Acidification

Strong acidification takes place in soil areas w'here metallic ore is mined and processed. Acidifying compounds emitted from smokestacks and draining acid from mine waters and tailings cause acidification. Metal processing does not remove all pyritic minerals such as pyrite, pyrrotite, and chalco- pyrite. The oxidation of pyrite and pyrrotite produces acid. The oxidation of ferrous to ferric cations is accelerated by the presence of a bacterium, as explained in Chapter 4. The amount of acidity produced is a function of many variables, such as temperature, oxygen supply, the concentration of sulphides, initial pH of the surroundings, total concentrations of Fe, and the presence of bacteria. Formation of sulphuric acid decreases the pH of the tailings and adjacent soils, which usually results in increased mobility of metals present there.

Additionally, the sulphur-dioxide emissions from smelters contribute to the soil acidification. The amount of sulphur measurement released varies depending on the origin of the ore. Sulphur emissions from copper smelters in Canada were about 0.7 Mg per Mg of copper produced vs. 11 in the United States, and 0.03 in western Europe. In Sudbury basin Cu-Ni mining and smelting basin soils are strongly acidified (pH values ranging 2.0-7.5) as a result of sulphur-di-oxide fumigation from two active copper-nickel smelters. Metals present in the acidic soils become easily mobile and available for plants, therefore their leaching, plant uptake, and runoff from soils increase. Sudbury soils had the concentrations of mobile A1 as high as 100 mg per kilogram, which is apparently one of the factors of plant toxicity of these soils. Also high concentrations of exchangeable Cu and Ni were detected in these soils.

Soil Biology

The compounds of soil biota are diverse. Included are bacteria, fungi, algae, and soil fauna. Soil microorganisms contribute to the changes in forms of plant nutrients through the mediation process of various biogeochemical cycles involved in nutrient recycling. These processes can alleviate adverse properties in the soils, thus improving conditions of growth of higher plants. The abundance and diversity of soil microorganisms are generally reduced by smelter emissions and acidic conditions. The soil flora of contaminated sites in Sudbury area shoed was characterized by a low diversity of chalcopyrite, absence of cyanobacteria. Similar results have been observed for soils subjected to emissions from various metallurgical plants in Russia. In these areas cyanobacteria were absent from soils within a radius of 20 km. The absence of cyanobacteria in Sudbury soils is apparently a result of strong soil acidification.

Trace Metals

There is much evidence that lead and zinc production results in most severe soil contamination, not only by lead and zinc but also by associated silver, arsenic cadmium, copper, and nickel. Soil contamination by metals from mining and smelting was comprehensively investigated in Japan, the UK, and Poland. Also, the contaminants from copper-nickel smelters in Sudbury in northern Ontario, Canada into the surrounding environment are well documented.

Although currently the UK no longer produces lead and zinc, several case studies show soil contamination by these metals. The most extensive source of metal concentration in the UK operating has been the metalliferous mining which commenced in Roman times and had been operating until the end of the 19th century. It has been estimated that >4,000 square kilometres of agricultural land in England and Wales is contaminated by one or metals because of the historical operations. It has been observed that extremely high concentrations of cadmium, lead, and zinc detected in the soils reclaimed from an old mine at Sipham in southwestern England, little of these metals have been transferred into pasture plants. This observation is good evidence of the effect of metal forms on plant life. High metal concentrations in Shipham soils result from mineralization, not the emission of contaminants. The metals are strongly fixed to primary soil minerals. The data information on Sudbury area has long history of metal mining. However, it seems that probably two factors are involved: (i) leaching and runoff metals into water systems (ii) removal of fine soil particles, enriched with metals, by erosion. However, it should be pointed out that erosion does not change metal concentration in soils. Erosion results in the translocation of the metal-contaminated soil over a bigger area and its dispersion. Leaching and washing of the metals soils are apparently facilitated by the low soil pH. An acidic reaction is the most important factor in increasing soil metal mobility. Erosion can be of importance for the reduction of local metal concentration, especially in barren and semi-barren areas.

Upper Silesia (southern Poland) is a heavily industrialized and agricultural area. The industries present there include coal mines, metal ore mines, lead-zinc smelters, iron smelters, coal-fired power plants, and many others. Metal pollution is mainly caused by two active lead-zinc smelters. The arable land covers about 321,000 ha of predominantly medium-quality soils, which accounts for about 48% of the total area. At some areas in upper Silesia the deposition of cadmium and lead exceeds more than ten times the proposed limit, which was 2.75 kg per km2 cadmium and 182.5 kg per km for lead. The arable soils are contaminated with cadmium, lead, and zinc; also occasionally high concentrations of copper have been detected. The most serious concentrations exist at the vicinity of the two active lead-zinc smelters. However, other areas are also affected by the long-range transport of contaminants. It is estimated that only 10% of the arable land has natural concentrations of heavy metals, 30% the soil is slightly contaminated, and 60% is medium to heavily contaminated.

Japan is well known for environmental contamination, including soil contamination from mining and smelting. There are several reasons for severe contaminations occurring in Japan. Japan has a high population density, a large number of metal mines and rapid economic development after the Second World War. The abrupt increase in metal production spread metals from the mines, smelters, and metal processing factories. Mining and smelting industries are the main sources of cadmium contamination of Japanese soils. There are also areas with soils contaminated by arsenic, bismuth, zinc, chromium, and lead from mining/smelting in Japan.

Trace Metal Contamination of Terrestrial Plants

Plants uptake from contaminated soils and deposit contaminants from the atmosphere onto the plant surfaces. They are the sources of elevated levels of trace elements in terrestrial plants growing in mining/smelting areas. The crops in upper Silesia in Southern Poland had elevated concentrations of cadmium, lead, and zinc apparently as a result of emissions from the two lead-zinc smelters in the area. However, the metal levels were not extremely high in agricultural products. In Sudbury soils in Ontario, Canada, areas remain barren or semi-barren of vegetation as a result of severe environmental conditions. Following the environmental improvements in the Sudbury area, several plant species developed colonized barren sites. However, recolonization was confined to relatively favourable sites by species that evolved metal tolerance.

Health Risk

It is a complex process to evaluate the health impacts of mining and smelting operations. The complex factors have to be submitted for assessment. There is no uniform methodology available. Different approaches may lead to conflicting results. For example, in Upper Silesia in Poland is a region with numerous diverse industries, ferrous and nonferrous mining and smelting, hard coal mines, and power plants. Upper Silesia frequently experiences peak ambient sulphur-dioxide concentrations of >300 pm/m3 and average values of more than 60 pm/m3, which is the level by which the health can be endangered. In addition, ambient concentrations of aerosols in many sites in Upper Silesia have ambient concentrations of acid aerosols that are high enough to cause a significant deterioration in lung function. Additionally, it has been estimated that because of a heavy load of air pollutants and stagnant air masses, the oxygen content of the air can decrease by as much as 20%. This can induce health hazard to heart patients asthmatics. The hazardous conditions prevailing in Upper Silesia are believed to be responsible for 15% higher circulatory problems, 30% more cancer cases, and 47% greater respiratory problems compared to other areas of Poland. The incidence of these diseases can be related to an overall deterioration in environmental quality in Upper Silesia caused by emissions from various industries, which includes metal ore mining and processing. However, it is difficult to quantify the relative contributions of particular sources.

Bibliography

  • 1. Dudka, S. and D. C. Adriano. Environmental impacts of metal ore mining and processing: A review, J. Environ. Qual. 26:590-602 (1997).
  • 2. Adamo, P. S., M. J., Dudka, M. J. Wilson, and W. J. Hardy. Chemical and Mineralogical forms of Cu and Ni in contaminated soils from the Sudbury mining and smelting region, Canada Environ. Pollut. 91:11-19(1996).
  • 3. Amiro, B. D. and G. M. Courtin. Patterns of vegetation in the vicinity of an industrially disturbed ecosystem, Sudbury. Ontario, Can. J. Bol. 59:1623-1639 (1981).
  • 4. Davies, В. E. and H. M. White. Environmental pollution by wind blown lead mine waste: A case study in Wales, U.K., Sci. Total Environ. 20:57-74 (1981).
 
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