In 2011 a tsunami caused by an earthquake hit the Fukushima nuclear power plant in Japan, resulting in three reactor meltdowns. Since then, scientists have been testing water in the Pacific Ocean at various distances from the site to determine what kind of contaminants have escaped from the site. The bad news is that contaminants keep entering the ocean from Fukushima, but the good news is that those levels are far lower than they were just after the event.
Cesium-134 is an isotope that acts as a sort of “fingerprint” for Fukushima, and finding it in water means provides the geographical sources for those particular isotopes. Cesium-134 has a half life of two years, meaning that every two years half of it decays, so based on the amount in a given body, scientists can tell how long it’s been there.
Lately, measurements have indicated that levels of Cesium-134 are elevated in water as close to the United States as 1,600 miles west of San Francisco. These samples have 50% more Cesium than previous samples, but those levels are still 500 times lower than safety limits for drinking water, and well below the levels where direct exposure is dangerous.
This information, coupled with samples taken from a kilometer from the site, indicates that Cesium-134 is still leaking out and getting into the water, but it can also allow scientists to figure out how much material actually made it into the ocean in the first place.
An interesting side effect too is that, since these isotopes can only have come from Fukushima, researchers can use them as markers to track how water moves though the Pacific Ocean. That could prove pretty useful for oceanographers, and it’s nice to know that there is at least some small benefit from that disaster.