In our latest article, Professor Justin Stebbing, Professor of Biomedical Sciences, explores the historical use of asbestos and its devastating health consequences, including lung cancer, asbestosis and mesothelioma. The article examines the scientific recognition of its dangers, ongoing regulatory efforts and the need for continued vigilance in managing asbestos-related risks.
Introduction and history
Asbestos, a group of naturally occurring fibrous minerals, has been widely utilised in various industries due to its fire-resistant and insulating properties. Its use dates back thousands of years, with ancient civilisations like the Egyptians, Persians and Romans incorporating it into textiles and pottery. However, it was during the Industrial Revolution that asbestos began to be used extensively in construction and manufacturing. By the late 19th century, asbestos was being incorporated into a wide range of products, including cement sheets, insulation materials, brake pads and floor tiles.
Despite its utility, asbestos exposure poses significant health risks, leading to severe diseases such as asbestosis, lung cancer and mesothelioma. The persistence of asbestos in older structures and its potential contamination in consumer products continue to pose challenges for both public health and legal frameworks. It remains the leading cause of occupationally related cancer deaths and the second most lethal manufactured carcinogen after tobacco. It has been commonly known as a hazard since the 1960s and 1970s. However, the knowledge that the material was fatal dates back at least a century and its carcinogenic properties have been understood for well over 50 years.
The scientific recognition of asbestos’s harmful effects began in 1898 when British factory inspector Lucy Deane highlighted asbestos manufacturing as one of several dusty occupations that warranted scientific scrutiny due to their evident health risks to workers. By 1927, the term “asbestosis” was coined to describe a severe lung disease commonly observed in asbestos workers and medical professionals started noticing that individuals with asbestosis often developed lung cancer as well. However, it took over three decades for the link between asbestos and cancer to be firmly established.
In 1960, a publication by E. I. du Pont de Nemours & Company openly acknowledged that lung cancer was observed with such frequency among asbestos industry employees that most authorities accepted a causal relationship. Four years later, Dr Irving Selikoff, a researcher at Mount Sinai Hospital in New York, conducted a landmark study that connected various lines of investigation – data for which he was vilified. His findings revealed a statistically significant higher incidence of mesothelioma, a cancer that is extremely rare under normal circumstances, among workers exposed to asbestos compared to the general population. Additionally, asbestos exposure was linked to increased rates of lung, pleura, stomach, colon and rectal cancers. Crucially, the evidence suggested that there was no safe level of asbestos exposure, underscoring the need for stringent safety measures to protect workers and the public.
The risk is not limited to occupational settings; para-occupational exposure can occur when asbestos dust is brought home on workers’ clothing, posing a risk to family members. However, asbestos was extensively used in construction, automotive, shipyards and other industries from the mid-20th century until its widespread ban in many countries. The European Union banned asbestos in 2005 and similar restrictions have been implemented globally. However, it remains present in many older buildings and products, necessitating ongoing vigilance and management strategies.
Cancer-causing properties
Asbestos is classified as a type I carcinogen, meaning that it causes cancer. The cumulative number of occupational deaths caused by asbestos over the course of the 20th century may be around 17 million, according to epidemiologic data, with perhaps another two million deaths from non-occupational exposures. Put another way, it causes more than 200,000 deaths per year. Research shows that it will likely take decades to see the effects of the ban. That is largely due to the long latency period of mesothelioma, a difficult-to-treat, incurable cancer of the lining of the lungs that’s caused by asbestos. It is the most well-known consequence of asbestos exposure, probably because it is justifiably the most feared. People exposed to asbestos today may not develop the disease until a median of 40 years later.
There are many different types and classifications of asbestos fibres. Short asbestos fibres are deposited in the upper respiratory tract, where they are cleared by mucociliary action. Longer fibres are carried into the alveolar regions and are cleared much more slowly, thereby being retained in the lungs for longer periods. Some fibres may be swallowed during inhalation due to mucociliary action.
The properties of the fibres play a role in their toxicity; shorter fibres, such as chrysotile, are generally less potent than amphibole fibres. The amphibole types of asbestos, particularly crocidolite and amosite, are considered the most hazardous due to their needle-like fibres, which can penetrate deep into lung tissue and cause severe health issues. Crocidolite is especially dangerous because its fine fibres are difficult for the body to break down, leading to a higher risk of diseases like mesothelioma and lung cancer. Also known as blue asbestos, crocidolite fibres are extremely fine and sharp, making them particularly hazardous. They were used in products requiring high fire resistance, such as steam engine insulation and some spray-on coatings.
Researchers don’t completely understand how asbestos causes cancer. The most common theory is that asbestos fibres accumulate in the lungs, causing constant irritation and oxidative stress that eventually lead to mesothelioma or other types of cancer. Exposure occurs, and then many years later, mesothelioma develops. The ‘latency period’ problem is that it is very difficult to replicate that in a laboratory setting.
Numerous studies have explored whether asbestos fibres interact with DNA directly or indirectly through the induction of oxidative stress. In cell-free assays, it has been shown that chrysotile, amosite and crocidolite all induce lipid peroxidation, altering the structure of fats in cells. Additionally, chrysotile has been found to cause breakage in isolated DNA, although this effect is hypothesised to result from the generation of reactive oxygen species (ROS) due to the surface area of the fibres.
In vitro studies conducted nearly 50 years ago using Chinese hamster cells demonstrated that exposure to chrysotile, amosite and crocidolite leads to genetic alterations, including sister chromatid exchanges, chromosomal aberrations and anaphase (cell division) abnormalities. These findings suggest that these types of asbestos are mutagenic.
The question of whether a single asbestos fibre can cause cancer is complex and involves understanding the mechanisms by which asbestos leads to carcinogenesis. Asbestos fibres, particularly those that are long and thin, can cause significant cellular damage and inflammation, leading to genetic mutations and cancer over time. However, the risk of cancer typically increases with cumulative exposure to asbestos fibres.
So, while it is theoretically possible for a single asbestos fibre to initiate the process leading to cancer, the likelihood is generally considered low. The development of asbestos-related cancers, such as mesothelioma and lung cancer, is more commonly associated with prolonged or repeated exposure to asbestos fibres. This is because multiple fibres are more likely to cause sustained inflammation and oxidative stress, which are key factors in the carcinogenic process.
Genetic factors and individual susceptibility can influence how likely someone is to develop cancer from asbestos exposure and smoking can synergistically increase the risk of lung cancer in individuals exposed to asbestos. In March 2024, the U.S. Environmental Protection Agency finally announced that it was banning the ongoing use of asbestos.
Asbestos-related diseases
Asbestosis
Asbestosis is defined as diffuse interstitial pulmonary fibrosis secondary to asbestos exposure and initially affects the lung bases. It is a chronic lung disease caused by the inhalation of asbestos fibres, leading to scarring of the lung tissue. It is characterised by symptoms such as shortness of breath, persistent cough, wheezing and fatigue, often appearing 15 to 30 years after exposure. Asbestosis is dose-related, meaning the risk increases with the amount of asbestos inhaled. While there is no cure, treatments like pulmonary rehabilitation and oxygen therapy can alleviate symptoms, but it remains a significant cause of both morbidity and mortality.
Lung cancer
Asbestos exposure significantly increases the risk of lung cancer, with the risk being linearly related to cumulative exposure. Approximately 4,000 – 6,000 people die annually from asbestos-related lung cancer in the United States and Europe. Asbestos can cause lung cancer identical that from other causes, affecting all major histological types of lung carcinoma. The risk of developing lung cancer depends on the level, duration and frequency of asbestos exposure. Some have called this an underappreciated issue: the diagnosis Asbestos-Related Lung Cancer (ARLC) is much more frequent (2 – 6 times) than mesothelioma.
Mesothelioma
Mesothelioma is a rare and aggressive cancer affecting the lining of the lungs (pleural mesothelioma) or abdomen (peritoneal mesothelioma). It is almost exclusively linked to asbestos exposure, with a latency period typically ranging from 20 to 50 years. Mesothelioma has a poor prognosis, with many patients dying within one year of diagnosis. Treatment strategies include surgery, radiotherapy, chemotherapy or multimodality treatment. There are no particularly new agents used in its management, with trials I have published showing poor outcomes. While very good outcomes are possible in theory, I have only seen this very rarely indeed, despite aggressive treatment.
Other diseases
In addition to asbestosis and malignancies, asbestos exposure can lead to several non-malignant pleural diseases. These include pleural plaques, diffuse pleural thickening, benign asbestos pleural effusions and rounded atelectasis. Pleural plaques are the most common manifestation of asbestos exposure, affecting up to 58% of asbestos-exposed workers. They are discrete areas of hyaline fibrosis that again develop 20 to 40 years after first exposure.
The presence of asbestos in talc-containing cosmetics, as I have highlighted, has raised concerns due to the proximity of talc deposits to asbestos. While gives products such as talcum powder their inherent softness, it also increases cancer risk. Regulatory bodies have proposed mandatory asbestos testing for these products to ensure consumer safety – a move that in itself highlights the ongoing need for vigilance in preventing asbestos exposure through consumer goods. The International Agency for Research on Cancer has associated asbestos exposure with ovarian cancer as well and asbestos within talcum powder is specifically implicated here as being part of a causative matrix.
Conclusions
Asbestos continues to pose significant health risks due to its persistence in the environment and potential contamination in consumer products. Understanding the diseases associated with asbestos exposure is crucial for both medical diagnosis and legal proceedings. A recurring theme here is the wide range of latency periods – the time from exposure to disease development. Ongoing regulatory efforts and public awareness campaigns are essential to mitigate these risks and ensure justice for those affected.
As per British Thoracic Society guidelines, a diagnosis of mesothelioma leads to automatic benefits, as mesothelioma is so rare outside of asbestos exposure. The history and dangers of asbestos use highlight the importance of learning from past industrial practices to prevent future health crises.
Asbestos-related diseases serve as a stark reminder of the need for stringent safety measures and responsible product management to protect public health. Few materials have fallen from grace like asbestos. Once cherished as an almost-magical material, it is now the archetypal carcinogen.