Radiation, Water Quality and the Fukushima Disaster

On March 11, 2011, Japan’s Fukushima No. 1 Nuclear Power Plant withstood shaking from the fourth largest earthquake recorded worldwide in over one hundred years. However, the 19 foot-high seawall separating the facility from potential oceanic onslaughts could not withstand the tsunami that followed. The plant flooded, electrical power to the cooling system was lost, and the reactors overheated, triggering a release of radioactive material into the environment. In the wake of the accident, there has been much discussion regarding the contamination of air, soil, food, the oceans and drinking water. Some concerns related to drinking water are addressed in this communication.

Radiation in Perspective

Accidents involving radiation elicit emotional responses worldwide. Such reactions are understandable, given the devastation wreaked by nuclear weapons at Hiroshima and Nagasaki, and the simple fact that radioactive phenomena are undetectable by our five senses. However, much of the angst concerning very low levels of radiation is unfounded, and the nuclear accident in Japan, and the ensuing exposures, should be considered in light of dosages, the power of dilution, and our natural radiation environment.

Radiation is a general process by which particles or waves move through matter or space, and describes phenomena such as visible light, radio waves, the radiation from radioactive materials, and X-rays. Radiation can be classified as ionizing or non-ionizing: examples include X-rays, and radio waves, respectively. Ionizing radiation, such as that produced as a consequence of radioactivity, is energetic enough to knock electrons from atoms, making them more reactive, and capable, therefore, of doing biological damage.

Although radiation sounds frightening, life on Earth has been bathed in a natural ionizing radiation environment for billions of years; uranium, thorium, potassium, and other radioactive elements are natural parts of the Earth’s crust. Our food, the soil in our backyards, and the masonry of our houses are naturally radioactive. Carrying a banana in your lunch bag exposes you to ionizing radiation by virtue of its potassium content: approximately one in every 10,000 potassium atoms in the banana is naturally radioactive.

All the sources of natural radiation contribute to our “natural radiation background” and in some places on Earth, the natural background is on the order of one hundred times higher than average, without ill effects to humans.  A major principle of environmental science states that “the dose makes the poison.” Ionizing radiation is not intrinsically dangerous: the danger lies in our being exposed to a sufficient dose to cause biological damage. Our bodies are continually damaged by the action of oxygen and other outside agents, including very low levels of ionizing radiation, and our bodies possess the ability to repair some of this damage.

Fukushima and Surrounding Areas


Two of the dominant radioactive substances released from the Fukushima reactor, iodine-131 and cesium-137 (I-131 and Cs-137, respectively), commonly form water-soluble compounds that can find their way into drinking water supplies. I-131 can be transported long distances in the atmosphere as a gas, and can be transferred from the air to water supplies by the action of rainwater. I-131 has a half-life of 8 days: that means a capped bottle of water containing I-131 will have only half the concentration of I-131 after 8 days, a quarter after 16 days, and so on. Cs-137 forms solid particles that can fall out of the atmosphere more easily than the gaseous forms of I-131.  With a half-life of 30 years, Cs-137 persists in the environment for much longer than I-131.

Following the tsunami, drinking water in Tokyo had measurable I-131 (e.g., 200 Becquerels [i]/liter of water). What was the risk to human health from drinking that water?  Let’s say that two liters of the water were consumed by an individual each day for two months. Assuming no further iodine is added to the water, the concentration of I-131 decreases with time due to its half-life. The effective dose, then, would amount to only about one-thirtieth of a yearly dose of the natural radiation background. Dilution, another important factor, can lower the radioactivity of I-131 in a water supply. Cs-137 persists longer, but dilution and dispersal of Cs-137 can reduce exposure. For a snapshot in time of the relative radioactivity of Cs-137 to I-131, in Ibaraki Prefecture, south of Fukushima, the relative radioactivity of Cs-137 in drinking water in late March was approximately 10 percent of that of I-131.

Outside of Japan, the effect of dilution and dispersal was apparent: I-131 in rain water from Berkeley, California in late March was 40-50 times lower than the concentrations found in Tokyo tap water. Compared to the natural radiation background in the U.S., these values were quite insignificant. By mid-April, both I-131 and Cs-137 were below detectable levels in the Berkeley rainwater.

The fact that we can analyze for a substance in water does not necessarily mean that substance will damage health.  This is another important environmental corollary of “the dose makes the poison.” Finally, the most commonly overlooked problem regarding water quality in the wake of the unfortunate events in Fukushima is the unwarranted fear of very low level radiation.

Philip A. Candela, Ph.D., is Professor of Geology at the University of Maryland, and is a physical geochemist specializing in economic geology, resources and security.

[i] A Becquerel is a unit that represents one radioactive disintegration of a radioactive atom per second.