Airborne Mercury From Gold Mining Is Contaminating African Food Crops
Mercury is often used to extract gold from ore in mining operations, but can pose serious health risks.
Food crops grown near artisanal and small-scale gold mining (ASGM) operations in Nigeria are absorbing mercury directly from the air, according to new findings published in Biogeosciences, a journal of the European Geosciences Union.
The study, led by researchers from Queen’s University in Canada and the University of Lagos in Nigeria, challenges long-held assumptions about how mercury enters plant tissues and raises concerns about food safety in mining regions.
Airborne mercury linked to elevated levels in staple crops
Researchers collected crop samples from two farms: one located 500 meters from an ASGM site and another 8 kilometers away. Mercury concentrations in the leaves and grains of crops grown near the mining activity were 10 to 50 times higher than those found at the distant site. Leafy parts of the plants contained the highest concentrations, while roots and grains had lower, yet still detectable, levels of mercury.
Traditionally, scientists believed mercury entered crops through the soil or water. However, this study used mercury stable isotope analyses to show that the primary source was atmospheric, with plants absorbing mercury through their leaves during photosynthesis.
Mercury stable isotope analyses
A technique used to trace the source and movement of mercury in the environment by measuring the ratios of its naturally occurring isotopes. It allows scientists to determine whether mercury in a sample originated from the air, soil or water.
Implications for food safety and public health
The study notes that while mercury levels in crops near the ASGM site were below international thresholds for human consumption, these limits assume conservative intake rates. In regions where people rely on subsistence farming, actual exposure may be higher. Mercury is a potent neurotoxin that can affect cognitive development, cardiovascular function and reproductive health, particularly with long-term exposure at even low levels.
ASGM is now the largest source of mercury emissions globally, driven in part by the rising price of gold. In many parts of the Global South, gold mining is a critical livelihood, but regulation and monitoring often lag behind.
Gaps in global monitoring efforts
Current monitoring programs under the Minamata Convention on Mercury focus mainly on aquatic systems such as lakes and rivers. The researchers argue that this overlooks a key exposure pathway. Crops, especially leafy vegetables consumed by humans and livestock, act as a sink for atmospheric mercury, potentially serving as an unmonitored route for human exposure.
A call for targeted interventions
The findings suggest that policymakers and public health agencies need to broaden their surveillance strategies to include airborne mercury exposure in agricultural regions. Without intervention, communities located near expanding ASGM sites across Africa, South America and Asia may face growing risks to food safety and long-term health.
Reference: Eboigbe EO, Veerasamy N, Odukoya AM, et al. Mercury contamination in staple crops impacted by artisanal and small-scale gold mining (ASGM): stable Hg isotopes demonstrate dominance of atmospheric uptake pathway for Hg in crops. Biogeosciences. 2025;22(20):5591-5605. doi: 10.5194/bg-22-5591-2025
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