Fewer trees, more mercury in the air: The alarming MIT study

A recent study by MIT has revealed that global deforestation is responsible for approximately 10% of human-caused mercury emissions into the atmosphere each year. This finding highlights the significance of forests, such as the Amazon rainforest, as mercury sinks, capturing this toxic substance from the air.


Mercury is a toxic pollutant whose management poses a global challenge, partly because it accumulates in food chains, leading to dangerous levels of methylmercury in the fish we eat. Deforestation plays a significant role in this issue, releasing about 220 tons (about 200 tonnes) of mercury into the atmosphere annually. This amount represents 10% of the total mercury emissions due to human activities.

Forests, by absorbing mercury from the air through tree leaves, play a crucial role in reducing the presence of this heavy metal in our environment. The vital role of the Amazon, responsible for about 30% of the world's land-based mercury absorption, is especially emphasized. Reforestation efforts could increase mercury absorption by 5% annually, but this cannot replace global pollution control measures.

The research, led by Ari Feinberg and Noelle Selin from MIT, with collaboration from Martin Jiskra, Pasquale Borrelli, and Jagannath Biswakarma, utilizes a chemical transport model to track mercury from its source of emission to its final deposit, often through precipitation or absorption by forests. This model has quantified for the first time the impact of deforestation on mercury emissions.

In tropical and subtropical countries, the share of emissions due to deforestation is even more significant. For example, in Brazil, these emissions account for 40% of the total human-caused emissions. The use of fire to prepare forest lands for agriculture releases even more mercury, previously stored by the vegetation.

This study highlights the necessity to consider deforestation in mercury management policies, an aspect so far overlooked by international agreements such as the 2013 Minamata Convention. It calls for a better understanding of the ecological systems involving human activities to effectively solve the environmental problems encountered.