Introduction
Asbestos is among important environmental and occupational carcinogens, which are associated with the occurrence of various types of cancer. It is a naturally occurring group of fibrous silicate minerals that has long been used in industries due to its unique properties, such as heat and chemical resistance, insolubility in water, high tensile strength and electrical insulation ability. Asbestos is characterized by its exceptional properties, which are still irreplaceable in some applications, together with characteristically low financial costs. It is able to withstand temperatures up to 1000 ° C and shows resistance to many aggressive chemicals. It has excellent electrical and thermal insulation properties, high elasticity. In addition, it is part of various bonding materials, which increases its versatility and practicality in industrial use (Kusiorowski et al., 2023).
Asbestos fibers, due to their extraordinary physical properties, have found wide application in industry all over the world. Their low thermal conductivity, resistance to biological decomposition, high resistance to electrical, alkaline and acid substances, as well as the ability to absorb sound, made asbestos fibers ideal components for various technical and industrial applications. Thanks to these properties, asbestos was widely used primarily as a building and insulation material. It has been found in acoustic and thermal sprays, plasters, coatings, floor coverings, flat boards, tiles, corrugated roofing sheets, rain and pressure pipes, and many other building materials (Castro et al., 2023).
Asbestos consists of six types of mineral fibers, which are divided into two groups according to their structure: amphibole and serpentine. The distribution of asbestos minerals is a consequence of their silicate crystal-chemical structure. Different types of asbestos differ in chemical composition, physical structure and specific properties that determine their industrial use. The amphibole group includes crocidolite (blue asbestos), amosite (brown or gray asbestos), anthophyllite, tremolite and actinolite, which have a needle-like appearance. Conversely, the serpentine group includes chrysotile (white asbestos), which has curved fibers. Chrysotile asbestos has crystals in the form of hollow fibers, while amphibole asbestos fibers have a "tube"-like shape. Chrysotile fibers are usually thinner, more flexible and softer, in contrast to the thicker and harder fibers of amphibole asbestos (Kusiorowski et al., 2023).
Asbestos is dangerous because of the size of its microscopic fibers. These fibers are less than 0.1 to 2 micrometers in diameter and 5 to 100 micrometers in length. Asbestos fibers can break down into microscopic particles that are released into the air and subsequently inhaled by the body. Blue asbestos, with its more durable amphibole fibers versus chrysotile fibers, is considered the most dangerous type of asbestos. These fibers penetrate the respiratory system and accumulate in the lungs, where over time they cause lesions and scars in the lung tissue. This process reduces the elasticity of the lungs and makes it difficult to breathe, which is manifested by symptoms such as difficulty breathing, a dry cough and increased mucus production. Long-term exposure can increase the risk of developing lung cancer and other respiratory diseases, with these health complications usually appearing many years after exposure to asbestos (Roselli et al., 2014).
Epidemiology and risk factors of asbestos
Asbestos is classified as a Group I carcinogen by the International Agency for Research on Cancer (IARC), which clearly indicates that there is significant scientific evidence of its ability to cause cancer in humans. Exposure to this mineral is associated with serious health problems, including malignant mesothelioma, lung, larynx, ovarian cancer, asbestosis, and pleural disease (Jung et al., 2021).
Asbestos is a global problem affecting millions of people, especially workers exposed during commercial activities. According to the WHO, it is estimated that approximately 1.3 million workers in the US and worldwide have been exposed to asbestos, and 125 million workers suffer from serious health problems (Gordon et al., 2014).
Between 1994 and 2010, asbestos caused 128,015 deaths from mesothelioma and 13,885 from asbestosis worldwide, representing a total loss of 2.18 million and 180,000 years of life (PYLL - Potential Years of Life Lost). The annual average of life lost was 201,000 years for mesothelioma and 17,000 years for asbestosis. The average loss of life per deceased was 17.0 years for mesothelioma and 13.0 years for asbestosis (Diandini et al., 2013). Annually, asbestos is estimated to contribute to 55,000 deaths worldwide. In the African, Asian and South American continents, asbestos is still being used as a cheap and durable material, especially in water supply and housing projects in rapidly developing areas (Furuya et al., 2018).
Occupational exposure to asbestos
Occupational exposure to asbestos can be direct or indirect. Direct exposure occurs when working with asbestos or materials containing asbestos, such as in the construction or mining industries. On the other hand, indirect exposure concerns workers who encounter asbestos in the workplace, such as electricians, plumbers, painters, brake mechanics, carpenters, welders, etc. Construction activities such as asbestos mining and milling, cement production and transportation, production and installation of insulation materials pose a significant risk to workers. Building maintenance, renovations of older houses and railways can also lead to significant exposure to asbestos (Lazarus et al., 2011).
There are studies that systematically examine occupational exposure to asbestos and its impact on workers' health. These studies focus on various aspects of exposure, such as intensity, duration, and type of asbestos fibers, which may affect the risk of developing asbestosis and other respiratory diseases. Research often uses a variety of methodologies, including calculations of standardized mortality ratios (SMRs) and analyzes of time-dependent variables (APCs), to examine mortality patterns and assess the risks associated with long-term exposure to asbestos. These studies are of key importance in shaping work standards and preventive health protection measures for workers in industries with high exposure to asbestos. An Italian study by Girardi et al. (2020) analyzed the asbestosis mortality of workers in Italy, following them for more than 40 years. The results showed a high number of deaths from asbestosis, with an emphasis on cumulative exposure to asbestos as the main risk factor. Exposure was estimated through an asbestos exposure index, taking into account the probability, intensity and type of asbestos fibers. The study's findings showed a higher risk of asbestosis-related mortality in men and women working in the asbestos industry, with women showing a lower risk compared to men, which may be explained by different levels of exposure. Analytical methods such as the SMR and APC regression model allowed for a more detailed examination of mortality patterns and their association with asbestos exposure. A high mortality from asbestosis has been detected in workers in the asbestos products sector, which implies the necessity of introducing safety measures for health protection and the need for further research in this area (Girardi et al., 2020).
A study by Buralli et al. (2023) also reports on workers in the cement industry in Brazil showing increased mortality from various types of cancer, including pleural, peritoneal, and lung cancer, and from asbestosis. Brazil, a historically significant producer and consumer of asbestos, especially chrysotile, used in asbestos cement products, has long lacked adequate measures to control workplace exposure. Thus, asbestos exposure in Brazil represents a long-term serious public health problem, as it causes more than 233,000 deaths annually and has a significant socio-economic impact (Buralli et al., 2023).
Exposure to asbestos in the environment
The environmental burden of asbestos occurs in countries with massive mining of this mineral, such as South Africa, Australia and Canada, and many other areas. In these regions, the dispersion of asbestos fibers was recorded at a distance of several kilometers from the mining sites. The main source of environmental exposure is the so-called "naturally occurring asbestos", which refers to asbestos as a natural component of soil or rock. In areas with high occurrences of natural asbestos, the fibers can be dangerous to humans after perturbation of the rocks by human activity or flowing water. The source of increased concentrations of asbestos fibers in urban areas is damaged and worn brake systems of cars and other materials and products, which contributes to contamination of the environment and thus the air (Campopiano et al., 2020).
Asbestos Related Diseases
Asbestos-related diseases include four main clinical forms of lung diseases that are confirmed in medical practice. In addition, asbestos can be one of the potential risk factors associated with the development of diseases in other organs as well, such as cancer of the stomach, intestines, bladder, ovaries and larynx.
Asbestosis is a disease that develops as a result of long-term exposure to asbestos dust. Like other asbestos-related diseases, symptoms appear several years after exposure. The latent period of asbestosis is usually between ten and fifteen years and is often referred to as "dusty lung disease". The lung tissue, which consists of approximately 300 million lung alveoli, which absorb oxygen from inhaled air and transport it to red blood cells, is affected in asbestosis by scarring of the connective tissue between the alveoli. This reduces the elasticity of the lungs and limits their ability to exchange gases, leading to hypoxemia. Symptoms include a dry cough, shortness of breath, and mucus production (Harris et al., 2019).
Mesothelioma is one of the most serious types of cancer associated with asbestos, affecting the lining of the lungs and some parts of the digestive tract. This type of cancer is almost always fatal, and patients often die within one to two years of diagnosis, appearing 30 to 40 years after exposure to asbestos. Asbestos can also be associated with cancer of the larynx, bronchi, kidneys and gastrointestinal tract (Roselli et al., 2014).
Pleural plaques are characterized as smooth, white lesions with irregular borders on the parietal pleura, often calcified in individuals with a history of asbestos exposure. They occur most often in the posterolateral regions of the mid-lung, and their presence is often asymptomatic or may cause nonspecific angina-like chest pain. If shortness of breath occurs, it is important to perform a differential diagnosis. Pleural plaques are often a sign of asbestos exposure and can cause short-term pleural irritation (Bird et al., 2021). The presence of these plaques on a chest X-ray indicates significant exposure and increases the risk of developing mesothelioma and lung cancer (Nielsen et al., 2014). Pleural plaques are formed when inhaled asbestos fibers enter the lungs through the airways and become deposited in the pleura (a thin membrane) that covers and protects the lungs. Each inhalation causes the penetration of asbestos fibers through the pleura, which leads to inflammation. This inflammation causes thickening of the connective tissue and can lead to calcification (hardening of the tissue) (Roselli et al., 2014).
Acute and chronic bronchitis can result from occupational or environmental exposure to asbestos. Acute bronchitis usually occurs suddenly and gradually improves within two to three weeks. The inflammation can be more severe in the elderly, children, and individuals with medical conditions. Chronic bronchitis is a condition that recurs and lasts for a long time. Patients suffer from cough with mucus most days of the month for three months of the year and for at least two consecutive years (Roselli et al., 2014).
Screening
Recommendations for screening patients at high risk of lung cancer after exposure to asbestos and smoking are unequivocal. Persons aged 50 years and older who have been exposed to asbestos for at least 5 years and have a history of smoking or other risk factors for lung cancer, such as asbestos-related fibrosis, chronic obstructive or interstitial lung disease, a family history of lung cancer, or multiple exposures to carcinogens, should be screened with low-dose CT of the chest. At the same time, workers who were exposed to asbestos for a shorter period of time, but intensively, should also participate in the screening. Even in the absence of further exposure to asbestos, it is not clear whether all benign asbestos diseases can progress to cancer, as the respiratory system is compromised and burdened by asbestos fibers. Occupational Safety and Health Administration (OSHA) standards require employers to provide regular training on work procedures, use of personal protective equipment, occupational safety and health effects for all workers exposed to asbestos above specified limits (Markowitz 2022).
Conclusion
Asbestos, with its exceptional physical properties such as heat and chemical resistance and high tensile strength, has historically been an irreplaceable material for many industrial applications. However, knowledge of its harmful effects on health has gradually led to bans and regulations on its use in most countries. The risks associated with asbestos exposure, such as lung cancer, mesothelioma, and other respiratory diseases, are well documented. These diseases often have a long latent phase, causing symptoms to appear many years after exposure. Despite bans on asbestos in many parts of the world, there are still areas where it is encountered, mainly in the renovation of older buildings and in some industrial processes. Therefore, it is important to continue to monitor and implement strict safety measures and regulations to minimize risks to human health. The global expansion of asbestos exposure highlights the need for global collaboration and research to better understand its impact on public health and develop effective protection strategies. Prevention remains a key tool in the fight against health complications caused by this harmful substance.
Acknowledgments The work is supported by grants KEGA MŠVVaŠ SR 001UPJŠ-4/2024 and 003UPJŠ-4/2024.
Authors: Mgr. Simona Miskárová prof. MUDr. Kvetoslava Rimárová, CSc. prof. Mgr. MUDr. Erik Dorko, PhD., MPH, MBA MVDr. Martina Hrubovčák Tejová Institute of Public Health and Hygiene, Faculty of Medicine UPJŠ, Košice
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