More than 40 million people around the world work in artisanal and small-scale mining where minerals including gold, diamonds and cobalt are dug up often by hand, a report by the World Bank and development organization Pact said on Wednesday.

Increasing demand for metals and rising prices have triggered a boom in small-scale mining in recent years, mainly in poorer countries in South America, Africa and Asia.

These mines are a vital source of income for communities, but many operate outside the law and leak chemicals into rocks, soil and rivers. Working conditions can be appalling, and the metal and stones dug up are often smuggled across borders on a vast scale, sometimes by criminal operations.