A drill echoes through narrow tunnels deep within the mountain where miner Hugo Flores bores into rock in search of one of Earth’s most toxic elements.

Buried in red stripes of minerals illuminated by his headlamp is mercury.

Here in the pine-covered mountains known as the Sierra Gorda – one of the most biodiverse stretches of Mexico – a "mercury boom” is underway.

Soaring international gold prices are driving up the price of mercury, a toxic metal key in illegal gold mining, to all-time highs. While the demand triggers a mining rush in central Mexico, sustaining thousands of miners and their families, it also exposes them and the fragile environment to mercury poisoning.

At the same time, this Mexican mercury is fuelling illegal gold mining in the Amazon, contaminating large areas and harming both people and the environment.

Global efforts to ban mercury mining have only made mercury from these centuries-old artisanal mines even more sought after.

"It’s a way of life here,” Flores said.

A miner transfers a sample of mercury into a bottle.