I used to work in chemical exposure insurance and to be honest, it would be very difficult to tell because of the increased risk of cancer from chemicals used in the growing process as it is. Most of the countries that have banana plantations can’t really defend their citizens against huge fruit companies, so if something has been declared illegal in Hawaii, they just use it in their other plantations, and of course the US is dismantling the EPA and NLRB, so soon they might not even be illegal there anymore. Organic fruit is not significantly different, because there are lots of things that are allowed for them that are still carcinogenic to humans in large concentrations.

I’m really sorry to be a downer, but sometimes the world sucks, and pineapple and banana companies suck even more.

A couple things we can gather from these sources:

1. Being near a banana is likely a much lower dosage. The BED article notes that eating a lot of bananas doesn’t give linear dosages, as the excess potassium is discarded. And if you’re not absorbing much radiation from it being literally inside you, I can’t imagine you’re getting much from having it further away (even at high quantities).
2. According to the xkcd chart, we receive a yearly dosage of 390uSv from the potassium naturally in our bodies, and living in a stone, brick, or concrete building for a year results in only 70uSv. I’m not sure what the equivalent exposure would be for injecting those materials, but the picture I’m getting at this point is that external exposure to bananas would likely be less fatal than the sheer mass of what would be required to give a significant dose.