Chrysotile Miners Research Articles

Effects of particulate matter on rates of membrane uptake of polynuclear aromatic hydrocarbons.

Investigations of the mechanism of particle-enhanced uptake of benzo [a] pyrene into model membranes and microsomes have been extended by studying the effects of particulates on the rates of uptake of four additional polynuclear aromatic hydrocarbons (PAH) into model membranes. Adsorption of dibenzo [a, h] anthracene, benzo [g,h,i] perylene, and 3-methylcholanthrene to the surface of particles resulted in enhanced rates of membrane uptake of these PAH. Adsorption to the fibrous asbestos minerals (chrysotile and anthophyllite) produced the greatest enhancement in membrane uptake rates compared to uptake from microcrystalline dispersions of the PAH. Adsorption of these PAH to nonfibrous minerals resulted in uptake rates intermediate between those of the asbestos-adsorbed and microcrystalline states. In contrast, adsorption of dibenzo-[c,g] carbazole to particles did not result in enhanced uptake. In this case, the rates of uptake in the absence and presence of particles were all extremely high, presumably as a result of the high water solubility of this PAH. The methods described in this paper permit characterization of particles-PAH mixtures in terms of the rate of PAH uptake into membranes.

Development of Radiographic Abnormality in Chrysotile Miners and Millers

Development of Radiographic Abnormality in Chrysotile Miners and Millers

Development of Radiographic Abnormality in Chrysotile Miners and Millers

It has been known for 50 years that inhalation of asbestos dust can lead to appearances on chest roentgenograms that are different from those associated with silicosis and coal workers’ pneumoconiosis.1 However, only the latest international classifications of the radiographic appearances of the pneumoconioses allow the recording of such shadows.2,3 These include what are now called small irregular opacities together with a variety of pleural changes. It is thought that small irregular opacities appearing first in the lower lung zones are characteristic of asbestos exposure.

Radiological findings as predictors of mortality in Quebec asbestos workers.

Two cohorts of chrysotile miners and millers in Quebec were selected to study the extent to which chest radiographs taken while still employed predict mortality. The paper presents mainly findings in much the larger cohort, which consisted of 4559 men (two-thirds past workers) whose latest radiograph had been assessed by one of six experienced readers into what became the UICC/Cincinnati (U/C) classification; by the end of 1975 there had been 1543 deaths in this cohort. The findings were generally confirmed in the other cohort, comprising 988 current male workers, who had been examined in 1967-8 by questionnaires on respiratory symptoms and smoking and by lung function tests, and for whom all six readers had assessed their 1966 radiographs into the U/C classification; 130 men had died by the end of 1975. Men with any radiographic abnormality, heavy dust exposure, or a history of cigarette smoking had relative risks (RRs) of total mortality greater than unity. Death from pneumoconiosis was associated with small parenchymal opacities, usually irregular, of profusion l/l or more, and with heavy dust exposure but not with smoking. Most who died from lung cancer had smoked cigarettes, or had been heavily exposed to dust, or both. Small parenchymal opacities were present in most but not all the excess deaths due to lung cancer. Deaths from other malignant diseases showed no consistent dust or x-ray patterns. RRs of deaths from most other causes were raised for certain radiographic features. Failures in forecasting mortality were primarily due to deaths in which asbestos-related disease was not the primary cause but may have been a contributing factor. The main findings validated the U/C classification convincingly, particulary as the films had been taken as routine and were of modest quality. Despite objective rules for the reading and the fact that all six readers were contributing to the development of the classification, there was inevitably some observer variation. The importance of radiographic technique and the need for careful control of the reading is evident. Our results provide support for the use of the chest radiograph for surveillance of asbestos workers, and for environmental monitoring. Its protective value for individual workers, however, is limited to the extent that radiological progression continues after withdrawal from exposure, and by the carcinogenic risk associated with dust already retained.

The effect of slime coatings of the serpentine minerals, chrysotile and lizardite, on pentlandite flotation

Serpentine minerals in the gangue often interfere with the concentration of nickel sulfide ores. The influence of slime coatings of the serpentine minerals chrysotile and lizardite on the flotation of unoxidized pentlandite has been studied. In addition to microflotation testing at pH 9 with potassium amyl xanthate collector, electrophoresis and scanning electron microscopy have been used. The formation of a slime coating was found to be directly related to the surface charges on the slime and the sulfide mineral. Chemical additives which modified the slime surface charge, such as carboxy methyl cellulose, dextrin, sodium pyrophosphate and sodium silicate, were shown to be effective in reducing the adverse influence of the slime on the flotation of pentlandite.

Putative Inhibitory Effects of Chrysotile, Crocidolite, and Amosite Mineral Fibers on the More Complex Surface Membrane Glycolipids and Glycoproteins

Putative Inhibitory Effects of Chrysotile, Crocidolite, and Amosite Mineral Fibers on the More Complex Surface Membrane Glycolipids and Glycoproteins

Benzo[ a]pyrene uptake into rat liver microsomes: Effects of adsorption of benzo[ a]pyrene to asbestos and non-fibrous mineral particulates

The fluorescence yield of benzo[ a]pyrene (BP) increases dramatically upon its transfer from the surface of particulates to rat liver microsomes. Adsorption of BP to Canadian chrysotile, anthophyllite, hematite and silica results in greatly enhanced uptake rates into microsomes when compared to uptake from a microcrystalline dispersion of BP. The fibrous minerals chrysotile and anthophyllite were more effective than silica and hematite in enhancing BP uptake. Simple mixtures of BP microcrystals and particles did not display enhanced transport, indicating that adsorption of BP to the particulate surface is necessary for enhanced microsomal uptake. BP was not released into microsomes from carbon black. We suggest that particulate-enhanced availability of BP may be of significance in the co-carcinogenesis between particulates and polynuclear aromatic hydrocarbons. However, other mechanisms are also possible, and are not excluded by our experiments. The fluorescence methodology described in this paper provides a novel and convenient means to quantify microsomal uptake of BP and thereby investigate further the mechanisms of cocarcinogenesis.

Serpentine Minerals: Intergrowths and New Combination Structures

The serpentine minerals chrysotile, lizardite, and antigorite have been found intimately intergrown with each other and with talc, chlorite, and amphibole in incompletely reacted chain silicates. High-resolution transmission electron microscopy has revealed new variations in serpentine planar and roll structures, as well as regions of mixed-layer silicate consisting of serpentine and talc layers.

Etiology of Pleural Calcification: A Study of Quebec Chrysotile Asbestos Miners and Millers

A review of 15,689 chest radiographs of Quebec chrysotile miners and millers, representing the latest film prior to November 1, 1966, for all such persons ever x-rayed, identified 206 men with pleural calcification. Of these, 198 had worked in the Thetford Mines area, 6 at Asbestos, and 2 at St. Remi de Tingwick; 2.5%, 0.08%, and 1% of the films from these areas, respectively. A series of case-control studies revealed that pleural calcification was concentrated in men employed at a small group of mines in Thetford Mines and occurred more often among miners and maintenance personnel than among millers. Calcification was not related to past history of illness or injury, place of residence, or employment in other industries. The distribution of pleural calcification in this Quebec industry suggests that it is related to some characteristic of airborne dust or mineral closely associated with the chrysotile that is encountered during mining in Thetford Mines but not in other mining areas. Possible minerals include mica, talc, and breunnerite.

Potential Sources of Asbestos in Lake Michigan

Chrysotile and amphibole mineral fibers, recognized carcinogens, have been found in Lake Michigan water. Since the sources of these fibers in Lake Michigan are unknown, a study was undertaken to determine potential sources. Information was gathered by contacting governmental agencies and reviewing literature. Two industries that used to discharge asbestos-containing effluents are located in the Lake Michigan drainage basin. Geologic deposits of mineral fibers occur in Marinette County, Wisconsin and the Upper Peninsula of Michigan. Currents and Army Corps of Engineers dredging and disposal activities were investigated as potential mechanisms of asbestos distribution in Lake Michigan. Limited environmental monitoring indicates that atmospheric loading and wash-out from numerous point and non-point sources may be an important mechanism of asbestos contamination of Lake Michigan. More environmental monitoring will be required in order to determine the relative importance of these potential sources.

Nature and range of mineral dusts in the environment

Mineral dusts are pollutants in air, drinking water, foodstuffs and even some drugs. Inhalation of the asbestos minerals amosite, anthophyllite, chrysotile, crocidolite and tremolite occurs not only in areas adjacent to industrial and mining activities and in the households of those industrially exposed to these minerals, but also by the general public due both to airborne dusts from industrial areas, mines and mine dumps and to the household use of asbestos-containing commodities such as talcum-powders and do-it-yourself plasters, fillers and insulation material. Inorganic particles are also inhaled in cigarette and cigar smoke. These include cristobalite - a known fibrogen - and result from use, during manufacture, of clay minerals, diatomaceous earth, glass fibre and other additives. Ingestion of asbestos minerals has resulted from the dumping of the gangue of taconite ores into water supplies. Both talc and asbestos are ingested from toiletries and other household commodities as well as in foods such as rice coated with mineral dust. With some of the mineral dusts in the environment being known carcinogens, or associated with other diseases, their identification and the determination of their sources are important aspects of environmental health.

Epidemiology of mesothelioma from estimated incidence

Malignant mesothelial tumors have been reported for at least 100 years but now appear more common. Between 1959 and 1976, 4539 fatal cases were reported from 22 countries. Evidence suggests that the annual incidence in Canada since 1965 has been about 10 per million in males aged 45 years and over but much lower at younger ages and in females. Ratios were calculated for cases observed in population surveys to numbers expected from Canadian experience. In nine countries with data, ratios ranged from 0.8 to 2.1; in certain cities, mainly with shipyards, ratios were much higher, many around 7 and some above 20. Two hundred and sixty-eight cases were reported in occupational surveys: Proportional mortality rates ranged from 5.2 to 8.8% in insulators, 0.8 to 6.9% in asbestos factory workers, and 0 to 0.19% in anthophyllite or chrysotile miners and millers, compared with 0.03 to 0.06% in general populations. Rates could not be calculated for crocidolite, but most cases in production workers were associated with this fiber type. The evidence suggests a gradient in mesothelioma-inducing potential, by type of fiber, from crocidolite down to chrysotile and anthophyllite. The special hazards of insulation and shipyard work are still not fully explained.

A Comparative Study of Thermal Effects on Surface and Structural Parameters of Natural Californian and Quebec Chrysotile Asbestos up to 700°C

AbstractThe effect of heat treatment on surface area, pore volume, pore size distribution, physical and chemical structure up to 700°C have been studied on samples of naturally occurring chrysotile minerals from California and Quebec. Techniques used included thermogravimetric analysis, low-temperature nitrogen adsorption, electron microscopy, X-ray powder and electron diffraction. The materials behaved similarly on heating to 100°C showing a 0.5% weight loss attributable to desorption of physisorbed water. At 500°C, Quebec samples retained the chrysotile crystal structure while Californian samples were X-ray amorphous. Forsterite was formed by dehydration of both chrysotiles at 700°C; the greater stability of the Quebec samples to this process is explained by the presence of brucite as an impurity which enters into stray solid-solid interactions with the chrysotile.

The zeta-potentials of natural and synthetic chrysotiles

Different specimens of the asbestos mineral chrysotile show widely different zeta-potentials. Strongly positive values are found with samples containing an excess of magnesia in the form of brucite, Mg(OH) 2. Synthetic chrysotile and natural samples containing little or no brucite give moderately positive ζ-values over the pH range 3–11. Feebly positive or weakly negative natural chrysotiles are materials which have suffered weathering; and deliberate acid-leaching of any chrysotile ultimately leaves a strongly negative pseudomorph of silica gel. Since the pH and the ambient concentration of Mg 2+ ions near the surface are the main factors controlling ζ, and since chrysotile is readily susceptible to leaching in practically all aqueous media and does not come to a true ionic equilibrium in any practical time, the zeta-potential of an ideal chrysotile surface is a hypothetical concept. The results also explain the temporary colloidal stability of very dilute suspensions of chrysotile in weakly acidic media and the mutual coagulation of chrysotile and amosite slurries.

Effect of Milling on the Crystal Structures of Chrysotile and Other Serpentine Minerals

The most prominent peaks of chrysotile are the 002 and 004 reflections, and in dilute mixtures of chrysotile in talc they are the only peaks that can be detected. Milling of chrysotile markedly reduces these peak heights and areas, and generates a new, sharp peak at d = 2.52 A. Milling of other serpentine minerals also results in line broadening and integrated intensity decrease of the 002 and 004 lines; a weak d = 2.52 reflection is initially present and milling causes this to increase slightly in intensity, without any detectable line broadening. The variations in relative intensities of these peaks for different size-classified fractions of the several minerals after prolonged milling confirms that the d = 2.52 A reflection is due to a phase that is different from the starting material. Investigation of specimens held at various temperatures up to 1000°C shows that the consequences of milling cannot be attributed to local heating effects. It is confirmed that chrysotile is readily attacked and dissolved by 1 M HCl, whereas the other serpentine minerals are relatively inert to this reagent. In the case of extensively milled chrysotile, the acid treatment causes the 002 and 004 peaks to weaken and eventually disappear, but the d = 2.52 A peak remains unaffected.

Dust-fiber relationships in the Quebec chrysotile industry.

Epidemiological studies of Quebec chrysotile miners and millers have related various indices of health to dust exposure, as measured with the midget impinges The interpretation of these relationships in terms of fiber necessitates the conversion of midget impinger (particle + fiber) counts to membrane filter (fiber) equivalents. An investigation in which 87 side-by-side midget impinger-membrane filter samples were taken at five mines and mills showed that the correlation was poor and no single conversion factor was justified. Until more detailed information on the relationships between midget impinger and membrane filter counts can be obtained, it is recommended that safety standards, at least in this industry, should continue to be based on dust counts, for which there is considerable epidemiological support, rather than on fiber counts, for which there is no direct evidence.

Transmission electron microscopy standards for asbestos

Abstract Electron micrographs and selected area electron diffraction patterns of all six recognized asbestos minerals (chrysotile, amosite, anthopyllite, crocidolite, tremolite and actinolite) are shown. These were all produced with the same parameters on one electron microscope and using the same sample preparative techniques. X-ray crystallographic and chemical data for the six asbestos minerals from various sources in the literature are also given. It is hoped that all the data may prove useful as a comparison to other researchers involved in identifying submicroscopic asbestos fibres.

Kinetic study of dissolution of asbestos fibers in water

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.

The Digestion of Lung Tissue for Mineral Dust Recovery

Methods for recovery of inhaled mineral dusts, from lung tissue, with minimal physical damage are suggested. Clorox solution. Hydroxide of Hyamine, and hydrogen peroxide were considered for digestion of lung tissue. Contact of these reagents with a group of minerals (quartz, chrysotile, amosite, and calcite) revealed that Clorox solution and Hydroxide of Hyamine have the least effect on the minerals. Coal dust was more easily separated from Clorox than from the Hydroxide of Hyamine reagent in digestions of lung tissue containing particles of coal, clay, and mica. However, Clorox solution was not suitable for extraction of coal dusts, owing to apparent oxidation. Both reagents seemed unreactive with the clay and micas. Preliminary tests involving low-temperature (<200°C) ashing off lung tissue in oxygen—plasma indicated that this method could be suitable for recovery of certain minerals.

Planar organosilicon polymers

AbstractWork on two sheet organosilicon polymers, one derived from the mineral chrysotile and the other from the mineral apophyllite, is described. This work provides direct evidence that both these polymers are composed of sheets. In addition, it shows that in the chrysotile‐derived polymer the sheets curl into scrolls, and that in the apophyllite‐derived polymer the sheets are essentially flat.