amounts reaching this country have been so low that there is no health concern with radioactivity left on vegetation, soil, water, or other media. In summary, I understand your concern, but I can assure you that you need not worry about any negative health effects associated with the tiny amounts of Fukushima-derived radioactive products and the radiations they emit. This assurance extends to considerations regarding your rain-soaked clothing and subsequently dried clothing, food or other packages wet by the rain, your automobile seat, and any other item that might have been affected by the rain. There is no need for you to take any action regarding any of the items you mentioned.

I hope this alleviates your concerns. I'm sorry that you have suffered some anxiety over the releases of radioactivity from the Japanese reactors. Based on actions that have been taken in Japan and the present state of the affected reactors, I expect that radioactivity releases will continue to decrease, reducing even further the quantities that get transported around the world.

George Chabot, PhD, CHP

Answer posted on 5 May 2011. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.