Two years ago, nuclear scientist Michael Pravikoff, an American ex-pat working in France, was shopping at the local supermarket when he came across a few bottles of Napa Valley Cabernet. It lead to a fascinating experiment that led to the discovery of radioactive isotopes generated by the 2011 Fukushima Daiichi nuclear disaster in California wines. (Completely harmless levels of radioactive isotopes, to be more specific.)
Pravikoff and colleagues at the Centre d'Etudes Nucleaires de Bordeaux Gradignan (CENBG) had been working on a unique method of authenticating rare and expensive wines. One of Pravikoff's colleagues, pharmacologist Philippe Hubert, had discovered in 2001 that he could date unopened bottles of wine by testing them for cesium-137.
Cesium-137 is a radioactive isotope of the element cesium that does not occur in nature. Any wines containing cesium-137 would have to have been vinified after the mid-20th century, when Cold War nuclear testing began. The presence of cesium-137, therefore, can be used as an identifying marker to authenticate when a wine was produced.
Aboveground nuclear testing is a thing of the past, but two events in recent decades added cesium-137 to the atmosphere: the Chernobyl nuclear plant disaster in 1986 and the Fukishima event of 2011. Studies have found that clouds of radioactive isotopes drifted from Fukushima across the Pacific Ocean to North America. Pravikoff wondered if the California wines in the store would bear the marker of the Fukushima radiation.
In their experiment, researchers tested 18 bottles of California Cabernet Sauvignon and Grenache rosé from each vintage between 2009 and 2015. The Cabs came mostly from the Napa Valley, while the rosé came from Livermore Valley and Central Valley fruit.
They found increasing levels of cesium-137 in those wines produced after the Fukushima disaster. Levels of the isotope in the Cabernets were more than double those found in the rosé, probably due to the increased skin contact.
Wine lovers need not be concerned, however. The amounts of cesium-137 found in the California wines were too low to cause harm. In fact, they were so minuscule that Pravikoff and his colleagues had to devise a new method of testing to search for it. Hubert had been able to measure gamma rays emitted by the cesium-137 in the wines while they were still in the bottle. But the levels were so low in this case that the researchers opened the bottles and "cooked" the wines, reducing them to ash, then measured the amounts of cesium-137 in the ashes.
The amount of radiation present in all the wine tested by their lab is too small to harm a person's health. "If you consume any wine from the late 1960s, there will be hundreds of times more radioactivity than in these Fukushima wines—a result of the nuclear testing from those times," said Andrew Waterhouse, former viticulture and enology department chair at the Univeristy of California at Davis and the newly appointed faculty director of the school's Robert Mondavi Institute. Low levels of radiation similar to those of the California wines have also been found in French wines from the vintages following Chernobyl.
"The California Department of Public Health's Radiologic Health Branch (RHB) performs weekly air monitoring along the California coast and tabulates and publishes the data on its website," said Corey Egel, a department spokesperson. "During and after the Fukushima incident, RHB increased its monitoring, with the results leading to the conclusion that no health and safety situation existed."
Perhaps of most significance to collectors of fine wines, the scientists' findings bolster the evidence that testing for radioactive isotopes can successfully expose fraudulent bottles billed as pre–nuclear age wines.
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