I live in Japan, many miles from the devistation caused by the recent earthquake and tital wave, and from the reactors at the stricken Fukushima Daiichi nuclear power plant. Recently the Japanese government has taken steps to keep food that may have been contaminated by nuclear waste coming from the power plants. This includes a variety of vegies and milk from the area. This made me wonder, though, how, if this is bad, purposefully irradiated food is any less dangerous.
My conclusion is that it is different because purposefully irradiated food is exposed to radiation, but the radioactive material does not remain on the food. With nuclear matter that settles on the food or is consumed by a food producing animal, the radioactive material remains on or in the food, later to be eaten by the consumer.
But I was wondering, then, if there are other effects on the food. It looks like there are. Even though radioactive material doesn't remain on the irradiated food, the food itself is changed in the process. Here are some materials that may be of interest.
This is an article on health risks and the misleading of consumers.
This is an article by the CDC on how irradiated food is safe.