How does food become radioactive?

We put this question to Dr Ian Farnan from the Department of Earth Sciences at Cambridge University...

Well, there are various ways that food can become radioactive.

It becomes radioactive when plants absorb it through their roots as they grow or animals ingest it and then you eat the animals.

You also get [nuclear] fallout. So, in the initial blast where they vented the steam, there would've been some dissolved caesium and iodine, and probably some particles of fuel - very small amounts - in those vents, and those would have then come down around about the Fukushima prefecture.

That's why the Japanese government has banned the sale of various different vegetables and milk within a certain radius of the plant.