Olympics Minister Tessa Jowell has told MPs "a very small amount of low level radioactive material" was found at the site in Stratford, East London.
In a Commons written answer she said specialists hired by the Olympic Delivery Authority found that no construction worker or member of the public had been "unnecessarily" exposed to radium found at the site.
Ms Jowell said in total around one million tonnes of soil from the site would require treatment to remove various contaminants.
She told independent MP Dai Davies (Blaenau Gwent) a small amount of asbestos-contaminated material had been removed to specialist sites for safe disposal.
She added: "Other contaminants discovered on site include hydrocarbons, industrial chemicals, heavy metals and a very small amount of low level radioactive material.
"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 ionising radiation', which registered low or very low levels of radioactivity."
The Health and Safety Executive were consulted immediately, she added.