The artisanal and small-scale gold mining industry (ASGM) is the largest source of man-made mercury contamination globally, and, according to a paper published in the International Journal of Environmental Research and Public Health, it is responsible for 37% of anthropogenic mercury emissions. 1
ASGM outfits in Asia, Africa, and South America commonly use the mercury amalgamation process to extract gold. The mercury-gold amalgam is heated to isolate the gold, which releases harmful mercury vapours into the atmosphere. These volatile and toxic vapours poison miners and create long term contamination of the soil and waterways, leading to an adverse impact on the health of communities that rely on subsistence agriculture in the surrounding areas.
Since the Industrial Revolution, the concentration of mercury in the ocean has tripled. Mercury in the atmosphere is brought back to the oceans by rain, snow, and dust particles, where it is converted to methylmercury — a bioaccumulative environmental toxicant. It is consumed by plankton, which is then eaten by small fish. Larger fish eat the small fish, and the cycle continues up the food chain. Every time methylmercury takes a step up the food chain, this neurotoxin becomes concentrated by a factor of 10. Eventually, the apex predators of the oceans, such as sharks, tuna, and swordfish, find their way onto our plates and into the human body. While the U.S. Food and Drug Administration considers the average yellowfin tuna to be safe for consumption, some fish tested in random samplings have contained mercury far in excess of the recommended limit. A recent University of Michigan study on yellowfin tuna caught near Hawaii also recorded a statistically significant increase of mercury levels since 1998. 2
When contaminated tuna and other such fish are consumed, ingested methylmercury is readily absorbed by the gastrointestinal tract of humans. Because of biomimicry and strong bonding to proteins, methylmercury can travel through the blood-brain barrier and across the placenta, where it is then absorbed by a developing foetus. Methylmercury has been linked to developmental deficits in children exposed in-utero, and may lead to decreased performance in cognitive functions.
The destructive and debilitating effects of mercury in the human body is not a recent discovery. In a 2003 article published in the journal NeuroToxicology, two groups of 22 adult male subjects that were habitual consumers of tuna were monitored to assess the early neurotoxic effects associated with consuming mercury absorbed through eating fish. The assessment measured vigilance, psychomotor function, hand tremor measurements, and found that with elevated levels of mercury in urine and an above-average organic component of mercury in blood levels, there was a corresponding decrease of neurobehavioural performance when the subjects were tested on colour-word reaction time, digit-symbol reaction time, and finger tapping speed. 3
As a toxic mining product, mercury pollutes the environment and harms communities. To have the assurance of safety in the mine and at our dining tables, it is clear that man-made sources of mercury contamination, such as those coming from ASGM outfits, need to be eliminated.
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[1] Kyrre Sundseth et al., “Global Sources and Pathways of Mercury in the Context of Human Health,� International Journal of Environmental Research and Public Health 14, no. 1 (2017): p. 105, https://doi.org/10.3390/ijerph14010105.
[2]  Paul E. Drevnick, Carl H. Lamborg, and Martin J. Horgan, “Increase in Mercury in Pacific Yellowfin Tuna,� Environmental Toxicology and Chemistry 34, no. 4 (2015): pp. 931-934, https://doi.org/10.1002/etc.2883.
[3]  Plinio Carta et al., “Sub-Clinical Neurobehavioral Abnormalities Associated with Low Level of Mercury Exposure through Fish Consumption,� NeuroToxicology 24, no. 4-5 (2003): pp. 617-623, https://doi.org/10.1016/s0161-813x(03)00080-9.
