Asbestos

Introduction

Asbestos is a widely used constituent in buildings and building materials, machines, transport vehicles and consumer products. Asbestos has a known historical use going back at least 4500 years when it was added as a reinforcing material to earthenware and cooking pots. Asbestos (Greek: inextinguishable) is the collective term for naturally occurring silicate minerals with a crystalline structure and a fibrous character. Inhalation of asbestos fibres may cause serious illnesses like lung cancer, mesothelioma and asbestosis. The European Union has banned all use of asbestos as well as the extraction, manufacture and processing of asbestos products. However, asbestos-containing materials are still present in many products and buildings manufactured before it was banned which means workers can still be exposed to asbestos.

General description

Asbestos was given its name initially by the Greeks around 300 BC. More accurately the term asbestos is traceable to Rome. Legend has it that a Roman Emperor possessed a tablecloth made of asbestos and the Persians amazed the population by cleaning the cloth simply by exposing it to fire. There is some evidence that asbestos cloths and shrouds existed in Persia and China.

Modern day industrial use of asbestos dates from the second half of 19th century with many applications in insulation, fire retardant and acid resistant parts, pipe insulation etc. The First World War saw an enormous increase in shipbuilding and this further increased the use of asbestos as fire retardants were of critical importance for warships. At that time, the dangers of asbestos to shipyard workers were not even considered. The Second World War stimulated even more asbestos use and the production rose from that time. An overview on the history of the use of asbestos and early warning signs of the causal relationship between asbestos exposure and diseases such as asbestosis and mesothelioma, can be found in Asbestos: from 'magic' to malevolent mineral (EEA)^[1].

In the 1970s, the manufacture and use of asbestos products were at their peak levels in Western Europe, Scandinavia, North America, and Australia when the worldwide production of asbestos exceeded five million tonnes every year. Since then, asbestos mine production has decreased considerably but still amounted to 1.3 million metric tonnes in 2023. Russia is the largest producer of asbestos in the world, with an annual production of approximately 630,000 million metric tonnes in 2023^[2]. In 2022, the largest use of asbestos was in Asia and the Middle East (estimated 1.3 million metric tons of asbestos). Most of the asbestos is used in asbestos-cement products, such as corrugated roofing, pipes, and wall panels. In the other regions of the world, the consumption of asbestos is relatively small. In Europe it still amounted to 767 metric tonnes^[3].

Asbestos minerals are not defined only on a mineralogical basis, but rather on the basis of their common properties which are the basis for their industrial uses. Asbestos minerals are fibrous in form and have many desirable properties such as high tensile strength, flexibility and chemical and physical durability. Asbestos minerals have been a valuable heat and fire insulation material in many industrial applications, particularly for the construction industry.

When asbestos was used for its fire/heat resistant properties, the fibres were often mixed with cement or woven into fabric or mats. Asbestos was also used in some domestic products in where heat and electric insulation was needed in hot environments e.g. ovens. Sprayed asbestos was used often as a layer of fire-protection and thermal insulation in industrial buildings, public buildings and domestic houses, on steel and concrete structures, especially on walls and ceilings, but also in boilers and chimneys^[4]. Spraying of asbestos was one of the most dangerous forms of application, since sprayed asbestos is extremely friable and therefore its fibres are very likely to be emitted into the ambient air. A large amount of asbestos can be found in civilian and military ships which were built using this technique.

The term asbestos is applied to six naturally occurring minerals: chrysotile, which is a sheet silicate, grunerite asbestos (amosite), riebeckite asbestos (crocidolite), anthophyllite asbestos, tremolite asbestos and actinolite asbestos, which have a structure of double chain of silica tetrahedra, cross-linked by major cations, i.e. magnesium, iron, calcium and sodium^[5]. All types of asbestos are classified as human carcinogen (carc. 1A). The identity and classification of various forms of asbestos is given in the table below.

Source: ^[6]

Chrysotile is categorised to the serpentine group (also referred to as white asbestos), with the remaining five types to the amphibole group of minerals. Chrysotile fibrils, about 30 nm in diameter, are flexible and form typically curvilinear bundles which break in the longitudinal direction into separate fibrils. Amphibole minerals are more brittle than chrysotile and divide along chrystallographic planes^[7]. Chrysotile has always been the principal commercially used asbestos worldwide and is the form used in most asbestos applications (> 90%)6.

The fibrous form of the particles can become airborne and inhaled deep into the lungs. This is linked to the poor solubility of the fibres in human body fluids and this one is the main characteristics making asbestos and asbestos dust both carcinogenic and fibrogenic (see below Health effects).

In addition to the six commercially exploited asbestos minerals, there are several other naturally occurring minerals which exist in a fibrous form, i.e. somewhere between 90 to 150 minerals may exist in a fibrous form. It has to be noted that these minerals are not defined as asbestos minerals. The important group of non-asbestos fibrous minerals are the man-made mineral fibres (MMMF), which is a generic term for fibrous vitreous inorganic substances made from rock, clay, slag or glass. They are better known as glass wool, rock wool or slag wool. The nominal fibre diameter in bulk MMMF-products is 2-20 micrometers in wool and textile products. Due to their amorphous nature, unlike crystalline asbestos, man-made mineral fibres tend to break predominantly across the fibre axis and thus no thinner fibres are produced during their handling. In the evaluation of cancer risk following the exposure to man-made mineral fibres it has been stated that there was a risk of lung cancer in the early phases of MMMF production, but no hazard of mesothelioma has been established^[8].

Health effects

The proven adverse health effects related to asbestos are caused by inhalation of asbestos dust. There is no convincing evidence that other routes of exposure can increase the risk of asbestos diseases. There is some evidence however that small fractions of ingested asbestos fibres may be able to penetrate the gastrointestinal tract. Inhaled asbestos fibres with an aerodynamic diameter of up to 10 µm may pass down into the lower respiratory tract. Due to the small diameter of the asbestos fibres, which range from less than 0.1 µm up to several micrometers, the length of the fibres can be tens of micrometers even more than 300 µm but the aerodynamic diameter of this fibrous particle still remains smaller than 10 µm. The adverse health effects of asbestos fibres are as follows:

• Pleural plaques are localised scars (fibrosis) consisting of collagen fibre deposits that form as a result of exposure to asbestos. They are the most common indication of significant exposure to asbestos. Pleural plaque is normally found in the parietal pleura, the lining of the inner wall of the chest. There are a few rare cases in which pleural plaques are found near a person’s rib cage^[9].
• Pleural thickening is a type of pleural fibrosis that often extends over the area of an entire lobe or lung and causes a significant restrictive impairment of lung function.
• Retroperitoneal fibrosis is characterised by a thick fibrotic mass covering the retroperitoneal structures. Retroperitoneal structures include the kidneys, the renal tract, the aorta, and other structures.
• Asbestosis (pulmonary fibrosis) is a serious lung disease characterised by inflammation and scarring of lung tissue. Over time, lung tissues and the lining of the chest wall thicken and harden causing shortness of breath, persistent cough, fatigue, laboured and rapid breathing and chest pain. Asbestosis develops when asbestos fibres are inhaled and get stuck deep inside the lungs. Asbestosis can lead to illness and death.
• Mesothelioma of pleura (membrane surrounding the lung) and peritoneum (membrane surrounding the abdominal cavity), is a rare form of cancer with a mean survival time of less than 12 months.
• Lung cancer can be caused by all asbestos species. Smoking and asbestos act synergistically, i.e. smokers run a disproportionally higher risk to get of lung cancer when exposed to asbestos than non-smokers.

Carcinogenicity and fibrogenicity of asbestos

The morphology of asbestos fibres plays a key role in the carcinogenicity and fibrogenicity of asbestos. The Stanton hypothesis states that long fibres (>8 µm in length) which are not easily engulfed by the macrophage cells (see below) in the lungs, and at the same time thin, i.e. less than 0.25 µm in diameter, have greater fibrinogenic and carcinogenic potential than shorter and thicker fibres^[10]. However, there is also some evidence, based on the analysis of lung tissues of exposed cancer patients that also shorter and thinner fibres than postulated by the Stanton hypothesis may be important in carcinogenesis.

Alveolar macrophages, mobile cells that have the major responsibility of removing extra material from the lungs, can phagocytise (engulf) asbestos fibres. In the process of engulfing the fibres, the macrophages release active oxygen and nitrogen species, cytokines and growth factors (see below) and initiate inflammatory changes in the tissue. Other cell types like neutrophils, T-lymphocytes and mast cells also accumulate in lungs triggering detrimental processes ultimately leading to scarring of the lungs (fibrosis).

After entering the gas exchange region of the lungs, i.e. the bronchial alveoli, asbestos is able to evoke the production of reactive substances in the cells. There are many reactive oxygen species (ROS), e.g. hydrogen peroxide (H₂O₂), the superoxide anion (O₂), the hydroxyl radical (HO), and reactive nitrogen species. In addition, nitric oxide (NO) production is induced in cells exposed to asbestos fibres. ROS and other reactive species attack DNA, some cellular proteins and lipid membranes and alter their function, and this is the reason why asbestos is mutagenic.

Some cell-signalling cytokines and growth factors like interleukin1 (IL-1), tumour necrosis factor α (TNF-α), transforming growth factor (TGF), platelet derived growth factor (PDGF), and interleukin 8 (IL-8) affect the cellular injury process and activate collagen deposition in the tissue as well as promoting fibroblast proliferation which leads to fibrosis (formation of scar tissue).

In animal experiments, some fibrous minerals other than asbestos have also been shown to be carcinogenic including palygorskite (attapulgite), erionite and nemalite^[11]. The evidence of carcinogenicity was evaluated by IARC as sufficient for erionite, as well as for talc containing asbestiform fibres^[12].

Mesothelioma

Malignant mesothelioma is a rare malignancy closely related to asbestos exposure. It is a cancer predominantly of the pleural cavity^[13]. In the early 1950s, at the time when mesothelioma was recognised as a malignancy associated with asbestos, the disease was generally regarded as a pathological rarity. However, case reports in the medical literature had been published already in 1930s and 1940s. The findings of Dr C. Sleggs led to a report in which 33 cases of pleural mesothelioma and exposure to crocidolite in South Africa were described in 1960^[14]. This report is a landmark in associating asbestos with mesothelioma and it is now known that over 80% of mesothelioma patients have had some occupational exposure to asbestos and furthermore some of the exposures had been low. The median age at diagnosis is 75 years and overall survival is 38% at one year and 7% at three years, which is a reflection of the poor prognosis^[15]. Typically, malignant mesothelioma has a long latent period after asbestos exposure and the onset of the disease from 25 years to 50 years and more^[13] . 

Lung cancer

Several studies have shown an elevated risk of lung cancer in association with asbestos exposure and asbestos is a recognised carcinogen^[16]. There is sufficient evidence that not only the amphiboles but also chrysotile asbestos cause lung cancer^[17]. Asbestos plays an important role in the development of lung cancer, and moreover, research shows a correlation with the damage caused by smoking^[18]. A health study which followed a group of asbestos exposed workers showed cigarette smoking alone caused an 11-fold, and smoking and asbestos together a 53-fold increase in lung cancer risk^[19].

Other cancers

Asbestos has been suspected of causing cancers in the pharynx, esophagus, stomach and intestine. However, only slightly increased risks have been shown for stomach and colorectal cancer, but there is some evidence that also laryngeal cancer may be caused by asbestos exposure^[20].

Occupational and environmental exposure

The industrial use of asbestos is closely related to its subsequent health effects. The life cycle of asbestos containing products begins in the primary asbestos industry and continues with their secondary manufacture, installation, usage and disposal. Worldwide, millions of workers have been exposed to asbestos in the workplace, most often during handling, maintenance, repair, and replacement of asbestos-containing materials. Since asbestos is banned in the EU, nowadays exposure to asbestos is mainly linked to

• repair, renovation and removal of asbestos by construction or maintenance workers;
• ship dismantling and recycling;
• treatment and disposal of asbestos-containing materials;
• people working and living in buildings containing asbestos^[21];
• areas where asbestos may be present in machinery or furnaces.

Asbestos, as dry material or embedded in hard material like concrete, readily produces dust and airborne particles when it is handled or crushed or the material is broken in some other way. Therefore, respirable asbestos fibres are released into the air easily, and in addition they stay airborne for a long time and travel long distances in the airstreams. Over time, the fibre burden in the lungs leads to serious health problems.

Everyone is exposed at least to low levels of asbestos at some time during their life. Asbestos is present in the air, water, and soil. People who become ill from asbestos are usually those who have been exposed in an occupation where they work directly with the material. In a study of 300 autopsied urban men between the ages of 33 and 69, fibre concentrations longer than 1 µm were found in a range from <0.3 to 163 million fibres per gram of dry tissue (f/g, dry tissue weight is about 10% of the weight of normal lung tissue). Asbestos fibre concentrations exceeding 1 million f/g were observed in 33% of the cases with probable occupational exposure to asbestos and in 1% of the cases with unlikely occupational exposure. In addition, concentrations between 0.3 to 1 million f/g, especially of crocidolite-amosite fibres, were rare among the men with unlikely occupational exposure. Fibre concentrations exceeding or equalling 1 million f/g were 10 times more frequent in the men more than 60 years of age as compared to those less than 40 years of age. Smoking habits had no significant effect on the pulmonary fibre counts. Asbestos fibre concentrations exceeding 1 million fibres per gram of dry tissue are highly indicative of past occupational exposure to asbestos. The distribution of fibre concentrations in the different age groups of this study was an indication of decreasing asbestos exposure in Finland since the 1970s^[22].

There is no safe level of asbestos exposure, and health effects mainly affect people who are occupationally exposed to asbestos. Exposures to asbestos have taken place in the mining and milling of asbestos and in the primary and secondary manufacturing of asbestos products like friction materials (automobile and other machinery brake pads, shoes, and clutch discs), asbestos cement, asbestos textiles, floor tiles, roofing felts, insulating and building materials, heating equipment and industrial process furnaces. Occupational groups known to be exposed to asbestos, such as workers in the shipbuilding and repair sectors, and in the construction industry as well as several other groups such as insulation workers, car mechanics, ship engine room personnel, and maintenance workers in industry, are at risk of asbestos related diseases.

Asbestos abatement can only be carried out when strict procedures are in place for protecting the workers. In addition to technical and organisational measures, workers must also wear personal protective equipment such as a powered and supplied-air respirator and close-fitting protective clothing covering the whole body and incorporating a hood^[23]. However, it should be noted that the performance of such personal protective equipment also depends on its practical application and does not always provide sufficient protection. A study of performance of full-face mask respirators with P3 filters and HEPA air filtration units at 21 work sites revealed that only 8 of the 21 tested respirators fully protected the workers against fibres. With the remaining 13 respirators, the fibre levels inside the respirator varied from 0.01 to 4.6 f/cm³, with a mean concentration of 0.46 f/ cm^3[24].

Legislation

The prohibition of asbestos use came into force at different times in the different EU Member States. Since 1st January 2005, the use of asbestos has been banned throughout the whole European Union. European legislation has set strict standards for the protection of workers in situation where they may be exposed. The following are some of the relevant directives.

Asbestos ban 

European Directive 1999/77/EC bans all uses of asbestos from 1 January 2005^[25]. Therefore, the asbestos exposure of the primary users of the asbestos-containing products and materials is no longer a threat. The directive has been repealed but the ban on the use of asbestos is integrated in the REACH legislation (EU Regulation No 1907/2006 for Registration, Evaluation, Authorisation and Restriction of Chemicals)^[26]. In its Annex XVII (entry 6), REACH prohibits the manufacture, placing on the market and use of asbestos fibres and of articles and mixtures containing these fibres added intentionally. However, much asbestos remains in place in buildings and other structures and the problems of exposure to asbestos in the removal, demolition, servicing and maintenance activities relating to these structures are still relevant and important.

Protection of workers

European Directive 83/477/EEC^[27] regulates the protection of workers from the risks related to exposure at work. This Directive has been amended several times. A significant modification was made by Directive 2003/18/EC^[28] which sets a single maximum limit value (Occupational exposure levels (OEL)) for airborne concentration of asbestos of 0.1 fibres per cm³ (= 100 000 fibres per m3) as an eight-hour time-weighted average (TWA) and prohibits activities exposing workers to asbestos fibres, with the exception of the treatment and disposal of products resulting from demolition and asbestos removal and updates the practical recommendations on the clinical surveillance of exposed workers in the light of the latest medical expertise, with a view to the early detection of pathologies linked to asbestos.

Because of the numerous amendments in the interests of clarity and rationality Directive 83/477/EEC and its amendments were replaced by a new asbestos Directive 2009/148/EC^[29].

Combating occupational cancer remains a high priority in OSH. Therefore, a further reduction of workers' exposure to asbestos is a key priority of the EU Strategic Framework for Health and Safety at Work 2021-2027. On 30 November 2023, amending Directive 2023/2668/EU^[30] was published, lowering the binding occupational exposure limit (OEL) for asbestos fibres from 0.1 fibres per cm³ to 0.01 fibres per cm³ as an eight-hour time-weighted average (TWA). Member States are required to enforce this lower exposure limit starting from 21 December 2025. Furthermore, by 21 December 2029, the OEL must be further reduced. The OEL depends on the fibre counting method used in a particular Member State: either 0.002 fibres per cm³ when counting fibres with a breadth between 0.2 and 3 micrometres, or 0.01 fibres per cm³ when counting fibres with a breadth smaller than 0.2 micrometres.

Amending Directive 2023/2668/EU also introduced a more sensitive method for measuring asbestos fibres. Analytical methods based on electron microscopy must be used instead of optical microscopy (phase-contrast microscopy (PCM)). Electron microscopy allows for the counting of thinner fibres and provides more accurate results. In order to allow sufficient time to comply with these new requirements relating to the measurement of asbestos fibres, the Directive provides for a transitional period until 21/12/2029.

The Carcinogens, Mutagens or Reprotoxic substances Directive (CMRD - Directive 2004/37/EC) contains provisions for substances classified as carcinogenic, mutagenic or reprotoxic Cat. 1A or 1B. As asbestos fibres are classified as carcinogenic cat. 1A, they are within scope this directive. However, the CMD acknowledges that the asbestos directive 2009/148/EC provides similar provisions and therefore the CMD states the following: As regards asbestos, which is dealt with by Directive 2009/148/EC of the European Parliament and of the Council, the provisions of this Directive shall apply whenever they are more favourable to health and safety at work^[31].

Asbestos waste

Directive 87/217/EEC^[32] contains provisions to prevent and reduce pollution caused by asbestos in order to protect human health and the environment.

There are synergies with the Directive 2009/148/EC (protection at work), in particular in relation to activities involving the demolition of buildings and installations containing asbestos, the removal of asbestos and products containing asbestos which may release asbestos fibres.

In addition, the Waste Framework Directive (2008/98/EC^[33]) and the Landfill Directive (1999/31/EC^[34]) lay down measures for the management of asbestos waste^[35].

Prevention of asbestos hazards

National bans of asbestos are already in place in more than 50 countries worldwide^[36]. However, the risk posed by asbestos has not disappeared especially for workers in maintenance and construction. Therefore, it is important that managers of maintenance companies and workers should become better aware of the risks of asbestos and develop the knowledge and skills to avoid exposure to the hazardous fibres^[37]. In the construction industry, it is important to be aware of the national legislation and good practices in renovation work and have detailed guidance about how to work safely with asbestos containing materials^[38].

In some countries, poor management of asbestos removal in the past, especially in the demolition of buildings, has resulted in the contamination of soil (and debris) with asbestos. Such contamination is not always apparent. A UK guide can provide some help in understanding and managing the risks arising as a result^[39].

In Europe, following the Dresden Declaration^[40], the Senior Labour Inspectors’ Committee (SLIC) took in 2006 the initiative to create a common pan-European campaign in order to increase the attention to health and safety when dealing with built-in asbestos. The main focus of the campaign was on the protection of workers in maintenance/demolition/removal activities and waste disposal. European best practice guidelines were issued to labour inspectors competent for occupational safety and health issues and for employers and workers engaged in work exposing them to asbestos risks^[41]. The SLIC initiative included the preparation of a practical guide on best practice to prevent or minimise asbestos risks^[42].