Hand-spinning chrysotile exposure and risk of malignant mesothelioma: A case-control study in Southeastern China.

While chrysotile has been commonly used by Chinese textile industry for many years, investigations on the association of chrysotile exposure with risk of mesothelioma in China are scarce. We conducted a case-control study in a county located at Southeastern China, including 46 cases and 230 individually matched controls. A semi-quantitative method based on experts' assessment was used for evaluating hand-spinning chrysotile exposure. Conditional logistic regression models were used to assess the association of asbestos exposure with risk of mesothelioma. We found that hand-spinning chrysotile exposure was associated with significantly elevated risk of mesothelioma, reaching OR =10 (95% CIs: 1.4-65) for possible exposure and 64 (12-328) for definite exposure. Our data suggested a dose-response relationship of chrysotile exposure duration with risk of mesothelioma, reaching 28 (6-134) for <6 years, 51 (11-247) for 7-17 years and 56 (9-351) for ≥18 years. A dose-response relationship of cumulative exposure index (CEI) with risk of mesothelioma was found, reaching 28 (6-137) for CEI at 0-0.5 fibers per milliliter years (f/mL-year), 36 (7-184) for CEI at 0.5-28.6 f/mL-years and 79 (14-451) for CEI > 28.6 f/mL-years. We found a dose-response relationship of chrysotile exposure duration and CEI with risk of mesothelioma in Southeastern China, adding valuable information on health hazards of chrysotile exposure in China where chrysotile is still used nationwide.

Cancer mortality in Chinese chrysotile asbestos miners: exposure-response relationships.

OBJECTIVE: This study was conducted to assess the relationship of mortality from lung cancer and other selected causes to asbestos exposure levels. METHODS: A cohort of 1539 male workers from a chrysotile mine in China was followed for 26 years. Data on vital status, occupation and smoking were collected from the mine records and individual contacts. Causes and dates of death were further verified from the local death registry. Individual cumulative fibre exposures (f-yr/ml) were estimated based on converted dust measurements and working years at specific workshops. Standardized mortality ratios (SMRs) for lung cancer, gastrointestinal (GI) cancer, all cancers and nonmalignant respiratory diseases (NMRD) stratified by employment years, estimated cumulative fibre exposures, and smoking, were calculated. Poisson models were fitted to determine exposure-response relationships between estimated fibre exposures and cause-specific mortality, adjusting for age and smoking. RESULTS: SMRs for lung cancer increased with employment years at entry to the study, by 3.5-fold in ≥ 10 years and 5.3-fold in ≥ 20 years compared with <10 years. A similar trend was seen for NMRD. Smokers had greater mortality from all causes than nonsmokers, but the latter also had slightly increased SMR for lung cancer. No excess lung cancer mortality was observed in cumulative exposures of <20 f-yrs/ml. However, significantly increased mortality was observed in smokers at the levels of ≥ 20 f-yrs/ml and above, and in nonsmokers at ≥ 100 f-yrs/ml and above. A similarly clear gradient was also displayed for NMRD. The exposure-response relationships with lung cancer and NMRD persisted in multivariate analysis. Moreover, a clear gradient was shown in GI cancer mortality when age and smoking were adjusted for. CONCLUSION: There were clear exposure-response relationships in this cohort, which imply a causal link between chrysotile asbestos exposure and lung cancer and nonmalignant respiratory diseases, and possibly to gastrointestinal cancer, at least for smokers.

Cause-specific mortality in a Chinese chrysotile textile worker cohort.

Chrysotile asbestos has continued to be mined and used in China, but its health effects on exposed workers have not been well documented. This study was conducted to give a complete picture about cause-specific mortality in Chinese asbestos workers. A cohort of 586 males and 279 females from a chrysotile textile factory were prospectively followed for 37 years. Their vital status was identified, and the date and underlying cause of death were verified from death registry. Cause-specific standardized mortality ratios by gender were computed with nationwide gender- and cause-specific mortality rates as reference. Male workers were 11 years older, and had 6 years longer exposure duration than females; 79% in males and 1% in females smoked. In males, the mortality rate of all cancers doubled; both larynx and lung cancer were four-fold, and mesothelioma was 33-fold. In females, there was slightly excess mortality from lung cancer and all cancers, and significant increase in mesothelioma and ovarian cancer. Other significantly increased mortality was seen from cancers of thymus, small intestine and penis in males, and cancers of bone and bladder in females. In addition to asbestosis, mortality from pulmonary heart disease was significantly elevated in both genders. The data confirmed significantly excess mortality from mesothelioma in either gender, lung and larynx cancers in males, and ovarian cancer in females. A gender difference in mortality from lung cancer and all cancers could be mainly due to the discrepancies in age, exposure duration and smoking between the male and female workers.

Exposures from chrysotile-containing joint compound: evaluation of new model relating respirable dust to fiber concentrations.

The potential for fiber exposure during historical use of chrysotile-containing joint compounds (JCC) has been documented, but the published data are of limited use for reconstructing exposures and assessing worker risk. Consequently, fiber concentration distributions for workers sanding JCC were independently derived by applying a recently developed model based on published dust measurements from sanding modern-day (asbestos-free) joint compound and compared to fiber concentration distributions based on limited historical measurements. This new procedure relies on factors that account for (i) differences in emission rates between modern-day and JCC and (ii) the number of fibers (quantified by phase contrast microscopy [PCM]) per mass of dust generated by sanding JCC, as determined in a bench-scale chamber study using a recreated JCC, that convert respirable dust concentrations to fiber concentrations. Airborne respirable PCM-fiber concentration medians (and 95% confidence intervals) derived for output variables using the new procedure were 0.26 (0.039, 1.7) f/cm(3) and 0.078 (0.013, 0.47) f/cm(3) , and corresponding total fiber concentrations were 1.2 (0.17, 9.2) f/cm(3) and 0.37 (0.056, 2.5) f/cm(3) , in enclosed and nonenclosed environments, respectively. Corresponding estimates of respirable and total PCM fiber concentrations measured historically during sanding of asbestos-containing joint compound-adjusted for differences between peak and time-weighted average (TWA) concentrations and documented analytical preparation and sampling artifacts-were 0.15 (0.019, 0.95) f/cm(3) and 0.86 (0.11, 5.4) f/cm(3) , respectively. The PCM-fiber concentration distributions estimated using the new procedure bound the distribution estimated from adjusted TWA historical fiber measurements, suggesting reasonable consistency of these estimates taking into account uncertainties addressed in this study.

[Do advers health effects of chrysotile and amphibole asbestos differ?]. / Gibt es Unterschiede in den gesundheitsschädlichen Wirkungen von Chrysotil- und Amphibol-Asbest?

Due to the current query whether the predominantly used chrysotile (white) asbestos comprises health risks we performed a literature search including in vitro and animal experiments as well as epidemiological studies.As shown by epidemiological studies chrysotile causes less pleural fibrosis and mesotheliomas when compared with other asbestos types. However, its otherwise inflammatory, toxic, carcinogenic, and fibrosis-inducing effects correspond to those of other occupationally relevant asbestos types. This is based on clinical, animal as well as on in-vitro findings. This means that denying a causal relationship, e. g. in a case with lung fibrosis (= asbestosis) or lung cancer with an asbestos load of 25 fiber-years in the absence of identification of a significant concentration of asbestos fibers or asbestos bodies in the lung (see so-called "hit and run" phenomenon), contradicts the medical-scientific knowledge.

Airborne asbestos exposures associated with work on asbestos fire sleeve materials.

Asbestos-containing fire sleeves have been used as a fire protection measure for aircraft fluid hoses. This investigation was conducted to determine the level of airborne asbestos fiber exposure experienced by mechanics who work with fire sleeve protected hoses. Duplicate testing was performed inside a small, enclosed workroom during the fabrication of hose assemblies. Personal air samples taken during this work showed detectable, but low airborne asbestos fiber exposures. Analysis of personal samples (n=9) using phrase contract microscopy (PCM) indicated task duration airborne fiber concentrations ranging from 0.017 to 0.063 fibers per milliliter (f/ml) for sampling durations of 167-198 min, and 0.022-0.14 f/ml for 30 min samples. Airborne chrysotile fibers were detected for four of these nine personal samples, and the resulting asbestos adjusted airborne fiber concentrations ranged from 0.014 to 0.025 f/ml. These results indicate that work with asbestos fire sleeve and fire sleeve protected hose assemblies, does not produce regulatory noncompliant levels of asbestos exposure for persons who handle, cut and fit these asbestos-containing materials.

Chrysotile biopersistence: the misuse of biased studies.

Although it is widely accepted that exposure to any asbestos type can increase the likelihood of lung cancer, mesothelioma, and non-malignant lung and pleural disorders, manufacturers and some chrysotile miners' unions contend that chrysotile either does not cause disease or that there is insufficient evidence to reach a conclusion. At the same time, Dr. D.M. Bernstein has published several animal studies, financed by the Québec Chrysotile Institute, to determine chrysotile biopersistence in the lungs. Bernstein's study protocol induces a very short fiber half-life, from which he concludes weak chrysotile carcinogenicity. Bernstein's findings contradict results obtained by independent scientists. Bernstein's results can only be explained by an aggressive pre-treatment of fibers, inducing many faults and fragility in the fibers' structure, leading to rapid hydration and breaking of long fibers in the lungs.

Long-term mortality from pleural and peritoneal cancer after exposure to asbestos: Possible role of asbestos clearance.

Models based on the multistage theory of carcinogenesis predict that the rate of mesothelioma increases monotonically as a function of time since first exposure (TSFE) to asbestos. Predictions of long-term mortality (TSFE >or= 40 years) are, however, still untested, because of the limited follow-up of most epidemiological studies. Some authors have suggested that the increase in mesothelioma rate with TSFE might be attenuated by clearance of asbestos from the lungs. We estimated mortality time trends from pleural and peritoneal cancer in a cohort of 3,443 asbestos-cement workers, followed for more than 50 years. The functional relation between mesothelioma rate and TSFE was evaluated with various regression models. The role of asbestos clearance was explored using the traditional mesothelioma multistage model, generalized to include a term representing elimination over time. We observed 139 deaths from pleural and 56 from peritoneal cancer during the period 1950-2003. The rate of pleural cancer increased during the first 40 years of TSFE and reached a plateau thereafter. In contrast, the rate of peritoneal cancer increased monotonically with TSFE. The model allowing for asbestos elimination fitted the data better than the traditional model for pleural (p = 0.02) but not for peritoneal cancer (p = 0.22). The risk for pleural cancer, rather than showing an indefinite increase, might reach a plateau when a sufficiently long time has elapsed since exposure. The different trends for pleural and peritoneal cancer might be related to clearance of the asbestos from the workers' lungs.

The defence of chrysotile, 1912-2007.

The commercial exploitation of asbestos may be dated from the late 1870s, when Canada was the major world source. Reports of severe and fatal respiratory disease in workers in asbestos factories appeared in Britain (1898, 1906), and in France (1906) and Italy (1908). In 1912 the Canadian Department of Labour denied that the health of Quebec's millers and miners was affected. A series of denials appeared for over 40 years, until in 1955 a Thetford Mines medical officer reported finding that between 1945 and 1953, among some 4,000 asbestos workers 128 had asbestosis of various degrees of severity, 121 diagnosed radiographically, and 33 confirmed at autopsy. Although a committee of inquiry into health in the asbestos industry (1976), and a Royal Commission on health and safety arising in the use of asbestos in Ontario (1984) confirmed that disease had occurred, these findings were to have no adverse effects on asbestos exports. Rather, the inquiries constituted elements in the industry's successful public relations exercise that continues to operate to this day. Even when an increasing number of national bodies have legislated for total bans on asbestos use, a policy with which all the international bodies concerned with public health agree, the Canadian PR apparatus continues to be able to call on physicians and scientists prepared to oppose the consensuses reached by the independent advisors to these bodies.

Asbestos fibers in ovarian tissue from Norwegian pulp and paper workers.

An elevated risk of ovarian cancer has been observed in Norwegian pulp and paper workers who were possibly occupationally exposed to asbestos. The present study was initiated to investigate if the increased risk could be associated with asbestos fibers in ovarian tissue from workers in this industry. Normal ovarian tissue specimens from three groups of women were included in the study. The case group included specimens from 46 women diagnosed with ovarian cancer in the period 1953-2000, and who had been working in one or more pulp and paper mills between 1920 and 1993. Normal ovarian tissue specimens from two control groups without occupational history from pulp and paper work were selected from the Cancer Registry database. Tissue blocks were digested and prepared for transmission electron microscopy. Number of fibers per gram wet weight was calculated. Asbestos fibers were found in normal ovarian tissue from two subjects in the case group, while no fibers were found in the control groups. The two asbestos positive cases had been working as paper sorter/packer and chlorine plant worker, respectively. Both were possibly secondary exposed to asbestos from family members working as insulators. We conclude that the findings in this study did not allow drawing any firm conclusion about an association between occupational exposure to asbestos and ovarian cancer in Norwegian pulp and paper workers. Our study confirms that asbestos fibers may reach the ovaries and demonstrates that the applied method is appropriate for identification of the fibers.

The art of perpetuating a public health hazard.

OBJECTIVES: Canadian chrysotile (white asbestos) could be a paradigm for those agents that are successfully exploited commercially long after they have been found to be lethal. Mining started in the late 1870s, and reports of disability and death followed in Britain (1898), in France (1906), and Italy (1908), but it was not until 1955 that Canada acknowledged asbestosis in its asbestos miners and millers. Even when shortly after asbestos was shown to be carcinogenic, Canadian Public Relations experts assisted by their scientists exculpated chrysotile by deeming other agents to have been causal. RESULTS: The PR techniques that have been successfully used in the defense of chrysotile are reviewed, to forewarn scientists involved in formulating public health policy for similar agents, as to the tricks that will be played on them.

[A meta-analysis of cohort studies on cancer mortality among workers exposure to chrysotile fiber alone].

OBJECTIVE: To determine there was excessive risk of malignant tumors or not among workers exposure to chrysotile fiber alone by applying a meta-analysis technique. METHODS: All data meeting the criteria of cohort studies on cancer mortality among workers exposed only to chrysotile would incorporate into the meta-analysis. The pooled standardized mortality ratios (SMR) and their corresponding 95% confidence intervals (95% CI) for main cancer sites were calculated using two approaches of unweighted ratio and random effects model. The heterogeneity and its sources of the results were examined with a Q-statistic and Z-score test. RESULTS: 26 chrysotile-exposed alone cohorts were summarized. The significantly elevated meta-SMRs for all deaths (1.28), all cancers (1.26), cancers of respiratory organs (2.24), cancer of lung (2.29) and cancer of stomach (1.27) were observed. The significantly elevated meta-SMRs for lung cancer within occupational strata were observed among textile workers (3.64), asbestos products manufacturers (3.07), miners and millers (2.24), cement products workers (1.22), and for stomach cancer among asbestos products manufacturers (1.48). Meta-SMRs for cancers at other sites were not significant. CONCLUSION: There were excessive risks of lung cancer and mesothelioma among workers exposure to chrysotile fiber alone, and likely no convincing indication of an etiological association between chrysotile exposure and cancers at other sites.

Lung function changes in pleural asbestosis.

The aim of this study was to examine the relationship between radiographically detectable pleural changes and lung function in pleural asbestosis. One hundred and twenty chrysotile asbestos-exposed workers were enrolled in this retrospective study. For each examinee the length of asbestos exposure and the degree of dust cover at the workplace were assessed as well as the radiological and functional tests has been performed. The examinees were divided into two groups based on radiologically detectable changes: a) group with pleural changes (29%) and b) group without perceived pleural changes (71%). The obtained results indicate association between the length of asbestos exposure, pleural changes and the impairment of lung function.

Asbestos poisons World Trade Organization atmosphere.

In September 2000, a World Trade Organization (WTO) panel published its findings in the dispute between Canada and the European Union/France over France's ban on the import and use of chrysotile (white asbestos). The panel upheld the French ban, established that the use of chrysotile is a health risk and the idea of "controlled use" a fallacy, and used (for the first time) an exception clause in the General Agreement on Tariffs and Trade that permits trade-restrictive measures to protect human life or health. At the same time, the panel concluded that the French ban violated international trade laws by treating chrysotile products less favorably than domestically produced alternatives. Some WTO watchers believe that with asbestos as the precedent for bans on toxic substances, the regulation of other, much less well-established, toxic exposures could prove much more difficult. Now the French ban has been upheld, chrysotile producers will increasingly target developing countries. Canada is appealing the WTO decision.