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Silicotic Lungs: The Minerals they Contain

Published online by Cambridge University Press:  15 May 2009

William R. Jones
William R. Jones
Affiliation:
From the Geological Department, Imperial College of Science and Technology, London. Published with the consent of the Committee on Industrial Pulmonary Diseases, British Medical Research Council.
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The results of these investigations on the mineral residues obtained from twenty-nine silicotic lungs, and of the examination of the rocks and materials which gave rise to the inhaled dusts causing these cases of silicosis, lead to the following conclusions:

(1) The bulk of the mineral residues obtained from every silicotic lung investigated by the author consists of minute fibres of the mineral, sericite, a hydrated silicate of aluminium and potassium known also as “secondary white mica.” This mineral is abundantly present also in all the rocks and materials which gave rise to the inhaled dust; and it is present in these rocks and materials in minute fibres and scales of the size it is found in the residues and also in the lung tissue.

(2) Silica in the uncombined state, as quartz, is also present in these residues as relatively coarse and fine grains; it occurs, however, in amounts subordinate to sericite. Especially is this so with regard to the small number of quartz particles, as compared with the countless fibres of sericite.

(3) One relatively large grain of quartz, measuring 10 × 8 × 5 microns such as is found in the residues, is equal in volume to 800 fibres of sericite measuring 2 × 0·5 × 0·5 microns, and contributes as much silica in the chemical analysis of a residue as would 1600 fibres of sericite. This would appear to be out of all proportion to the silicotic effect of one such quartz in the bronchi and bronchioles, compared with the effect in the alveoli of hundreds of fibres of sericite.

(4) Silica in the uncombined state, as quartz, is not the chief cause of silicosis in these and certain other cases. This appears to be conclusively established, it is submitted here, by the following facts: (a) The amount of quartz and the size and form of the quartz grains in the sandstones occurring in the underground working-places in the Scottish Coalfields and in the South Wales Coalfield, are alike. The latter sandstones give rise to dust that has caused scores of cases of silicosis, whereas no authenticated case of silicosis has been produced in the Scottish Coalfields. (b) The gold-bearing quartz conglomerate of South Africa gives rise to dust that has caused thousands of cases of silicosis; the gold-bearing quartz rock of the Kolar Goldfield, India, contains more quartz than the South African rock and yet produces dust that has caused no case of that disease. (c) No quartz-bearing rocks investigated by the author are known to have given rise to silicosis-producing dust except those which also contain abundance of fibrous aggregates of sericite or of fibrous silicate minerals, loosely held together and easily freed into the atmosphere when the rock is drilled and blasted. (d) Rocks which contain a relatively small percentage of quartz (well below the minimum amount in the rock types named in the Silicosis Schemes under English law) but which do contain fibrous silicate minerals such as sericite and sillimanite, as for example at Broken Hill Mines, New South Wales, produce dust that has caused a large number of silicosis cases.

(5) These investigations are not concerned with the pathological condition produced by the minerals in the lungs. Whether they merely act as mechanical irritants causing the growth of fibrous tissue as advocated by some well-known authorities, or induce chemical changes as maintained by certain eminent pathologists, is a question entirely beyond the province of the author. His conclusions do not militate against either theory; on the contrary, they provide the former school with evidence of the presence in the lungs of thousands of acicular fibres that presumably could act as mechanical irritants, and the latter school with evidence of the presence of silicate minerals less stable than quartz and which, because of their physical form, expose far greater surface to volume for any chemical action than do the more compact grains of quartz.

(6) Lastly, it is submitted here that it is mainly the presence in the exploited rocks and materials of fibrous minerals, be they sericite, sillimanite, tremolite, etc. (or a fibrous form of free silica as in chert or of a fibrous rock as in pumice) in aggregates which during the impact of drilling, blasting, or crushing, become freed into the atmosphere as individual fibres, that enables sufficient material in course of time to enter the lungs to cause silicosis. It is not suggested that sufficient minute particles of quartz could not, under any circumstances whatever, enter the lungs to cause silicosis, although the cases here investigated appear to show conclusively that they have not done so; but it is maintained that the fibrous minerals hasten the process so very considerably that their presence in the exploited rocks and materials is of far greater importance in causing this disease than is the presence of quartz.

Type
Research Article
Information
Journal of Hygiene , Volume 33 , Issue 3 , August 1933 , pp. 307 - 329
Copyright
Copyright © Cambridge University Press 1933

References

page 307 note 1 The part of the Silicosis Scheme applicable to the majority of underground workers in collieries (those engaged in sinking pits, driving cross-measure drifts, or in narrow working places come under a special part of the scheme) is as follows:

“This Scheme (No. 342 of 1931) shall apply to all workmen employed at any time on or after the commencement of this Scheme in any of the following processes:

(i) Mining and quarrying of silica rock: For the purposes of this Scheme silica rock means quartz, quartzite, sandstone, gritstone, or chert, but does not include natural sand or rotten rock.

(ii) Drilling and blasting in silica rock, in or incidental to the mining or quarrying of other minerals.”

In a previous Order (No. 975) the latter part of (i) read “but does not include natural sand or rotten rock or any rock containing less than 50 per cent, free silica.”

page 309 note 1 “Silicosis”: Records of the International Conference at Johannesburg 13–17 August, 1930, p. 86.Google Scholar

page 309 note 2 Forty-eight lungs have so far been treated and the residues examined; some of these were from workers who had died of pulmonary diseases other than silicosis, and one was a normal lung used as control.

page 310 note 1 A beaker of 2 litres capacity, measuring 19 cm. in length and 14 cm. in diameter, is very suitable for this purpose.

page 311 note 1 Analysis of the whole filtrate from the acid treatment of lung A was made in order to determine the amount of each constituent leached by the acid. The filtrate gave the following weights in grams: SiO2 0·048, Al2O3 0·057, Fe2O3 0·264, CaO 0·254, MgO 0·077, K2O 0·798, Na2O 0·488, P2O5 1·187, MnO 0·005. By calculation it is found that the total silica leached by the acid is only 1·6 per cent, of the silica content of the residue; similarly, 4·3 per cent, of the total alumina was leached.

page 313 note 1 It has been suggested that as some of the readers may not be familiar with the petrological microscope, an explanatory note here would be useful. The most distinctive features of the petrological microscope are the Analyser and Polariser (the nicol prisms) each of which is constructed so as to allow the passage of one ray vibrating in one plane (polarised light) and to eliminate the other vibrating at right angles to it. When the nicol prisms are crossed there is total darkness unless the object is doubly refracting. When, for example, a section of a lung containing minute colourless crystals of an anistropic mineral is examined in Ordinary light (as under a biological microscope) the crystals are not visible. Under crossed nicols there is total darkness except where the minerals occur; these will show up clearly, and by slight rotation of the Analyser or Polariser the exact location of the minerals, in relation to the lung tissue, can be determined.

page 314 note 1 Shannon, E. V. (1926). The Minerals of Idaho, U.S. Nat. Mus. Bull. No. 131, p. 273.Google Scholar

page 316 note 1 This is easily demonstrated. By breaking a piece of the Transvaal “Banket,” or of a sericitic sandstone, the fibres released into the atmosphere can be collected on a gelatine plate.

page 317 note 1 Church, (1889). Milroy Lectures, Lancet, i, 615. The analysis was made for Dr Arlidge in 1875.Google Scholar

page 317 note 2 The presence of other silicate minerals in clays used in the pottery industry is discussed on p. 320.

page 317 note 3 Hodenpyl, (1899). New York. Med. Record, 56, 942.Google Scholar

page 317 note 4 McCrae, (1913). The Ash of Silicotic Lungs, S. Africa Inst. for Med. Research, March 3rd.Google Scholar

page 318 note 1 Zircon and other aluminium-free silicates occur in the Banket.

page 319 note 1 Before examining this material under the microscope, Dr McCrae digested it with HCl and KClO3, thus decomposing most of the silicates, including sericite. What he examined, therefore, was not the residue but the particles of quartz and the remnants of the silicates which survived this harsh chemical treatment.

page 320 note 1 Other silicate minerals are also present in clays, but they need not be considered here because they would not affect the calculations except to an infinitesimal degree.

page 322 note 1 Statement by Mr Barry in the Records of the International Conference on Silicosis held at Johannesburg, August, 1930, p. 84.Google Scholar

page 322 note 2 The total underground labour force at the four goldmines at Kolar is 12,000, of whom 300 are Europeans. The latter undergo periodic X-ray examination; the natives object to such examination. The present average length of underground service of the Europeans is over 15 years and a large number have over 20 years' service. Hundreds of natives are in receipt of gratuities paid by the Company for 20 and more years' service underground. The natives are employed underground throughout the year. Pulmonary diseases among the undergound workmen are not more common than amongst the 6000 employed on the surface, and amongst those employed in industries in Bangalore. Reports of the Mysore Government show this.

page 324 note 1 The total absence of cases of silicosis in the Scottish coalfields has been kindly confirmed by the Government Mines Dept.

page 324 note 2 A reference to the excellent coloured charts issued recently by the Geological Survey of Scotland, showing numerous vertical sections through various parts of the Scottish coalfields establishes this fact as also does the authoritative information supplied to the author.

page 324 note 3 The names of the collieries have been purposely omitted, on advice.

page 325 note 1 Silicosis: Rec. Internal. Confer, held at Johannesburg, August 13th–27th, 1930, Dr W. E. George, p. 67.Google Scholar

page 325 note 2 Silicosis: Rec. Internal. Confer, held at Johannesburg, August 13th–27th, 1930, Dr W. E. George, pp. 39 and 40.Google Scholar

page 325 note 3 Sayers, R. R. (1925). Silicosis among Miners. Bureau of Mines, Washington.Google Scholar

page 325 note 4 Rec. Internal. Confer. pp. 39 and 40.Google Scholar

page 325 note 5 Rec. Internal. Confer. p. 384.Google Scholar

page 325 note 6 Rec. Internal. Confer. p. 62.Google Scholar

page 326 note 1 The mineralogical term “asbestos” is restricted to certain kinds of amphiboles which pass into fibrous varieties.