Anyone who has read the first two articles in this series is quite aware that the health hazards associated with asbestos, including asbestosis, mesothelioma, etc., is not a new phenomenon, but can be traced back to prehistoric times. Archeological digs in Scandinavia revealed evidence of the use of asbestos in pottery and chinking of log homes manufactured 5,000 years ago (See: A Brief History of the Use of Asbestos and Associated Health Risks). Written history has recorded the health hazards associated with asbestos as far back as the 1st century AD. The first century geographer Strabo noted that workers exposed to asbestos had many health problems; and Pliny the Elder went so far as to recommend that quarry slaves from asbestos mines not be purchased because "they die young."
While evidence of health hazards associated with the use of asbestos goes back centuries, it wasn't until the Industrial Revolution that the extent of the problem was realized. In the late 19th century large quantities of asbestos were needed for the ever-expanding textile and building industries. The first documented case of an asbestos related death was reported in 1906. After generations of asbestos related health problems, an autopsy of an asbestos worker revealed that he had died of lung fibrosis. By 1918 life insurance companies were charging higher premiums for asbestos workers.
By the 1970's an array of health problems had been found to be associated with the mining of asbestos, and the manufacture and use of asbestos products. If the use of asbestos were confined to a relatively few products, it would have been a simple process to find alternatives to asbestos, discontinue the manufacture and distribution of products containing asbestos and recall products that were already in the hands of consumers. Unfortunately, asbestos was being used in the manufacture of thousands of diverse products. Ranging from brake shoes, and insulation for houses and pipes to clothing and other textiles. As we will discuss in detail later, asbestos was even showing up in products in which insulation was not an intended ingredient. Once the health risks associated with exposure to asbestos were brought to the forefront, it was too late to confine the corrective action to a few isolated incidents. Asbestos related diseases had reached all parts of the industrialized world and had become a global problem in the work place and in the living spaces of millions of individuals.
There is a wide range of occupations that have the potential of elevating an individual's risk to the asbestos related health problems. The following is a list of industries most commonly associated with asbestos exposure and the possibility of work related asbestos diseases:
And now added to the list:
While individuals employed in industries associated with asbestos are at highest risk, families of such workers can also be placed at risk if the workers bring home their work clothes for laundering. Today it is common for workers to remove uniforms and shower prior to leaving the facility. Clothing that might be contaminated is laundered professionally.
The general public is exposed to small doses of environmental asbestos from the natural erosion of rocks containing asbestos. These low levels of asbestos (known as "background") seem to be of little consequence in the development of asbestos related diseases. Occasionally an individual may be exposed as a result of exposure to non-work related friable asbestos in building products such as tiles or insulation.
Exposure plays a significant role in the manifestation of asbestos related diseases including asbestosis, mesothelioma, etc. In one study, 10% of individuals exposed to high levels of asbestos for 10-19 years developed asbestosis; 73% of individuals exposed to high levels of asbestos for 20-29 years developed asbestos and 92% of individuals exposed to high levels of asbestos for over 40 years developed asbestosis. The research didn't indicate if those who were exposed for 10-19 years were still working in an asbestos related job or if they had left. One can only wonder if individuals exposed for 10-19 years would still develop asbestosis after 40 years indicating a latent period, or if the high rate of asbestosis in the individuals who had been employed in high asbestos exposure rates for extremely long periods was due to the length of exposure.
A Finnish study indicated that the rate of asbestosis was 22% in construction workers employed for ten years, and 22% for workers in the ship building industry after 1 year. Ship builders were exposed to significantly more asbestos on a daily basis than construction workers.
There is evidence to suggest that a high exposure rate for short periods (a year) is more important in the development of mesothelioma than continued exposure to lower concentrations of asbestos. It is generally acknowledged that the average latency period for asbestosis is 13-20 years, though there are many contributory factors, including length of fibers, and whether or not the exposed worker was a smoker.
It is interesting to note that in the mid-90s there was a decrease in the rate of newly diagnosed asbestosis, but an increase in asbestos related cancer deaths. In the 1990s there was a sudden decline in the exposure level of workers to asbestos due to stricter regulations. As a result there were fewer individuals developing asbestosis. However, asbestos related cancer has a longer latent period than asbestosis, so individuals exposed 30 and 40 years earlier were now developing cancer even though they were no longer being exposed to asbestos.
The degree of risk for developing lung cancer seems to be rather complex. Level and duration of exposure as well as size of the fibers are important factors in determining the likelihood of developing cancer and what type of cancer is most likely to occur. Long thin fibers usually make their way to the lower respiratory tract where they are found in the alveolar region of the lung. Shorter, thicker fibers are likely to be found in the upper respiratory. As a result, long fibers are usually involved in diseases to the lungs and lower target organs, while short fat fibers are most often involved in diseases of the upper respiratory tract. Short fibers are also more likely to be phagocytized and cleared away than long fibers, making them generally less toxic.
While continued exposure may make an individual more susceptible to asbestos related diseases, progression of an asbestos related disease may occur without continued exposure.
Earlier research suggested that there was little pathophysiological relationship between the development of asbestosis and the future development of lung cancer. Research reported in 2004 involving the study of thousands of asbestos disease victims dating from the 1920s to present suggests that the relationship between the two is highly correlated and that there is likely a pathophysiological link.
While the pathophysiological pathway connecting lung cancer to asbestosis has been disputed by many researchers, there is evidence to suggest that there may be a link between asbestosis and lung cancer. During the stage of fibrosis development in asbestosis, growth factors, active oxidants and proteases are released. Some may cause mutations of cells, and others may cause proliferation of cells. These phenomena may increase the chance for errors to occur during DNA replication that in turn could lead to malignant changes.
There is considerable evidence to suggest that asbestos related lung cancer occurs almost exclusively in patients that already have asbestosis. Individuals may have pleural plaques but no asbestosis. Such individuals do not appear to have increased rates for developing lung cancer. Increased risk for asbestos related lung cancer seems to be linked to asbestosis. The correlation is so high that it has been suggested that occurrence of asbestosis rather than measurement of exposure level of asbestos should be used as a reliable marker for increased risk for asbestos related lung cancer.
Cigarette smoking causes lung cancer as does exposure to asbestos. However, when individuals who are exposed to asbestos also smoke, the risk of cancer is greater than both risks added together. Asbestos workers who also smoked cigarettes had a 50 to 90 times increase in lung cancer deaths when compared to people who neither smoked nor were exposed to asbestos. For non-smokers, the rate of lung cancer deaths was 5 times greater than the general population.
Smoking also makes an individual more susceptible to asbestosis than non-smokers. There are conflicting views concerning the correlation between smoking and the development of mesothelioma. Some researchers contend that there is no relationship between smoking and the development of asbestos related mesothelioma while others report a fairly high correlation between the two.
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Roberta C. Barbalace. Asbestos: A Manufacturing Health Hazard Dating to Prehistoric Times. EnvironmentalChemistry.com. Oct. 2004. Accessed on-line: 7/5/2020