Researchers came to this conclusion when they studied satellite images taken by US space agency Nasa and related them to the evolution of the price of gold and to Peru's mercury imports.

“Virtually all mercury imported to Peru is used for artisanal gold mining and imports have risen exponentially since 2003, mirroring the rise in gold prices,” Swenson said.

“Given the rate of recent increases, we project mercury imports will more than double by the end of 2011, to about 500 tons a year,” she said.

The highly poisonous metal is used by poor gold-diggers to wash gold off rock and sand. It is not only harmful to the health of those who handle it, but it also pollutes the region's rivers and air.

Mercury also gets into the food chain and harms local indigenous communities and even those that live further away. Once the gold searchers are done, they leave behind a desert landscape that is poisoned by mercury.

Peruvian Environment Minister Antonio Brack said gold-diggers have already destroyed 32,000 hectares of rainforest in Madre de Dios.

In March, a large joint operation by police and the military targeted tens of thousands of gold searchers, and 32 floating dredges were seized, Brack said. The minister said he was sorry about the death of two prospectors during the raid, although he stressed that the use of force had been justified in the face of an “environmental tragedy.”

However, the problem is far from solved. Police assume that at least 250 floating dredges are in use in the region. According to Brack, it will take at least five years to get those searching for gold to leave.

And yet poverty in Peru continues to push more and more people into searching for gold, as well as into other equally illegal activities like logging or settling in the rainforest.