silicon and Mesothelioma

Approximately three million workers in the United States are estimated to be exposed to silica, man-made mineral fibers, and asbestos. The lung is the primary target organ of concern. Each of these substances is composed predominantly of silicon and oxygen; asbestos and silica are crystalline, and asbestos and man-made mineral fibers are fibers. Man-made mineral fibers and asbestos are used as insulating agents, with the former having generally replaced the latter in recent years. Silica is used in foundries, pottery, and brick making, and is encountered by miners. A meta-analysis of 16 of the largest studies with well-documented silica exposure and low probability of confounding by other occupational exposures, indicates a relative risk (RR) of 1.3 (95 percent confidence interval [CI] = 1.2-1.4). Lung cancer risks are highest and most consistent for silicotics, who have received the highest doses (RR = 2.3, CI = 2.2-2.4, across 19 studies). The data for mineral fibers continue to support the International Association for Research on Cancer's 1988 judgment that mineral fibers are a possible human carcinogen (Group 2B). Recent epidemiologic studies provide little evidence for lung carcinogenicity for either glass wool or rock/slag wool. Ceramic fibers, a much less common exposure than glass wool and rock/slag wool, are of concern because of positive animal studies, but there are insufficient human data. Regarding asbestos, its carcinogenicity for the lung and mesothelium is well established. With regard to the controversy over chrysotile and mesothelioma, the data suggest chrysotile does cause mesothelioma, although it may be less potent than amphibole asbestos.

Topics: Animals; Asbestos; Asbestos, Serpentine; Carcinogens; Ceramics; Confidence Intervals; Confounding Factors, Epidemiologic; Construction Materials; Crystallization; Disease Models, Animal; Glass; Humans; Lung Neoplasms; Mesothelioma; Meta-Analysis as Topic; Mineral Fibers; Mining; Occupational Diseases; Occupational Exposure; Oxygen; Probability; Risk Factors; Silicon; Silicon Dioxide; Silicosis; United States

Consideration of the human epidemiology of diseases arising from exposure to naturally occurring and man-made mineral fibers encompasses the several forms of asbestos (chrysotile, crocidolite, amosite, anthophyllite, tremolite-actinolite), other naturally occurring silicates (talc, sepiolite, erionite, attapulgite, vermiculite, and wollastonite), and man-made mineral fibers (glass continuous filament, glass/rock/slag insulation wools, ceramic and other refractory fibers, and glass microfibers). The diseases arising from exposures to some of these fibers include pleural thickening (plaques, diffuse pleural thickening, and calcification), pulmonary fibrosis, lung cancers, mesothelioma of the pleura and peritoneum, and other cancers). Risk factors important in assessing these diseases include assessment of latency, duration of exposure, cumulative exposure, fiber origin and characteristics (length and diameter), other possible confounding occupational or environmental exposures, and smoking. Methodological issues commonly presenting problems in evaluation of these data include assessment of the adequacy of environmental exposures, particularly in regard to fiber identification, distribution, and concentration over the duration of exposure, and the adequacy of study design to detect health effects (disease frequency, latency, and cohort size). Research priorities include further assessment and standardization of pleural thickening relative to fiber exposure, uniform mesothelioma surveillance, further epidemiological assessment of certain silicate and man-made mineral fiber cohorts with emphasis given to assessment of tremolite and small diameter glass and ceramic fibers. Further assessment of possible health risks of the general public should await improved definition of relevant fiber exposure in ambient air.

Topics: Asbestos; Asbestosis; Humans; Lung Neoplasms; Mesothelioma; Minerals; Neoplasms; Pleural Diseases; Respiratory Tract Diseases; Silicon

Mesothelioma is a malignant tumor mainly correlated to occupational asbestos exposure. Rare reports describe its occurrence also in animals, mainly linked to asbestos in the environment. Asbestos exposure is demonstrated by the appearance of characteristic histological hallmarks: asbestos containing ferruginous bodies that are iron-based structures forming around fibers and also other dust particles. Here we present a clinical case of a suspect of mesothelioma in the peritoneum of a dog with parallel histological observation of ferruginous bodies. To possibly correlate the dog tumor to environmental exposure, we performed X-ray fluorescence (XRF) analyses at two different synchrotrons to resolve the ferruginous bodies' composition. While the histological examination diagnoses a tubulo-papillary mesothelioma, the XRF analyses show that ferruginous bodies contain Si particles, resembling formations of exogenous origin; however, the morphology is unlikely that of asbestos fibers. We speculate that the peritoneal mesothelioma of this dog could be related to environmental exposure to non-asbestos material.

Topics: Animals; Asbestos; Dogs; Environmental Exposure; Immunohistochemistry; Iron; Lung; Lung Neoplasms; Male; Mesothelioma; Mesothelioma, Malignant; Peritoneal Neoplasms; Silicon; Spectrometry, X-Ray Emission; Synchrotrons

Conflicting data are found in the literature concerning the carcinogenic potency of attapulgite. We tested the carcinogenic potency of French attapulgite in rats, and compared it with 2 chrysotile samples: Rhodesian UICC (Ch A) and short Canadian fibres (Ch C). The mean length of the fibres was 0.77 micron (attapulgite), 3.21 microns (Ch A) and 1.25 microns (Ch C). The mean diameter was 0.06 micron in the 3 samples. The particles (20 mg) in saline were inoculated into the pleural cavity of Sprague-Dawley rats allowed to survive for their full lifespan. The incidence rates of mesothelioma were: 0% (saline controls), 0% (attapulgite), 19% (ChC) and 48% (Ch A). In vitro studies were carried out using cultures of rat pleural mesothelial cells (RPMC). Attapulgite and Ch C did not modify cell growth except at high doses of 10 micrograms/cm2. Unscheduled DNA synthesis (UDS) was detected using [3H]thymidine incorporation in confluent RPMC (GoG1 arrested) and a scintillation method. UDS was stimulated with either Ch A or Ch C at doses ranging from 2 to 10 micrograms/cm2. In contrast, attapulgite did not significantly enhance [3H]thymidine incorporation at doses ranging from 2 to 20 micrograms/cm2. The results show that the attapulgite tested here had no carcinogenic potency. The in vivo and in vitro reactivity of the fibres used in this experiment might perhaps be related to the fibre size; however, other parameters may also be important.

Topics: Animals; Asbestos; Asbestos, Serpentine; Carcinogens; Cells, Cultured; DNA Replication; Magnesium; Magnesium Compounds; Male; Mesothelioma; Particle Size; Pleura; Pleural Neoplasms; Rats; Rats, Inbred Strains; Silicon; Silicon Compounds

The carcinogenicity of several samples of mineral fibers was tested following injection of 20 mg in the pleural cavity of noninbred Sprague-Dawley rats. Three samples of chrysotile asbestos (mean length: 3.2, 2.1, and 1.2 micron) induced mesotheliomas at a rate of 48, 52, and 19%, respectively. The first sample was acid leached prior to intrapleural injection; in that group, the percentage of mesotheliomas was reduced to 25%. Treatment with amosite and crocidolite resulted in the occurrence of 57 and 56% of mesotheliomas. Acid-treatment of amphiboles did not significantly modify the percentage of mesotheliomas. When the Stanton's fiber dimensions were taken into consideration to correlate with mesothelioma incidence, the observed number of mesotheliomas in the chrysotile-treated animals was much lower than that expected, suggesting that other fiber parameters (chemistry, physicochemistry) play a role in the carcinogenicity. Attapulgite fibers (mean length: 0.77 micron) did not induce tumor, and the mean survival time was of the same order as that observed in the control groups. The injection of quartz resulted in no mesothelioma but did result in 6 malignant histiocytic lymphomas (17%) and 2 malignant schwannomas (6%). In vitro experiments did not show strong correlation between cytotoxicity and the carcinogenic potency of these minerals, but the qualitative cellular responses might give some indications on the fiber's potency. In addition, the in vitro effects of the fibers seem to be modulated by their size.

Topics: Animals; Asbestos; Asbestos, Serpentine; Cell Survival; Cells, Cultured; Macrophages; Magnesium; Magnesium Compounds; Male; Mesothelioma; Particle Size; Pleural Neoplasms; Pulmonary Alveoli; Rats; Rats, Inbred Strains; Silicon; Silicon Compounds

As the preliminary results of experimental studies on dust from the palygorskite group have led to some confusion a detailed description of the completed investigation is given for clarification. As in other experiments the biological effects have been shown to be associated with the physical characteristics of the fibres in these specimens. Samples of sepiolite and attapulgite from Spain and a single sample of palygorskite from the United Kingdom have been studied. Serious abnormalities were produced only by the palygorskite and one of the attapulgite dusts. The palygorskite is of no commercial interest and the attapulgite was from one small deposit and was used only in the preparation of drilling mud in the exploration of oil deposits.

Topics: Administration, Inhalation; Animals; Dust; Female; Magnesium; Magnesium Compounds; Magnesium Silicates; Male; Mesothelioma; Microscopy, Electron; Minerals; Pleural Neoplasms; Pulmonary Fibrosis; Rats; Rats, Inbred F344; Rats, Inbred Strains; Silicon; Silicon Compounds

Topics: Adenofibroma; Animals; Asbestos; Carcinogens; Female; Hyperplasia; Lymphatic Diseases; Lymphoma, Large B-Cell, Diffuse; Magnesium; Male; Mammary Neoplasms, Experimental; Mesothelioma; Minerals; Neoplasms, Experimental; Pleura; Pleural Neoplasms; Rats; Silicon; Time Factors; USSR

Topics: Animals; Asbestos; Carcinogens; Female; Glass; Mesothelioma; Neoplasms, Experimental; Nickel; Pleural Diseases; Pleural Neoplasms; Rats; Silicon; Stainless Steel