Informal miners ("Informales" is the Spanish term) are locals who hand dig or pan for gold. Mercury is used to separate the gold from the dirt and rock. When they've extracted the separated gold, they dispose of the mercury, often just dumping it on the ground or down the stream. This is type of activity that causes environmental concern, not only in Peru, but all over the world. The miners that use this method are touching and handling mercury the whole time they are mining, so natually is poses a high risk to their health.