Fukushima's radioactive sea contamination lingers

Levels of radiation in the sea off the Fukushima-Daiichi nuclear plant remain stubbornly high six months after the earthquake and tsunami struck Japan on 11 March.

After levels peaked at around 100,000 becquerels per cubic metre of seawater in early April, much of the radioactive iodine, caesium and plutonium from Fukushima was expected to rapidly disperse in the Pacific Ocean.

Instead, it seems that the levels remain high. That could be because contaminated water is still leaking into the sea from the nuclear plant, because currents are trapping the material that's already there, or both.

Ken Buesseler of Woods Hole Oceanographic Institution, Massachusetts, has told The New York Times that he has received samples of seawater taken in July from near the plant that contained 10,000 becquerels per cubic metre. The corresponding level last year, only months before the disaster, was just 1.5 becquerels, he says.

Simon Boxall, an oceanographer at the University of Southampton, UK, says that much of the radioactive material will still be sinking down to the seabed and being absorbed by marine life.