(CNN) -- There might be an unexpected ingredient in your glass of California red wine.
If your bottle of choice was made after 2011, it could have small amounts of radioactive particles from a major nuclear accident: Japan's Fukushima meltdown.
Years after the 2011 disaster, a group of French nuclear physicists wanted to see whether cesium-137, a radioactive isotope, was more present in wines made after the disaster than those made before.
They tested bottles of two well-known types of California wines -- rosé and Cabernet sauvignon -- that were made from 2009 and 2012. And their study, submitted to the Cornell University Library on July 11, highlights what they found.
The bad news: Some wines from after 2011 had twice as much radioactive material.
The good news: The levels are still too low for you to worry about.
What the study found
Radioactive cesium-137 is made when other radioactive materials undergo nuclear fission. In short; it's manmade and would show up more after a nuclear event.
After Fukushima's nuclear reactors melted, radiation made it across the Pacific Ocean to California.
Since that's where the wine hub of Napa Valley is, the researchers wondered whether cesium-137 levels in California's wine would be higher after the disaster.
The answer: in some cases, much higher.
Using a gamma detector, the researchers tried to figure out what radioactive particles were inside the bottles without opening them. That didn't work, so they used a "destructive analysis" to vaporize the wines into ashes, the study says.
Wines made after 2011 had higher levels of radioactive particles, the researchers found. In the Cabernet bottles, there was twice as much cesium-137 as there was before the disaster.
This isn't the first time radioactive materials have shown up in the alcoholic drink. The Chernobyl accident, which took place in Ukraine during the Cold War, caused wines made in parts of Europe to have larger amounts of the radioactive isotope, the study says.
What happened in Fukushima
Fukushima was one of the worst nuclear accidents in history.
In March 2011, a 9.0-magnitude earthquake and a tsunami hit Japan. The natural disasters damaged three Fukushima Daiichi Nuclear Power Plant reactors, and radioactive materials were released into the air.
More than a year after the accident, fish off Japan's coast showed high cesium levels, causing the country to ban the sale of several species. At the same time, wild boars contaminated by radioactive material continued to reproduce and eat crops in the Fukushima area.
Both had serious effects on the nation's economy.
You can safely drink your favorite California wine
Cesium-137 can get into your body if it's inhaled or ingested. If that happens, it could cause cancer and decrease life span, the US Environmental Protection Agency says.
Its effects depend on how much exposure a person has to the material.
But don't worry, the amount of radioactive material that spread to other countries after Fukushima is much lower than what people are exposed to normally, the World Health Organization says.
People can get exposed to cesium-137 through such things as nuclear weapons testing or radioactively contaminated soils and waste. It's also found in low-level radioactive waste at hospitals and research facilities, according to the EPA.
Radioactive levels in wine used to be a lot higher
Wine's cesium-137 levels after Fukushima are nothing compared with what they used to be.
A few things spiked radioactive levels in the early 1950s. The first thermonuclear weapon was tested by the US in 1952. Two years later, the Castle Bravo test set off the largest thermonuclear device ever detonated by the US.
The amount of cesium-137 in wines skyrocketed after those events, the report shows.
Levels dropped toward the end of the decade, but they shot up again in the 1960s with the Cuban Missile Crisis, a 13-day confrontation that almost ended in a nuclear war.
Since then, levels have been much lower around the world, the researchers found.
Agreements have set limits on countries' uses of nuclear weapons. A 1963 treaty banned testing them in outer space, underwater or in the atmosphere. Another signed in 1968 meant to prevent these technologies from spreading.
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