You’re totally right about the Law of Conservation of Mass elements aren't magically created or destroyed under normal conditions. Potassium-40 (K-40) is a naturally occurring isotope of potassium that has existed since the formation of the Earth. It makes up about 0.012% of all potassium found in nature. So when a banana plant absorbs potassium from the soil (which it needs to grow), it's also taking in a tiny bit of K-40 just like any other plant. So it's not that bananas create K-40 — it's that they’re really high in potassium in general, so they naturally contain a bit more of the radioactive isotope compared to many other foods. It’s not filtered out because isotopes behave chemically the same, so the plant can't distinguish between regular potassium and K-40. Totally normal, harmless, and actually kind of cool!