Hair samples taken from residents living near Tucuruí Dam found that more than half of the 37 participants had mercury concentrations 20 times higher than that which is considered safe by the World Health Organisation.

By flooding hundreds of square miles of forest, dams cause mercury that is stored in soil and vegetation to be released into the water. These waterlogged conditions favour methanogenic bacteria, which ‘transforms inorganic mercury into organic mercury – its most toxic form,’ according to Professor Maria Elena Crespo-López, co-author of the study published in Ecotoxicology and Environmental Safety.

Organic mercury accumulates in the fish that are a key part of local diets. This allows it to enter the human food chain and accrue to dangerous levels; around 80 per cent of the mercury detected was in its organic form.

‘Acute exposure to organic mercury can cause Minamata disease,’ says López. ‘[This is] a severe condition which includes, co-ordination problems, progressive visual deterioration and even paralysis.’

More than 400 hydropower dams are currently operating or under construction in the Amazon. Brazil hopes to increase hydropower capacity by 27 gigawatts by 2024.

This article is from the April 2018 issue of New Internationalist.

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