The use of asbestos has gone through many phases. Continuing research and studies, with time, eliminated the risks from this activity, as they proposed solutions that aimed at ensuring the safety of all the workers involved in the process. Currently, the risks of chrysotile have ceased to be a public health problem and have become an occupational health issue.
The first reports on asbestos date from 1906 and were written by an English physician, Dr. M. Murray. The study of asbestos can be grouped in three phases:
FIRST HALF OF THE 20TH CENTURY
In Europe and in the USA, most of the asbestos mined (up to 40%) was used in the production of insulating and fire proofing materials and was applied mostly in the form of spray. The industry used mostly friable products, which we now know caused the largest and more serious exposure-related damage to the workers health. Because of the tropical climate prevalent in Brazil, neither this use nor this form of application were ever encouraged or needed. During this period, most of the asbestos consumed in the United States and Europe was the amphibole type (blue and brown asbestos), which represented more than 20% of the mixture used. In Brazil the use of amphibole asbestos was very restricted.
1960
A study performed by the epidemiologist Dr. J. C. Wagner reported on 33 cases of mesothelioma, a rare form of tumor that occurs in the pleura, in workers who were employed in the blue asbestos mines of South Africa. He also reported on cases found in people living near the extraction area and those who transported the ore. Others studies followed this one, and they all showed several cases of lung cancer in American workers who applied insulation material or lagging in ships.
1964
Dr. Selikoff presents new works on asbestos-related pulmonary diseases seen in others countries, such as in the United States of America. These reports raised a lot of concerns and caused a tremendous repercussion in the media. The flurry of studies published by 1975 also established a clear relationship between asbestos and four main diseases:
Asbestosis
A pulmonary disease caused by long-term inhalation of dust containing a high concentration of asbestos fibers. Asbestos fibers find their way to the alveoli in the lung, and these foreign bodies cause the activation of the lungs local immune system provoking a defensive inflammatory reaction, which produces a cement-like protein that cause alveolar walls to thicken, resulting in shortness of breath. The repetition of this process throughout many years can cause a drastic reduction in lung function due to lung stiffening, which results in respiratory failure.
Asbestosis is similar to silicosis, which is caused by exposure to silica. Clinically speaking, it is not possible for a person with asbestosis to contract silicosis.
Mean time for the disease to appear: 15 years.
Benign asbestos pleural disease
In addition to the diseases described above, exposure to asbestos fibers can cause diffuse pleural thickening, effusions or pleural plaques. These diseases are considered benign because they rarely cause any pulmonary deficiency and are interpreted as being a sign of exposure to asbestos. They are not related to dysfunctions or other pulmonary diseases, such as asbestosis and cancer.
Lung cancer
Studies indicate that smokers have a higher risk of developing this type of cancer. That is, tobacco smoking and exposure to asbestos fibers constitute an important risk factor. New research has shown that this risk seems to be restricted to workers with radiological evidence of asbestosis.
Mean time for the disease to appear: 20 years
Mesothelioma
It is a rare form of malignant tumor that develops in the mesothelium (membrane that involves the lung, the abdomen and its organs).
Fibers with longer biopersistence (long and fine) present a higher risk for this type of cancer to develop. This explains why the vast majority of mesotheliomas observed in the studies is related to exposure to amphiboles (blue or brown asbestos).
More recent studies indicate that the incidence of mesothelioma in the general population in Canada, the USA and in England is around 1 to 6 cases a year per one million inhabitants.
Mesotheliomas are not restricted to workers in asbestos mines or in the asbestos industry. This form of cancer is also not related to smoking.
Mean time for the disease to appear: 30 to 40 years
During that period, working conditions were very aggressive to the workers health. Intense exposure to asbestos dust, especially in the mines and during spray applications of thermal insulation in ships, houses and buildings was the norm. Fiber concentrations in the air, especially during spraying, were absurd, relative to current standards, and varied from a few hundred to more than 1,000 fibers/cm³. Brazilian legislation establishes that the highest fiber concentration allowed is 2 fibers/cm³. However, the Cana Brava mine and fiber cement industries enforce stricter policies for the controlled and responsible use of asbestos and work with limits of 0.3 to 0.1 fibers/cm³.
Around 1980, measures for achieving dust control in the work place were developed. While studies published between 1964 and 1975 reported on cases of exposure to more than 100 fibers/cm³, more recent studies show the effect of dusts with much lower levels, of less than 5 fibers/cm³, in which changes in the lung are already detected. More recent studies state that:
- Asbestos can only harm one organ of the body: the lungs. This fact was preponderant for the development of more efficient control methods.
- Only workers exposed to high concentrations of asbestos fibers for long periods of time can be included in the group at risk of contracting the disease. Workers who are employed in industries that enforce policies calling for the controlled use of asbestos are completely safe.
- The disease cases found during the first phase of the studies were more frequently associated to exposure to amphiboles, a type of asbestos with a high biopersistence rate. Currently, only chrysotile asbestos is used.
Biopersistence: time that a substance remains in the body. In the case of asbestos, it means the period in which fibers of this mineral remain in the body. The carcinogenic potential of a mineral is determined by this period of time.
A Directive issued by the European Community considers that only fibers with a biopersistence of more than 10 days are considered carcinogenic. The differences in chemical composition of the several types of asbestos determine how they are absorbed by the body. See below the difference in biopersistence rates between amphibole and chrysotile asbestos.
Amphibole asbestos
Amphibole asbestos, also known as blue or brown asbestos, has a high iron content (a chemical element which is not absorbed by the body) and the fibers are stiff, straight and pointed. The biopersistence rate for this type of mineral is more than a year. These characteristics mean that this type of asbestos is potentially carcinogenic, and for this reason it was banned throughout the world.
Chrysotile asbestos
Chrysotile asbestos, known as white asbestos, the variety used in Brazil, on the other hand, has a high magnesium content and is therefore easily absorbed. The fibers are curved, silky and do not have a sharp point. Additionally, the biopersistence rate is of two days, maximum.
