Researchers created a way to measure radiation exposure in units of mushroom sandwiches, as in, if you're foraging somewhere in Sweden, for instance, maybe avoid having more than half a wild mushroom sandwich per day. 

In 1986 Chernobyl's radioactive fallout covered a lot of Sweden, including the edible mushrooms growing there. And those radioactive substances still affect the plant and animal life today. In one study, teen citizen scientists collected mushrooms to test their radioactivity. 

And to put the amount of radioactive contamination in the different mushrooms into context, researchers created the mushroom sandwich index, or like, how much you'd have to eat in a year to go above permissible radiation levels. 

In places with more fallout, mushroom radiation was generally higher than normal. But only two samples had higher radiation than what the Swedish government allows in mushrooms being sold. So thanks to citizen scientists, we know Swedish mushrooms still hold the effects of an event from years ago in a completely different country.