By Matt Smith
May 29, 2012
Madigan is the lead author of a paper published in this week's edition of "Proceedings of the National Academy of Sciences". One of his co-authors, Nicholas Fisher, said levels of both isotopes detected in fish caught in August 2011 are one-thirtieth the amount of naturally occurring radioactive potassium found in all marine life.
"Scientists don't yet know whether this year's catch will have more or less cesium in their bodies, said Fisher, a marine science professor at New York's Stony Brook University. The particles that blew into the ocean could have been diluted by the vast Pacific, or the fish could have taken in more of them as they grew up.
Even if there's no change, the presence of cesium in the fish can be useful for scientists like Madigan who track the migration of species like the bluefin. "We've established that this marker can be used as a tracer to follow which fish came over from Japan," he said. Before the accident, there was no trace of cesium-134 in bluefin tuna.
Pacific bluefin tuna are among the largest and fastest fish in the world. They're heavily fished and higly prized for sushi and sashimi; one nearly 600-pound specimen sold for a reported $700,000 at Tokyo's Tsukiji fish market in January. The samples Madigan, Fisher and colleague Zofia Baumann examined came from fish caught by recreational anglers near San Diego.
Madigan said the concentrations were likely higher in smaller fish, but shrank as the bluefin grew during their migration and processed some of the cesium in their bodies. Japanese government figures estimate cesium levels in fish caught off its shores at between 61 and 168 bq/kg.
The three operating reactors at Fukushima Daiichi melted down after the earthquake and tsunami that struck Japan in March 2011, creating the worst nuclear disaster since Chernobyl. Most of the radioactivity released by the plant blew out to sea.