Small amounts of cesium-137 and cesium-134 were detected in 15 tuna caught near San Diego in August 2011, about four months after these chemicals were released into the water off Japan's east coast, scientists reported on Monday.
The amount of radioactive cesium in the fish is not thought to be
damaging to people if consumed, the researchers said in a study
published in the journal Proceedings of the National Academy of
Without making a definitive judgment on the safety of
the fish, lead author Daniel Madigan of Stanford University's Hopkins
Marine Station noted that the amount of radioactive material detected
was far less than the Japanese safety limit.
"I wouldn't tell
anyone what's safe to eat or what's not safe to eat," Madigan said in a
telephone interview. "It's become clear that some people feel that any
amount of radioactivity, in their minds, is bad and they'd like to avoid
it. But compared to what's there naturally ... and what's established
as safety limits, it's not a large amount at all."
He said the scientists found elevated levels of two radioactive
isotopes of the element cesium: cesium 137, which was present in the
eastern Pacific before the Fukushima Daiichi disaster in the spring of
2011; and cesium 134, which is produced only by human activities and was
not present before the earthquake and tsunami hit the Japanese plant.
Because cesium 134 is generated only by human activities - nuclear
power plants and weapons - and there was none in the Pacific for several
years before the Fukushima accident, they reckoned that any cesium 134
they found in tuna off California had to come from Fukushima.
There was about five times the background amount of cesium 137 in the
bluefin tuna they tested, but that is still a tiny quantity, Madigan
said: 5 becquerels instead of 1 becquerel. (It takes 37 billion
becquerels to equal 1 curie; for context, a pound of uranium-238 has
0.00015 curies of radioactivity, so one becquerel would be a truly