Asbestosis in South African asbestos miners

ENVIRONMENTAL

RESEARCH

Asbestosis

3, 310-319

( 1970)

in South G.

K.

African

Asbestos

Miners

SLUIS-CKEAfER

Since 1950 when a radiological snrvcy was carried out on South African crocidolite and amosite mints it has been known that asbestosis was being produced in these mines. The North West Cape Uluc (crocidolite) asbestos fields commenced operations about 1893, but it was not until 1949 that production exceeded 10,000 tons; however, since then expansion has been rapid and production nom cxx~& 100,000 tons per anmmi. The Northern Transvaal amositc field commenced operations, largely concentrated in one mint (Pcngc) in 1910; 6,700 tons vvcrc produced in 1928 and production is now about 80,000 tons per a~mum. In 1950 it bccamc compulsory for thrsc mines to employ mine medical officers, and in 1954 almost all of the asbestos mints hccame controlled under the Pneumoconiosis L44ctNo. 47 of 1936. This cntailcd among other things regular prcemployment and periodical clinical and radiolosical examinations of employees. On most mints thesr examinations eommenccd about 1956. The cardiorespiratory organs of deceased employees who were not receiving compensation had to be removed for csamination at the Pathology Division of the Pncumoconiosis Kcscarch Unit in Johannesburg-except in cases when the next-of-kin refused permission for an autopsy examination. Thcrc is no information available as to how long it takes after commencement of cxposurc for asbestosis to occur and at what rate asbcstosis is being produced in South African Mines. A study was, therefore, undertaken of the fate of white miners on crocidolite and amosite asbestos mints who were employed in these mints between 19S4 and 1958 as far as mint records could provide the information. These records turned out to be imperfect, and the populations for the North West Cape and Penge are, therefore, incomplete. The Caucasian labour on these mines was fairly unstable. As will be seen from Tables 2 and 3 a significant proportion period of less than 10 years and a large proportion have short have a follow-up service only. No attempt was made to study thr Bantu labour force, who are in the majority ,310

ASBESTOSIS

311

as labour turnover is very high and records kept are such that follow-up of individuals over a period of time is impossible. The postmortem protocols of thr Rantu labourcrs on the mines have, however, been esamined to determine the incickncc~ of asbcstosis found during the period Jan. 1. 196%Dee. 31. 1969. Thea grade of asbestosis is assessed on the microscopic and macroscopic csamination of thcx lmlgs. Data are also available for part of the North West Cape arca of obscrvations of the diffusion for carbon monoxitl~~ ( DC0 ) and vital capacity (VC ) of white rnimrs who have no radiological cavidcncc of aslwstosis. No knowletl~~ cssists of dust conditions in these mints prior to 1940. Recorded dust conditions since that time arc’ shown irr Table 1 (du Toit. 1970).

It \vill be sun that conditions both surface and mldcrground have improved greatly in the North West Cape but less so in the amosite mints. Great efforts to improve conditions have been exercised since 1950 but since that time there has been great expansion in production. Surface occupations in both areas are dustier than underground with a higher proportion of fibre in the dust. It should bc noted that both crocidolitc and amosite occur in banded iron stone and the ambient dust consists of a mixture of 30% fibre and 36% free silica. the rcmainder bring of iron osidcas and other minerals.

Records 1958 were

of white obtained.

workers in the employ of the mines during the years -4s has been mentioned, these records are incomplete.

1954The

312

G. K. SLUIS-C:REI\IEl?

files of the Miners’ Medical Bureau and its branch at Kuruman were then checked if a dossier existed for the individual, and if so, the service data were recorded and the last X-ray was read. The vast majority of the X-rays were on 14 x 17-inch plates; a few were lOO-mm film. In the North West Cape vital capacity of white miners was measured on a Godart puhnonet and DC0 single-breath estimation with a Beckman infrared CO analyser. The method used was the Krogh breath-holding technique as modified by Ogilvic et n2. ( 1957 ).

5 Figures b Indicates

in parentheses indicate the nruuher of cases of asbestosis years of follow-up since first, expcwlre to asbestos.

it1 the group.

ASBESTOSIS

313

Tables 2 and 3 give the details of service and length of follow-up between first exposure to asbestos and radiological diagnosis of asbestosis or otherwise for the North West Cape and Transvaal areas separately. It will be seen that diagnoses of asbestosis increase with service but that one case each in North West Cape and Transvaal were diagnosed after short service (less than 5 years) after an appreciable period of follow-up ( 15-19 years). The North Transvaal miner had worked from 1953 to 1955 underground. His X-ray now shows evidence of fibrosis (T l/l Right Lower Zone by UICC-Cincinnati X-ray classification; (Gilson et al., 1970). The North West Cape miner had short service, mining in the early 1950’s. The diagnosis of asbcstosis was made after long follow-up. (S l/l Right Lower Zone by UICC-Cincinnati X-ray classification; Gilson et c/l.. 1970). Slight asbcstosis was confirmed at autopsy in 1969.

FIG.

1.

Lamellar pleural thickening.

314

(:.

K.

SLUIS-CREMER

It is clear that apart from length of service the time from first exposure to last follow-up is important, and it must be expected that with increasing follow-up period more casts of asbestosis with relatively short service will occur. However, medical examinations for people who cease to work in a controlled dusty occupation arc not compulsory and, unless they go to work in other mines, persons who have ceased asbestos exposure tend to become lost to the study populations. It should also be pointed out that of the long-service group with long follow-up (more than 20 years ) a number had apprcciablc service prior to 1954 in a period before the time when measurements of dust conditions were made. This is purely a radiological study; cases did occur in which persons came to postmortem and slight or even moderate degrees of asbestosis wcrc reported by the pathologist. These were not rccordcld as casts of asbestosis for this study if the .X-rays were normal. ;\linor degrees of lamellar pleural thickeninY (7 were encountered but unless this was unmistakable it was not considered as diagnostic. Figure 1 shows lamellar pleural thickenin, 0 considered indicative of asbestosis. Irregularity of the cardiac outline or diaphragms, if occurring alone, was not considrrccl as diagnostic; parcnchymal changes or calcified pleural plaques had Calcified plcbural plaques to be present before a diagnosis of asbcstosis was made. without parenchymal changes are considered diagnostic of asbestosis.

FIG.

2.

Parenchymal

asbestosis.

315

ASBESTOSIS

Figure 2 shows a typical cast of parrnchymal asbestosis, and Fig. 3 shows a calcified plaque. ‘4 large number of the persons studied had service on other mines including some with a silica risk. The greatest possible care was taken in the differential diagnosis between asbestosis and silicosis-a few cases of the latter condition OCcurrcd in this group. Calcifiecl pleural pbayucs. These, in general, did not occur in lessthan 20 years from commencing service. In the exceptions there is reason to suppose that nonindustrial exposure may have occurred in youth as the persons had lived in childhood in the same district as the mine. One case was, however, found in which plaques appeared 15 years after initial mining csposure to asbestoswithout any evidence of previous exposure ( Fig. 3).

(3)

FIG.

3.

Calcified

plaque.

316

G.

BRONCHIAL

K.

SLUIS-CREMER

CARCINOMA

AND

PLEURAL

MESOTHELIOMA

No person commencing work during 1954-1958 has developed either of these tumours. One person in the North West Cape group developed a carcinoma of the bronchus in 1965. He started service in 1928 and had developed asbestosis. The other in the Transvaal group started service in 194”he developed the tumour in 1963. A slight degree of asbestosis was found at autopsy. One whose service started in 1937 developed a mesothelioma of the pleura. He was in the North West Cape group. There was no radiological evidence of asbestosis. AUTOPSY

DATA

ON

BANTU

LABOURERS

Table 4 shows the findings at autopsy of the lungs examined during the period Jan. 1, 1965-Dec. 31, 1969 separately for the North West Cape and the Transvaal amosite area. These examinations were carried out by the pathologists of the Pathology Division of the Pneumoconiosis Research Unit in Johannesburg.

Total ilumber of ~wIch No :mbestosis Slight asbcst,osis &Iodernte asbestosis 8evere asbestosis Total asbestosis Car plllnlonnle Active tubetudosis Average age (yeus) Mean service (years 1

A high incidence of asbestosis mainly of slight degree occurs after relatively short service, It should be borne in mind that service details in Bantu are \rer) unreliable and almost certainly very often an underestimate-frequently a gross underestimate. The incidence of active tuberculosis is consistent with findings at autopsy in other Bantu populations and indicates that medical control in the two areas is similar and that the two populations are comparable. The population had been radiologically examined once every 6 months during their working life and clin-ically detectable cases of tuberculosis were removed from the working population. Those cases discovered at autopsy are mainly minimal lesions not detectable radiologically. RESULTS

OF

LUNG

FUNCTION

STUDIES

The men were separated into four age groups-20-29, 3039, 40-39, and 50-59 in the successive years of age. There are 64, 68, 41, and 6 men, respectively, ,groups. For the DC0 there was no statistically significant fall with service in any age

317

ASBESTOSIS

group. In no case was there an unmistakably abnormal result. One man in the SO- to 59-year age group and one in the 30- to 39-year age group had diffusions of 20 cc/min/mm Hg. For the VC there was a significant fall only in the 40- to 49-year age group. The detailed observations for the 40- to 49-year age group are given in Table 5. The standard normal figures used to calculate the percentage predicted normal are derived from Kory et al. ( 1961).

171 1
::.SfI .!I .‘3.i

ss toti

1s:;

.i Y' <*

I Iti

IS.’

.-I !I0

11;

IiS

4
10:;

170

:; !Jti

0’;v

170 1s:;

:: .,., -.> 4.71

1 YL'

.i 4tI .i .OO

SO 91 IO!) 11:; IOh 1%
Ii:; I 73 I ti.z 1 7.i is::

.i. 12 .i til’ :: .!I0 .-I I YL’ 4 “ti

Ii1

.5 2;

Ii.7

4 1-i 1 :I.?

1%

ISI) 1AS 1x2 IV 1 sx IS:: 17s 171 1 S!I 1 ST, ISS IS0 IS:; I77

4 .iS .i.44 4 tit; ,i citi

4 ?!I .-I .‘;‘:. 4 :;:: 4 !)I 4.40 ti .iti 4 Sh 4.42 4.93

1Oi

!)I

:; 91

I:! 00 ti .“‘, I. .i !I1

11.otI I .tii I0.00 1 .ot1 s I7 2 ()(I 17

INI

:: 00 12. 00 1:;. 60 lL’.li 4.s s 00

S.i

.i .iO 1s 67

I IO O!l ‘1’;, Si

IS 00 17.00 ,i .OO

I (I.-l

2 ,io

0. tio

1.2:; !!!I !I0

(i 00 16 .iO

1 I ).-I 120

0.17 :;.!)I .i 00

I 7.i IS:! 1 i!4

.i 4!l 5 '2 I

IOL' IIH

IX14 Ii7 It;!1 I!)1

4 .i .i 0

7s Iti (hi !U5

!lli 111 11s 1%

Ii:: I Si

.i t )I I .i !Ni

IX4

4 :;i

1111 !I" SS

5 0,i

:1. 00 ti .L’o 1 .oo !I. 00

..io fi so 1.5ll 2 ti ti .i 1.i

.O(I tit1 2.i :c< ,, ':';

318

G.

K.

SLUIS-CREMER

The VC expressed as predicted normal is negatively correlated with asbestos service (p < .OI). It should be noted, however, that none of the observations are definitely abnormal.

Length of exposure and length of residence of asbestos in the lungs both appear to be of significance in determining the onset of asbestosis. Two cases in miners with very short service (O-4.9 years) were diagnosed after moderately long follow-up and there arc four other cases in workers with fairly short service (5-9.9 years) that were diagnosed after prolonged follow-up, There is, in addition, a clear relation between length of service and the in& dence of asbestosis demonstrated in this population. It is known that slight and even moderate degrees of asbestosis may not be detectable radiologically. The large number of people with slight asbestosis found at autopsy is, no doubt, the population from which the casts appearing after cessation of exposure arise, and the suggestion is that the disease, in some‘ cases at least, is progressive despite cessation of exposure. The significance of the high incidence of histological changes at postmortem should not be exaggerated. In thfx majority of cases the). are of most minor degree. The findings on physiological testing trnd to bcaar out that these changes are of little clinical significance at present as, although there was found a fall of vital capacitv with scrvicc in the 40- to 49.year age gvllp, there were, on the other hand, no definitc~ly abnormal findings (2 SD from the predicted) either in the case of the DC0 or thy \‘C. It is, of course, unknown how many of these subclinical cases \vill progress with time. or whcthrr the, majority will remain in status quo on cessation of csposmc~. Some \rill probably progress. This study indicates that there is no way to pinpoint persons with minimal asbestosis in life in order to remove them from further c>xposurcs early; clubbi~l~ has not been a feature in this population and the physiological tests in this series do not indicate persons who might have early asbestosis \vith normal X-rays. No person starting service on these mines iu the early 1950’s has 50 far developed carcinoma of the bronchus or mesothelioma of the pleura. This is in accord with the general finding that the latent period is usually longer than 20 years and in the case of mesothelioma often 40 years or longer. Twenty-sis of the 147 people in the Transvaal group and 53 of 391 in the North West Cape group had service prior to 1950. Calcified pleural plaques are considered as diagnostic of asbestosis in this study. There are some who would still consider this a controversial attitude. In five cases each in the North West Cape and Northern Transvaal calcified pleural plaqucss were the only radiological sign of asbestosis. The incidence of asbestosis discovered at autopsy in Bantu is appreciably lowcxr than that in a similar study published in 1965. This study dealt with the postmortem material from Bantu who died between July 1, 1959-June 30, 196-1. In that study asbestosis was foulid in 71.5% of cases from the North West Cape and 79.7% from the Transvaal. The appreciable improvement is, no doubt, the result

ASBESTOSIS

of accelerated mills.

endeavour

to improve

dust conditions

319 in and around the mines and

REFERENCES Dr

R. S. J. (1970). Personal comnl~mication. J. C., ROHLIG, II., BRISTOL, L. J,, CAIITIEH, P. H.. FELSON, B.. CILUNGEI~, T. R., JACOHSON. G., KIVILUOTO, R., LAINIIART, 6'. S., MACDOKALD, J. C., PESDEHGHASS, E. P., ROSSITEK. (1. li:., SELIFOFF, I. J., SLUIS-CHEMEH, c:. li., AND ~~HIGHT, c. \Y. UICC/Cincinnati classification of the radiographic appearances of pncumoconioses. ( In press) ICONY. H. C., CALLAHAK, R., ROHEN, H. (Z., ANI) SYNER, J. C. (1961). The Veterans AdIninistr;ltiorl-Arlene co-operative stud!. of pulmonary function. I. Clinical spirometry in normaI men. r\rner. J. Med. 30, 24:3-058. OGILVIE, C. hi., FOHSTEH, R. E., BLAKEMORE. \V. S., AND MOHTON, J. \Y. (1937). A standardised breath-holding technique for the clinical measurement of the lung for carbon monoxide. J. Clin. In~xst. 36, 1-17. Pnerllnoconiosis Act No. 47 ( 1936). Cgovernment Printer, Pretoria. 1‘01T,

Grrsos.