Asbestos: current knowledge and perspectives

Diseases due to asbestos inhalation are not only a concern for occupational physicians, but also for general practicioners and pneumologists. The real or supposed risk has extended beyond the factories employing "primary asbestos workers" to thousands of people exposed to this material or simply working in buildings insulated with asbestos. The spectrum of asbestos-related diseases has changed: asbestosis (parenchymal fibrosis due to asbestos) tends to disappear, whereas the incidence of pleural lesions, which can be associated with lower cumulative exposures, increases. Patients with asbestos related diseases do not die any more from respiratory failure but from late neoplastic complications, such as mesothelioma and lung cancer. The lack of interest and of training in occupational medicine leads to an underrecognition and an underestimation of cancers due to asbestos by the physicians. Recent progresses in CT imaging and evaluations of exposure to fibers through mineralogical analysis of lung samples have led to improve the diagnostic approach of fiber-related diseases.     

Asbestos in the air of public buildings: a public health risk?

The Environmental Health and Safety Council of the American Health Foundation has examined current estimates of cancer risks associated with the presence of asbestos-containing materials (ACM) in public buildings. The Council finds that even complete removal of asbestos from all of these buildings will provide no measurable benefit to public health. The removal of nonfriable ACM only can be postulated to protect the public against a small hypothetical risk that cannot be measured epidemiologically. Moreover, examination of the assumptions used in the risk assessment calculations leads to the conclusion that these small calculated risks are likely to represent overestimates. In recent surveys, the measured asbestos levels in indoor air cast some doubt on whether occupant exposure to asbestos levels are contributed to significantly by ACM even when some of the material is friable or in bad condition. Furthermore, the models used for cancer risk estimates assume no threshold level for cancer and conclude that any exposure is carcinogenic. This may be unjustified in light of information on the mechanisms for some asbestos-caused disease. Based on the best available data, it is very unlikely that cancer will result from indoor asbestos exposure, especially where ACM is well maintained.     

Lung cancer mortality in Casale Monferrato (Italy) and attributable risk to occupations in the asbestos-cement production

The study presents mortality rates for lung cancer in the town of Casale Monferrato, where the largest Italian asbestos cement-plant was located. Cases of lung cancer dying in 1989-94 were exhaustively searched for in the register of deaths. Each case of lung cancer has been identified as ever or never employed in the factory with a linkage to the rosters of employees in the plant. Women were also identified as ever or never married to an asbestos-cement worker. The number of person-years at risk for asbestos cement workers and their wives was measured on the basis of the most recent follow-up. Mortality rates were computed separately for those exposed (workers and wives of workers) and for those with no evidence of exposure. Mortality rates for non-exposed were similar to rates in Piedmont (the region where Casale is located). The relative risk (ever exposed vs. never exposed) was 2.8 among men and 2.1 among women. Attributable risk among the exposed was 64.5% for men and 53.1% for women while among the general population it was 18.1% for men and 13.2% for women. The study confirms the dramatic effect of occupational asbestos exposure in Casale Monferrato but does not suggest an increase in lung cancer mortality among people with no occupational activity in the asbestos-cement production.     

Contrast nephrotoxicity: predictive value of urinary enzyme markers in a rat model

Asbestos, proven to be carcinogenic in humans and animals, is reported to have no genotoxic effect. Asbestos workers have an increased risk of lung cancer, mesothelioma, and other tumours. Earlier findings showed that crocidolite can induce DNA strand breaks in cultured rat embryo cells as assessed by nick translation. We investigated DNA double-strand breaks in white blood cells (WBC) of ten workers occupationally exposed to asbestos. According to our results, obtained with neutral filter elution, individuals who had been exposed to asbestos fibres showed two to four times more DNA double-strand breaks (dsb) in white blood cells than ten non-exposed persons. The induced DNA fragments are of about 250 kb (compared to chromosomal DNA of Saccharomyces cerevisiae standard marker). Using additionally the chromosomal DNA protective method of agarose-plugs, DNA fragments in the range of 200 to 1000 kb have been found in the white blood cells of the same ten workers occupationally exposed to asbestos. In the white blood cells of non-exposed subjects no DNA fragments could be detected with this method. Compared to 51 non-exposed persons, elevated anti-ds DNA antibody concentrations were found in ten workers occupationally exposed to asbestos. The fact that workers occupationally exposed to asbestos have distinctly more double-strand breaks and anti-ds DNA antibodies could mean that an increased incidence of DNA-fragments may be an important indicator in the chronic effect of asbestos-associated carcinogenesis. Apparently, the chronic effects of asbestos observed here do not seem to be identical with that of previously reported acute in vitro effects.     

Disabilities resulting from traffic injuries in Barcelona, Spain: 1-year incidence by age, gender and type of user

Pleuropulmonary cancers are recognized asbestos-related diseases. Mesothelioma occurs almost uniquely in individuals exposed to asbestos whereas lung cancer is strongly associated with smoking. If the asbestos exposure is sufficient however, the incidence of lung cancer is higher than would be expected from the smoking effect alone. For lung cancer in asbestos workers, asbestosis is not a prerequisite for recognition as an occupation-related disease. The intensity and duration of exposure to asbestos are factors associated with higher risk of lung cancer. These factors can be estimated on the basis of the work history or, when necessary, by analyzing mineral dust from available lung tissues.     

Predictive tests of response to radiotherapy. Assessment and perspectives in 1997

A cohort study was carried out in order to evaluate the cancer risk in the asbestos-cement industry workers. The cohort consisted of workers employed in four asbestos-cement plants. One of those plants was established in 1924, the other three in the 1960s and 1970s. Currently only two of these plants continue their production. The plants used mainly chrysotile asbestos as well as crocidolite and amosite. Amphibolite asbestos was used before the mid-nineteen eighties in production of pressure pipes utilising about 15% of the total quantity of asbestos used. The measurements of the asbestos fibre concentration at work-sites have been taken occasionally since the mid 1980s, thus, the determination of a cumulative dose for individual persons in the cohort and the evaluation of the dose-effect relationship were not feasible. It could only be supposed that the concentrations at the preparatory work-site during first years of the plants' operation accounted for several tens fibres/cm3 in the production that employed the dry method. The cohort consisted of workers employed in the plant for at least three months between beginning of the plant during the post-war period, and 1980, that is during the period when amphibolite asbestos was in use. The retrospective observation was completed on 31 December 1991. The analysis of the death risk by causes was based on a standardized mortality ratios (SMRs) calculated using the person-years method. Statistical significance of SMRs was assessed by means of Poisson distribution one-sided test. The general population of Poland was used as the reference population to estimate the death risk. The cohort comprised 4,712 persons (3,563 males and 1,149 females). Of this number 4,500 persons (3,405 males and 1,095 females) were followed. The cohort availability were 95.5%. Male mortality, both total (473 deaths; SMR = 83) and due to malignant neoplasms (108 deaths; SMR = 86) was lower than in the general population. An excess of deaths from neoplasm of the pleura was by about 23 times higher (5 deaths; SMR = 2,288) and from neoplasm of the large intestine by two times higher (7 deaths; SMR = 214). Among females (41 deaths; SMR = 50) death risk was lower than in the reference population. At a low level of total mortality from neoplasms (13 deaths; SMR = 52) a statistically significant excess of deaths from neoplasm of the pleura (2 deaths; SMR = 2,112) was observed. In the plants investigated the analysis revealed a considerably diversified mortality from asbestos-related neoplasms. The incidence of pleura mesothelioma should be attributed to the use of considerable quantities of crocidolite asbestos and high concentrations of fibres in the air in plants II and IV, particularly during the first years after their establishment. In view of a long period of latency the excess of this neoplasm can be expected till 2020.     

Occupational exposure to chrysotile asbestos and cancer risk: a review of the amphibole hypothesis

OBJECTIVES: This article examines the credibility and policy implications of the "amphibole hypothesis," which postulates that (1) the mesotheliomas observed among workers exposed to chrysotile asbestos may be explained by confounding exposures to amphiboles, and (2) chrysotile may have lower carcinogenic potency than amphiboles. METHODS: A critical review was conducted of the lung burden, epidemiologic, toxicologic, and mechanistic studies that provide the basis for the amphibole hypothesis. RESULTS: Mechanistic and lung burden studies do not provide convincing evidence for the amphibole hypothesis. Toxicologic and epidemiologic studies provide strong evidence that chrysotile is associated with an increased risk of lung cancer and mesothelioma. Chrysotile may be less potent than some amphiboles for inducing mesotheliomas, but there is little evidence to indicate lower lung cancer risk. CONCLUSIONS: Given the evidence of a significant lung cancer risk, the lack of conclusive evidence for the amphibole hypothesis, and the fact that workers are generally exposed to a mixture of fibers, we conclude that it is prudent to treat chrysotile with virtually the same level of concern as the amphibole forms of asbestos.     

Occupational and geographical factors in the epidemiology of malignant mesothelioma

In most industrialised countries mortality from malignant mesothelioma has risen steeply since about 1950 and is likely to go on doing so well into the next century. This increase, which has lagged behind the level of asbestos use by some 30 or more years, is most evident in men but less clear in women. Amphibole asbestos fibre types, crocidolite in particular, carry the greatest risk and chrysotile the least. Studies in chrysotile miners and millers, in whom the overall frequency of mesothelioma is low suggest the risk is mainly determined by the presence of contamination with amphibole fibres in the tremolite series. There is wide variation in mesothelioma incidence geographically and occupationally. Regions with the highest rates are those where crocidolite is mined; within countries, dockyard areas are most affected, probably because of amphibole use for insulation in naval ships. Occupations at high risk, apart from crocidolite miners and millers, include shipyard and insulation workers and those employed in construction trades. Data on exposure-response are scanty although occupational cohort studies suggest that risk is related to both duration and intensity of exposure. More specific confirmation of an exposure-response relationship has been obtained from lung fibre analysis in a limited number of case-referent studies.     

Performance of Masonry Stone Buildings during the March 25 and 28, 2004 A?kale (Erzurum) Earthquakes in Turkey

This paper reviews the performance of stone masonry buildings during the March 25 and 28, 2004, A?kale (Erzurum) earthquakes. A?kale is a township located 35?km from Erzurum city in Turkey. A majority of the buildings in the affected region are built in masonry. Most of the masonry buildings were formed with random or coursed stone walls without any reinforcement supporting heavy clay tile roofing over wooden logs. A large number of such buildings were heavily damaged or collapsed. The cracking and failure patterns of the buildings are examined and interpreted relative to current provisions for earthquake resistance of masonry structures. The damages are due to several reasons such as site effect, location, and length of the fault, and the poor construction quality of the buildings. In addition to these reasons, the two earthquakes hit the buildings within three days, causing progressive damage. Low strength stone masonry buildings with mud mortar are weak against earthquakes, and should be avoided in high seismic zones.     

Asbestosis and silicosis

Interstitial fibrosis resulting from workplace exposure to asbestos and crystalline silica persists throughout the world despite knowledge of the causes and effective means for prevention. Asbestosis and silicosis occurrence is predictable among people overexposed to dusts in various industries and occupations such as mining, construction, manufacturing, and building maintenance. Asbestosis and silicosis are incurable and may be progressive even after dust exposure has ceased, therefore early recognition and supportive interventions are important. Although current disease is a result of past exposures, effective control of current workplace exposures is the only way to prevent continued occurrence of these potentially debilitating diseases. Physicians can contribute to this effort through accurate diagnosis and disease reporting.     

A multi-institutional study confirms the presence and expression of simian virus 40 in human malignant mesotheliomas

Exposure to the carcinogen asbestos is a major factor in the development of malignant mesothelioma. However, not all mesotheliomas are associated with asbestos exposure, and only a small minority of people exposed to asbestos develop mesothelioma. Therefore, the identification of the cofactors that render certain individuals more susceptible to asbestos or that cause mesothelioma in people not exposed to asbestos has been a major priority of the International Mesothelioma Interest Group. The possible association of SV40 with mesothelioma was recently discussed in a special session at the Fourth International Mesothelioma Interest Group Conference, and it was decided to conduct a multi-institutional study to independently verify the presence of this tumor virus in mesotheliomas. We report the results of this investigation: (a) DNA and protein analyses revealed SV40 sequences and SV40 large T antigen expression in 10 of 12 mesotheliomas tested (83%); and (b) electron microscopy demonstrated variable amounts of asbestos fibers in 5 (71%) of 7 corresponding lung tissues available for analysis. Our results demonstrate that SV40 DNA is frequently present and expressed in mesotheliomas in the United States. Because our data demonstrate that some patients test positive for both SV40 and asbestos, the possibility that these two carcinogens interact should be investigated in future studies.     

Alerting the general population to genetic risks: The value of health messages communicating the existence of genetic risk factors for public health promotion.

Background: Health messages alerting the public to previously unknown genetic risk factors for multifactorial diseases are a potentially useful strategy to create public awareness, and may be an important first step in promoting public health. However, there is a lack of evidence-based insight into its impact on individuals who were unaware of the existence of genetic risk factors at the moment of information exposure. Method: The authors conducted 3 experimental studies with health messages communicating information about genetic risk factors for salt sensitivity (Studies 1A and 1B) and heightened cholesterol (Study 2) compared with general information without reference to genetic risk factors as a between-subjects variable and risk perception and intention to engage in preventive behavior as dependent variables. Results: All 3 studies revealed lower perceived susceptibility among participants who received information on genetic risk factors, which was associated with lowered intentions to engage in preventive behavior. In Studies 1A and 1B, these effects were observed only for previously unaware individuals, whereas in Study 2, they were observed for the entire sample. Conclusion: Alerting the public to the existence of genetic risk factors may not necessarily be beneficial to public health. Public health promoters should be aware of the possible adverse effects of alerting the general population to genetic risk factors, and should simultaneously educate the public about the meaning and consequences of such factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retention of asbestos bodies in the lungs of welders

Examination of asbestos bodies (AB) retained in the lungs is a useful way of assessing past occupational exposure to this material. AB retention has been extensively studied in workers directly exposed to asbestos, but less so in those end users, such as welders, who use asbestos-containing products. We therefore retrospectively studied AB retention in 211 welders, for whom biological testing procedures had been requested by a chest physician, between 1988 and 1991. Optical microscopy of AB was performed on samples of sputum (40 subjects), bronchoalveolar lavage fluid (BAL) (147 subjects), and lung tissue obtained after thoracotomy (38 subjects). Information on previous jobs and exposure was obtained using a questionnaire (the mean duration of welding activities was 16.6 years). Eighty-two subjects (38.9%) had elevated lung retention of AB in all the samples studied. Significant AB retention occurred in only 30% of sputum samples, but in 40.1% of BAL samples and 39.5% of lung tissue samples. The duration of welding activities correlated with the density of AB in BAL or lung tissue (r = 0.31, p < 0.01 and r = 0.49, p < 0.05, respectively). On the basis of the questionnaire, only two of the welders with significant AB retention had other occupational exposure to asbestos. Our findings suggest that welding activities may increase lung retention of AB, and consequently might produce higher risks of fibrotic and/or malignant pulmonary diseases. These potential risks need to be brought to the attention of doctors; a longitudinal follow-up may also be warranted in such populations, even after individuals have ceased their welding jobs.     

Behavior and Design of Commercial Multistory Buildings Subjected to Blast

The behavior of nonmilitary buildings subjected to blast is considered. Case studies from World War II are described, as well as more recent events from the detonation of large vehicle borne devices in the Middle East, North America, and Europe. Conventional methods for nonseismic design are shown to lead to frames with overstrong beams connected together by relatively weak connections. This may explain much of the evidence from bomb damaged buildings in which building connections have been observed to fracture in a brittle manner when subjected to blast. The risk of progressive collapse may be minimized by strengthening beam to column connections located at close proximity to potential vehicle borne devices and a capacity design method for such strengthening is advocated.     

Mitigating Risk from Abnormal Loads and Progressive Collapse

A progressive collapse initiates as a result of local structural damage and develops, in a chain reaction mechanism, into a failure that is disproportionate to the initiating local damage. Such collapses can be initiated by many causes. Changes in building practices to address low probability/high consequence events and to lessen building vulnerability to progressive collapse currently are receiving considerable attention in the professional engineering community and in standard-writing groups in the United States, Canada, and Western Europe. Procedures for identifying and screening specific threat scenarios, for assessing the capability of a building to withstand local damage without a general structural collapse developing, and for assessing and mitigating the risk of progressive collapse can be developed using concepts of probabilistic risk assessment. This paper provides a framework for addressing issues related to low probability/high consequence events in building practice, summarizes strategies for progressive collapse risk mitigation, and identifies challenges for implementing general provisions in national standards such as ASCE Standard 7, Minimum design loads for buildings and other structures.     

Exposure-response analysis of risk of respiratory disease associated with occupational exposure to chrysotile asbestos

OBJECTIVES: To evaluate alternative models and estimate risk of mortality from lung cancer and asbestosis after occupational exposure to chrysotile asbestos. METHODS: Data were used from a recent update of a cohort mortality study of workers in a South Carolina textile factory. Alternative exposure-response models were evaluated with Poisson regression. A model designed to evaluate evidence of a threshold response was also fitted. Lifetime risks of lung cancer and asbestosis were estimated with an actuarial approach that accounts for competing causes of death. RESULTS: A highly significant exposure-response relation was found for both lung cancer and asbestosis. The exposure-response relation for lung cancer seemed to be linear on a multiplicative scale, which is consistent with previous analyses of lung cancer and exposure to asbestos. In contrast, the exposure-response relation for asbestosis seemed to be nonlinear on a multiplicative scale in this analysis. There was no significant evidence for a threshold in models of either the lung cancer or asbestosis. The excess lifetime risk for white men exposed for 45 years at the recently revised OSHA standard of 0.1 fibre/ml was predicted to be about 5/1000 for lung cancer, and 2/1000 for asbestosis. CONCLUSIONS: This study confirms the findings from previous investigations of a strong exposure-response relation between exposure to chrysotile asbestos and mortality from lung cancer, and asbestosis. The risk estimates for lung cancer derived from this analysis are higher than those derived from other populations exposed to chrysotile asbestos. Possible reasons for this discrepancy are discussed.     

Problems Associated with Removal of Asbestos

Asbestos has been a very useful construction material, and because of this has had widespread use. However, it can be harmful if not handled correctly or removed in a safe manner. The health hazards associated with asbestos exposure have been known since the early 1900s, however, it has only been within the past 10 yrs that serious consideration has been given to the removal of asbestos from buildings. Asbestos removal has been fraught with numerous problems. Some of these include the high cost of removal, changing and nonspecific regulations, various agencies claiming jurisdiction over the substance, lack of information about the seriousness of asbestos‐related diseases, and insurance‐liability considerations. This paper outlines some of the problems associated with asbestos removal and provides recommendations to ameliorate the situation.     

Current status of HIV infection in Yunnan Province of China

In cooperation with the Chinese Academy of Preventive Medicine and Yunnan Province Provincial Office for AIDS Control and Prevention, we studied the current status of HIV infection intravenous drug users (IVDUs) and other high risk groups in Yunnan province of China. As of the end of 1995, 1,807 HIV cases were officially reported (Positive rate was 0.6%), of which 1,278 (77.9%) were IVDUs, and 24 were their spouses. The majority of cases were found among the Dai minority male farmers near Ruili which borders on Myammar, but HIV also appears to be spreading among the Han people. HIV antibody positive rates among commercial sex workers, pregnant women and blood donors were 0.2%, 0.07% and 0.04%, respectively. A system for surveillance of HIV has been developed, but preventive strategies to cope with HIV epidemic are not sufficient. As HIV/AIDS is now a global issue, (1) the integration and coordination of such preventive strategies in cooperation with community health workers, (2) general health education for condom use promotion and (3) care of psychological vulnerable person such as IVDUs, should be developed.     

Strategies for Wind Damage Mitigation—Summary

Wind damage to buildings and structures in the United States costs approximately $4 billion a year, mostly to nonengineered buildings. Civil engineers should help identify structural problems (weak links) in these buildings and effective ways to correct the problem so that improved building codes and better construction practices can result in a reduction of damage. Strategies for mitigation involve many facets, such as educating the public that much can be done to reduce wind damage with minor improvement of buildings and minor cost increases; disseminating research findings and new knowledge to engineers, architects, builders, contractors, insurance companies, building code officials, and the public; incorporating key research findings into building codes and common practice; improving code enforcement; providing incentives through insurance‐premium reduction; and intensifying research to identify the most effective and economical ways to improve building performance. An international effort to share information and knowledge in wind‐disaster mitigation—the concept of International Decade of Disaster Mitigation, proposed by Dr. Frank Press, President of the National Academy of Science—should also be part of a global strategy.