[Optical and electron microscopic methods for counting respirable fibers of asbestos: considerations on relative standards]. / Osservazioni sulle metodiche microscopiche ottiche ed elettroniche per il conteggio delle fibre respirabili di amianto: considerazioni sulla relativa normativa.

The paper reports experience of the use of optical and electronic microscope methods for assessment of the concentration of airborne asbestos fibres and their respective identification. The results described are derived from the extensive experience of three Italian university institutes, which have used optical methods of observation for over 35 years (phase contrast technique, at times associated with the use of polarized light) and have examined altogether about 11,000 samples of airborne dust and fibres. After considering in more detail certain values of asbestos fibre concentrations in various environments, measured parallely with optical and electronic microscope, and assessing their basic comparability, attention is drawn to a number of ambiguities and contradictions contained in Law D.M. 6/9/1994, which tends to discourage the use of the optical microscope (especially using the phase contrast technique), without however taking into consideration the improved cost/benefit ratio in the assessment of respirable asbestos fibres present in working and living environments. On this topic, attention is drawn to the fact that the limits for occupational exposure to asbestos, proposed and/or adopted in the international scientific literature, are based on the numerical count of fibres with the optical microscope using the phase contrast technique (MOCF).

[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.

[Corpuscular pollutants: the problem of particles and fibers (optic microscopy)]. / Inquinamenti corpuscolati: il problema delle particelle e delle fibre (microscopia ottica).

The "Clinica del Lavoro" had already begun work on dust pollution in the working environment in the mid-1930's but was only able to study the problem more in depth at the beginning of the 1950's when the Industrial Hygiene Laboratory was established under the fortunate direction of Professor Nicola Zurlo. The first research studies in that period were aimed at the correct choice of the most suitable sampling equipment and analytical methods for assessment of the extent of such types of pollution. The results achieved in these initial studies, the experience acquired in the field and further, more detailed research enabled Professor Zurlo to develop and perfect new types of sampling instruments that were more appropriate to the goals it was desired to achieve and these instruments are still widely used to-day. The paper also considers the evolution of analytical methods using the optical microscope for determination of the concentration of particles and fibres, most of which were developed and perfected in our Laboratory, up to the present time. It is stressed that phase contrast microscopy is still indispensable for dust analysis and still offers ample scope for research in the field of artificial fibres that have recently been put on the market, even though the electron microscope is now the only acceptable solution for research in living environments.

Effects derived from long-term low-level chromium exposure in ferro-alloy metallurgy. Study of absorption and renal function in workers.

Ferro-chromium production is based on the use of chromium oxide (III) and it is generally accepted that chromium in this form is not able to cross biological barriers. However, the data on the toxic and carcinogenic effects of hexavalent chromium in man are now firmly established. Some studies have questioned these data, calling for a clarification as to whether exposure to trivalent chromium can also produce human effects, perhaps with different latency time. A study was carried out on the exposure conditions (type and degree) in a ferro-chromium foundry that had been in operation since 1972. The absorption levels in the working population of the foundry, and the possible toxic effects on the kidney have been investigated. A total of 236 workers (142 employed in production departments, 33 office workers and 61 sub-contractor employees) were examined with measurement of the indicators of dose (urinary-chromium) and of effect on the kidney (albumin, retinol binding protein, and renal tubular epithelium antigens in the urine). Environmental hygiene measurements showed relatively low values of total chromium in the air (always less than 0.160 mg/m3). Hexavalent chromium was absent or, if present, at levels below the sensitivity of the analytical method used (0.001 mg/m3). The values of urinary chromium measured at the beginning and at the end of the working day and at the end of the work shift were always less than 5 micrograms/g creatinine, which has been proposed as a biological limit in chromium exposure. However, differences were observed between groups of subjects employed on different jobs, which is indicative of an absorption process varying according to the degree of exposure. The indicators of effect did not reveal any renal impairment, even early, that could be attributed to the toxic action of chromium.