We already knew that thawing Arctic permafrost would release powerful greenhouse gases. On Monday, scientists revealed it could also release massive amounts of mercury -- a potent neurotoxin and serious threat to human health. From a report: Permafrost, the Arctic's frozen soil, acts as a massive ice trap that keeps carbon stuck in the ground and out of the atmosphere -- where, if released as carbon dioxide, the greenhouse gas would drive global warming. But as humans warm the climate, they risk thawing that permafrost and releasing that carbon, with microbial organisms becoming more active and breaking down the ancient plant life that had previously been preserved in the frozen earth. That would further worsen global warming, further thawing the Arctic -- and so on. That cycle would be scary enough, but U.S. government scientists on Monday revealed that the permafrost also contains large volumes of mercury, a toxic element humans have already been pumping into the air by burning coal. There are 32 million gallons worth of mercury, or the equivalent of 50 Olympic swimming pools, trapped in the permafrost, the scientists wrote in a study published in the journal Geophysical Research Letters. For context, that's "twice as much mercury as the rest of all soils, the atmosphere, and ocean combined," they wrote.