Mercury has a chemical affinity for precious metals, which is why gold mines are the world's number two source of mercury pollution

Gold is very chemically non-reactive, as a general rule, which can make it difficult to separate out from the other metals that it naturally occurs with. However, gold readily forms an amalgam with mercury, and this amalgam can be easily separated back into its two component parts. Although there are other methods for separating gold out from the ore it is found in, amalgamation with mercury is by far the cheapest. Mercury has a similar affinity for silver and copper, and is also used in the mining of those metals.

However, mercury is a highly potent neurotoxin, made even more dangerous by its tendency to accumulate in the tissues of animals, including humans. Mercury pollution that finds its way into the water is the ultimate cause behind widespread mercury contamination of seafood. In addition to causing serious developmental problems in infants and children, mercury poisoning can cause sensory impairments, lack of coordination and other neurological symptoms in adults.
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