Iodine-131 is a dangerous radioactive isotope. It can clog up your thyroid gland and contaminate food. It's been a big problem in Japan (for obvious reasons), but now it's been scarily detected throughout Europe. And nobody knows the source.
Germany, Hungary, Slovakia, Austria, Sweden, and the Czech Republic have all detected clouds of iodine-131 within their borders—that's a very large swath of Europe. Nobody is sure of where it's coming from, Reuters reports, though speculation includes pharmaceutical companies, nuclear submarines, and the transportation of radioactive materials—but scientists are sure it's not from Fukushima. So how would that explain contamination that spans hundreds and hundreds of miles?
The International Atomic Energy Agency says "the current trace levels of iodine-131 that have been measured do not pose a public health risk," but we've heard that so many times before. It's not a cause for panic, but an unexplained cloud of dangerous radioactivity is absolutely cause for concern. It certainly deserves more than 129 words on the IAEA's website, at any rate. [Reuters]