Some 3,000 households are taking part in a major investigation into the presence of radon and thoron gas in the Netherlands.

The public health body RIVM is carrying out the research on behalf of the health ministry to find out how much exposure there is to these gases in the Netherlands’ housing stock.
Radon and thoron are radioactive gases that occur naturally when uranium and thorium in soil and rock – used in concrete – break down through radioactive decay.
They are invisible, odourless and tasteless and when released from the ground into the outdoor air they are not considered a problem. However, in enclosed spaces like homes, they can sometimes accumulate to high levels.
Although the levels of these gases is relatively low in the Netherlands, a pilot study has shown far greater density of thoron than earlier thought, prompting the new research, the ministry said.