Next month 140 countries will sign the U.N. Minamata Convention, which aims to regulate the use of mercury to reduce rates of contamination in countries where small-scale gold miners operate.

The convention is named after the world's biggest mass mercury poisoning, which occurred 60 years ago in Japan.

The cause of the poisoning was identified only 30 years later as a local plastics factory that was dumping mercury into a nearby bay.

Mercury is a neurotoxin that affects the cerebellum, the part of the brain that controls movement. It also harms the kidneys and other organs.

Hand tremors, coordination problems and headaches are among the early symptoms of mercury intoxication, which can also cause birth defects. — Reuters