Minute amounts of radioactive strontium have been detected in soil at 11 locations in Fukushima Prefecture, including the city of Fukushima 62 km from the crippled nuclear power plant, according to the science ministry.
Strontium tends to accumulate in bones and is believed to cause bone cancer and leukemia.
The Nuclear Safety Commission said they are unlikely to pose an immediate threat to human health but warned people about the intake of radioactive strontium into their bodies.