Small-scale mining can result in a range of negative environmental and social impacts (see Table 4: Potential Environmental and Social Impacts from Small-Scale and Industrial Mining).
Soil and Water Damage
Although underground mining generally has less dramatic environmental impacts than other forms of small-scale mining, it carries the potential for a collapse of the underground shaft. In addition, the movement of large amounts of waste rock and vegetation can lead to the same pollution problems as an industrial mine, such as acid mine drainage which is discussed further in this section.
Most small-scale mining operations increase sedimentation in rivers, especially through the use of hydraulic pumps and suction dredges. By blasting hillsides with water under high pressure, hydraulic pumps leave scars on the landscape, which may take years to develop even the lightest covering of vegetation. [79] According to a study published by the local electric company in Bolivar state, EDELCA, in 1991, small-scale mining using both suction dredges and hydraulic pumps increased the sediment load in the Caroni River ten times over what could be considered normal. [80] Deforestation, contributing to erosion and loss of fauna, is also associated with small-scale mining. The same EDELCA study found that small-scale mining had eliminated over 60 percent of the vegetation in an 8,000 square kilometer area, most of which had been forested. [81]
Since most small-scale miners do not preserve the topsoil removed before excavation begins, this topsoil is often washed away into surface water, carrying with it ecologically valuable seed banks that are necessary for the regeneration of vegetation. In addition, few small-scale miners engage in reclamation or post-mining recovery practices.
Damage from Mercury Use
The use of mercury in small-scale mining techniques has health and environmental consequences. Mercury is discharged into the environment when miners fail to recover mercury tailings, either by dumping waste directly into rivers or by releasing mercury vapors into the atmosphere when the mercury-gold compound is burned. Small-scale miners use inorganic mercury, which is often converted through natural processes into toxic organic and inorganic compounds. Of greatest concern is the highly toxic organic compound, methyl mercury, which forms in rivers and lakes when micro-organisms metabolize metallic mercury. This toxic form of mercury then accumulates in fish and when ingested causes mercury poisoning in humans. Metallic or inorganic mercury can also be hazardous if it is transformed into gas from its liquid state; in a recent case, teenagers in the United States who handled liquid mercury were hospitalized for mercury poisoning after samples of the silvery substance formed a hazardous vapor [82] Although symptoms differ for poisoning by inorganic and organic mercury, both kinds may result in nervous system disorders, birth defects, or death.
Estimates for the amount of mercury released into the environment as a result of small-scale mining vary from 1-4 kilograms per kilogram of gold extracted.83 In the Amazon Basin alone, between 90-120 tonnes of mercury are discharged annually into local rivers.84 In Venezuela, the amount of mercury lost in the environment is estimated to exceed 10 tonnes per year.85 While the impact of mercury pollution may be severe at the site of mining activity, it is by no means restricted to that area and can affect communities many kilometers away. [86]
In Venezuela, substantial metallic mercury deposits have been found to exist in the bottom of the river where mining is occurring, and as of 1989, fish were beginning to show evidence of mercury contamination. [87] Nonetheless, without baseline data on the water quality and composition of the river bottom materials before mining began, it is difficult to determine with any certainty how much mercury has been deposited in local riverbeds as a result of small-scale mining operations.
References and notes
79. Severely degraded areas were cited in W. Franco et al., “La situaci
