Assylbek K. Zeinidenov, Gulmira M. Tykezhanova, Roza T. Musina

Academician E.A. Buketov Karaganda State University

To the question on expediency of use of chrysotile-asbestos in Kazakhstan (Review)

In the article the question on properties of chrysotile-asbestos, its ecological danger and expediency of use in Kazakhstan are considered.

Now there is an opinion of scientists on danger amphibole asbestos which are already included in the Appendix of III Rotterdam convention and fall under procedure preliminary proved agreement concerning separate dangerous chemical substances and pesticides in international trade, in comparison with chrysotile asbestos [1].

Researches of scientists confirm that all kinds of asbestos are capable to cause a cancer of lungs, mesothelioma and asbestosis. It is impossible to define threshold level below which asbestos does not represent cancerigenic danger [1].

Asbestos is referred to the group of fine-fibered minerals of a silicate class. In the nature these aggregates with spatial structure are in a kind of thinnest flexible fibres.

The majority of researchers refer asbestos both to initiators and to the pro-motors of carcinogenesis. Damaging action on DNA and infringement its reparation, damage of many endocellular signal ways, infringement of an expression of some oncogene, genes suppressors and factors of growth are shown. Thus, studying of mutagen activity of fibres, independent from its reasons, represents a great interest [2]. Now an essential role in the mechanism of cancerogenic action of asbestos from properties of a surface of its fibres, sorption on it generation on electrically charged on the centres of a surface of the active and oxygen radicals possessing, in particular, mutagen properties. Change of properties of a surface can change biological activity of asbestos [3]. Carcinogenicity of asbestos in many respects depends on physical and chemical properties of fibres surface. For example, calcinations reduces bioaggression of an asbesto-cement dust and the fibres liberated from slate at its operation.

It is experimentally proved that asbestine minerals in a human organism are capable to initiate growth of malignant new growths. In many countries extraction, manufacture and their application are partially forbidden. [4].

There are two basic types of asbestos - serpentine (chrysotile-asbestos, or white asbestos) and amphibole (amphibole-asbestos). Serpentines form the combined, braided or bent fibres and represent smaller health hazard. Amphiboles have direct needle-typed fibres - because of fragility of these structures the particles are formed which inhalation has the cancerogenic factor [5].

The chrysotile-asbestos also named white asbestos, meets in the nature. It is the fibrous hydrosilicate of magnesium belonging to serpentine group of minerals. Chrysotile-asbestos is the magnesium hydrosilicate by a chemical compound closed to well-known to all talc minerals, i.e. from the chemical point of view it is absolutely harmless to an organism. The main components are dioxide silicon and oxide magnesium (to 45 % and 42 % accordingly). Other components do not rise up 1-2 %. Chrysotile-asbestos crystals have an unusual structure: they represent the most thin hollow 2.6∙10-5 mm and rub-flanks-fibrilly length in diameter to 2…3 cm. Such crystals remind soft cellulose fibres of cotton wool [6].

After enrichment of asbestos rock the bunches of fibres in diameter 10–100 microns have breaking strength, comparable with durability of the best marks of a steel (1700–3700 MPа). Fibres have low heat conductivity (0.3–0.4 Vt / (м∙К), the stability to the raised temperatures (their structure does not collapse at heating to 500–600 ⁰C), a fusion heat (about 1500 ⁰C) [7].

Fibres possess high firmness in alkalis, do not decay in water. They can be split (fluff up) on thin, soft, flexible and elastic fibrils which have high adhesive and cohesive ability, high spinning properties.

It is necessary to notice that the human body regularly contacts to fibres chrysotile, constantly present at environment air as serpentine minerals are soil-forming and are found out everywhere in the ecosystems which part is the person. A source of environmental contamination by chrysotile fibres are also industrial workings out of its deposits and production use on its basis that promotes increase in the maintenance of fibres of the given mineral in air inhaled by the person.

As well as concerning other inhaled firm particles to which heavy influence people are exposed or have been exposed owing to the trade, also exists that certificate that heavy and long influence chrysotile can cause a cancer of lungs.

Value of similar researches consists that influence by low doses chrysotile do not represent obvious risk to health. As the general dose believes eventually probability of occurrence and disease development, the risk of adverse result can be low if any, even the high transferred doses of influence took place in a short time [8].

Amphiboles. The chemical compound of fibres of amphiboles is more combined, in present time five kinds of amphiboles are distinguished. Though their structures are similar, property of instability is a direct consequence of the fact that the crystal lattice of dioxide silicon can accept in itself a mix many various ions (that is caused by containing breeds) in the space between tapes of structure which form fibres [9].

The external surface of crystal structures Amphiboles is similar to quartz and has properties of chemical stability of quartz.

On a chemical compound asbestos represents water silicates of magnesium, iron, partly calcium and sodium.

Last quantitative reviews of epidemiological researches of mineral fibres have defined potential possibility that chrysotile and amphibole asbestos cause a cancer of lungs and mesothelioma to the types of fibres that also is differentiated between these two minerals [10]. Under the last analyses the conclusion was also made that longer, thinner fibres have the greatest potential possibility it was informed in reports on studying of respiratory toxicology of animals. However one of the basic difficulties in interpretation of these researches were that primary calculations on influence were poorly differentiated between chrysotile and amphiboles.

Researches have shown that the dust containing chrysotile-asbestos, chemically inert and the mechanism of its action on a human body essentially does not differ from action of other kinds of a mineral dust (cement, quartz, etc.). At the small maintenance of fibres of asbestos in air they basically stay in the top respiratory ways also are produced from an organism by natural way (for example with sputum). Those fibres which penetrated into lungs can penetrate into pulmonary fabric. Thus they are exposed at once to attack of phagocytes – the cages which are carrying out in organism protective functions. Phagocytes accumulate round a foreign matter and, perishing, create round it the aggressive (sour) environment which is destroying and tearing away a fibre. Chrysotile-asbestos in these conditions collapses, and products of its disintegration are deduced from an organism.

Amphiboles asbestoses being acid-resistant, are not damaged by phagocytes. Besides, they contain impurity biologically active substances (connections Fe, Co, Ni, etc.) that was at the bottom of an interdiction of their extraction and application by the International convention on a labour safety at using asbestos in 1986.

Chrysotile-asbestos combines high mechanical durability fibers, fire - and thermal resistance, sound - and electricisolating properties, ability to form steady connections with inorganic and orgnical substances that has made its irreplaceable by manufacture more than 3000 kinds of industrial materials [11].

Now there are no substitutes which would possess are unique properties of asbestos, and alternative materials have higher carcinogenicity. The analysis of a current state of studying of properties of asbestos shows their ambiguity. Researches of properties of chrysotile-asbestos allows to deal with a question on expediency of their further use in industrial production [3].

In connection with the inconsistent data Kazakhstan initiated own researches. The Government of the Republic of Kazakhstan has ordered the National centre of occupational hygiene and professional diseases carefully to study influence chrysotile on health of the person. On this point in question there was organized a panel discussion on a theme "Asbestos and stable organic pollutants (SOP): the policy and practice in Kazakhstan and the countries of European Union".

State position: before to accept any strict measures concerning chrysotile-asbestos manufacture, it is necessary to obtain the accurate and true data of scientific and medical researches which accurately allow to understand that the use of chrysotile-asbestos injure health of the person very much.

In 2007 Kazakhstan ratified the Rotterdam convention, that regulates international trade of separate dangerous chemical substances and by that has taken up a number of obligations on dangerous pesticides.

Within the limits of the accepted obligations the question on expediencychrysotile-asbestos using is considered. It is connected by that in many countries including Europe, all kinds of asbestos are forbidden to application. Meanwhile the manufacture and distribution question chrysotile asbestos is sensitive enough for Kazakhstan as chrysotile-asbestos is potentially dangerous substance - carcinogen. Nevertheless, some Kazakhstan’s enterprises make production in which structure there is a maintenance chrysotile-asbestos, its share is insignificant, but made production cheap enough, and it is in demand among the population[3].

In Kazakhstan amphibole asbestos is not used, the unique enterprise for extraction, enrichment of ores and release of commodity asbestos is the joint-stock company "Kostanai minerals" where about 3500 people work. The enterprise produces about 200 thousand tons of chrysotile-asbestos a year, among them for internal consumption 16 thousand tons of asbestos, or about 7 % of all volume of output is used. The basic consumers of Kazakhstan chrysotile fibres are India - 29 %, Uzbekistan - 27 %, China - 18 %, Ukraine - 11 % [3,12].

REFERENCES

[1] Speranskaya O.,Tsygunova O., ,Astanina L., Asbestos: reality, problems, recommendations. Astana-Moscow-Kiev, 2008.

[2] Bernstein, D. M., J. Chevalier, P. Smith. Comparison of kalidry chrysotile asbestos and pure tremolite: respiratory biostability and histopathology after short-term influence (2003). Respiratory Toxicology 15 \14.

[3] Kosaev K., Kazakhstan supports carrying out of in-depth studies of influence of chrysotile asbestos. Astana, 2009.

[4] Bernei I.I., Theory of formation of asbestos cement sheets and tubes: scientific editions, (1988), Р. 275-289.

[5] Glushkov L.A., Ventilation and air clearing on asbestos processing factories, 1957.

[6] Izmerov N.F., Elovskaja L.T., Burmistrova T.B. etc., Medicine of work and industrial ecology. 10 (1998), Р.1-7.

[7] Kashanski S.V., Kochelaev V.A., Preventive maintenance asbestos-conditioned diseases: Collection of publications. Asbestos, 2002.

[8] Kashanski S.V., The social responsibility of the employer for workers’ health: Theses of International conferences. 2003. Р. 44-50.

[9] Pylev L.N., Vasileva L.A., Stadnikova N.M. etc., The characteristic of biological properties of fibres of the chrysotile-asbestos, the processed acid // Hygiene and sanitary. 4 (2006). Р. 70-73.

[10] Petrov V.P., Stories of three unusual minerals: scientific edition, 1978.

[11] Pluchin A.E., Hygienic aspects of workers’ health state of under extraction and the reference chrysotile asbestos. Hygiene and Sanitary. 3 (2006). Р. 26-28.

[12] http://www.a-rti.com