Introduction
Asbestos is defined as a Group I carcinogen by the International Agency for Research on Cancer (IARC). It is one of the most important carcinogens, more than half of occupational cancer deaths are related to asbestos [
1,
2]. Because of its good thermal stability, flexibility, wear resistance and corrosion resistance, asbestos has a wide range of applications, such as roof cover, textiles, electrical insulation, cement pipes, friction materials (clutch pads, brake pads), etc [
3]. The widespread use of asbestos has increased occupational and environmental exposure to populations. According to the World Health Organization (WHO), about 125 million people worldwide are highly exposed to asbestos at work. More than 255,000 people die each year from asbestos-related diseases [
4]. With increasing concern about the health effects of asbestos products, 66 countries have banned the production and use of all types of asbestos [
5]. In developing countries where chrysotile is widely used, policies have been adopted to control the use of asbestos in the occupational environment. China has centralized supervision over relevant enterprises and actively promoted the development of asbestos substitutes [
6]. Mongolia has issued relevant resolutions to restrict the scope of application of asbestos and only allow the use of asbestos in thermal power plants [
7]. Russia, Kazakhstan and other countries have also introduced national plans and carry out epidemiological investigation on asbestos [
8].
Exposure to asbestos at any level is not safe. Asbestos fibers are mainly inhaled with air, and have local carcinogenic effects on target organs (lungs, larynx, ovaries) and related serous membranes (pleura, pericardium, peritoneum, vaginal membranes), resulting in lung cancer, larynx cancer, ovarian cancer, pleura, and peritoneal mesothelioma. Asbestos-induced lung cancer accounts for 55–85% of occupational cancers [
9]. In addition, the fibrotic effect of asbestos can also develop into pulmonary asbestosis [
3]. One-quarter of asbestos-exposed people had CT evidence of asbestosis [
10]. Due to their extreme biological persistence, asbestos fibers, which cannot be effectively cleared by macrophages, cause continuous irritation to the lungs and lead to chronic inflammation, so they can remain in the human body for years [
11]. Ovarian cancer caused by asbestos exposure has been designated as the first gynecological occupational disease in Germany, and the risk of ovarian cancer was approximately doubled in females with occupational asbestos exposure [
12]. Of the many mesothelioma carcinogens (erionite, fluoro-edenite fibrous amphibole and occupational exposure to firefighters and painters), asbestos exposure is the more commonly recognized cause, with 80% of mesotheliomas primarily caused by exposure to asbestos [
13]. Due to its long latency period of 30–43.9 years, mesothelioma is typically diagnosed in elderly individuals [
14]. This highlights the different health problems and diseases that occupational asbestos exposure can cause in humans.
Understanding the trend of the burden caused by occupational asbestos exposure over time and space is crucial for better constructing occupational asbestos exposure prevention and control regulatory systems and reducing the risk of the asbestos working environment. At the same time, we need to make it clear that asbestos exposure is not only an occupational problem, but also a risk for the general population, and the potential impact of non-occupational asbestos exposure (residents living near asbestos mines due to air pollution, improper disposal of asbestos-containing construction waste, household exposure, etc.) should be taken into account [
15]. However, no studies have been conducted to comprehensively and systematically report the burden of disease due to occupational asbestos exposure. Therefore, this study obtained the latest data from the GBD 2019 database to analyze and compare the deaths and disability-adjusted life years (DALYs) of non-communicable diseases (NCDs) (lung cancer, mesothelioma, ovarian cancer, larynx cancer, and asbestosis) due to occupational asbestos exposure, aiming to promote the governments of various countries to timely introduce regulatory policies, particularly arouse the attention and provide the management basis for the countries where asbestos is mined and the countries where asbestos is still used and increase investment in health and safety education activities for special groups, to jointly create a good and safe working environment.
Discussion
This study provides a comprehensive and systematic description of the disease burden attributed to occupational asbestos exposure. From 1990 to 2019, the burden of NCDs from occupational asbestos exposure has been increasing, with deaths and DALYs nearly tripling, especially among the elderly. Of the five diseases, lung cancer was the leading cause of death, accounting for 83% of the total, while mesothelioma was the most common primary disease in all regions. The NCDs burden was concentrated in high SDI regions such as Western Europe and Australasia. It is important to note that people aged 15–24 years were the primary group for asbestosis, suggesting that the health effects of occupational asbestos exposure may be progressively younger.
The number of deaths and DALYs caused by occupational asbestos exposure worldwide in 2019 mainly occurred in the elderly. We found that DALYs-PAF was the highest in people aged ≥ 85 years, which may be due to the rapid increase in demand for asbestos in the 1940s as industrial expansion followed World War II. At the same time, asbestos, with its unique advantages (simple process manufacturing, low investment cost, superior performance), had become the best choice and was widely used in the construction industry, automobile manufacturing industry, textile industry, shipbuilding industry and other industries, which may lead to people born in this period have a higher probability of exposure to asbestos at a younger age [
23,
24]. At the same time, due to the unique pathogenesis of asbestos exposure and the long latency period, people who are exposed at a young age are usually diagnosed as elderly. For example, mesothelioma is a common asbestos-related disease, with over 80% caused by asbestos, its DALYs-PAF ranked first among all diseases in our study. However, the latency period from asbestos exposure to mesothelioma development is as long as 35–40 years [
13], and we also found that the DALYs-PAF of mesothelioma in people aged ≥ 85 years maintained a higher level compared to other diseases.
Despite the subsequent decline in asbestos use in industrialized countries and the tightening of occupational environmental exposure limits, this had little effect on workers who accumulated high exposure levels in the early decades of work [
25]. It is consistent with the trend in this study of asbestos-related lung, ovarian, and larynx cancer mortality that increases with age starting at age 50. However, we need to consider that the risk of disease after exposure to asbestos does not increase indefinitely, according to the latest research, the incidence of mesothelioma due to asbestos removal in the body will level off after many years of exposure to asbestos [
26]. This may also be responsible for the slight decrease in mesothelioma and lung cancer mortality in people aged 90–94 years. It is worth noting that the PAF of asbestosis was higher in adolescents aged 15–24 years, which may be due to the lower diffusion capacity of lung gases in younger, which is more likely to produce asbestosis [
27].Increasing genetic susceptibility and/or early exposure to carcinogenic mineral fibers may be responsible for these young patients [
28]. It should be taken into account that the burden of NCDs caused by occupational asbestos exposure varies greatly among different populations, and the registration and monitoring tracking system needs to be continuously improved to reduce the health impact of the related disease.
In 2019, the global overall burden of NCDs due to occupational asbestos exposure was higher among males. Compared with females, males are more likely to engage in construction, railway, cement processing, and other industries with high asbestos exposure, with more frequent asbestos exposure [
29]. The gender difference in mesothelioma cases is mainly related to occupational exposure and is more susceptible to the effect of asbestos exposure. Unlike occupational exposure in males, non-occupational exposure in females plays a key role in mesothelioma. Influenced by various asbestos exposure factors such as occupation, natural environment and family, females are prone to bias in determining occupational exposure when asbestos-related diseases occur, and social welfare and economic compensation cannot be effectively guaranteed [
30]. Therefore, it is necessary to improve the ability to trace the etiology, enhance the awareness of exposure risk, and better protect female health rights and interests. In addition, relevant studies have shown that the mortality rate of asbestosis increased significantly in the environment of occupational asbestos exposure, and the standardized mortality rate was higher in females than that in males [
31]. We found that the main contributor to the gender difference was lung cancer, and the association between asbestos and larynx cancer was only observed in males. Males are at a higher risk of exposure to risk factors associated with these cancers [
32], such as smoking. At the same time, asbestos fibers can increase the uptake and metabolism of PAHs (one of the most typical carcinogens in cigarette smoke) by lung epithelial cells, while cigarette smoke can increase the binding of asbestos fibers to lung epithelial cells, and the multiplier effect of both may increase the risk of lung cancer [
33]. In addition, IARC pointed out that quitting smoking can reduce the incidence of larynx cancer by 90% [
34].
Of the disease burden from occupational asbestos exposure, lung cancer, mesothelioma and ovarian cancer are the three leading causes of death. Lung cancer is the first cause of death, and the risk of lung cancer is increased five-fold by exposure to asbestos [
35], which may be due to DNA damage caused by asbestos fiber mediated reactive oxygen species and active nitrogen, resulting in tissue inflammation and cell death, and leading to the occurrence of lung cancer [
36].Studies have shown that the risk of ovarian cancer is approximately doubled in females with occupational exposure to asbestos, in which inflammatory damage also plays an important role [
12]. Mesothelioma tops the PAF list of deaths attributed to occupational asbestos exposure, with 80% of mesothelioma mainly caused by asbestos exposure [
13]. In addition, mesothelioma prediction studies have found that due to its long latency period and many factors, its incidence and mortality will continue to increase, and it is expected to peak before 2030, and there will still be a high disease burden in the future [
37].
The burden caused by occupational asbestos exposure was positively correlated with SDI as a whole. In areas with SDI greater than 0.8, the burden was higher, but ASMR and ASDR declined faster. In contrast, ASMR and ASDR had risen steadily in low-middle SDI regions (mainly low-middle income countries) [
38]. It may be closely related to countries’ level of economic development and the degree to which asbestos bans are enforced. It may also be influenced by other policies: conduct professional training and qualification recognition for workers engaged in the construction and demolition of historic asbestos buildings, accelerate the establishment of occupational asbestos exposure tracking network, conduct health registration and monitoring of past and current asbestos exposed workers and their relatives, research on early biomarkers of asbestos-related diseases such as mesothelioma and lung cancer to achieve early detection and treatment, and promote asbestos substitutes and etc [
39]. One study found a co-dependency between the use of asbestos and GDP. The use of asbestos follows the environmental Kuznets curve, the trend of change is first to increase and then to stabilize, and the inflection point appears at 10,000–15,000 GKD (Geary–Khamis Dollars) [
40]. High-income countries have reached this tipping point and made the transition away from asbestos, with increased awareness of its carcinogenic risks, bans, and the emergence of asbestos alternatives. However, since that developed countries in the 1970s accumulated a high level of asbestos in the early years to accelerate the transformation and upgrading of industrialization, although the current incidence of the disease has declined in high SDI areas, they still bear most of the global burden of NCDs due to the early accumulation effect. Western Europe has the highest number of deaths and DALYs. Due to the large-scale reconstruction work in Europe after World War II, countries such as Italy and Greece in the region became the main contributors to world asbestos production in the 1980s, accounting for 63% [
41]. We found Australasia had the highest ASMR/ASDR and the DALYs- PAF was also much higher than other GBD regions. This may be since that Australia in the region was the world’s largest consumer of asbestos in the 1950s, which was widely used in house building industry. Due to various factors, the implementation of the ban was repeatedly delayed, resulting in an epidemic of asbestos-related diseases in the region that continues to this day [
42]. In addition, developing countries, including major asbestos fiber users and producers (such as Russia, Kazakhstan, and India) lack the technology and experience to diagnose mesothelioma, which may have difficulties in diagnosis and is lack of relevant mesothelioma surveillance data, thereby underestimating the risk of the disease. This could lead to a higher disease burden that needs to be dealt with in the coming decades [
43]. It also suggests that we should strengthen the sharing of experience and technology in asbestos control between developed and developing countries, and work together to reduce the global burden of asbestos-related diseases.
The global increase in ASMR/ASDR attributed to occupational asbestos exposure from 1990 to 2019 was the fastest in Central Europe, including Georgia. Asbestos has not been completely banned in this area, high per capita asbestos consumption, high exposure level, and potentially high lung cancer incidence have accelerated the rise of its disease burden [
44]. Low and middle-income countries are experiencing a development model similar to that of developed countries, and the demand for the use of cheap and durable building materials such as asbestos is becoming more prominent to accelerate infrastructure construction. As the world’s largest consumer of chrysotile asbestos, China, located in the middle SDI region, grew at an annual rate of 7% and suffered a major disease burden in 2019. High exposure levels, inadequate regulatory systems, and slow progress in asbestos replacement may have contributed to the high disease burden.
There are some limitations in this study. The asbestos-related data comes from model reconstructions in the GBD 2019 database and may be biased from the real data. Due to differences in the level of economic development in different parts of the world, the degree of supervision and prevention of asbestos-related diseases is different, so the collection of relevant data is insufficient. Furthermore, the interaction between diseases caused by occupational asbestos exposure and possible potential risks is not sufficiently considered.
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