In artisanal gold mining, gold is extracted mainly from alluvial deposits along rivers, waterways and terrestrial soils. Gold is then processed by crushing and grinding of the gold-bearing ore. The gold is extracted from the concentrate by adding Hg to form gold-amalgam which is normally roasted in open air to obtain “raw gold”. The elemental Hg evaporates into the air and is subsequently deposited onto land and surface waters, after undergoing oxidation to ionic Hg (Hg2+) through reactions mediated by ozone, solar energy and water vapour.
Mercury, once exposed to atmospheric, aquatic and terrestrial influence, may undergo a series of transformations, eventually becoming Methyl-mercury which is a neurotoxin and the most toxic form of the metal. Methylmercury is easily incorporated in living organisms and accumulates in the food chain. Consequently, fish and other aquatics are contaminated, endangering populations consuming the fish. In addition, Hg entering the environment is transported downstream of river systems, probably reaching the coastal region in the Gulf of Guinea.
Children who are exposed to mercury are particularly at risk of developmental problems. Exposure to mercury can cause kidney problems, arthritis, memory loss, miscarriages, psychotic reactions, respiratory failure, neurological damage and even death.
Both the inorganic and organic forms can cause neurological problems. However, methylmercury, which passes more easily into the brain is generally considered the more toxic species, particularly among children, who can experience IQ losses, delayed speech, and other neurodevelopmental deficits from exposure. Early-life exposures are the most harmful, says Roberta F. White, Chair of Environmental Health and associate dean for research at the Boston University School of Public Health, because they can damage the whole brain. Exposures later in life, on the other hand, produce more localized damage to the cerebellum, visual cortex, and motor strip. In adults, these exposures can lead to visuospatial problems and effects on executive functioning, memory, and mood.
The most direct pathway, however, is the inhalation of mercury vapours created during the burning process. An immediate toxic exposure to miners and their families are most affected by these noxious vapours. A study of artisanal gold mining in Peru concluded that for every gram of gold that is produced, at least two grams of mercury are emitted into the atmosphere.
In addition to the afore-mentioned environmental impacts, artisanal gold mining contributes significantly to land degradation, dust production, pollution of soils and agricultural sites, diversion of river courses, exposure of large areas to erosion and subsequent release of other heavy metals into waterways, and complete deforestation and loss of biota. Hg may also disperse to other distant uncontaminated locations, making those habitats vulnerable to Hg poisoning. This may occur through deterioration of air and water quality and subsequent deleterious effects on living organisms as well as humans. In effect, there is loss of biodiversity and conservation of natural resources.
Cyanide (CN-): A chemical containing carbon and nitrogen
Cyanidation: A method of extracting exposed gold or silver grains from crushed or ground ore by dissolving it in a weak cyanide solution
Fish and aquatic invertebrates are particularly sensitive to cyanide exposure. Concentrations of free cyanide in the aquatic environment ranging from 5.0 to 7.2 microgrammes per liter reduce swimming performance and inhibit reproduction in many species of fish. Other adverse effects include delayed mortality, pathology, susceptibility to predation, disrupted respiration, osmoregulatory disturbances and altered growth patterns.
Concentrations of 20 to 76 microgrames per litre free cyanide cause the death of many species, and concentrations in excess of 200 micrograms per litre are rapidly toxic to most species of fish. Invertebrates experience adverse nonlethal effects at 18 to 43 micrograms per liter free cyanide, and lethal effects at 30 to 100 micrograms per liter (although concentrations in the range of 3 to 7 micrograms per liter caused death in the amphipods/amphibian species .
Cyanide prevents the body from taking up oxygen, resulting in suffocation, which may be fatal to humans and animals without prompt first aid treatment. However, people and animals can rapidly detoxify non-lethal amounts of cyanide without negative effects, and repeated small doses can be tolerated by many species. Some long-term health effects have been observed in people who consume a diet high in cyanide-containing plants such as cassava, and include goitre and depressed thyroid function.
Mammals range from 2.1 milligrams per kilogram of body weight (coyote) to 6.0-10.0 milligrams per kilogram of body weight (laboratory white rats). Symptoms of acute poisoning usually occur within 10minutes of ingestion, including: initial excitability with muscle tremors; salivation; lacrimation; defecation; urination; laboured breathing; followed by muscular incoordination, gasping and convulsions. In general, cyanide sensitivity for common livestock decreases from cattle to sheep to horses to pigs; deer and elk appear to be relatively resistant.
Fortunately, cyanide oxidises (breaks down) in the presence of oxygen so degrades faster in such environments. The issue is the level of cyanide that would be released at a particular point and time.
The incessant use of these chemicals by miners, almost all over the country, calls for concerted efforts to find prudent solutions to help the miners regulate their activities in order to save life and property. A stakeholders meeting should be called where the issue should be evaluated and appropriate measures adopted to curb the menace.
written by Nana Dwomoh Sarpong,Environmentalist.