A new study has revealed that mercury pollution from artisanal and small-scale gold mining (ASGM) in Nigeria is contaminating nearby farmland and food crops, with airborne mercury playing a bigger part than previous thought.
Mercury, a powerful neurotoxin, is commonly used to extract gold from raw ore in artisanal mining. Long-term exposure, even at low doses, can damage the nervous system, impair cognitive development in children and cause heart and reproductive problems.
Using mercury passive air samplers (MerPAS) to measure gaseous elemental mercury concentrations
This study, conducted by an international team of scientists led by Excellent O. Eboigbe and David McLagan at Queens University, and Abiodun Odukoya Mary at the University of Lagos, compared samples from a small-scale gold mining site, a nearby farm just half a kilometre away and another farm eight kilometers upwind.
They found that the air and soil at the mining area were, as expected, heavily polluted with mercury but the levels in leaves and grains on the nearby farm were around 10-50 times higher than that at the farm further away.
The study focused on three staple crops commonly grown and eaten in Nigeria – cassava, maize and peanuts.
The researchers found that the highest levels of mercury were in leaves, especially in peanuts and cassava. By examining chemical signatures known as mercury isotopes, they determined that most of the contamination comes from mercury gas in the air, which plants absorb through their leaves.
In contrast, mercury in the soil was found to stay mostly on the outside of roots and rarely traveled upward into edible parts of the plants.
David McLagan said: ‘Mercury uptake by plants from air represents the largest sink of mercury from air to terrestrial [land and freshwater] systems. While this critical ecosystem service helps reduce the amount of mercury being globally redistributed through the atmosphere, it raises human health concerns when it is staple crops that are the mechanism stripping the air of mercury.’
While the detected amounts remain below international safety thresholds for mercury intake, the authors point out that these standards are based on conservative assumptions about how much locally grown food people consume. In reality, they warn, rural families who rely heavily on their own harvests may face higher long-term exposure.
The study calls on governments and international organisations to expand the scope of mercury monitoring programs under the Minamata Convention on Mercury, a global treaty aimed at reducing mercury pollution. Current monitoring efforts largely focus on water, sediment, and fish – traditional sources of mercury exposure – while agricultural products remain overlooked.
The full research can be read here.
Leave a Reply