So much that in post Soviet countries it’s common to bring a Geiger counter to buy real estate. Usually the contamination is from natural sources like stone quarry that hasn’t been properly inspected.
There was the Kramatorsk radiological accident in the Soviet Union (Ukraine) where a cesium 137 source used at a gravel quarry was lost. Ended up in the wall of an apartment. Four people died of leukemia over 9 years.
You should know that Mexican steel was circumspect for years after this, with shipments regularly being checked at the border for contamination.