This is completely impossible to answer. Not all lightweight concrete is blue concrete made from alum shale, and not all blue concrete is sources of radon gas.
Then there's also the fact that an extreme number of houses in Sweden are built on granite ground that contains uranium, and where radon gas can leak up from underneath. So, it's not only building materials that can be sources of radon.
One should ask for measurement protocols if they are a house prospect interested in a property where radon might be suspected. If detectable levels of radon are present, there are plenty of good solutions for this, which work well in most cases. A common standard solution for slightly elevated levels is to increase ventilation.
