Mercury

But the problem is that the amount of mercury in the environment's increasing. The main reason for this is the power [blank] used to produce electricity. The main source of energy that most of them use is still [blank] , and when it's burned it [blank] mercury into the atmosphere. Some of this gets deposited into lakes and rivers, and if it's [blank] by a fish it's not excreted, it stays in the fish's body and it enters the food [blank] . So it's been known for some time that birds which eat fish may be affected, but what wasn't known until quite recently is that those that eat [blank] can also be affected.