Posted on July 6, 2018
By Francisco Báez Baquet
Dedication: I am pleased to dedicate the present work, to the doctors Jaume Ferrer Sancho and Josep Tarrés Olivella, in gratitude for their professional dedication to the study of asbestos-related pathologies.
In 1899, the Dr. Henri Montague Murray, in London, makes the first observation of a death associated with the asbestos, diagnosing autopsy a pulmonary fibrosis in a worker who had worked for fourteen years in the carding workshop of an asbestos spinning, and who had died at thirty-five years of age.
This man was the tenth victim in his area of work (in which mortality was 100%), and in it the Dr. Murray noted the interstitial fibrosis, and some “curious bodies” he had in the lungs, thus being the first in warning about the presence of asbestos bodies.
The so-called “asbestos bodies” or “ferruginous bodies“, were described as such for the first time by Marchand in 1906.
However, it is not until Stewart & Haddow (1929), that these authors recommend replacing the term “curious bodies”, with the term “asbestos bodies“.
They identify their presence in samples of sputum and lung tissues. See also: Greenberg (1997).
They are found in the sputum and / or in the fluid recovered from the bronchoalveolar lavage, as well as in the histological preparations of biopsies and autopsies, and consist of particles, already visible under an optical microscope, after staining, and formed by the encapsulation of a central fiber. (which is confirmed to be asbestos, by elemental analysis or analogous procedure), and whose coating has a characteristic silhouette, in the form of halters, seesaws, dumbbells or drumstick, due to the bulges of the two ends, formed by the biological material of the coating, and that in optical microscopy have a characteristic coloration, such as rust, to which one of its denominations refers, and, also, to the fact that the above-mentioned coating material, is constituted by a ferroprotein.
The magnetic susceptibility, brought about by the presence of iron, has been used for its isolation and identification, without the need to resort to any chemical modification, and respecting, therefore, its integrity and composition: Borelli et al. (2007).
“Recent” studies -Pascolo et al. (2011) – show both the importance of iron (which was already known), and magnesium, in the formation of asbestos bodies.
This verification opens the way to the study of a possible role of Mg in the tissue response to the toxicity of asbestos, an eventuality that shows us that on this issue, the last word has not yet been said.
In Alexopoulos et al. (2011), the authors make a comparative cytological study between the material obtained by bronchoalveolar lavage and by facilitating sputum, in the preventive monitoring of the same subjects, members of templates of asbestos industries, reaching the conclusion that both methods They show similar results, so they opt for the use of the least invasive and least expensive, that is, by sputum analysis.
The stability of ferruginous bodies in human lung tissue, after death, embalming and burial, is the subject of study in: Dodson et al. (2005), these authors concluded that said stability, months after the aforementioned events, allows the use of this type of evidence, regarding the confirmation of the exhibition, and for its quantification.
However, in Mollo et al. (2000), based on previous experimental results, it was held precisely the opposite: that, under normal conditions of putrefaction after burial, there is a progressive decrease in the number of detectable asbestos bodies, to conclude in its total disappearance, months later of the death.
This result would impose a limit on the effectiveness of this type of evidence, to be taken into account, for legal purposes. The alternative, for this preferable reason, would be the analysis, by means of electron microscopy, to directly quantify the presence of asbestos fibers -which are indestructible-, as well as to be able to determine their nature (elongation coefficient, and, above all, chemical composition). elementary or the diffraction pattern).
The permanence of the asbestos bodies in the alveolar cavity of the lungs, during decades, is reviewed in Rivolta (2003).
In 1964, the attorneys of “Turner & Newall” recognize that “it is already clearly established that when “asbestos bodies” have caused fibrotic changes in the lungs, the lung cancer can arise”.
In fact, it is only a restrictive recognition, since, in order for the asbestos to trigger lung cancer, the concurrence of asbestosis is not necessary: dialectically, it is only a tactical retreat to a trench slightly more to the rear, metaphorically speaking.
Note, too, how the role of etiological agent, both for the cancer and for asbestosis, is attributed to the “asbestos bodies“, rather than directly to the fibers.
Of course, since the role of asbestos had been established, no scientific evidence ever supported such an interpretation.
In 1956, Dr. Christopher Slegg establishes in South Africa the causal link between occupational and environmental exposure to crocidolite and mesothelioma involvement.
Indeed, the first South African case of diffuse pleural mesothelioma, with asbestos bodies in the lungs, was diagnosed in the “Pneumoconiosis Research Unit” of Johannesburg: Wagner (1965).
However, it will not be until 1960 when the widespread recognition of the causal relationship between asbestos and mesothelioma will be established, after joint publication, by Wagner, Sleggs and Marchand, of the total registered South African cases.
It was the asbestos bodies, present in the lung tissue from autopsy, which put the team Dr. Wagner on the trail of the causal nexus between asbestos and mesothelioma: Wagner (1991). See also: Basset (1968), Warnock (1989).
In 1964, the South African J.G. Thomson finds asbestos bodies in the lungs of one of every four autopsied in the South African province of Cape Town, headquarters of the asbestos mines.
For the asbestos bodies, in general, and for those located in the sputum, in particular, see: (1).
In Auerbach et al. (1980), the authors detected “asbestos bodies“, not only in the lung, but also in other organs: spleen, myocardium, pancreas, kidneys…
The etiological relationship with asbestos exposure, in some cases of pericardial mesothelioma, has been evidenced through the presence, quantified, of asbestos bodies, in the lung parenchyma, and in some of them, through the X-ray analyzer, in electronic microscopy, its concrete variety of asbestos could be established, thus confirming its nature, with total concretion.
In some cases of desmoplastic malignant mesothelioma -Ishikawa et al. (2003)-, histological variety, of especially difficult diagnosis, has been the presence of asbestos bodies in the histological preparations, the one that has oriented the diagnosis towards its correct conclusion, in spite of the initial difficulties.
On other occasions, the finding of asbestos bodies has been made post mortem, and when the difficult diagnosis of this histological variety of mesothelioma, had already been made: Matsuzawa et al. (1995).
In Wu et al. (1988), the most intense pleural adhesion is related, in the cases of greater number of asbestos bodies found in the autopsy, which puts in evidence its dependence of the intensity, with the degree of exposure had; a quite predictable result.
In the work of Doniach et al. (1975), in a series of necropsies, the authors found a significantly elevated presence of asbestos bodies, in the cases of patients who died of carcinoma of the stomach, and also in the deaths due to breast cancer.
In the work of Szendröi et al. (1983), the authors recommend the digestive examination of malignant tumors, when an asbestos exposure has mediated, in order to identify the possible presence in them of asbestos fibers, eventually acquired through ingestion.
This recommendation was due to the fact that in the case referred to in the article, the patient, with confirmed occupational exposure, and with advanced asbestosis, also had a malignant tumor of the bile ducts, with the presence of numerous asbestos bodies in the tumor tissue, in the same concentration range as those found also in his lungs.
When such a search has been carried out, it has usually been done by optical microscopy, and then what is sought are the so-called “asbestos bodies” or “ferruginous bodies” (and not the fibers directly), for which use is made of the coloration of Perls (Prussian blue). See: Bacci (2006).
Therefore, in the majority of these cases, when the use of electron microscopy is abandoned, with in situ analysis of the fibers, by activation by the dispersive energy of the x-rays, those fibers that, for example, are being discarded its dimensions, would be outside the power of resolution of optical microscopy, and, at the same time, its nature (type of asbestos that it would eventually be), would not be determined either.
The pulmonary tissue is preferably the place of search for asbestos fibers, either directly or inferred by the presence of asbestos bodies that, as is known, are reactive structures, each of which houses in its interior one of said fibers.
Thus we will have, for example, that in Matsuda et al. (2009), we are presented with the case of a mesothelioma patient, in whose resected lung tissue, in a count made on one gram of dry tissue, 443,571 asbestos bodies were detected.
In suspension in the fluid of the pleural effusion, it is usual not to find asbestos bodies: Roach et al. (2002), although in some cases they can be detected (see Figure No. 12, included in the aforementioned work).
The “asbestos bodies” have also been detected in the excrements of the patient of asbestosis: Gloyne (1931).
In Wälchli et al. (1987), these authors express, already in the title of their article, their criterion that asbestos bodies in the lung have to be considered an indicator of the damage caused by asbestosis, but such statement must be understood as referring to the quantification of the aforementioned ferruginous bodies, since their presence is already observed in the exposed groupers, without affecting detected.
An interesting result is obtained by Christensen et al. (2008), in a work that, as its own title indicates, makes dependent, among other factors already recognized, also on the asbestos load of the patient, in the determination of the survival in the patients of malignant pleural mesothelioma, estimated by the number of asbestos bodies per gram of lung tissue (wet weight), and, failing that, by self-report of those affected.
Obviously, the greater the load, the less survival will be due (abstraction made of the other concurrent factors).
The detection of asbestos bodies, in patients subjected to occupational exposure to various minerals susceptible to be naturally contaminated by asbestos (actinolite, anthophyllite, chrysotile, tremolite) -see Finkelstein (2013) – present in the same site of origin, as it may be the case of taconite or talc, it is another of the potential qualities of said diagnostic tool.
Already in Hunt (1956), in a case of massive pneumoconiosis by talcum, the presence of asbestos bodies in the pulmonary tissue of a worker deceased by acute cardiac failure, originated by the pneumoconiosis suffered by the same one was put in evidence.
In Montoya et al. (1988), the comparative study of the performance of several techniques of identification and counting of asbestos bodies in sputum, in groups with suspicion or certainty of occupational exposure to the asbestos, demonstrates the superiority of the Smith and Naylor method, for this purpose.
In any case, it should be noted on our part, that the use of a certain technique, conditions, to some extent, the validity and representativeness of the counts.
Special mention deserves the experimental work with animals, by Williams et al. (2001), demonstrating that asbestos bodies can be formed in extra-pulmonary sites, singularly, in liver and spleen, although, the effectiveness of coating the fiber by the lung, is clearly superior.
Of particular relevance are those found in lymphatic nodes, as their presence suggests a possible access route, from the lung, to other diverse organs, where they are also located. See: Dicke & Naylor (1969), Godwin & Jagatic (1970).
The performance of the autopsy, in asbestosics or even in merely exposed persons, may result in the finding of asbestos bodies in unexpected settlements. See: Szendröi et al. (1983).
In Bellis et al. (2003), the authors present the case of a patient with bladder cancer, in which the detection of asbestos bodies by optical microscopy, led to a mineralogical check using an electron microscope, which confirmed the presence of asbestos fibers, that the patient had not been recognized for any work exposure.
The asbestos has also been related to cancer of the bile ducts (even with the presence of asbestos bodies in them): Malker et al. (1986), Szendröi et al. (1981) & (1983).
In Ehrlich et al. (1991), the authors found in their cohort of asbestos workers with colon cancer, 31.8% with asbestos fibers and / or asbestos bodies present in the tissue of the colon, in concentrations of up to 15.2 million of fibers per gram of tissue dry.
On the part of Kobayashi et al. (1983), we are told a case, revealed by the autopsy, of pulmonary asbestosis with generalized fibrosis in several organs. In addition, with simultaneous affectation due to lung carcinoma and glomerulonephritis. Asbestos bodies and non-encapsulated asbestos fibers were identified in the organs that presented fibrosis: lung, liver, kidney, heart and thyroid gland.
The authors also identified asbestos fibers in the spleen, detected by electron microscopy, taking advantage of the fact that the said organ had been resected six years earlier, due to idiopathic portal hypertension.
These authors present the hypothesis, quite logically, that the generalized fibrosis observed was due to the fibrosing action of the fibers detected.
In fact, an extreme example of affectation by asbestos, with the characteristic of non-localisation with respect to the usual settlements, is the case already mentioned, described in Kobayashi et al. (1983), of generalized fibrosis, which is appropriate to consider in detail, so that we are all aware of what asbestos does to some workers, in the past and in the present, where their use has not been banned.
It is not appropriate to speak, without nuances, of “pulmonary diseases” or “diseases of the respiratory system”, mediating an etiology for asbestos.
The case reported, corresponded to the patient we have mentioned, with pulmonary asbestosis, with lung carcinoma, and with fibrosis of various organs, such as the liver, kidney, and thyroid gland.
Asbestos fibers and asbestos bodies were detected in each organ, including some lymph nodes.
He was a 53-year-old patient, who had worked, from 1962 to 1971, on asbestos-spraying tasks, in a construction company.
In the thorax radiography, infiltrates, reticular shadows and pleural effusions were observed.
Anoxia and wasting gradually increased, dying of respiratory failure, in June 1979.
The pleura showed pleuritis, in the pericardium a marked hyalinized thickening was observed, the kidneys showed generalized glomerular lesions, and the thyroid gland showed a moderate fibrosis; the bone marrow revealed mild fibrosis in some areas. Several foci of fibrosis were detected in the heart.
A scenario of morbidity in the spleen, which has also been observed in animal experiments: Boor et al. (2009).
The fibrosing action of asbestos on the spleen is also treated in the following works: Plamenac et al. (1974), Robinson (1972), and William (2009).
Although it is true that poly-morbidity due to simultaneous concurrence of several malignant neoplasms in the same patient, is a circumstance that is not limited to those cases in which an asbestos exposure has mediated, however, which is also true, as evidenced in Kishimoto (1992), is that this circumstance shows a clear proclivity towards malignant poly-morbidity.
In fact, in this work it was found that, in the studied cohort, almost all multiple cancers, including those of simultaneous affectation for lung and gastric cancers, were also cases with exposure to asbestos. In the aforementioned study, autopsies of 533 patients at a Japanese hospital were examined.
To determine the relationship between malignant tumors and exposure to asbestos, the number of asbestos bodies in wet lung tissue, counted by optical microscopy, was counted, and the work history was also considered.
The results revealed that exposure was manifested in 89% of mesothelioma cases, 38% of lung cancers, 37% of gastric cancers, and 28% of colon cancers.
These values were significantly higher than those corresponding to the control group, formed by patients who died due to non-malignant etiology.
At work: Arenas Huertero (1990), the counts made allow the author to conclude that, in Mexico, “the non-occupational exposure to asbestos is patent”.
Beyond the mere presence, it is quantification that allows the identification of occupational exposure: in Churg & Warnock (1977), these authors identify the presence of asbestos bodies in the lungs of 96% of the general population. See also: Ghezzi et al. (1967).
An individualized consideration deserves the work of Haque & Kanz (1988), on the finding of asbestos bodies in the autopsied pulmonary tissue of a cohort of deceased infants in lactation age, with an association of 46.6% with the syndrome of sudden death, and of 42.8% with bronchopulmonary dysplasia.
The authors consider that this correlation should not be interpreted as a causal relationship between asbestos and the aforementioned diseases, and that, consequently, it should be interpreted as merely casual.
However, some details invite reflection. The concentration of asbestos bodies in the lung tissue, in some cases, is comparable to that observed in the mesothelioma patients.
The authors venture an explanatory hypothesis of the presence of asbestos bodies in babies of so young age, attributing the contamination to the presence of asbestos in the boards of the incubators, in which supposedly they would have remained. See also, in this regard: Fuenfer (1984).
An explanation, in our opinion, that hardly seems compatible with the concentration levels of fibers found, and the state of conservation that can reasonably be attributed to facilities of such a sensitive nature, such as the aforementioned life support devices.
Abundant in the reasoning, it should be remembered that, regardless of what is the medical literature, there are recorded cases of contamination at such early ages, as has been the case, for example, of Adam Sager, who died of mesothelioma on April 29 of 2007, in Queensland (Australia), at 25 years of age, and after, when he was only 18 months old, he had been playing, at home, on the ground covered by a grayish dust, generated by the repair of some panels, which later could be verified that they contained asbestos.
If we look at all the bibliographical references included, corresponding to the authorship of Haque, we can verify the concern of this author for the possibility of a mother-child biological transfer, for asbestos, and on the involvement of children for asbestos pathologies .
In these questions, as well as regarding the finding of asbestos bodies in infants, and the correlation of this with sudden death syndrome or with bronchopulmonary dysplasia, our criterion is also that only the carrying out of appropriate epidemiological studies can clarify those disturbing possibilities.
Is the incidence of sudden death syndrome higher in the families of asbestos workers?
We do not know, because those surveys have never been carried out. See, in this regard: Haque, Vrazel & Burau (1996), work in which the authors highlight the absence of epidemiological surveys, clarifying aspects such as: effects of maternal or fetal exposure, presence of asbestos fibers in stillbirths, prevalence of abortions, premature births, defects, etc.
Faced with this widespread absence, we will have to work on Haque et al. (1998), in which the results of the discovery of asbestos in human placentas and in the tissues of deceased newborns are exposed, these authors find a highly significant statistical correlation between the finding of asbestos fibers in the aforementioned settlements, and the history of previous abortions of the mothers. You can not react looking the other way.
They are evidences that, honestly, can not be overlooked. It is not that other contrast studies have not found consistent results: it is that such studies have not been carried out.
Nobody has considered it pertinent, or the authorizations and financing necessary to carry them out have not been achieved.
For its eventual realization, it would be an invaluable help that provided by unions and / or associations of victims, something that can never materialize, if the incentive to mobilize by such agents of social intermediation, should be of a purely economic nature.
In all this question, there is also a difficulty: the name of sudden death syndrome, responds to the definition of a pathological phenomenon, through the expression of its result, and not to that of a single and defined disease.
Therefore, its etiology, generally idiopathic, can be due to various causes, such as, for example, the inhalation of a mold, as in some cases it has been possible to specify.
Therefore, even admitting the aforementioned correlation with the finding of asbestos bodies, this would not prevent the possibility that in the formation of a cohort of deceased with the aforementioned syndrome, could not be included members of the same, who, for not having maintained No sort of exposure to asbestos, nor any possibility of presence of true asbestósicos bodies, and that is precisely the difficulty we alluded to before, when weighing the relevance of any epidemiological study that could clarify this whole issue, if the extraction of this cohort is intended to be from the general population, and not from a recognized and previous environmental link with exposure to asbestos, in the environment of the deceased.
There would be, under this premise of generality, always an unavoidable uncertainty about the quantification of that supposed or real correlation.
Nevertheless, and despite this, our criterion is that such studies should be carried out, both those that already started from a prior identification of the condition of exposed, and those that, with the difficulty mentioned above, started from an extraction of cases, from its location among the general population.
Except for some authors -McLarty et al. (1980) – already cited above – that find a statistically significant correlation between involvement by interstitial lung disease or pleural fibrosis and the production of asbestos bodies, in general it is considered that they are only indicative of mere exposure to asbestos, and not affected by any of the multiple pathologies associated with said pollutant, but, in any case, they are important, for the following reasons:
They are found in members of the general population, with no occupational relationship with asbestos -Recuero et al. (2006), Anjilvel & Thurlbeck (1966), Dimov & Beritić (1969) -, and in the urban domestic animals -pet animals- evidencing their presence in the external environment to factories, warehouses and workshops, being significantly more abundant, among those who live or work in proximity to highways, parking areas or streets with heavy traffic, because of the detachment of fibers, brakes of motor vehicles, made with pills (so-called “ferodos”) , in which asbestos appears as an obligatory ingredient, except for the use of a substitute material, as is the case of the countries where the prohibition of asbestos – including crisotyl – prevails, and from the corresponding year of manufacture or equipment of the vehicle motorized. See: Rangé (1998), Castleman (1998), Saito (1995).
In Argentina, where in its large cities the layout of its streets is a grid of perpendiculars, and where, in the absence of traffic lights, road traffic is regulated by frequent and repeated braking more or less abrupt, popular wisdom crystallized in the expression “evil of the corners“, the recognition of the accumulation of diverse pathologies among the inhabitants of such environments, originated, possibly, by the action of the combustion gases of the engines of the vehicles, but possibly also by the action of the fibers of asbestos detached in the repeated braking in the same places, given the use that has been of said mineral, in the manufacture of ferodos and clutches, although it is true that up to the present, nobody pointed that possible link between the “evil of the corners” and asbestos. (Source: Francisco Puche Vergara, personal communication).
In the case of a positive finding, the count of asbestos bodies allows to distinguish between environmental or occupational contamination, respectively. See: Velasco-García et al. (2010), Monsó et al. (1995), Dodson et al. (1991).
The University Hospital of Vall d’Hebron, Barcelona, as published in “Medical Journal”, has detected the presence of asbestos, in 10% of patients with lung cancer, and who were unaware of having been exposed to the inhalation of said pollutant. In the biological material obtained from the tumor resection, a pathological level of concentration of “asbestos bodies” was found.
Bearing in mind these findings, and at the same time, those outlined in the work of the Haque team and collaborators, it would be interesting that, referring to the general population of the city of Barcelona and the geographical environment covered by the area of action of the aforementioned hospital, it could be possible to carry out some study, about the presence of “asbestos bodies” (and, possibly, of fibers of asbestos without encapsulating, with the aid of the electronic microscopy), that could be present in the placentas discarded in the hospital operation ordinary, proceeding to the timely recount. This observation, obviously, is equally applicable to any other hospital institution in our country or any other.
In Vincent et al. (2011), the histopathological analysis of lung tissue, to look for the presence of asbestos fibers, in a cohort of lung cancer patients, from the same hospital center, together with the application of a history questionnaire on the professional life of the same, showed that almost a third presented evidence of an etiology for asbestos.
In Hiraoka et al. (1990), the authors studied the content of asbestos bodies in the lung tissue of 476 patients with lung cancer and of 369 with other diseases, and all of them inhabitants of a Japanese industrial city. Eleven patients with histologically confirmed asbestosis were also included.
One of the conclusions of the study, established that patients with lung cancer, among those with high register of asbestos bodies, were significantly younger than those with lower counts.
That is, those who showed a higher cumulative dose through the high level thrown in the count of asbestos bodies in lung tissue, were also those who at earlier age had succumbed to lung cancer.
At the same time, a significant number of patients with lung cancer were observed among those with high records of asbestos bodies.
To the extent that some of these patients, with high counts and lung cancer, had not previously been identified as subject to exposure, either for work or for work (kinship, neighborhood, “worker bystander”), this represented underreporting , that the post-mortem examination practiced came to be corrected, therefore, if it had not been carried out, this under-registration would have been maintained.
To the extent that one is the usual, and the other exceptional, the generalized under-registration will be present.
In the work of Recuero et al. (2006), it is noted that:
(a) – the majority (77%) of the population of Barcelona have lung asbestos levels, greater than 300 “asbestos bodies” for each gram of dry heavy lung tissue,
(b) – half of patients with lung cancer have a history of occupational exposure to asbestos,
(c) – a considerable percentage (20%) of patients with lung cancer have high values of asbestos in the lung,
(d) – lung asbestos levels are higher in patients with lung cancer than in the autopsied population as a whole.
These findings show that there is an appreciable underreporting of carcinomas with a causal relationship with respect to asbestos, primarily without known occupational exposure. See: (2).
These authors abound, all of them, in similar findings and conclusions.
It highlights, for our part, the extraordinary importance that can be attributed to these results, verified, at least, by eight of the aforementioned medical teams.
This is a circumstance that, although attenuated, we find also in the case of mesothelioma: Okello et al. (2009).
In this work, we investigate the percentage of death certificates, referring to a series of cases from the southeast of England, with a confirmed diagnosis of mesothelioma, in which the cause of death is correctly identified, concluding that only 87% comply with that requirement.
Bearing in mind that not a few epidemiological studies are based on the exploitation of the registry of such certificates, it is necessary to conclude that even in nations with a good reputation for statistical reliability, underregistration is made possible by deficiencies.
The same cause of under-registration, in the general context of the various occupational risks, is highlighted in Selikoff (1992) and Ribak et al. (1991).
In Ishikawa et al. (2004), a comparative study of quantification of the number of asbestos bodies found in autopsied pulmonary tissue among deceased due to lung cancer is presented, distinguishing between primary lung cancers, on the one hand, and metastatic cancers, on the other.
There is a clear difference, statistically significant in males, with higher counts in the primary ones.
This strongly suggests that, among the general population, with no known occupational exposure to asbestos, apart from the usual synergistic effect attributed to smoking (so widespread), there is also an unrecognized role of asbestos present due to environmental contamination -see : Omenn et al. (1986) -, or by the occupational one not recognized.
Of the two alternatives, the first is an absolutely disturbing possibility, and one that undoubtedly deserves further clarification, through new studies, well planned, and that allow to reach, on this subject, better founded conclusions.
Claude Got, in his statements (page 220), in the “Rapport fait au nom of the Mission d’Information sur les Risques et les Consequences de l’Exposition a l’Amiante” – No. 2884 – 22 février 2006, addressed to the French National Assembly, will say: “Some countries have implemented a systematic search for the fibers of all primary lung tumors, and allocate bronchial cancer to asbestos, from a certain threshold. We know that this agreement leads to injustice, since certain fibers disappear faster than others, and can not be shown when the cancer occurs twenty years after exposure of the subject. But it is an advance in terms of compensation.”
In turn, Jean Claude Pairon (page 222) of the same parliamentary document, will say: “In Belgium, the fact of having more than 5000 asbestos bodies per gram, is associated with an automatic recognition of the link between exposure to asbestos and cancer of lung“.
In the work of Bhagavan & Koss (1976), the secular tendency in the prevalence and concentration of asbestos pulmonary bodies is analyzed, by means of necropsies referred to the general population, and for the time lapse between 1940 and 1972, observing an increase in consonance with the increasing consumption of asbestos, culminating with a prevalence of 91.1%, for the population of the port area of Baltimore.
Concurrent results, for a different geographical scenario, and for the time interval 1936-1966, are exposed in: Um (1971), making clear the dependence of this prevalence of the asbestos bodies in the general population, with respect to the import figures and of industrial use of asbestos.
In this context of reasoning, it is especially pertinent to attend to the results shown in Kishimoto (1992), work in which the author presents his inquiries regarding the autopsies of a general population in the environment of a source of industrial pollution by asbestos, such as this is the case of the inhabitants of the Japanese city of Kure, headquarters of some shipyards, confirming levels of presence of asbestos bodies, clearly higher than those of other districts of the same country, and, at the same time, detecting an elevated rate of pathologies that had previously been associated with exposure to asbestos: lung cancer, mesothelioma, gastric cancer, colon cancer, and acute leukemia.
They are not worth subterfuges or look the other way, when we come across epidemiological evidence like this one.
If already in the general population of the environment of a source of industrial pollution by asbestos, we can see how the epidemiological study marks us a causal link, evidenced by the correlation found, with greater reason has to be admitted for the workers themselves, submitted to an undoubtedly more intense exposition.
Esa elevada tasa de cuerpos asbestósicos hallados en las autopsias, se configura así como una esencial pieza de convicción.
This high rate of asbestos bodies found in the autopsies, is configured as an essential piece of conviction.
Attending, not only exclusively to the presence of asbestos bodies, but also to a whole series of exposure indicators, we will have, in Vilkman et al. (1993), and for a consecutive group of lung cancer patients, 30% showed evidence of asbestos exposure.
Figures of this nature, although referred to a general population, depend heavily on the degree of linkage to the industrial use of asbestos, which has occurred in the respective location to which the study is oriented.
In the case of the work of Bianchi et al. (1999), in which the locality in question was that of Monfalcone, in Italy, with a marked link to asbestos, in a review of 414 consecutive necropic cases of lung carcinoma, the corresponding data were the following:
1) – Male patients had worked in the industry, in 74%, of which 60% corresponded to shipbuilding.
2) – The men presented pleural plaques in 82% of cases.
3) – Asbestos bodies were located in 34.8% of the lung sections, and in 31%, with a value higher than 5,000 per gram of dry tissue.
4) – Among the women, work history or domestic exposure, they showed a link in 36% of the cases, and the prevalence of pleural plaques was 34%, with 15% of large plaques.
5) – In them, the asbestos bodies, in the routine lung sections of the autopsy, were found in 3.3% of the cases, and none in body load values, of more than 5,000 per gram.
6) – Depending on the criteria used in the attribution, the percentage of lung carcinomas linked to asbestos varied between 24.7% and 61%.
7) –The different criteria used made it plausible that approximately 60% of lung carcinomas in males were attributable to asbestos.
From all of this it can reasonably be inferred that, in a certain proportion of the cases, in spite of not having proven the existence of an occupational exposure, there was evidence, however, that, of whatever nature, an exposure to the asbestos did exist, and in this the presence of asbestos bodies in the autopsied lung tissue was one of several evidences managed to reach that conclusion.
With this, in a further step, we will move towards the content of our next section:
a) – They allow, based on a certain quantification, evidence of an employment relationship, which may be necessary to prove judicially, because it is questioned. See: Churg (1982).
It will be the case, frequently, of the so-called “spectator worker”. Even when asbestos bodies can be identified in the sputum, the counts for quantification of exposure, both environmental and occupational, are usually made from bronchoalveolar lavage. See: Cordeiro et al. (2007).
However, it is necessary to keep in mind certain limitations. As already indicated in a work by Whitwell (1978), asbestos bodies are formed only from a fiber length, equal to or greater than 12 microns, but all generate equally asbestosis, although histologically it is not easy diagnosis, when asbestos bodies are absent.
Normally, the worker inhales fibers of the whole range of lengths, but in certain situations, only the short fibers are evidenced by electronic microscopy, which is the only one that will allow it, given that with that limitation in the lengths, the asbestos bodies will not have come to form.
The aforementioned conditions that only show the inhalation of short fibers, we will have them at least in two different scenarios: when working at a distance from the source of the dust (case, frequently, of the so-called “spectator worker”), or when the use of masks retained exclusively or preferably the longest fibers.
The aforementioned author indicates that throughout his professional experience, he was able to observe occasional cases, in which, through a long history of exposure to asbestos, the asbestosis could be evidenced, but not that of asbestos bodies, so that in them , to be able to show the presence of asbestos (and to rule out that the fibrosis could correspond to any of the other causes that could have originated it), the recourse to the electron microscope was obligatory.
It is worth highlighting the fact that, since the asbestos bodies are not formed but from a certain length of the generating fiber (approximately 10-12 microns), these reactive structures are only a minority, with respect to the number total of fibers present, and at the same time, when they are merely identified by optical microscopy, the asbestos bodies thus identified do not constitute, in turn, more than a minority of them (which, by their larger dimensions, are observable by said technique), so that, in relation to the actual number of fibers present in the sputum or in the histological sample, they only represent a minority … of another minority: Hueto & Almudévar (2005).
This is a matter of paramount importance, because it often happens, that in the expert reports provided by the defendant in the litigation for asbestos, happily talk about “asbestos fibers“, when in reality, if you go into the question , what has really been sought, and, in his case recounted, have been asbestos bodies, observed through optical microscopy, which is, coincidentally, the most affordable and cheap.
Needless to say, there will be many judges who, in front of this “prestidigitation pass”, will swallow it whole, without question, and the same can be said about the legal representatives of the plaintiff.
All this, of course, to the detriment of true justice towards the victims, since there will be occupational exposures, which will not be recognized as such, despite being perfectly true and real.
b) – Because of the approximate proportionality between the degree of accumulated labor contamination, and the quantification of the count of asbestos bodies found, this count can be used, in the absence of records, which can be defective, incomplete, or simply not exist.
This is important, both individually, in the processing of lawsuits, and equally, collectively, in epidemiological studies, when it is required to relate the results, with the degree of accumulated contamination.
In this type of studies, however, when they are referred to mortality, and not to mere morbidity, and there is availability of autopsy material, direct counting of fibers is usually preferred, per unit weight of dry lung tissue, and transmission electron microscopy, which is the one that provides the possibility of a more exhaustive count, and, at the same time, allow the undoubted identification of the mineralogical species of the fibers.
Therefore, the advantage of such a procedure is twofold: on the one hand, it allows the exhaustive count of fibers, even those not visible to the optical microscope, which are the vast majority, and on the other, they allow, on the fly, the accurate identification of the asbestos, through the opportune probe of excitation of the atoms, whose atomic number supplies the desired identifying fingerprint. With this technique, the count is not limited either to the encapsulated fibers, in the form of “asbestos body“, but they are all counted.
Exceptionally, it has been possible to confirm the absence of asbestos bodies in the pulmonary parenchyma, in patients considered as affected by asbestosis, based on other diagnostic elements. See: Gaensler et al. (1991).
These authors, however, play at ambiguity, describing as “idiopathic” the fibrosis of workers exposed to asbestos, concerned by such concurrence of circumstances, attributing their inclusion in the study, to a presumed artifact of the selection.
If we are allowed to express our criteria, such an explanation turns out to be highly improbable, and possibly obeys rather to the preconceived ideas of those who formulated it.
With regard to all this, we consider it appropriate to bring up the content of our work:
La duda que no ofende: Amianto y fibrosis pulmonar idiopática (The doubt that does not offend: Asbestos and idiopathic pulmonary fibrosis)
The quantification, in autopsy, of the asbestos bodies found, with the intensity of pleural adhesions suffered, is a result reviewed by Wu et al. (1988), according to what has already been stated by us, with the occasion of dealing with the aforementioned pleural adhesions.
Its mere presence, even without quantifying, was already indicated early as a diagnostic element in the necropsies: Stewart (1928).
The search for asbestos bodies in sputum, is a non-invasive and inexpensive technique, which, with perseverance and patience, can yield unexpected results in the screening of populations supposedly not subject to exposure to asbestos.
Indeed, if the presence of asbestos bodies in sufficiently significant amounts, is merely indicative that confirms the exposition, its search in working populations of which there is already certainty of that exposition, has no more justification, than that of the material test, the objective and impersonal ratification that provides the obtained result.
On the other hand, when applied to cohorts that supposedly have not been exposed to asbestos, a positive finding comes to remedy a registry defect, which in the case of asbestos assumes a certain probability, due to multiple factors, among which it is worth mentioning, in the first place, the ignorance in which the daily work of the workers has often been developed, with respect to the substances present in their working environment, and, secondly, by the insidious and silent progressive progress of the pathologies associated with asbestos, until the emergence of symptoms, which, in addition, and for a long time at least, are not identified in their true etiology, first by the interested party, but even by the physicians themselves, who usually proceed by successive diagnoses of presumption, and consequently discarding those who do not meet expectations, all when an essential element of the anamnesis, which is the data or information of the history, fails to work of the patient, which would have allowed to relate to the asbestos the clinical picture under study.
The presence of asbestos bodies in sputum, is highly specific with respect to its connection, strictly, with occupational exposure, when the research is done on a large cohort of general population, not selected.
This follows, in effect, from the results of the work of Modin et al. (1982), in which the few findings, from several tens of thousands of analyzes, all corresponded to a labor exposure, confirmed later.
Therefore, the analysis of asbestos bodies in sputum, is perfectly suitable for the purposes that we previously mentioned, with respect to the investigation in populations that supposedly were not exposed to labor contamination, or, at least, it turns out to be doubtful or merely suspected .
If an inclusion of the analysis of the presence of asbestos bodies in the sputum, referred to the general population, can, perhaps, be considered excessive, there is no doubt that, in certain geographical regions, in which so much has been the settlement of industries that they handled asbestos, and in situations of more or less generalized underreporting, as is the case of Spain, such a resource may constitute an interesting complement to the surveys, which, for the reasons previously adduced, may be appreciably fallible.
Let us think, singularly, in the case of those industrial polygons, in which some of the industries based in them, and by the very nature of the same, of them it is certain, or at least have the vehement suspicion, that in the there has been industrial use of the asbestos.
Such a procedure would also be fully justified, in cases in which “officially” there has been no occupational exposure to asbestos, and yet, the epidemiological analysis of the available pathological evidence points decisively to another interpretation, diametrically opposed.
An example of all this would be the indications referring to the industries of sugarcane and its refining, on the one hand, and the textile industries, supposedly “without” asbestos, on the other (and, therefore, excluding those factories that do recognize the past or present use of asbestos in the production process and in the final product produced): Chiappino et al. (2003) & (2005), Mensi et al. (2006) & (2007).
The result of such forecasts would be important for the interested parties themselves, but it would also be very convenient to be able to quantify the true extent of the exposure to asbestos in the geographical area in question, or, where appropriate, in the productive sector concerned by such questions.
In rural areas, an incidence of mesothelioma, above the national average, has been related to the reuse, in the past, of jute sacks that had previously been used for the transport of asbestos, a circumstance that we also discuss elsewhere of the present text.
This hypothesis also provides a possible opportunity for the use, rationally justified, of the count of asbestos bodies in the sputum of agricultural workers, who, in the absence of other evidence, in principle have not been considered as occupationally exposed to asbestos.
The aforementioned practice of reuse is also at the origin of some of the cases of mesothelioma, registered among workers in the textile industry, in those factories in which apparently asbestos was not part of the production process: Barbieri et al. (2008).
The distinction between occupational and environmental pollution is sometimes, in our opinion, highly questionable and merely conventional.
This is the case, for example, of the two cohorts used in the work of Alderisio et al., of 1996, in which one of them, the railroaders, is considered for occupational exposure, while the other, that of the policemen traffic of the municipal district of Rome, is assumed as subject to environmental exposure, despite the obvious fact that, in one or in another case, the exposure has occurred in the performance of their respective work, and not, for example , for taking the dog for a walk.
In the case of traffic police, their permanence in the workplace has forced them to breathe especially high concentrations of asbestos fibers, and that is precisely why they have been selected for the study, without this being an obstacle for them. that the concentrations of fibers in the atmosphere, in both cases, are quantitatively different.
These distinctions, taken from the purely academic sphere, can have undesirable negative connotations, because we consider that workers in situations like the referred one, of traffic policemen, should also be protected by justice, in their respective just claims for compensation, by the sequels derived from its exposure, generated in the usual performance of their job functions.
In any case, the availability of the technique of identification of asbestos bodies in sputum is a valuable epidemiological tool in any circumstance (also in the tracking of former asbestos workers, recognized as such), given the high prevalence found in some cohorts of active workers at the time of epidemiological research, as well as the verification in situ of the poor hygienic conditions in which they have had to perform their work, are premises that indicate the relevance of active search measures . See: Roel Valdés et al. (2004).
In the specific case of welders, the confirmation of their exposure has been evidenced through the use of analysis and counting of asbestos bodies: Pairon et al. (1994).
The possibility of the concurrence, in the same worker, of several pollutants, including asbestos (evidenced by the latter, among other factors, by the presence of asbestos bodies), is no theoretical elucubración of anyone, but a reality that eventually becomes revealed in the medical literature.
From this we will quote an example, which can certainly be described as extreme -and, therefore, not representative of the generality of cases-, but which, precisely because of its extreme nature, serves to show us all the open field of possibilities , of which said case could be considered as a frontier: up to that point it can be reached.
We are referring, specifically, to the case described in Anttila et al. (1984), in which the patient, a 74-year-old man, had a tumor resected in the upper lobe of his right lung, but to which, at the same time, it could be proven that, in fact, the patient was suffering from simultaneously of two malignant tumors, both pulmonary and primary: one central -with resection-, one small cell carcinoma, and another peripheral, a squamous cell carcinoma.
In addition, the peripheral lung tissue showed generalized peribronchiolar fibrosis, which extended from the non-respiratory bronchioles to the level of the alveolar ducts.
Abundantes cuerpos asbestósicos y grandes cantidades de un polvo negro, fueron vistos alrededor de los bronquiolos.
Pulmonary mineral particles were analyzed, identifying a total of nine different natural minerals, among them: anthophyllite and chrysotile asbestos, talc, quartz, feldspar and muscovite, part of which are components of the sand, and also of two artificial mullites, used in the composition of a fire retardant clay.
The patient’s work history explained the most probable origins of the minerals detected: for 23 years, he had worked as a mason, in the repair and demolition of stoves and chimneys, including the presence of asbestos in the isolation works.
Up to this point, we have considered asbestos bodies, merely as indicators of exposure, but that paradigm has not been generally accepted: in Flowers (1974), for example, the author argues in favor of a role of obligated mediator of the ferruginous body, both in the genesis of carcinoma and asbestosis, and in light of recent research, in any case that paradigm related to the passive role of asbestos bodies, may have to be widely reformed (and, in any case, already in the work of Governa et al., 1999, already mentioned above, is also assigned to the asbestos body a role not merely passive, and also, in Lund et al. (1994), is attributed to the iron of ferruginous bodies, a genotoxic effect, confirmed in vitro).
Indeed, taking into account the results of the work of Nakamura et al. (2009), we would have the following facts: when the elemental composition of the proteins of the asbestos bodies coming from mesothelioma patients or other neoplasms associated with the exposure to asbestos is investigated, a radio presence is found, which turns out to be in concentrations higher, millions of times, than that corresponding to sea water, which is the ideal base reference, for its stability and uniformity. See: Broecker et al. (1967).
Los citados autores, ponen de relieve el efecto continuado y persistente de las radiaciones en el entorno biológico de los cuerpos asbestósicos, con el consiguiente supuesto rol en la cancerogenicidad del amianto.
The aforementioned authors highlight the continued and persistent effect of radiation on the biological environment of the asbestos bodies, with the consequent supposed role in the carcinogenicity of asbestos.
The presence of radio in the proteins of the asbestos bodies, is put in relation, by Nakamura and its associates, with the presence, also, of this highly radioactive element, in the tobacco -see: Santos et al. (1994), Tso et al. (1964) & (1966) – an explanatory hypothesis, which to our understanding suffers from a weak point: mesothelioma, epidemiologically, does not show positive correlation with smoking, which, however, does not rule it out, referring to the pasive smokers.
In any case, what is well established is the affinity of the tobacco plant for the radio, which selectively concentrates it, from its natural presence in the mineral salts of the soil, or because of the fertilization with phosphate rich in uranium.
From all the above, it seems reasonable to deduce, that, with a sufficiently long exposure time, and the use of photographic plate of high sensitivity, a self-microphotography of asbestósicos bodies is feasible..
It would be a possibility that we consider extremely interesting, for demonstrative purposes, especially beyond the strictly academic sphere: for example, in a possible judicial use.
The self-radiography of asbestos bodies is a technique that has already been used -Moalli et al. (1987) -, but on that occasion it proceeded to confer radioactivity to the studied preparation, by incorporating tritium in the composition of the material constituting the asbestos bodies.
The foregoing is only a personal opinion of ours, which, to verify its reality, would have to be tested experimentally, which, as far as we know, has not been done so far.
The explanatory hypothesis that we have previously taken into consideration here, relating radioactivity with tobacco, has a large bibliography: (3).
Although radioactive elements are not the main carcinogen of tobacco, their presence causes, on its own, thousands of deaths per year throughout the world.
The tobacco industry knows its presence, for almost fifty years.
Faced with the incessant voice of denunciation of the scientific community in the face of this situation that overlaps the intrinsic noxiousness of tobacco, the silence and ineffectiveness of politicians and health authorities stand out, because, unlike what happens with other pollutants in the tobacco, also undesirable, the elimination of the main radioactive contaminant, the polonium, would be relatively easy and economical to carry out.
According to Brianna Rego (2009) & (2011), there are internal documents that demonstrate that the manufacturers devised methods to drastically reduce the concentration of the Polonium-210 isotope in tobacco smoke, but they decided not to do anything and kept their investigations secret.
Having acted otherwise, would have entailed additional costs. What other industrialists are reminding us of these behaviors?
The asbestos bodies are not the only reactive structures generated in the animal species, including the human being itself, in front of the contamination by the asbestos.
In fact, deposits of calcium oxalate crystals, a compound that is naturally generated in living matter, in kidney stones, and assuming the function of “windows” to accumulate sunlight, are also generated with lower prevalence. in certain desert cacti plants.
It is also found in plants of the genus Dieffenbachia, in those of the genus Oxalis, in those of the family of the Araceae, in the plant Colocasia esculenta, in the Actinidia deliciosa (kiwi), in those of the genus Agave, and, in small quantities, in Spinacia oleracea (spinach).
On the detection of oxalate, in those exposed to asbestos, see: de Vuyst et al. (1982), Ghio et al. (2003), Le Bouffant et al. (1976), Roggli (2004). On the presence of crystalloid structures, in general, in mesotheliomas, see: Ordóñez (2012).
The presence of asbestos bodies in a pleural biopsy can be demonstrative of the etiology of a pathology associated with asbestos, such as mesothelioma, but the opposite, its absence, is not proof that such etiology should be discarded, since In the tissue examined, non-encapsulated asbestos fibers can be present -only detectable by electron microscopy-, and, however, no structures reactive to their presence have been formed, such as the aforementioned asbestos bodies, which are usually detected by optical microscopy. , comparatively of lower resolution.
In spite of all this, the defendant companies will put the emphasis on this absence, and so, for example, in the request for reform by extending the text of the judgment, the company NAVANTIA, in the STSJ GAL 6966/2012, requested the inclusion of the following paragraph: “On 27-05-02 a pleural biopsy was performed in which no bodies of asbestos were observed”.
They are tricks that can only prosper, where they faced scrutiny without the indispensable knowledge of the real nature of the issues discussed.
Let us add to all this, that there exists, at least in Spain, the extremely inadequate custom, with bias that may be interested, of making equivalents to fibers and asbestos bodies, which, as we have already said, are microscopic reactive structures that surround the fibers, and which, therefore, are always larger than the fiber itself, which totally or partially encapsulates; in addition, the asbestos bodies are not always formed, but only in a minority of the fibers, and by more signs, such bodies, where they are usually located in the lung parenchyma of the patient biopsied or autopsied, and only very exceptionally are they reached to be found in the mesothelioma tumor tissue, when it is referred to said malignancy, which is trying to link the result of the corresponding inquiry.
It is not equivalent, count fibers or count asbestos bodies. Who, counting only the latter, bases in it the quantification of the cumulative exposure evident, commits a heavy underreporting.
Unfortunately, in our country it is common currency to act, even for reasons of mere cost, with these conditioning distortions.
The identification of asbestos bodies, usually is done by optical microscope; that of fibers seated in tissues of the patient, can be done by one or another method, but it is the electron microscope that yields much higher counts, and that, therefore, is closer to the actual existing load.
En Jurikovic et al. (1983), los autores, en una misma cohorte, localizan un 65% de examinados evidencian la presencia de fibras de asbesto libres, detectables sólo mediante el uso de microscopía electrónica, mientras que sólo en un 46% se pudo evidenciar, a través del microscopio óptico, la presencia de «cuerpos asbestósicos».
In Jurikovic et al. (1983), the authors, in the same cohort, found 65% of examinees evidenced the presence of free asbestos fibers, detectable only through the use of electronic microscopy, while only 46% could be evidenced, through the optical microscope, the presence of “asbestos bodies“.
Consequently, there was 19%, in which, despite having been exposed to asbestos, however, this circumstance was not demonstrated by any presence of the aforementioned “asbestos bodies“.
In Pooley & Ranson (1986), the authors state that: “The diameter distribution of the accumulated fiber, obtained using the electron microscope, suggests that the optical microscope is capable of visualizing only 5% of the crocidolite, 26.5 % of the amosite, and 0.14% of the chrysotile present in the lung tissue.
In Fondimare & Desbordes (1974), the authors, in a comparative study between the counts made in the same samples of human lung tissue, between asbestos bodies (identified by optical phase contrast microscope), and uncoated asbestos fibers (visualized by electron microscopy), present their results in a table of six determinations, among which we can see proportions such as, for example, 200 times higher than the second, with respect to the first (other values: 145’45, 140’91 , etc.). See also: Dodson et al. (1985).
How many business responsibilities will have run off the generous pores of this imperfect network? … ALL THIS, is overlooked in certain Spanish judgments on asbestos. And it is worth asking: would the magistrate rapporteur know? … If he did not know, bad, and if he knew it, worse.
1 Alderisio et al. (1996), Auerbach et al. (1980), Bignon et al. (1973), Billon-Galland (2012), Botham & Holt (1968) & (1971), Capellaro et al. (1997), Churg & Warnock (1979) & (1981), Cooke (1929), Das et al. (1977), Davis (1970), De Vuyst et al. (1982), (1987) & (1988), Dodson el al. (1982), (1989), (1985) & (1983), Farley et al. (1977), Gaensler & Addington (1969), Governa et al. (1999), Gross et al. (1969), Johansson et al. (1987), Labbate et al. (1994), Mace et al. (1980), McDonald et al. (1992), McLemore et al. (1980), McLarty et al. (1980), Moalli et al. (1987), Montoya Cabrera et al. (1988), Morgan & Holmes (1985), Pairon et al. (1994), Paris et al. (2002), Pettazzoni et al. (2007), Planteydt (1968), Planteydt et al. (1964), Roberts (1967), Roggli et al. (1982), (1983) & (1986), Scansetti et al. (1996), Simson & Sutherland Strachan (1931), Smith & Naylor (1972), Stewart et al. (1932), Stumphius (1971), Sulotto et al. (1997), Suzuki & Churg (1969), Szendröi et al. (1983), Teschler et al. (1996), Wälchli et al. (1987), Wheeler et al. (1988).
2 Andrion et al. (1982), Barroetavena et al. (1996), Bianchi et al. (1999), Kimizuka & Hayashi (1983), Martischnig et al. (1977), Mollo et al. (2002), Rubino et al. (1980), Thimpont et al. (2009), Warnock & Churg (1975), Yamada et al. (1997), Karjalainen et al. (1994).
3 Anonymous (1974), Berger et al. (1965), Black & Bretthauer (1968), Bogden et al. (1981), Bretthauer & Black (1967), Cohen et al. (1980), Cross (1984), Desideri et al. (2007), Ermolaeva-Makovskaia et al. (1965), Evans (1993), Fletcher (1994), Fu et al. (1987), Gregory (1965), Holtzman & Ilcewicz (1966), Joyet (1971), Kelley (1965), Khater (2004), Kilthau (1996), Lal et al. (1983), Little et al. (1965), Marmorstein (1986), Martell (1974), Moeller & Sun (2010), Muggli et al. (2008), Mussalo-Rauhamaa & Jaakkola (1985), Nikolova (1970) & (1972), Papastefanou (2001), (2007) & (2009), Peres & Hiromoto (2002), Radford & Hunt (1964) & (2008), Radford & Martell (1975), Rahman et al. (1987), Rego (2009) & (2011), Samuelsson (1989), Savidou et al. (2006), Schayer et al. (2009), Shabana et al. (2000), Singh & Nilikami (1976), Skrable et al. (1964), Skwarzec et al. (2001), Spiers & Passey (1953), Tahir & Alaamer (2008), Tidd (2008), Tso et al. (1964) & (1966), Turner & Radley (1960), Westin (1987), Winters & Di Franza (1982), Zagà & Gattavecchia (2008).
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