Derek Muller from Veritasium went on a wild hunt for the most radioactive place on Earth. Regularly we get about 4 micro Sieverts of radioactivity in our bodies daily, which is a-ok, but you can get about 1.5 mSv, miliSieverts in one year.
A CT scan is about 7000 micro Sieverts or 7 mili Sieverts. The people living near Fukushima will receive and extra 10 000 microSieverts during their lifetime. In about 6 months an astronaut will receive 80 000 microSieverts.
But the most Sieverts in each year receives a smoker’s lung: 160 000 microSieverts each year. That means a smoker eats up radiation 100 times more than the natural background radiation. Quite a lot. And this happens because the existence of radioactive polonium and lead present in the tobacco.