Chrysotile and chrysophosphate chemical modification of the chrysotile surface and its effect on biological behavior.

Chrysotile asbestos was reacted with phosphorus oxychloride (POC) gas to produce a chemically modified fiber referred to as chrysophosphate. The presence of phosphorus and chlorine on the fiber surface and in small fiber bundles was verified by means of energy dispersive x-ray spectrometry and laser mass spectrometry. The altered fiber exhibits different physical-chemical properties when compared with the unaltered precursor material. In addition to marked surface changes, fibrils of the reacted material appear to be cross-linked increasing the size of particulates, fiber bundles and increasing their mechanical stability. The reacted specimens exhibit fewer fibrils reducing their surface area. In vitro testing using the human erythrocyte model showed the membranolytic activity of the reacted fiber to be substantially reduced to the background level measured for mechanical membrane breakage during manipulation. Membranolytic activity of unreacted chrysotile displayed values reported previously in the literature. These data support the observation made in other studies that fiber surface modification by means of an industrial process may be a method for reducing the biological potential of mineral particles. The membrane model is considered a useful and preliminary examination. These materials will require further testing in more complex in vivo systems. Some in vivo assays were performed on chrysophosphate with results that appeared to differ from our membrane tests. These differences are described and the variation of batch chemistry, stability of the reacted surface, and the resulting surface chemistry, are discussed.

A risk assessment for exposure to glass wool.

Synthetic vitreous fibers (SVFs) have been widely used as insulation material in places where asbestos was used many years ago and therefore the hazards have been compared. Since the three principal types of asbestos fibers types have caused lung cancer at high exposures, there is a widely held belief that all fibers are carcinogenic if inhaled in large enough doses. Hence, on a morphological basis, SVFs have been studied for their carcinogenic potential. However, there is considerable evidence that differences exist among fibers in their potency to produce a carcinogenic response. In this attempt to carry out a numerical risk assessment for the installers of blown glass wool (fiber) insulation, we start with a characterization of the material; then we review the exposures both in manufacturing and installation. Neither the epidemiological studies of human exposure nor the animal studies have shown a marked hazardous effect from glass wool and we can therefore be sure that any effect that might exist is small. But in this case, as in many other situations where there is a potential hazard, society desires further reassurance and therefore we have made a mechanistic calculation. There are good estimates of the risk associated with exposure to chrysotile asbestos at high exposures and doses. We have therefore taken these numbers and discussed how much less risky an exposure to glass wool fibers might be. We conclude that for a given fiber count, glass wool is five to ten times less risky (and of course the risk might be zero). The risk for a nonsmoking installer of glass wool fiber insulation who wears a respirator is about 6 in a million (and might be zero) per year. This means that out of a million installers there might be six lung cancers from this cause every year or out of 10,000 installers there might be one in 16 years. The low risk of 6 in a million per year of a worker blowing glass wool is consistent with the fact that no one has found any of cancer attributable to the manufacture or installation of glass wool fibers in spite of diligent searches. This is compared with several other occupational risks. Nonetheless common prudence suggests that any installer of blown glass wool fiber insulation wear a respirator.

A risk assessment for exposure to grunerite asbestos (amosite) in an iron ore mine.

The potential for health risks to humans exposed to the asbestos minerals continues to be a public health concern. Although the production and use of the commercial amphibole asbestos minerals-grunerite (amosite) and riebeckite (crocidolite)-have been almost completely eliminated from world commerce, special opportunities for potentially significant exposures remain. Commercially viable deposits of grunerite asbestos are very rare, but it can occur as a gangue mineral in a limited part of a mine otherwise thought asbestos-free. This report describes such a situation, in which a very localized seam of grunerite asbestos was identified in an iron ore mine. The geological occurrence of the seam in the ore body is described, as well as the mineralogical character of the grunerite asbestos. The most relevant epidemiological studies of workers exposed to grunerite asbestos are used to gauge the hazards associated with the inhalation of this fibrous mineral. Both analytical transmission electron microscopy and phase-contrast optical microscopy were used to quantify the fibers present in the air during mining in the area with outcroppings of grunerite asbestos. Analytical transmission electron microscopy and continuous-scan x-ray diffraction were used to determine the type of asbestos fiber present. Knowing the level of the miner's exposures, we carried out a risk assessment by using a model developed for the Environmental Protection Agency.

Asbestos in the lungs of persons exposed in the USA.

Tissues obtained at autopsy or biopsy from 81 workers and 2 household persons, were chemically digested. The asbestos fibres recovered were characterized by analytical transmission electron microscopy. Among the 83 causes of death were 33 mesotheliomas, 35 lung cancers, 12 asbestosis and 3 from other cancers. Of the three major commercial asbestos fibre types, amosite was found to be the most prevalent fibre, occurring in approximately 76% of the cases, followed by chrysotile in approximately 60% and crocidolite in approximately 24%. Amosite and chrysotile were observed as the single commercial fibre in approximately 22 and approximately 17% of the cases respectively, whereas crocidolite and tremolite were found as the single fibre type in only approximately 2.5% of the cases. Among the fifteen cases where chrysotile and tremolite occurred together, the amount of chrysotile fibre always exceeded tremolite. However, tremolite was also found in ten additional cases where chrysotile was not detected. Amosite was present in four, amosite plus crocidolite in three, and crocidolite alone in one. Amosite was present in all of the insulation workers' lungs studied and was found in the highest concentration in this exposure category. The highest chrysotile concentration was found among workers in general trades. Although most prevalent in shipyard workers lungs, crocidolite concentration is not statistically different among the exposure groups studied. Although crocidolite was found in twenty cases, amosite accompanied it in eighteen of these. Eleven of the 20 cases were from shipyard workers. Of the 8 mesothelioma cases, 7 also contained amosite. Crocidolite alone only occurred in 1 of the 33 mesothelioma cases analysed. We concluded the following: crocidolite exposure occurred among USA insulators and a large percentage of other workers as well; insulation workers are primarily exposed to amosite; mixed fibre exposures are associated with more mesotheliomas than single fibre exposures; chrysotile only exposure is associated with approximately 12% of the mesothelioma cases studied; and if tremolite exposure is associated with chrysotile exposure, the chrysotile amount exceeds that for the associated tremolite.

Asbestos in New York City public school buildings--public policy: is there a scientific basis?

The most recent of New York City's asbestos emergencies occurred in the late summer of 1993. It prevented schools from opening that fall, precipitated much media excitement, and caused a flurry of widespread abatement activities. This resulted in large measure from the U.S. Environmental Protection Agency's subjective school building inspection policy concerning identification of asbestos hazards in buildings and the subsequent Asbestos Hazard Emergency Response Act mandate for inspection. Data on concentrations of asbestos in the air, important for the calculation of risk to building occupants, were not required and therefore not obtained, as part of the abatement strategy or priority setting. Based on fiber-in-air measurements obtained elsewhere, the calculated risk to NYC school children, using the most pessimistic models, was less than six excess cancer deaths per million lifetimes equivalent to smoking less than a dozen cigarettes in a lifetime. The NYC administration responded to pressure from parent groups concerned with perceived asbestos risks to their children by closing the schools. The hysteria occurred because much of EPA's policy lacked a scientific basis for risk evaluation and assessment.

Chrysotile biopersistence in the lungs of persons in the general population and exposed workers.

Lung burden analysis was performed on 126 autopsy cases of persons who died in New York City from 1966 through 1968. Of the 126 cases, 107 were probably non-occupationally exposed, judging by occupational history and asbestos body content of lung. Fifty-three of the 107 cases contained short chrysotile fibers/fibrils, < 5 microns in length, present in 3-fold greater amounts than were found in laboratory background controls. The fiber concentrations ranged from 1.8 to 15.7 x 10(6) f/gm/dry lung tissue, and the proportion of fibers > or = 5 microns in length was only 0.34% of the total chrysotile population found. Other inorganic particles present included fragments of amphiboles. In contrast to these data, the lung parenchyma of persons occupationally exposed to asbestos commonly showed the presence of other fiber types, especially amosite and crocidolite, at very much higher concentrations and greater fiber length. Any chrysotile present would usually be in fiber bundle form, with both fibers and fibrils > 5 microns in length. Comparison of the lung fiber content of occupationally exposed persons with that of the general population showed marked qualitative and quantitative differences. Fibers are durable, and are retained in a range of concentrations. Their length and dose, among other factors, which control their biological potential are different in the two populations; the risk factors for chrysotile-induced disease are not the same.

Lung content analysis of cases occupationally exposed to chrysotile asbestos.

The lung contents of six workers who had been occupationally exposed to chrysotile asbestos were examined. Five were lung cancer cases from Quebec, Canada. The sixth, an American worker who had developed pleural mesothelioma, was particularly interesting, with the lung content strikingly distinct from the Canadian cases; chrysotile, the predominant fiber in his lung, was present at a concentration 300 times that of the average total fiber content in the Canadian cases. The fiber length distribution of the chrysotile recovered from the U.S. mesothelioma case was indistinguishable from that of chrysotile specimens known to produce mesotheliomas in rats. It was also found that the characteristics of the calcium-magnesium-iron silicate fibers present in all six cases were not readily comparable to tremolite asbestos specimens known to induce mesotheliomas in animals.

Chrysotile: its occurrence and properties as variables controlling biological effects.

Chrysotile formation arises through serpentinization of ultramafics and silicified dolomitic limestones. Rock types tend to control the trace metal content and both the nature and amounts of admixed minerals in the ore, such as fibrous brucite (nemalite) and tremolite. Some associated minerals and trace metals are thought to play a role in biological potential. Tremolite, one of the important associated minerals, may occur with different morphological forms, called habits. These habits range from asbestiform (tremolite asbestos) to common blocky or non-fibrous form (tremolite cleavage fragments). The latter is most common in nature. Tremolite in chrysotile ore varies in habit and concentration, both factors determining the degree of risk following inhalation. Tremolite fibre is thought to be important in relation to the occurrence of mesothelioma. Chrysotile fibrils may vary in diameter. Dust clouds generated following manipulation vary in fibre number and surface area. Chrysotile fibres exhibit a range of physical characteristics. The fibre may be non-flexible ('stiff') and low in tensile strength ('brittle'), and may lack an ability to curl. This fibre, referred to as 'harsh', sheds water more quickly than its curly, flexible 'soft' variety. The behaviour of the harsh fibres is more amphibole-like and their splintery nature suggests an enhanced inhalation potential. Slip fibre ore from Canada tends to contain more fibrous brucite (nemalite) than cross-fibre ore in the same mine. Industrial manipulation, which includes chemical treatment, heating and milling, may impart new surface properties to chrysotile dusts. Biological potential may be enhanced (opening of fibre bundles) or reduced (disruption of surface bonds and lessened ability to interact with organic moieties). Leaching of magnesium from chrysotile occurs at a pH less than about 10. Chrysotile has been demonstrated to lose magnesium in vivo and undergo clearance from the lung. The biological potential of magnesium-depleted chrysotile is much reduced, or even eliminated. Reduction of mesothelioma-inducing and cytotoxic potential has been observed and quantified experimentally. Use of chrysotile products in high-temperature environments may heat the mineral to the point where it undergoes alteration of properties, especially by dehydroxylation. Chrysotile ore may vary in properties and associated minerals: it may form aerosols with different size distributions, especially fibre/fibril diameters and surface areas; it may be associated with varying quantities of tremolite (with differing habits); it may be manipulated both industrially and environmentally to yield surfaces with different properties and, hence, differing biological potentials. Chrysotile's properties may vary from place to place and among different user industries.

Characterisation of palygorskite specimens from different geological locales for health hazard evaluation.

Palygorskite, a fibrous clay mineral, is being used as a substitute for asbestos in some applications. Nine specimens obtained from different geological locales were studied for mineral purity, elemental composition, fibre size distribution, and surface binding characteristics. The membranolytic activity of each was determined using a human erythrocyte model. The membranolytic behaviour and surface binding characteristics were compared with three chrysotile specimens employed as positive controls. The palygorskite specimens derived from the different geological locales display a range of physicochemical properties. This study shows the importance of selecting several mineral specimens for a health hazard evaluation. The current carcinogenic classification of the mineral may be limited due to the number of specimens used for that particular evaluation.

Desquamative interstitial pneumonia associated with chrysotile asbestos fibres.

The drywall construction trade has in the past been associated with exposure to airborne asbestos fibres. This paper reports a drywall construction worker with 32 years of dust exposure who developed dyspnoea and diminished diffusing capacity, and showed diffuse irregular opacities on chest radiography. He did not respond to treatment with corticosteroids. Open lung biopsy examination showed desquamative interstitial pneumonia. Only a single ferruginous body was seen on frozen section, but tissue examination by electron microscopy showed an extraordinary pulmonary burden of mineral dust with especially high concentrations of chrysotile asbestos fibres. This report emphasises the need to consider asbestos fibre as an agent in the aetiology of desquamative interstitial pneumonia. The coexistent slight interstitial fibrosis present in this case is also considered to have resulted from exposure to mineral dust, particularly ultramicroscopic asbestos fibres.

Fibre type and burden in parenchymal tissues of workers occupationally exposed to asbestos in the United States.

Lung tissues obtained from 53 asbestos-exposed workers, and one person exposed in a domestic setting, were studied. Amosite is the most prevalent fibre, occurring in 74% of the specimens. Amosite is always found in the lungs of insulation workers whereas chrysotile is found in only 50% of this population. Crocidolite has been detected in 24% of the lungs examined, but this increases to 40% in workers with shipyard histories. Exposure to chrysotile is widespread; the fibre has been observed in 61% of the tissues studied. Chrysotile occurs as the lone fibre in about 22% of the tissues examined, but tremolite is present in one-third of these. Fibre consumption data cannot be used as indices of exposure in the workplace; amphibole exposure appears to be product- and job-category-related. The assessment of risk to asbestos disease in the general population of the United States, exposed to chrysotile, should be based on appropriate chrysotile-exposed cohorts.