Low levels of Fukushima nuclear radiation found in bluefin tuna off the California coast

 

Low levels of nuclear radiation from the tsunami-damaged Fukushima power plant have turned up in bluefin tuna off the California coast, suggesting that these fish carried radioactive compounds across the Pacific Ocean faster than wind or water can.

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 yesterday.

That is months earlier than wind and water currents brought debris from the plant to waters off Alaska and the US Pacific Northwest.

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 Sciences.

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 miniscule proportion.)

The researchers figured that the elevated levels of cesium 137 and all of the cesium 134 they detected came from Fukushima because of the way bluefin tuna migrate across the Pacific.

Bluefin tuna spawn only in the western Pacific, off the coasts of Japan and the Philippines. As young fish, some migrate east to the California coast, where upwelling ocean water brings lots of food for them and their prey. They get to these waters as juveniles or adolescents, and remain there, fattening up.

Judging by the size of the bluefin tuna they sampled - they averaged about 15 pounds (6 kg) - the researchers knew these were young fish that had left Japanese water about a month after the accident.

Most of the radiation was released over a few days in April 2011, and unlike some other compounds, radioactive cesium does not quickly sink to the sea bottom but remains dispersed in the water column, from the surface to the ocean floor.

Fish can swim right through it, ingesting it through their gills, by taking in seawater or by eating organisms that have already taken it in, Madigan said.

Bluefin tuna typically have low levels of naturally occurring radioactive material, such as potassium 40, which was present in the world's oceans long before human beings walked the Earth.

Compared to these natural levels of radioactivity, the amount contributed by Fukushima raised the level about 3 percent, Madigan said.

He said there were probably much higher levels of cesium 134 present in bluefin tuna off Japan soon after the accident, as much as 40 to 50 percent higher than normal. Cesium 134 decays quickly, with a half-life of two years. Bluefin tuna excrete it on a daily basis and it also gets diluted in their bodies as they grow.

Reuters

PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
News
ebooksAn evocation of the conflict through the eyes of those who lived through it
Sport
Neil Warnock
football'New' manager for Crystal Palace
News
peopleGerman paper published pictures of 18-month-old daughter
Arts and Entertainment
'A voice untroubled by time': Kate Bush
musicKate Bush set to re-enter album charts after first conerts in 35 years
Sport
Angel Di Maria poses with Louis van Gaal after signing for Manchester United
sport
Arts and Entertainment
BBC series 'Sherlock' scooped a hat-trick of awards on the night. Benedict Cumberbatch received the award for Actor, Miniseries or Movie ('Sherlock: His Last Vow') while Martin Freeman won the award for Supporting Actor, Miniseries or Movie. Neither actor was present to collect their awards
tv
Life and Style
tech
Independent
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
santorini
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Oracle DBA (Database Administrator, 10g, 11g, PL/SQL)

£45000 - £50000 Per Annum + £5k shift allowance, 12% bonus, benefits: Clearwat...

Oracle DBA (Database Administrator, 10g, 11g, PL/SQL)

£45000 - £50000 Per Annum + £5k shift allowance, 12% bonus, benefits: Clearwat...

Cover Supervisor

£45 - £65 per day: Randstad Education Chester: Job Opportunities for Cover Sup...

IT Teacher September strt with view to permanent post

£110 - £130 per day + Competitive rates of pay: Randstad Education Reading: IT...

Day In a Page

Kate Bush, Hammersmith Apollo music review: A preamble, then a coup de théâtre - and suddenly the long wait felt worth it

Kate Bush shows a voice untroubled by time

A preamble, then a coup de théâtre - and suddenly the long wait felt worth it
Robot sheepdog technology could be used to save people from burning buildings

The science of herding is cracked

Mathematical model would allow robots to be programmed to control crowds and save people from burning buildings
Tyrant: Is the world ready for a Middle Eastern 'Dallas'?

This tyrant doesn’t rule

It’s billed as a Middle Eastern ‘Dallas’, so why does Fox’s new drama have a white British star?
Rachael Lander interview: From strung out to playing strings

From strung out to playing strings

Award-winning cellist Rachael Lander’s career was almost destroyed by the alcohol she drank to fight stage fright. Now she’s playing with Elbow and Ellie Goulding
The science of saturated fat: A big fat surprise about nutrition?

A big fat surprise about nutrition?

The science linking saturated fats to heart disease and other health issues has never been sound. Nina Teicholz looks at how governments started advising incorrectly on diets
Emmys 2014 review: Can they genuinely compete with the Oscars

Can they genuinely compete with the Oscars?

The recent Emmy Awards are certainly glamorous, but they can't beat their movie cousins
On the road to nowhere: A Routemaster trip to remember

On the road to nowhere

A Routemaster trip to remember
Hotel India: Mumbai's Taj Mahal Palace leaves its darker days behind

Hotel India

Mumbai's Taj Mahal Palace leaves its darker days behind
10 best pencil cases

Back to school: 10 best pencil cases

Whether it’s their first day at school, uni or a new project, treat the student in your life to some smart stationery
Arsenal vs Besiktas Champions League qualifier: Gunners know battle with Turks is a season-defining fixture

Arsenal know battle with Besiktas is a season-defining fixture

Arsene Wenger admits his below-strength side will have to improve on last week’s show to pass tough test
Pete Jenson: Athletic Bilbao’s locals-only transfer policy shows success does not need to be bought

Pete Jenson: A Different League

Athletic Bilbao’s locals-only transfer policy shows success does not need to be bought
This guitar riff has been voted greatest of all time

The Greatest Guitar Riff of all time

Whole Lotta Votes from Radio 2 listeners
Britain’s superstar ballerina

Britain’s superstar ballerina

Alicia Markova danced... every night of the week and twice on Saturdays
Berlin's Furrie invasion

Berlin's Furrie invasion

2000 fans attended Eurofeurence
‘It was a tidal wave of terror’

‘It was a tidal wave of terror’

Driven to the edge by postpartum psychosis