Africa's growing cancer burden: Environmental and occupational contributions

Article Outline

• Abstract
• Abstract
• 1. Introduction
• 2. Africa's cancer burden
• 3. Epidemiologic studies of cancers attributable to the environment
• 4. Circumstances leading to environmental carcinogen exposure
• 5. Environments with possible carcinogenic exposure
  • 5.1. Exposure in industry
  • 5.2. Air pollution
  • 5.3. Hazardous wastes
• 6. Example: asbestos exposure with occupational, para-occupational and wider environmental exposures
• 7. Concluding remarks
• Conflict of interest
• References
• Copyright

Abstract 

Background: Primary prevention measures are needed for Africa's cancer burden (715,000 new cases and 542,000 deaths in 2008), a burden projected to double by 2030 due to demographic changes alone. Control of cancer-causing infections and lifestyle-related carcinogens will play a significant role in prevention, but less often addressed are environmental and occupational contributions. Methods: We review environmental issues that contribute to Africa's Cancer burden. Results: We demonstrate evidence of the impact of environmental carcinogens on the cancer burden as of now and that circumstances present today may increase their contribution further. Suboptimal implementation and monitoring of environmental protection and of occupational health standards, including in the informal sector, use of outdated technologies in industry and lack of awareness of potential hazards in the specific employment structure give rise to high levels of exposures. Carcinogens of concern include (i) those that have been long present (e.g. indoor air pollution) whose contribution may increase as life-expectancy increases and long latency periods for cancer are realised, (ii) exposures in mining and agricultural sectors and (iii) modern environmental hazards, including urban air pollution and agents arising from the mis-management of hazardous waste from local, industrial and trans-boundary sources. Conclusions: Actions taken to reduce exposures and research to fill gaps in knowledge, adapted to local settings, could help mitigate the cancer burden.

Keywords: Africa, Cancer, Environment, Occupation, Hazardous waste

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1. Introduction 

Communicable diseases have dominated Africa's disease burden for much of the past century. Today, however, Africa is in a period of dynamic change; the continent has the world's fastest rates of population growth, urbanization and of increases in life-expectancy. As a consequence its disease profile is evolving and non-communicable diseases (NCD) are increasing in incidence. Cancer constitutes 17% of Africa's NCD mortality burden, i.e. the second most common cause of NCD death [1]. In most of sub-Saharan Africa health services required for early detection, diagnosis, treatment and care of cancer are critically lacking. Furthermore the outlook is of an increasing burden.

Cancer control measures, ideally prevention, are needed in this setting, as recently highlighted by Sylla and Wild [2]. An estimated 19% of cancers in men and 29% in women in sub-Saharan Africa are attributable to 9 modifiable factors [3]. Of these, much research and public health policy is deservedly devoted to the control of infection-related cancers, e.g. HPV vaccination and screening in cervical cancer, hepatitis B vaccination in liver cancer, HIV-related cancers, and lifestyle factors including tobacco consumption in men or physical inactivity in urban areas [4], [5], [6]. We do not address these factors here, but instead focus on the less-studied contributions of environmental and occupational exposures to Africa's cancer burden. The latter factors need consideration because they are often preventable and because circumstances in many African countries give rise to conditions where unnecessary exposures, at times at high levels, are present. These include suboptimal implementation and monitoring of occupational health and environmental protection, use of outdated technologies in industry and lack of hazard awareness. Industrialisation in this mineral and agriculturally rich continent has multiple positive benefits, but also introduces modern environmental hazards.

Herein we address environmental and occupational contributions to Africa's cancer burden. After summarising the burden, we provide evidence from epidemiologic studies of its environmental contributions. The environment is considered as the external natural and physical environment, i.e. exposure to chemicals or radiation in the air, water, soil or food, and in the workplace, thus not including lifestyle factors. We then describe both circumstances present today that give rise to likely environmental exposures and exposure settings in Africa that need monitoring for their effect on cancer. We include (i) established and probable carcinogens to humans (International Agency for Research on Cancer (IARC) classification Groups 1 and 2A) and (ii) possible carcinogens (Group 2B) whose large exposure contrasts and unique exposure characteristics in certain African situations provide research opportunities to clarify their carcinogenicity to humans. We attempt to obtain estimates of exposure prevalences, but as systematic data are generally scarce, we have also included situational examples.

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2. Africa's cancer burden 

Africa is made up of 53 countries and a total population close to 1 billion (in 2008, 987 million, 15% of the world's population). The largest countries, with populations exceeding 50 million, are Nigeria, Egypt, Ethiopia, Democratic Republic of the Congo and South Africa. Although here we attempt to cover relevant continent-wide issues, its ethnic, cultural, lifestyle and genetic diversity cannot be overlooked in a continent 3 times the area of Europe and with a north–south distance as far as London to Beijing. In 2008, there were an estimated 542,000 cancer deaths and 715,000 new cancer cases in Africa (considering the whole continent, countries included in footnote to Table 1) [7]. Table 1 summarises the total cancer mortality and incidence burden, age-standardised incidence rates and lists the 5 most common cancers by African region. More than half of the cancer burden (56%) is in women, a pattern unique to this continent due in part to the large cervical cancer burden. Large regional variations in age-standardised incidence rates exist within the continent, with lowest rates in Middle Africa and highest in Southern Africa. In men prostate cancer appears within the 3 most common cancers in all regions other than Northern Africa, liver is the most common in Western and Middle Africa and Kaposi's sarcoma, an AIDS-defining malignancy, is common in Eastern, Southern and Middle Africa and lung in Northern and Southern Africa. Among women, cancers of the breast and cervix dominate; thereafter the third most common cancer in women is liver, colorectum, oesophagus and NHL, depending on region (Table 1). Although age-standardised incidence rates for the continent as a whole are considerably lower than the world average (47% lower in men and 30% lower for women), corresponding gains do not apply to mortality for which rates are reduced to a lesser degree, by 32% in men, and a mere 4% in women.

Table 1. Incident cases, deaths, age-standardised incidence rates and most frequent cancers in African regions in 2008.

KS: Kaposi's sarcoma; NHL: non-Hodgkin's lymphoma; ASR: age-standardised incidence rate (World standard population). Countries by region; Eastern: Burundi, Comoros, Djibouti, Eritrea, Ethiopia, La Reunion (France), Kenya, Madagascar, Malawi, Mauritius, Mozambique, Rwanda, Somalia, Tanzania, Uganda, Zambia, Zimbabwe. Southern: Botswana, Lesotho, Namibia, South Africa, Swaziland. Middle: Angola, Cameroon, Central African Republic, Chad, DRC, Rep of Congo, Equatorial Guinea, Gabon. Northern: Algeria, Egypt, Libya, Morocco, Sudan, Tunisia, Western Sahara. Western: Benin, Burkino Faso, Cape Verde, Cote d’Ivoire, Gambia, Ghana, Guinea Bissau, Buinea, Liberia, Mali, Mauritania, Niger, Nigeria, Senegal, Sierra Leone, Togo.

Africa's population is expected to grow by 50% between 2010 and 2030, to 1.52 billion, i.e. the continent with the highest population growth rate [8]. Although life-expectancy is lowest worldwide, it is projected to have the greatest increase, of over 7 years from 2010 to 2030 in both men (from 54.3 to 61.3 years) and women (from 57.2 to 64.4). The future cancer burden is thus projected to double, from 0.7 million to 1.3 million between 2008 and 2030. In Southern and Eastern Africa life-expectancy was shortened in the past 2 decades by HIV/AIDS, but scaling-up of effective antiretroviral treatments means that the large HIV+ population survive longer and are at risk of all cancers (not just AIDS-defining malignancies) and other chronic diseases [9].

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3. Epidemiologic studies of cancers attributable to the environment 

The known epidemiology of cancers in Africa has been comprehensively compiled [10], but the overall environmental contribution has not been quantified. For comparison in developed countries such as the UK, 8% of cancer mortality in men and 1.5% in women have been attributed to occupation alone, mostly lung, non-melanoma skin, mesothelioma, leukaemia, nasopharynx and bladder cancer [11]. In Africa, studies of contributing risk factors for lung cancer come predominantly from Southern and Northern Africa, where this cancer is common in men (Table 1). If we assume that the population attribution fraction (PAF) of lung cancer not attributable to smoking is due to environmental exposures, then we can gauge its contribution. Table 2 presents PAF estimates calculated in this way from African case–control studies. In Southern Africa, PAFs not attributable to smoking were 10–20% in men in South Africa, and higher (over 40%) in women [12], [13], [14]. Factors associated with increased risks, other than tobacco smoking, were asbestos (residentially and in mines), gold-mining, dusty occupations and non-electrical heating/cooking fuels. Increased lung cancer risk in gold miners came from silica dust exposure and not uranium exposure [15]. Notably in the most recent update of the largest hospital based case–control study in Johannesburg/Soweto, South Africa, with cases spanning 1995–2004, PAFs of lung cancer not attributable to tobacco smoking were 13% in men and 62% in women [12]. As lung cancer is one of the more common cancers in South Africa (15.4% of all cancer deaths in men and 6.9% in women in 2008), the environmental contribution to lung cancer alone would represent 2 and 4% of total cancer mortality in men and women respectively. An earlier estimate from Zimbabwe was higher, with 40% of lung cancer not attributable to smoking, possibly coming from occupational exposure in copper, gold and nickel mines, but no increased risk was observed for asbestos [16]. In Northern Africa, where lung cancer is common in men (12.7% of incident cancers) but not in women (<2%), PAFs due to smoking were generally over 90% in men, revealing a smaller environmental contribution (<2% of incident cancers). In a case–control study in Morocco, Tunisia and Algeria (combined), 5% of cases had occupational exposures to nickel, asbestos or arsenic (relative risks not provided).

Table 2. Population attributable fraction estimates of environmental factors to cancer in Africa (examples).

Cancer	Setting; calendar year; n=number of cases (reference)	Attributed to:	Population attributable fraction (%)
			Men	Women
Lung	Bulawayo, Zimbabwe; 1963–1977; n=121 men, n=6; women [16]	Not attributable to smoking	39.2	–
	South African gold miners; 1970–1986; n=78 [15]	Not attributable to smoking	<20b
	Northern Province, South Africa (asbestos mining area); 1993–1995; n=288 men, 60 women [13]	Not attributable to smoking	22.2	61.8
		Dusty occupations	63.5	0.0
		Wood/coal in house	42.8	24.3
		Asbestos—current residential	12.5	5.3
		Asbestos—residence at birth	13.0	7.1
	Johannesburg, South Africa; 1995–1999; n=105 men, 41 women [14]	Not attributable to smoking	18.6	44.7
		Kerosene heating fuel	4.7	0
	Johannesburg, South Africa; 1995–2004; n=333 men, 90 women [12]	“Noxious”a job	58.5	1.6
		Not attributable to smoking	12.6	61.8
		Non-electrical cooking fuels	29.0	7.1
	Algeria, Tunisia, Morocco [50]	Not attributable to smoking		NA
	1996–1986; n=114	Morocco	8.9
	2000–2003; n=149	Tunisia	17.6
	2003–2004; n=167	Algeria	7.3
	Casablanca, Morocco; 1996–1998; n=118 [51]	Not attributable to smoking	10.8c
Bladder	Bulawayo, Zimbabwe; 1963–1977; n=494 men, 187 women [52]	History of bilharzia/hematuria	28.0
	Alexandria, Egypt; 1994–1996; n=151 men, n=39 women	Urinary schistosomiasis	20.5

Mesothelioma, caused by asbestos, is almost entirely attributed to environmental or occupational exposure. A rising mesothelioma epidemic in Egypt, where 65% of cases had residential exposure near asbestos factories, made up 1.3% of all cancer registrations in Cairo in 2003 [17]. In South Africa in 2003, this cancer represented 0.53% of all cancers in men and 0.16% in women (National Institute for Occupational Health, South Africa, Incidence of Histologically Diagnosed Cancer in South Africa, 2003). The number of lung cancers caused by asbestos is likely to be as large, thus twice this percentage of total cancer would be attributed to asbestos alone.

Other major cancers in Africa with identified environmental contributions include liver and bladder cancer. Aflatoxin is a mycotoxin that grows on maize and peanuts in hot humid storage conditions and may account for up to 40% of hepatocellular carcinomas in Africa [18]; liver cancers make up 12% of all cancers Africa. Infection with the schistosoma parasite (bilharzia) which lives in trematode flatworms released by freshwater snails causes squamous cell carcinoma of the bladder and a higher incidence in men in North Africa arises from agricultural exposure [19].

Environmental contributions to the cancer burden may increase further for two reasons. Firstly, given the same exposure circumstances, longer life-expectancies imply that underlying initiated carcinogenic processes have necessary latency periods to progress to clinical disease, given the very long latency period of most cancers. Indeed, competing risks from HIV-related deaths have been suggested as the reason for a lack of a worsening expected mesothelioma epidemic in South Africa [20], but as these and other competing risks are combatted, mesotheliomas would be expected to arise. Secondly, in some industrial sectors, as outlined below, there is increasing exposure to carcinogens.

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4. Circumstances leading to environmental carcinogen exposure 

Africa's gross domestic product derives from industry (41.7%), agriculture (14.0%) and the service industry (44.3%). Regional variations are significant, with agriculture a larger contributor (20–30%) in Eastern and Western Africa, and the industrial sector larger in Southern and Northern Africa. In 2000–2006 the largest growths were in industry (annual percent change 6.5%), services (5.2%) and agriculture (3.0%) and greatest industrial growth in eastern (18.5%) and northern (14.3%) regions. A significant factor in industrial growth has come from China's foray for natural resources and raw materials, especially in extractive industries. With the arrival of job seekers, Africa's urban population rose from 29.9% to 39.9% between 1985 and 2010 and is highest in Northern, Southern and Western Africa (>45%). The informal employment sector is large, especially among women, e.g. among non-agricultural activities, it makes up 30–40% of employment in South Africa, Lesotho and Namibia, 50–59% in Egypt and Zimbabwe and over 65% in Uganda, Zambia and Mali (International Labour Organization). 50 million children in Africa are employed, i.e. during a more critical period of exposure.

Africa's workforce characteristics and working conditions give rise to situations where exposures are more likely, sometimes at high levels. Issues that affect the occupational health of workers in Southern Africa but apply to most African countries, have been highlighted by Loewenson [21] and are being targeted by the International Labour Organization. These include (i) slow ratification and implementation of safety standards for the protection of workers and the surrounding environment, (ii) when it is unclear whether a substance is hazardous, continued exposure rather than cautious withdrawal is the norm, (iii) small-scale or artisanal industries, particularly mines, and the informal sector are less likely to implement standards (e.g. purchasing modern ventilation systems) and these industries are more difficult to monitor, (iv) obsolete technologies and machinery that are banned in more developed countries continue to be used, (iv) personal protective devices are not routinely available, and if they are, are not necessarily used by workers who are often not trained in hazard awareness [22]. Monitoring of occupational health is lacking, and systemic reports of occupational diseases are unusually much lower than survey-based estimates. Industrial hygienists are scarce in the continent, and are mostly clustered in South Africa. The vulnerability of workers is further increased during periods of high unemployment. In African industrial and especially mining sectors, workers originate from large distances, often from neighbouring countries, and thus if they return home when ill, linking their disease to original occupational exposure becomes more difficult to establish and to attribute accountability.

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5. Environments with possible carcinogenic exposure 

5.1. Exposure in industry 

Mining of fuels and metals has for centuries been a major economic activity in this mineral-rich continent, most especially so in South Africa where 6% of the workforce is employed in mines and quarries. Minerals extracted in Africa that have carcinogenic potential are provided in Table 3, alongside the locations where they are present. Aluminium production is a major economic activity in Guinea and Ghana, among other African countries [23], and in the smelter potrooms inhalation of airborne polynuclear aromatic compounds cause lung and bladder cancers [24]. Beryllium, a light rigid metal carcinogenic to the lung is mined in Mozambique [25]. Asbestos is of particular relevance because it was mined in South Africa, Swaziland and Zimbabwe and is consumed in some of the larger of the African economies. Occupational exposure to quartz/crystalline silica dust, a lung carcinogen [26], occurs across the mining sector as silica is abundant in most rock types, particularly granite and sandstone. Highest exposures to silica dust are experienced in poorly ventilated underground mines, e.g. in the underground coal mines of Tanzania where 47% and 9% of the development (blasting/drilling) and mining teams, respectively, had silica levels exceeding safe threshold limit values [27]. The prevalence of silicosis, a more easily attributed lung disease, is 18% among gold-miners in South Africa [28]. Artisanal and small-scale mining (ASM) employs 0.2 million workers each in Ghana, Mali and Burkina Faso, 0.06 in Mozambique, 0.01 in South Africa and 0.55 in Tanzania, 0.35 in Zimbabwe (International Institute for Environment and Development, Global Report on Artisanal & Small-Scale mining 2002). ASM is typified by unmechanised labour-intensive operations, and in Africa has a greater proportion of women and child miners than does large-scale mining. Exposure to radon may contribute to lung cancer risk in miners, and are a potential problem in the open-pit uranium mines of Niger and Namibia, two of the world's largest and expanding producers of uranium. During mining of low-grade ore, in milling processes to produce yellowcake and from mill tailings, radiation levels and use of personal protection by workers need to be monitored as per international standards. Preliminary studies of uranium miners in Namibia do not show an increased rate of chromosomal aberrations associated with exposure in this setting [29].

Table 3. Examples of environmental and occupational circumstances in Africa with potential carcinogenic exposures.

In Southern Africa, the textile and clothing industry grew rapidly from the 1990s onwards, and now employs over 0.25 million workers, mostly women. Exposures to chemicals and dyes need monitoring for their effect on bladder cancer and leukaemia. Commercialised agriculture utilises a range of pesticides, including IARC Group 1 carcinogens (2,3,7,8-tetrachlorodibenzo-para-dixon, a polychlorinated dibenzo-paradioxins (PCDDs) contained in herbicides), probably carcinogenic (Group 2A, including captfol) and possibly carcinogenic (Group 2B, e.g. dichlorodiphenyltrichloroethane (DDT, the parent of DDE), chlordane, atrazine) [30], [31]. Of particular concern are those that persist in the environment and via endocrine disruption may increase risks of cancers of the testes, prostate and breast (if exposed at young ages). Intensification and commercialisation of parts of the agricultural sector in Africa have led to their increasing use in insecticides, herbicides, fungicides, dip ticks and disinfectants that contain a large range of chemicals, e.g. to the 50,000 employees in Kenyan cut-flower industry, 283,000 in South African deciduous fruit and 10,000 in Zambian vegetable/cut-flower industry. Tobacco, a pesticide-intensive crop, is grown in Malawi (7th largest producer worldwide), Mozambique, Tanzania, Zambia and Zimbabwe and other cash crops (coffee, cotton, tea) have large economic value in East Africa. In some areas, such as Malawi, child labour makes up a large percentage of the workforce, a susceptible time-period where exposure is potentially more potent. Lack of awareness of the toxicity of pesticides (of poisoning, regardless of any carcinogenic hazards) are revealed by hazardous practices during use and storage, e.g. keeping pesticides near food and in bedrooms, with problems being worse in small-scale than in commercialised farms [32], eating and drinking during spraying and lack of protective clothing. Serum-levels of insecticide residues exceeding no-observable-adverse-effect levels and the problem of accidental pesticide poisoning in children demonstrate the extremes of this exposure problem. Storage and safe disposal of the 20,000tonnes of obsolete pesticides being dealt with by the Africa Stockpiles Programme is a further potential exposure route, especially if they reach water supplies and enter the food chain. Pesticides are also used for the important purpose of vector control, especially of the mosquito (DDT indoor residual spraying, DDT-treated bednets) and tsetse fly (organochlorines), and any cancer-related risks need to be considered against their benefits for malaria, Burkitt's lymphoma in children and veterinarian health. Domestic pest control also gives rise to exposure. The long-term consequences of possible inhalation, dermal exposure and ingestion of pesticides on unwashed fruit and vegetables are not clear. Exposure at young ages is exemplified in South Africa, e.g. accidental exposure of children to pesticides, mostly organophosphates, accounts for 11% of paediatric admissions [33]. Studies in the malaria-inflicted Limpopo province of South Africa have detected DDT/DDE in all media inside and in the immediate vicinity of houses after indoor residual spraying, i.e. potable water, human serum, floor dust, indoor air and in live chicken (due to be consumed) [34].

5.2. Air pollution 

Indoor combustion of solid fuels (dung, wood, coal) for cooking and heating is the major source of air pollutants in sub-Saharan Africa. An estimated 75% of sub-Saharan African households burn solid fuels, with lowest percentages in Southern Africa (<50%), and highest (>95%) in Central and Western Africa (this does not concern North African countries which mostly have no such use). Lower socio-economic groups and rural areas have highest use. Surveys of mean respirable dust levels have demonstrated that, for example in Malawi, all homes exceed WHO's maximum safe limits of 25μg/m³, with half of rural homes having levels above 250μg/m³ for at least 1h per day, during burning [35]. Indoor use of kerosene and diesel lamps, commonplace where an electricity supply is lacking, add to pollution levels [36]. In Johannesburg hospital inpatients 30% currently used non-electric domestic cooking fuel [12]. Levels of outdoor pollution have risen steeply in urban areas, notably Cairo, Cape Town, Dakar, Nairobi and Johannesburg, due mainly to a rapid increase in industrial and motor vehicle diesel/gasoline exhaust. Vehicle fleets have at least doubled over a decade in South Africa, Botswana, Uganda (from 151,000 to 383,000 between 1997 and 2007 [37]) and Zimbabwe. Average emissions per vehicle are also high as cheaper, lower quality fuels were or are being used; the phase-out of leaded petrol in Africa was achieved in 2010, over a decade later than most of the rest of the world; vehicles are on average older (average age of vehicle in Uganda 15 years). Other sources of outdoor air pollutants include diesel-exhaust emissions from vehicles and the use of diesel-power generators in businesses and more well-off homes (30% use in Nigeria) to overcome frequent power-cuts [38], [39].

5.3. Hazardous wastes 

Impacts of modern environmental hazards on general health in Africa have been raised by Nweke and Sanders [40]. Industrial activities in Africa have among the world's highest pollution intensities [41]. Discharges or leaching of chemicals into the soil, that possibly reach ground/drinking water and the food chain, from industrial or other activities renders the presence of genotoxic chemicals, such as polycyclic-aromatic hydrocarbons (PAHs) or metals. In mining, aside from the targeted mineral being extracted, acid main drainage (especially from abandoned mines) and mine tailings of unwanted extracted rock and toxic extraction chemicals (uranium, arsenic, other metals) may leach into the wider environment. In the oil-producing areas of the Niger delta, air, water and soil contamination by crude oil and its refined derivatives release PAHs into the environment from motor exhaust, gasoline spills caused by poor management, corroded pipes or oil theft, used engine oil and petroleum production. This delta is the oil pollution capital of the world. PAHs such as benzo[a]pyrene cause lung and skin cancer and possibly other cancers. High lead levels in children in Nigeria have been associated with living near gasoline sellers, battery smelters and exposure to chipping paint in houses [42]. In addition to locally sourced waste, West African and other coastal countries endure the problems of trans-boundary hazardous waste, i.e. waste that originated beyond national borders, typically from Europe, North America and the Soviet Union. Dumped materials include e-waste (e.g. computers in Ghana), obsolete machines (e.g. fridges, electronic equipment, lead acid batteries) and chemical and radioactive waste and these potentially contain a range of metals and chemicals, including lead, cadmium (in semi-conductor chips), chloroform (from fridges), PAHs and dioxin (from combustion of PVC that encases most e-waste) [43]. Their presence in the environment has been postulated as a reason for high levels of polychlorinated biphenyls (PCBs) and brominated flame retardants in breast milk in Ghana [44]. Materials may be recycled for other purposes in make-shift homes in poverty-stricken slum areas, giving rise to further or new exposures and risk.

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6. Example: asbestos exposure with occupational, para-occupational and wider environmental exposures 

The example of asbestos use in Africa is provided to illustrate the multiple factors at play that influence potential exposure. From the 1950s to 1980s South Africa was the world's second largest producer of asbestos and Swaziland did and Zimbabwe still does mine asbestos [45], an IARC class 1 carcinogen to the lung, larynx, mesothelium, and ovary [25]. South Africa's production was predominantly of crocidolite and amosite, the two most carcinogenic fibre forms for mesothelioma. Africa's asbestos consumption as a whole has not been very large, but was concentrated in North African countries which imported large quantities of crocidolite into the mid-1990s. More recent imports of chrysotile continue in Algeria, Morocco, Nigeria, Senegal and Angola. Algeria is the highest importer today, but has recently undertaken measures to close several asbestos-cement factories. South Africa was the first African country to ban all forms of asbestos use in 2008, whilst Zimbabwe is reviving old asbestos mines. Exposure routes and cancer burdens due to asbestos are multi-fold and are already being borne out in the countries where consumption was highest. In South Africa, the mesothelioma burden lies in miners, workers in secondary industries and environmental exposures in the vicinities of old mines/industries, from dust and waste disposed nearby [46]. Egypt and Algeria have begun to suffer the start of their mesothelioma epidemics [17]. Lung cancers caused by asbestos, will be exacerbated in these countries owing to their very high male smoking rates. In Alexandria (Egypt) both occupational and environmental exposures are present and may explain much lower male:female ratios of the number of mesotheliomas than observed in other settings [47]. In Nigeria, chrysotile asbestos continues to be widely used in construction, including in schools with little apparent knowledge of its hazards. Labourers renovating old buildings are exposed [48] and frequent roof failures and disintegration of roofs, 23% of which are asbestos-cement sheets, by wind and rain erosion, spread fibres to occupants of a wider area. Finances needed to fix or render safe buildings in disrepair may not be available. Even if asbestos is removed, it may end up forming the roofs/walls of unregulated shanty town dwellings. Exposure to asbestos is a good example of how exposures that result in cancer after typically very long latency periods (mesothelioma and lung cancers are mostly diagnosed over age 60) would have had little contribution to the cancer burden when life-expectancy was short, but as it increases in Africa, these exposures will become contributors to the cancer burden at older ages.

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7. Concluding remarks 

The long-term carcinogenic effects of both naturally occurring and manmade environmental factors need to be taken into account, alongside their more immediate harms, as priority concerns in Africa. Herein we hope to stimulate research and international collaborations in this field and reiterate the March 2011 Asturias Declaration for the primary prevention of environmental and occupational cancer throughout the world [49]. In addition to lifestyle factors, environmental and occupational sectors constitute important targets for prevention in this setting precisely because they are modifiable and because their relative contribution within Africa is likely to be high given the exposures present and lack of protections, and because their contributions will increase as life-expectancy lengthens. Interventions required to reduce environmental and occupational exposure are typically not in the hands of the vulnerable exposed groups who often lack awareness and lobbying power to campaign for workers’ and environmental protection. There remain many gaps in knowledge that need urgent research attention. Estimates of population attributable fractions to known causes need to be established on a wider scale to optimize prevention strategies. With different exposure patterns (higher cumulative exposure or greater exposure contrasts), exposure or population characteristics (age at first exposure, nature of exposures, co-morbidities), some African settings may provide settings to study agents for which carcinogenic effects are so far inconclusive (possible/not classifiable IARC Groups 2B and 3). Such research would be informative for cancer aetiology in general and for the local cancer burden in particular.

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Conflict of interest 

None declared.

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