LONDON — Radioactive material was found at the main site to be used for the London 2012 Olympics, requiring 1 million tons of soil to be decontaminated.

The announcement today by Olympics Minister Tessa Jowell came less than a week after the discovery of asbestos temporarily halted construction at the Olympic stadium.

Jowell said the Olympic Delivery Authority's contractors had not been "unnecessarily" exposed to radium at the East London area being turned into the Olympic Park, which will also house swimming and diving, cycling and basketball.

"Other contaminants discovered on site include hydrocarbons, industrial chemicals, heavy metals and a very small amount of low level radioactive material," Jowell said in a written parliamentary answer. "A report on the radium find from the ODA's specialist contractor stated that 'no worker or member of the public has been unnecessarily exposed to ionizing radiation,' which registered low or very low levels of radioactivity."