Last week, amid anti-nuclear protests, Japan restarted its first nuclear reactor since the Fukushima disaster in March 2011. Despite strong opposition, including from former prime minister Naoto Kan, Kyushu Electric Power put one of the two reactors at its Sendai facility along the nation’s southwestern coast back online. The second is scheduled to restart in October.

In the face of opinion polls showing most voters oppose restarting the country’s nuclear power generation, prime minister Shinzo Abe argued that it is not economically feasible to keep importing foreign oil and natural gas, and that the nation’s increasing dependence on thermal energy threatens greenhouse gas emission reduction goals.

But as Japan’s concerns about its nuclear future grip the nation, North America continues to worry about the ongoing fallout caused by the Fukushima meltdown as ocean currents carry radioactivity to the western coasts of Canada and the United States.

Ethan Stewart, a reporter for the Santa Barbara Independent, wrote about the “drumbeat of terror” that gripped California in early 2014:

The panic started sometime after the New Year. It found its way to my inbox and my Twitter feed, took up residence on my Facebook wall, and dominated conversations with friends and colleagues. I read reports titled “Holy Fukushima — Radiation Already Killing North Americans” and “28 Signs That the West Coast Is Being Absolutely Fried with Nuclear Radiation from Fukushima” and “The Worldwide Nuclear Crisis That No One Is Talking About.” These were no-holds-barred declarations that Japan’s Fukushima nuclear disaster was now a threat to life as we know it here on the West Coast.

But scientists who have analyzed the effects of the nuclear fallout in North America have found precious little to fret about. A month after the disaster, kelp beds off the California coast were contaminated with the short-lived iodine-131, a radioactive isotope with an 8-day half-life. “Kelp forests are some of the most productive ecosystems on Earth,” said Steven Manley, a biologist and kelp expert at the California State University at Long Beach. “One thing about [kelp] is it has a large surface canopy,” he said, pointing to the fact that, because it is always exposed to air, kelp absorbs all the various contaminants in the air. Though Manley said that the presence in the marine environment of iodine-131, a product of nuclear fission that is not found in nature, “was significant,” he added that “it’s definitely not harmful to humans.”

In June 2012, two radioactive isotopes, cesium-134 (with a half-life of two years) and cesium-137 (with a half-life of 30 years), were detected in the seawater at a location some 1500 km (930 miles) west of British Columbia, according to a study published in December and conducted by scientists from the University of Rhode Island and Canada’s Department of Fisheries and Oceans. Cesium isotopes have been released into the atmosphere ever since nuclear testing began in 1945. Today, it is a component of radioactive fallout.

By June 2013, the “Fukushima signal,” as it is known, had reached the Canadian continental shelf. By February of this year, the signal had increased to a value of 2 Becquerels (Bq) per cubic meter throughout the upper 150 meters (500 feet) of the water column. The study’s authors said that the increase resulted in “an overall doubling of the fallout background from atmospheric nuclear weapons tests.”

Global cesium-137 levels, pre-Fukushima. (Image: Woods Hole Oceanographic Institution)

While “doubling of the fallout background” may sound somewhat ominous, 2 Bq per cubic meter is a tiny amount of radiation. Ken Buesseler, an oceanographer at the Woods Hole Oceanographic Institution, put it into perspective in a Reddit AMA last fall. He said that if you went swimming in a part of the Pacific Ocean that had 10 Bqs per cubic meter of cesium-134 or 137, you could swim six hours day, 365 days a year and still only get a radioactive dose that was “more than 1,000 times less than a single dental x-ray.”

Pavel Povinec of Comenius University in Slovakia and Katsumi Hirose of Sophia University in Japan studied seawater and biota samplings collected offshore from Fukushima and the Pacific northwest. They found that the total effective dose from an average annual consumption of contaminated fish, shellfish and seaweed caught in coastal waters off Fukushima was estimated to be anywhere between 0.2 to 1.0 millisieverts (mSv) a year.

Again, it’s a tiny amount. According to the American Cancer Society, the average American is exposed to about three times that amount from natural sources over the course of a year. You would receive about 8 mSv from a single standard x-ray of your abdomen. The estimated individual doses of eating fish and seafood from the Fukushima region, the researchers concluded, “have been below the levels when any health damage of the Japanese and world population could be expected.”

Still, scientists continue to measure the Fukushima signal. Last month, the icebreaker CCGS Sir Wilfrid Laurier collected samples of surface seawater as it traveled between Victoria, British Columbia, to Dutch Harbor, Alaska. The mission was the latest chapter of the ongoing research conducted as part of the Integrated Fukushima Ocean Radionuclide Monitoring (InFORM) Network, a collaborative radiation monitoring program to understand the environmental risks for Canada’s Pacific and Arctic oceans from the Fukushima disaster. Results will be made available on the InFORM website in a few months.

“This information will help to determine how well model predictions of the activities and progression of ocean-borne contamination across the Pacific Ocean match with observations,” said Jay T. Cullen, a marine chemist and oceanographer at the University of Victoria. “Understanding the spread of this contamination provides important information on the impact of the Fukushima Dai-ichi disaster on the health of the Pacific ecosystem and the North American public.”

Locations where surface seawater samples were collected for the InFORM project in July 2015. (Image: InFORM)

The researchers from the University of Rhode Island and Canada’s Department of Fisheries and Oceans estimate that the future total level of cesium-137 will reach maximum values by 2015-’16 “before declining to levels closer to the fallout background” by 2012. They conclude: “The increase in cesium-137 levels in the eastern North Pacific from Fukushima inputs will probably return eastern North Pacific concentrations to the fallout levels that prevailed during the 1980s but does not represent a threat to human health or the environment.”

But while scientists have failed to find reason for concern, there continues to be public worry about the radioactivity that leaked from the Fukushima plant and how it may impact the food system and human health. Donald W. Miller, Jr., professor emeritus of surgery at the University of Washington in Seattle, explains our seemingly irrepressible fear of radiation:

Along with the EPA and NRC [Nuclear Regulatory Commission], elected government officials, newspapers science writers, TV reporters and journalists, and, consequently, most Americans believe that low doses of radiation are harmful. People have “radiophobia” — the fear that any level of ionizing radiation, no matter how small, is dangerous. Why? For one thing, the news media fosters it because fear sells. Scary stories about the dangers of radiation keep people tuned in. Another reason, which lies deeper in the collective psyche, is that this phobia expresses the deep-seated sense of revulsion that Americans feels over the devastation and loss of life cause by the atomic bombs that its country dropped on Hiroshima and Nagasaki at the end of World War II.

In addition, many people don’t realize that radioactivity is not only all around us, but within us. As Stephen Frantz, former director of the Reed College Nuclear Reactor, points out:

The human body contains radioactive elements. Naturally occurring potassium-40, carbon-14, uranium, and thorium are present in every human body. Together they undergo about half a million decays every minute … Approximately half a million times every minute of your life a radioactive atom in your body decays and irradiates you from inside with radiation. This has happened every minute of your life.

Radioactivity in Some Natural and Other Materials:

(Chart: World Nuclear Association)

“Life on earth has developed with an ever present background of radiation,” notes Eric J. Hall, a professor of radiology at Columbia University, in his book Radiation and Life. “It is not something new, invented by the wit of man: radiation has always been there.”