Abstract  Topics: animal experiments; asbestosis; cancer; carcinogenic effects; asbestos; erionite; cocarcinogenic effects; cytological effects; glass fibre; IARC; in vitro experiments; inorganic man-made fibres; lung deposition; mineral fibres; pulmonary fibrosis; report; synergism.

Abstract  This book evaluates the risks to human health and the environment posed by exposure to chrysotile asbestos, a naturally occurring fibrous hydrated magnesium silicate having many commercial applications. Chrysotile is released to the environment from industrial sources; natural weathering of serpentine rock also results in emissions to air and water. The asbestos cement industry is identified as the largest current global user of chrysotile fibers. The report reviews methods used for collecting and analyzing samples, and discusses sources of occupational and environmental exposure. For humans, the report concludes that exposure to chrysotile asbestos poses increased risks for asbestosis, lung cancer, and mesothelioma in a dose-dependent manner, and confirms previous findings that asbestos exposure and cigarette smoking interact to greatly increase the risk of lung cancer. The report calls for the use of engineering and other control measures in workplace settings where occupational exposure occurs, and recommends use of safer substitutes when available.

Abstract  Identity; physical and chemical properties: The commercial term asbestos refers to a group of fibrous serpentine and amphibole minerals that have extraordinary tensile strength, conduct heat poorly, and are relatively resistant to chemical attack. The principal varieties of asbestos used in commerce are chrysotile, a serpentine mineral, and crocidolite and amosite, both of which are amphiboles. Anthophyllite, tremolite, and actinolite asbestos are also amphiboles, but they are rare, and the commercial exploitation of anthophyllite asbestos has been discontinued. Other natural mineral fibres that are considered potentially hazardous because of their physical and chemical properties are erionite, wollastonite, attapulgite, and sepiolite. Environmental levels and exposure: Asbestos is ubiquitous in the environment because of its extensive industrial use and the dissemination of fibres from natural sources. Once in the environment, fibres are mainly transported and distributed vie air and water. Available data using currently-accepted methods of sampling and analysis indicate that fibre levels (fibres : 5 um in length) at remote rural locations are generally below the detection limit (less than l fibre/litre), while those in urban air range from < l to l0 fibres/litre or occasionally higher. Airborne levels in residential areas in the vicinity of industrial sources have been found to be within the range of those in urban areas or occasionally slightly higher. Non-occupational indoor levels are generally within the range found in the ambient air. Occupational exposure levels vary depending on the effectiveness of dust control measures; they may be up to several hundred fibres/ml in industry or mines without or with poor dust control, but are generally well below 2 fibres/ml in modern industry. Reported concentrations in drinking-water range up to 200 x 106 fibres/litre (all fibre lengths). Toxicological effects on animals: Fibrosis in many animal species, and bronchial carcinomas and pleural mesotheliomas in the rat, have been observed following inhalation of both chrysotile and amphibole asbestos. In these studies, there were no consistent increases in tumour incidence at other sites, and there is no convincing evidence that ingested asbestos is carcinogenic in animals. Data from the inhalation studies have shown that shorter asbestos fibres are less fibrogenic and carcinogenic. Few data are available concerning the pathogenicity of the other natural mineral fibres. Fibrosis in rats has been observed following inhalation of attapulgite and sepiolite; a remarkably high incidence of mesotheliomas occurred in rats following inhalation of erionite. Long-fibred attapulgite induced mesotheliomas following intrapleural and intraperitoneal administration. Wollastonite also induced mesothelioma after intrapleural administration. Erionite induced extremely high incidences of mesotheliomas following inhalation exposure and intrapleural and intraperitoneal administration. The length, diameter, and chemical composition of fibres are important determinants of their deposition, clearance, and translocation within the body. Available data also indicate that the potential of fibres to induce mesotheliomas following intrapleural or intraperitoneal injection in animal species is mainly a function of fibre length and diameter; in general, fibres with maximum carcinogenic potency have been reported to be longer than 8 um and less than 1.5 um in diameter. Effects on man: Epidemiological studies, mainly on occupational groups, have established that all types of asbestos fibres are associated with diffuse pulmonary fibrosis (asbestosis), bronchial carcinoma, and primary malignant tumours of the pleura and peritoneum (mesothelioma). That asbestos causes cancers at other sites is less well established. Gastrointestinal and laryngeal cancer are possible, but the causal relationship with asbestos exposure has not yet been firmly established; there is no substantial supporting evidence for cancer at other sites. Asbestos exposure may cause visceral and parietal pleural changes. Cigarette smoking increases the asbestosis mortality and the risk of lung cancer in persons exposed to asbestos but not the risk of mesothelioma. Generally, cases of malignant mesothelioma are rapidly fatal. The observed incidence of these tumours, which was low until about 30 years ago, has been increasing rapidly in males in industrial countries. As asbestos-related mesothelioma became more widely accepted and known to pathologists in western countries, reports of meso- thelioma increased. The incidence of mesothelioma prior to, e.g., 1960, is not known. Mesotheliomas have seldom followed exposure to chrysotile asbestos only. Most, but not all, cases of mesothelioma have a history of occupational exposure to amphibole asbestos, principally crocidolite, either alone or in amphibole-chrysotile mixtures. There is strong evidence that one non-asbestos fibrous mineral (erionite) is carcinogenic in man. This fibrous zeolite is likely to be the cause of localized endemic mesothelioma in Turkey. Non-malignant thickening of the visceral pleura is frequently associated with asbestosis. Thickening of the parietal pleura, sometimes with calcification, may occur in the absence of detectable asbestosis. It is seen in those occupationally exposed to asbestos and also occurs endemically in a number of countries, but the causes have not been fully established. Tremolite fibre has been implicated as an etiological agent in some regions.

Abstract  Kinetics of dissolution of asbestos minerals in water were studied over a temperature range of 5 to 45°C. A parallelism was noted between the rate of dissolution of magnesium from magnesium silicates and the rate of pH drift. The rate of dissolution reaction was directly proportional to the specific surface area of the asbestos minerals. Both magnesium ion and hydroxyl ion concentrations were temperature-sensitive only in the initial stage of the contact between chrysotile mineral and water. The mechanism of dissolution of dissolved species from chrysotile was discussed in terms of the energy of activation. The activation enthalpies were calculated to be 5.5 and 6.5 kcal/mol for dissolution of magnesium and increasing of hydroxyl ion concentration, respectively. These results indicate that the rate controlling mechanism for both magnesium and hydroxyl ion dissolution is diffusion from the surface into water.

Abstract  Asbestos (Greek: inextinguishable) is the common name of a number of naturally occurring, hydrated silicate minerals that possess a crystalline structure and low thermal conductivity. They are incombustible in air and separable into filaments. These minerals occur as extremely thin flexible fibers having great tensile strength and thermal stability, and they can be spun into yarn and made into textiles. There are some 3000 recorded uses of asbestos including ‘‘fireproof’’ textiles, paper and boards, clutch and brake linings, asbestos cement sheets and pipes, flooring and roofing products, electrical and thermal insulating materials, coatings, and heat shields. The term asbestos was first used mineralogically in the middle of the 19th century with regard to a fibrous amphibole mineral discovered in the Italian Alps. The six major types of asbestos in use fall into two major groups: serpentine, having a layered silicate structure, and amphibole, having an SiO4 chain structure. Chrysotile (white asbestos) is the sole member of the serpentine group. Chrysotile asbestos accounts for over 90 % of the world’s asbestos production. Of the five members of the amphibole group, crocidolite (blue asbestos) and amosite (brown asbestos) are widely used commercially and tremolite and actinolite less so (Table 1). Asbestos has been known and used in small amounts for thousands of years, but it was not widely used prior to the latter part of the 19th century [3]. Asbestos was first mined in the Quebec, Canada, chrysotile fields in 1878, followed by Russia in 1885 and South Africa in 1906. Within 20 years of the first industrial production of asbestos, the public health hazards associated with asbestos started to come to light. Between 1890 and 1895, 16 out of 17 workers in a French asbestos weaving factory had died; by 1899, 11men who had worked in an asbestos spinning factory in the United Kingdom had died at aboutthe age of 30, having spent the whole of their working lives in this occupation (cording). The last of these deaths was reported to the Departmental Committee for Compensation for Industrial Diseases (U. K.) in 1906; this was the first recorded case of the disease that has become known as asbestosis [5]. The first complete description of asbestosis appeared in 1927 [6], [7]. Asbestosis and other asbestos-related diseases are treated in detail in Chapter 9. The widespread commercial use of asbestos over the past 100 years has led to its uncontrolled distribution throughout much of the industrialized world and its appearance in the general environ ment. The concentration of asbestos fibers in the urban atmosphere is actually in the lower part of the range 10 – 100 ng/m3 , but this can rise substantially in certain locations [8–12]. For example, in the vicinity of factories using asbestos, concentrations of asbestos fibers in the external atmosphere up to 5000 ng/m3 have been reported. In buildings where asbestos is being worked with or damaged, the concentration of asbestos in the air can be as high as 800 ng/m3 [11], [13], [14]. Low concentrations of asbestos are also found in water, beverages, and pharmaceutical and other medical products [9], [11], [15–23]. All commercial asbestos minerals are hydrous silicates of either the serpentine or the amphibole group. The serpentine minerals, which include chrysotile, have relatively simple chemical formulas; e.g., for chrysotile it is Mg3[Si2O5](OH)4. (See Figs. 1,2,3) Amphiboles have a widely varying nature and they are best considered by the general formula A0-1X2Y5Z8O22(OH, F)2; the substituents are: A ¼ sodium or potassium; X ¼ sodium or calcium; Y ¼ magnesium, iron, or aluminum; Z ¼ aluminum or silicon. It is not uncommon that small amounts of elements such as chromium, nickel, and titanium occur; usually many other elements are present in trace amounts. Minerals can have wide ranges of composition but still possess their characteristic structure and general formulas.

Abstract  Much of the more than 30 million tons of asbestos used in the United States since 1900 is still present as insulation in offices and schools, as vinyl-asbestos flooring in homes, and in other common products. This volume presents a comprehensive evaluation of the relation of these fibers to specific diseases and the extent of nonoccupational risks associated with them. It covers sources of asbestiform fibers, properties of the fibers, and carcinogenic and fibrogenic risks they pose.