Radioactivity from Japan heading for N America

Low concentrations of radioactive particles are heading eastwards from Japan's disaster-hit nuclear power plant towards North America, a Swedish official said on Thursday.
Lars-Erik De Geer, research director at the Swedish Defence Research Institute, a government agency, was citing data from a network of international monitoring stations.
He stressed that the levels were not dangerous for people.
Meanwhile, Japan instructed local authorities on Thursday to start screening food for radioactivity.
It is the first time Japan has set radiation limits on domestically produced food, a health ministry official said.
The limits are in line with an anti-disaster programme prepared in advance by the government's atomic power safety commission, said the official.
Limits vary depending on the type of foodstuff but have been set in consultation with internationally accepted levels and average intake in the Japanese diet.
Radioactivity leaked into the air after explosions at the Fukushima No 1 plant, where last week's quake and tsunami knocked out the reactor cooling systems.
Several Asian nations have said they will screen food imported from Japan for radiation while the European Union has called for similar checks.