[The preparation and characterization of fine dusts carried out in the Clinica del Lavoro di Milano in support of experimental studies]. / Preparazione e caratterizzazione di polveri fini effettuate nella Clinica del Lavoro di Milano a supporto di studi sperimentali.

This paper aims to illustrate the conditions selected at the Clinica del Lavoro of the University of Milan to prepare and analyze a large number of fine dust samples produced over a period of about 50 years, that were initially used for studies within the Clinic performed in its own facilities, and since 1956 were sent to other Italian and overseas laboratories (Luxembourg, UK, Germany, Norway, Sweden, South Korea, USA). The total quantity of material distributed (with maximum size 7-10 microns) was about 2 kg and consisted of the following mineral and artificial compounds: quartz, HF-treated quartz, tridymite, HF-treated tridymite, cristobalite, chromite, anthracite, quartz sand for foundry moulds, sand from the Lybian desert, vitreous silica, pumice, cement, as well small quantities of metallic oxides, organic resins, chrysotile, crocidolite, fibres (vitreous, cotton and polyamidic). About half of the entire quantity of dusts produced consisted of partially HF-treated tridymite. Initially, research on the etiology of silicosis used quartz dust samples, simply sieved or ventilated (consisting of classes finer than 0.04 mm, containing a 15-20% respirable fraction). From 1956 to 1960 the dusts were produced by manual grinding in an agate mortar, below about 10 microns, starting from quartz from Quincinetto (near Ivrea, Province of Turin), containing about 99.5% quartz: particle size and composition were checked using an optical-petrographic technique, with identification of the free and total silica content. Subsequently, the dusts used for biological research were obtained by grinding coarse material with a cast iron pestle and planetary mills, agate and corundum jars. The grinding products were sized by means of centrifugal classification, using the selector developed by N. Zurlo, ensuring control of dust size both optically and by means of wet levigators and hydraulic classifiers (in cooperation with the Institute of Mines of Turin Polytechnic School). After 1990 pestles and rotating drum mills with autogenic grinding load were used for grinding: the size of the treated samples was reduced to 0.05 mm and an extremely fine fraction was extracted, smaller than 7-10 microns, which was used for pneumoconioses research. The characterization of the dust produced was in any case achieved by means of preliminary examination under the optical microscope (polarized light, sometimes supplemented with phase contrast), followed by quantitative analysis using chemical/petrographic, chemical diffraction or, more commonly, petrographic/diffraction techniques. Microscopic examination, if necessary supplemented with photo-micrography, was also used for particle size control, for numerical counting and subsequent reference to weight proportion. For all operational procedures the essential data on instruments and methods are reported. During studies on production, separation of fine dusts and their characterization, partly performed with support from the European Community (EEC/European Coal and Steel Commission), the following topics in particular were addressed: connections between particle size and free silica content in the measurable dust size fraction of the grinding products and in airborne dusts; characteristics of the dusts and risk indices in Italian iron and pyrite mines; possibility of abatement of the ultrafine classes of airborne dusts in pneumatically filled stopes by the addition of salts; comparison of the latest dust selectors used within the European Community; influence of the grinding methods on the results of fibrous and soft mineral measurement using X-ray diffraction analysis.

[Diffractometric analysis of non-pulverized coherent materials]. / Analisi diffrattometrica su materiali coerenti non polverizzati.

The paper presents an initial series of results of diffractometric assays, carried out by directing an X-ray beam on glossy sections of coherent, rigid materials (asbestos-cement blocks, insulation panels, ceramic tiles). The study, which is an introduction to another concerning crystalline rocks, is aimed at assessing the possibility of increasing the diffracted intensities, using samples with high mass concentration, avoiding the consequences of loss of crystallinity following extremely fine grinding, which is considerable especially when compounds having very different mechanical resistance and elastic modulus are simultaneously present. The assays carried out demonstrated the validity of the method for qualitative analysis, whereas in quantitative terms the diffracted intensities were mainly increased (up to 40%), but not in a manner directly connected with the type and macro- and microscopic structure of the compounds under study. Thus, the method guarantees an effective increase in sensitivity only in certain cases.

[Sensitivity, precision and resolution of the optical microscope in the study of environmental pollution by asbestos fibers]. / Considerazioni sulla sensibilità, precisione e risoluzione del microscopio ottico nello studio dell'inquinamento dell'ambiente di vita da fibre di amianto.

The authors comment on the methods and equipment used in two Italian laboratories for sampling and microscopic phase contrast analysis of asbestos and other respirable fibres in the air of the general environment, i.e., the Dust Analysis Laboratory, Industrial Hygiene and Toxicology Department of the Institute of Occupational Health (Clinica del Lavoro), University of Milan and the Technical Microscopy Laboratory, Ground Resources and Land Control (Georisorse e Territorio) Department of Turin Polytechnic, which use identical methods. Airborne dust samples are taken with personal samplers, 1 l/min air flow (sample duration 4-8 h), filtering air on 25 mm diameter, 0.8 micropore cellulose filters (about 300 mm total net surface of dust deposit). The following equipment is used for counting and analysis of fibres: a) Clinica del Lavoro, Milan: Polyvar Reichert-Jung microscope, 500 magnitudes, Zernike positive phase contrast; numerical counting on 100 whole ocular fields, equal to 6.38% of the total net surface of dust deposit on the membrane; b) Turin Polytechnic: Leitz Ortholux microscope, 500 magnitudes, Heine and Zernike phase contrast with mean standard contrast; numerical counting on square grid, with explored surface total equal to 1.68% of the total net surface of dust deposit on the membrane. Measurements performed: Clinica del Lavoro, Milan: 2,980 since 1960; Turin Polytechnic: 875 since 1965. The sensitivity of the methods for counting airborne fibres is discussed, concluding that the methods used by the two laboratories have a sensitivity between 0.05 and 1.6 fibre/litre of air, according to the overall dustiness of the environment under study. Analysis of the accuracy of the optic determinations, based on the repeated counts, shows a repeatability of 0.4 (40%) within 95% confidence limits. A resolution power of 0.35 microns is reported; however, the possibility exists (and is normally achieved in analytical practice in both laboratories) of identifying and counting fibrous elements up to 0.1-0.3 microns in diameter; this is possible in particular conditions, i.e., when there is a marked difference between the "mean" refraction index of the fibres and that of the diaphanizing liquid. For qualitative determinations of the various types of asbestos, however, analyses are limited to diameters greater than 0.5-0.8 microns, since it is necessary to be able to assess optical properties (refraction indices, basically). In the concluding discussion, comments and bibliographic references are also given concerning the comparisons with possibilities of studying fibrous particulate matter via electron microscopy.

[Refinement of the methods of diffractometric analysis in relation to the preparation surface exposed to X rays]. / Affinamento delle modalità di analisi diffrattometrica in rapporto alla superficie di preparato esposta ai raggi X.

The aim of the study was to assess the degree of X-ray diffractometric response using preparations having a surface exposed to X-rays other than 2 cm2, which is standard for sample-holders supplied with a goniometer, coupled to a commercially available analytic apparatus. Two samples of commercial talc were examined with dust size below 30 microns (and having different content of "respirable" or "alveolar" dust classes), as regards chlorate, talc and asbestos constituents and quartz. Twelve different experimental conditions of the preparations permitted X-ray exposure of surfaces between 6.25 and 500 mm2. For the low angle positions it was possible to obtain a substantial improvement in the overall diffractometric response by increasing the surface of the preparations; however, in each case, a reduction in the surface produced, in addition to a better definition of the peaks, an increase in the diffracted intensities per unit of surface of the preparation; this is clearly related to the collection spectrum of the radiant energy of the incident beam in space, and leads to the possibility of reducing to an order of magnitude of milligrams the mass of samples that can still be submitted to qualitative and quantitative diffractometric analysis.