Hazards identified and the need for health risk assessment in the South African mining industry

Abstract

Although mining plays a prominent role in the economy of South Africa, it is associated with many chemical hazards. Exposure to dust from mining can lead to many pathological effects depending on mineralogical composition, size, shape and levels and duration of exposure. Mining and processing of minerals also result in occupational exposure to toxic substances such as platinum, chromium, vanadium, manganese, mercury, cyanide and diesel particulate. South Africa has set occupational exposure limits (OELs) for some hazards, but mine workers are still at a risk. Since the hazard posed by a mineral depends on its physiochemical properties, it is recommended that South Africa should not simply adopt OELs from other countries but rather set her own standards based on local toxicity studies. The limits should take into account the issue of mixtures to which workers could be exposed as well as the health status of the workers. The mining industry is also a source of contamination of the environment, due inter alia to the large areas of tailings dams and dumps left behind. Therefore, there is need to develop guidelines for safe land-uses of contaminated lands after mine closure.

Keywords

Mining hazard dust silicosis cyanide heavy metals

Introduction

Although mining is a cornerstone of the South African economy (Figure 1), it generates copious amounts of dust.¹ The dusts may be toxic since they may also be contaminated with various toxic metals. For this reason, the prevalence and severity of occupational diseases in the mining industry depends on the ores mined, the contaminants present and also on the levels and duration of exposure and coexisting illnesses in the exposed population and their environmental conditions and lifestyles.² Moreover, the unclaimed ore and spent processing chemicals, known as tailings,^3,4 are discharged into waste streams, which may be an additional source of exposure if not properly contained.¹

Figure 1.

Map showing mining areas in South Africa. Adapted from source.⁵

Due to policy and legislative reform the techniques for mining in South Africa have improved to include sophisticated ventilation and chemical extraction of minerals from low-grade ores. However, mining in South Africa has the legacy of silica exposure, silicosis and tuberculosis, which contribute substantially to mortality and morbidity of miners. In this review, particulate and chemical hazards associated with mining industry in South Africa are identified and critical issues in the management of those hazards are discussed.

Hazards from mining processes

Mining involves rock drilling, related milling operations and dredging.⁶ These processes generate copious amounts of dust, which is mainly made up of crystalline silica. Exposure to respirable dust is an important risk factor for many respiratory diseases. Short-term exposure to respirable dust can cause irritation of the upper respiratory tract. Long-term cumulative exposure in workers is likely to develop into silicosis, silico-tuberculosis, pulmonary tuberculosis (PTB), obstructive airways disease and occupational asthma.² Moreover, it has been found that human immunodeficiency virus (HIV) with silicosis exacerbates PTB⁷ and other infectious diseases, including bacterial pneumonia, cryptococcosis, enteritis, bronchitis, urinary tract infections and soft tissue infections.^8,9 Despite efforts to reduce exposure to chemical hazards in mines prevalence of occupational diseases have been persistently high among miners. A 33-year study has shown no reduction in the proportion of miners coming to autopsy with pathologic evidence of silicosis.¹⁰ In addition to silicosis in gold and platinum mines due to exposure to silica,¹¹ there is coal workers’ pneumoconiosis (CWP) among coal mine workers¹² and asbestosis among workers and individuals who live in areas surrounding asbestos mines.¹³ There is also a risk of asbestosis, lung cancer and mesothelioma in diamond mines since asbestos and asbestos-like deposits exist very close to diamond deposits.¹⁴ In addition, there could also be occupational exposure to dusts from industrial mining of clay, limestone, sand, gypsum, gravel, and so on, important materials in the manufacture of cement. Cement dusts have been observed to, among other effects, cause indirect haematological damage resulting in abnormal blood cell counts, minor chromosomal aberrations, decrease in mitotic index and increased frequency of sister chromatid exchanges.¹⁵

The prevalence of occupational diseases have been persistently high among miners.^10,16 A study on the prevalence of silicosis among black migrant contract workers on a South African goldmine indicated prevalence levels of 18.3–19.9%.¹⁷ The prevalence of CWP has been determined to be 7.3%.¹² At the same time, the prevalence of tuberculosis and HIV among miners is said to be high.¹⁸

Hazards from mineral processing

There are many hazards that can result from processing of minerals. For example, the method that is widely used in South Africa for extraction of gold is the cyanidation process which uses cyanide.¹⁹ The process involves dissolution of gold from the ore in a dilute cyanide solution and extraction of the gold in a complex in the presence of lime and oxygen. Cyanide is a very fast-acting poison that prevents oxygen from being used by the cells resulting in tissue hypoxia and cyanosis. This results in rapid and deep breathing followed by convulsions, loss of consciousness and suffocation.²⁰ In South Africa the cyanide in the spent leaching solutions is discharged into large mine tailings dams. Seepage escapes from some of the tailings dams and contaminates soil and water. Dispersion modelling indicates that tens of thousands of people that reside in areas adjacent to tailings dams within the City of Johannesburg may even be exposed to atmospheric cyanide concentrations above international standards.²¹

Mercury (Hg) can also be used for extraction of gold. With artisanal small-scale gold mining reported as one of the sources of Hg, South Africa is ranked second in the world in terms of Hg emissions to the environment.²² Inhalation, ingestion, or dermal absorption of Hg can result in neurological and behavioural disorders, tremors, insomnia, hallucinations, memory loss, neuromuscular effects, headaches and cognitive and motor dysfunction.²³ In one study on Hg exposure in a gold mining community, 50% of urine samples exceeded the guideline among individuals that were not occupationally exposed.²⁴

Hazards from minerals and contaminants in the minerals

According to the Mining Intelligence Database,²⁵ South Africa is currently the world’s largest producer of chromite, platinum group metals (PGMs), manganese (Mn), vanadium and vermiculite, and is the second largest producer of ilmenite, palladium, rutile and zirconium. There is also smaller scale mining and/or processing of other metals, such as copper, zinc, uranium, aluminium, nickel, lead, cobalt and iron, as well as industrial minerals such as andalusite, fluorspar, phosphate, clay, limestone, gypsum and gravel.⁵ Mining of these commodities is one of the major sources of metal dispersion into the environment. In addition, acid mine drainage from mining operations and mine tailings dams and dumps contains a variety of toxic metals, some of which are found in high concentrations in soils surrounding mining areas in South Africa.^26
–28

There is a number of hazards associated with mining of minerals in South Africa. For example, mining of Mn, a well-established neurotoxin²⁹ may cause pulmonary emboli, bronchitis and impotence; symptoms of chronic Mn toxicity have also been observed in children living in areas around open Mn mines, where environmental exposure to Mn is high.³⁰

Mining of PGMs, ruthenium, rhodium, palladium, osmium, iridium and platinum,^31,32 involves the processing of platinum ore and extraction and refining of the concentrate to separate and purify the PGM. Platinum compounds are well known for inducing hypersensitivity, shown by the development of allergic symptoms including cutaneous eruptions and severe asthma^33,34 as well as severe skeletal deformities.^32,35,36 Most of the exposure to platinum salts occurs in the later stages of the refining process.³⁷ Platinum salt sensitivity has been diagnosed among platinum refinery workers in South Africa,³⁴ but there is no published literature on this condition in platinum miners.³⁸ There is also the risk of environmental exposure to PGM.³⁹

Titanium is mined as ilmenite, an iron titanium oxide ore. Overexposure by inhalation of titanium dioxide dust can cause tightness and pain in the chest, coughing and difficulty in breathing. Contact with skin or eyes may also cause irritation. South African ilmenite contains many impurities, including manganese oxide and aluminium oxide,^40,41 so airborne particles from ilmenite mining may elicit a variety of health effects specific to the individual component metals. Despite an indication of radiation-induced genotoxicity in ilmenite processing workers in other countries⁴² and the fact that heavy mineral sand deposits from which ilmenite is mined in South Africa contain radionuclide impurities,^43,44 there appears to be no study of hazards of radioactivity among workers that deal with ilmenite in South African mines. It is important to monitor exposures to radioactivity from these non-nuclear industries that ‘have the capability for low-level but consistent exposure to radiation’, which can endanger both the health of workers and to populations living in the neighbourhoods of mines and associated plants.⁴⁵

Chromite, the mineral ore that contains chromium (Cr), is mined in South Africa.²⁶ Chronic inhalation of Cr(VI) in humans results in shortness of breath, coughing, wheezing, perforations and ulcerations of the nasal septum, bronchitis, decreased pulmonary function, pneumonia, asthma and nasal itching and soreness.^46
–48 In addition, hexavalent Cr is a strong oxidizing agent that is also potentially mutagenic and carcinogenic.^49,50 These effects were observed in studies conducted in countries other than South Africa where in the latter, very few studies investigated the exposure to Cr in South African mines.⁴⁸

A considerable proportion of the world’s total vanadium production comes from mining in South Africa. Vanadium, a well-known occupational hazard,⁵¹ causes irregular respiration, diarrhoea, ataxia, paralysis,⁵² decreased fertility, embryolethality, fetotoxicity and teratogenicity in mice and rats.⁵³ Very few studies appear to have been conducted on hazards and risks of occupational exposure to vanadium in mines in South Africa.⁵⁴ The focus of the studies has been on the consequences of environmental exposure, particularly to livestock. Vanadium was suspected to have caused deaths of some cattle when a dam collapsed and caused vanadium to contaminate grass.⁵⁵ However, a risk assessment showed that consumption of meat and milk from cattle that grazed in areas close to a vanadium processing plant would pose no health risk to the consumers.⁵⁶ This notwithstanding, vanadium remains both an occupational and environmental hazard in South Africa.

Other metals that are mined and/or processed in South Africa include zinc, aluminium, copper, nickel, lead, cobalt and iron. The toxicities of these metals are well-documented. However, there appears to be no records in the literature of studies of exposure to these metals in South African mines.

Finally, uranium (U), a radioactive substance of moderate acute toxicity,⁵⁷ is found in South African gold ore in concentrations of around 100–300 ppm. Mining of U-bearing ore often releases and mobilises high concentrations of the radionuclide in the biosphere. Mine tailings dams and dumps are known to contain elevated levels of uranium.⁵⁸ Contamination of streams due to uranium leached to ground and surface water bodies has also been reported.⁵⁹ Studies conducted by the Department of Water Affairs and Forestry a few decades ago showed only a few hotspots of water sources with high levels of radioactivity,⁶⁰ making it essential to conduct new studies to investigate this further.

Hazards from other activities

There are many other hazards from mining. In particular, underground miners are exposed to high levels of diesel particulate matter (DPM) from the use of diesel-powered mobile equipment. In addition to causing cardiovascular dysfunction, eye and nose irritation, headaches, nausea and asthma,⁶¹ it also causes neuroinflammation and neurodegenerative disease.⁶² DPM is classified as an IARC Group 2A probable human carcinogen.⁶¹ Very recent reports on the greater than additive risks from combination of exposures to metals and particulate matter have caused the research community to re-think the risks of cancer and neurotoxicity using cumulative exposure models. They have hypothesized that oxidative stress and neuroinflammatory pathways may be commonly induced by both unrelated exposures and cause the greater health impacts.^63
–65

Lack of health risk assessment and the associated critical issues concerning setting exposure limits in the South African mining industry

The South African government is committed to controlling the hazards of mining. However, there are a number of issues concerning management of the hazards and risks in South African mines. Health and safety in mines in South Africa is regulated by the Mine Health and Safety Act 29 of 1996 and the Mine Health and Safety Act regulations. The Act and the regulations forbid work in an environment containing hazardous concentrations of dust, noxious fumes and harmful gases without effective protective apparatus. The Act and regulations also set limits for mine dusts and other air pollutants. For example, the occupational exposure limit (OEL) for respirable quartz has been set at 0.1 mg/m³. However, a prevalence and exposure-response study among gold workers shows that this value is insufficiently protective.¹⁷ The study, showing a mean respirable crystalline silica (quartz) concentration of 0.053 mg/m³, demonstrated a prevalence of silicosis affecting 18.3–19.9% of workers in a gold mine. A similar study in the United States of America⁶⁶ showing a similar average respirable silica exposure concentration of 0.05 mg/m³, indicated a prevalence of silicosis of less than 1%. The huge difference in prevalence of silicosis is a result of differences in the composition of the mineral dusts as it is known that crystalline silica (such as quartz) is more toxic than amorphous silica.⁶⁷ In addition, the ability of the silica to cause a toxic effect can be modified by substances on the surface of the dust particles, some of which originate from other minerals. There can also be environmental and social factors that may predispose some groups of workers and communities to the risk of silicosis. Therefore, the risk posed by the silica may depend on the origin of the silica and/or the chemicals/minerals with which it has come into contact,^{66,68

–72} and underlying environmental and social factors.

This fact is portrayed well in Figure 2 which shows the different dose-response curves found in different areas. The figure shows that similar cumulative doses of silica may not result in the same degree of risk of silicosis.

Figure 2.

Comparison of the risk of silicosis risks in three studies⁶⁹ with permission.

Similarly, the incidence of CWP at a given coal dust concentration has been found to vary with countries and regions.⁷³ This is partly as a result of the chemical content of the coal. Studies indicate that the risk of CWP depends on the carbon content of the coal; anthracite has more carbon than bituminous coal, which contains more carbon than sub-bituminous and lignite coal.^2,74 In addition, the iron content also seems to play a major role in the harmfulness of coal dusts.⁷⁵ Therefore, although the OEL of 2 mg/m³ has been shown to reduce the incidence of CWP in other countries,⁷⁶ South Africa needs to assess the impact of this standard on the incidence of CWP in those exposed in its own mining industry.

In addition to OELs on silica and coal dust, the Department of Labour has prepared a more comprehensive list of OELs for hazardous substances (including metals) for all working environments.⁷⁷ However, the adequacy of the OELs to protect employees may have to be re-assessed. These OELs are supposed to be integrated with OELs in the Mine Health and Safety Act regulations to avoid contradictions. For example, the time-weighted average-OEL for respirable crystalline silica in the Department of Labour Hazardous Chemical Substances Regulations is 0.4 mg/m³, whereas the Mine Health and Safety Act regulations OEL for the same is 0.1 mg/m³.

For these OELs, in addition to differences in toxicities of minerals from different countries/regions, South Africa may have other risk factors that may not be prevalent in western countries. For example, confounding factors such as malnutrition and HIV/AIDS are known to be prevalent in South Africa and may act synergistically to enhance the toxicity of a material.⁷⁸ It is also known that ‘economically disadvantaged groups are likely to be systematically more exposed and more susceptible to environmental pollution’.⁷⁹ These same populations may also have higher background rates of many diseases such as cancer and asthma, therefore the additive impacts of these exposures on an already unacceptably high disease rate is one that can cause concern for public and occupational health workers.

The US National Academy addressed the philosophy of risk assessment when there are high background rates of disease that may differentially impact humans by defining an expanded risk framework to broaden the conventional approach to include many other coexisting factors.⁸⁰ There is precedent in the international community for setting some OELs with adjusted values for individuals who have a higher background rate of disease that may be due to genetic predisposition. This was done in setting acceptable exposure levels for workers with sickle cell disease.^81
–83 It is important to evaluate these significant susceptibility factors in the derivation of OELs and risk characterization. South African OELs are based on the UK values in its current legislation.⁸⁴Therefore, rather than simply adopting OELs from other countries, South Africa should develop her own.

The development of OELs in South Africa would involve the establishment of quantitative health-based limits from dose–effect data from in vitro and in vivo studies carried out on representative local mineral samples and other related pollutants. In addition, epidemiologic data should be used whenever possible.⁸⁵ Extra uncertainty factors may be added in the derivation of the OEL from toxicity thresholds, such as the No-Observed-Adverse Effect-Level, to account for other vulnerabilities such as immune suppression. The establishment of OELs should also take into account the issue of co-exposure to mixtures; for instance, workers could be simultaneously exposed to silica and diesel exhaust particulates, and workers in diamond mines in South Africa are usually exposed both to silica and asbestos-like mineral dust.⁸⁶

Monitoring and enforcement of OELs requires accurate sampling protocols. Comparison of sampling practices in one mine with the Department of Minerals and Energy guidelines and internationally accepted protocols found a number of serious short falls.⁸⁷ A number of recommendations were made in the study including updating of the guidelines and performance of independent audits.

Section 10.25 of the Mine Health and Safety Act regulations⁸⁸ also controls the use of internal combustion engines in underground mines. The regulations stipulate that no diesel engine shall be used in underground mines unless there is sufficient ventilation to render harmless the exhaust gases produced. The regulations require periodic determination of carbon monoxide or oxides of nitrogen in the air. As for DPM, the US Mine Safety and Health Administration have set the exposure of miners in an underground mine to DPM to a maximum average 8-h airborne concentration of 160 μg/m³ as total carbon. Unfortunately for South Africa, diesel exhaust particulates are not addressed in the mining regulations and currently there is no OEL for diesel particulate matter.⁸⁹

There are also issues regarding reclamation of contaminated land. South Africa has many decommissioned mines and large mine tailings dumps and dams. It has been estimated that there are more than 270 tailings dams related to gold mining alone, covering a total area of about 180 km².⁹⁰ Most of the tailings dams and dumps are located close to human dwellings and agricultural land.⁹¹ When mining ceases, the land is redeveloped. This land is potentially contaminated and a risk assessment should be done before allocating the land to various uses, especially human habitation.⁹² For this purpose there is need in South Africa to develop locally applicable environmental standards and guidelines for safe use of contaminated land after mine closure. These guidelines should be prepared after a thorough risk assessment performed on mineral samples from mine dumps that are typically encountered in areas around decommissioned mines.

All in all, there have been more studies of exposures to dust in gold, diamond and coal and asbestos mines than in other mines such as mines for vanadium, iron, uranium, nickel, copper, and so on. There is a need, therefore, to assess the hazards as well as to undertake health risk assessments for mines for which there is little information.

Conclusions

Mining in South Africa has a legacy of various occupational diseases that contribute substantially to mortality and morbidity of miners. As a way of addressing this it is recommended that South Africa should not simply adopt OELs from other countries but rather set her own OELs for silica and other mineral dusts from local toxicity studies. The limits should take into account the issue of mixtures to which workers could be exposed and the nature and state of health of the local populations.

The mining industry is also a source of contamination of the environment, as among other things it leaves behind huge areas of tailings dams and dumps. This makes it necessary to develop guidelines for safe use of contaminated land after mine closure. It is concluded that mining in South Africa is a source of both occupational and environmental hazards that need cooperation between the government, the private sector and civil society in order to reduce the morbidity and mortality from these exposures.

Footnotes

Conflict of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

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