ORIGINAL ARTICLES. In the course of a case-control study of mesothelioma in South. Cases

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1 ASBESTOS EXPOSURE AND MESOTHELIOMA IN SOUTH AFRICA Dayid Rees, Kim Gdman, Ewe Furie, Rnald Chapman, Charlme Blignaut, Max 0 Bachmann, Jnny Myers Objectives. T describe the expsure experiences f Suth African mesthelima cases, with emphasis n the cntributin made t the caselad by different fibre types, the prprtin f subjects with n recall f asbests expsure and nly envirnmental cntact, and the imprtance f putative causes ther than asbests. Design. A multicentred case-cntrl study. Subjects and setting. 123 patients with mesthelima interviewed by trained interviewers in study centres established in Jhannesburg, Kimberley, Pretria, Blemfntein, Cape T~ and Prt Elizabeth. Results. A cnvincing histry f asbests expsure was btained in the verwhelming majrity f cases (nly 5 cases had unlikely asbests expsure). Twenty-three subjects had wrked n Cape crcidlite mines, 3 at Peng~ (an amsite mine), 3 n mines prducing amsite and Transvaal crcidlite and 1 n a Transvaal crcidlite mine. Exclusively envirnmental expsure accunted fr at least 18% f cases; 91% f these cases (20/'22 subjects) had had cntact with Cape crcidlite. There was a relative paucity f cases linked t amsite and n cnvincing chrystile case. Nn-asbests causes ccur rarely, if at all; in Suth Africa. Cnclusin. The prepnderance f crcidlite cases, fllwed by amsite and then chrystile cases, is cnsistent with the view that there is a fibre gradient f mesthelimagenic ptential fr Suth African asbests (crcidlite > amsite > chrystile). 5 Afr Med J1999; 89: Natinal Cmtre Jr Occupatinal Health and Departmmt fcmmunity Health, University fthe Witwatersrand, Jhannesburg David Rees, MB BCh, DOH, MSc, PhD, MFOM Natinal Cmtre fr Occupatinal Health, Jhannesburg Kim Gdman, RNRM, MBA Departmmt fhealth, Welfare and Envirnmmtal Affairs, Kimberky, Nrthern Cape Elize Furie, MB ChB, MMed (Rad T) Departmmt fcmmunity Health, University fthe Orange Free State, BlemJntein Rnald Chapman, BSc, MB BCh, MMed (CH) Departmmt fcmmunity Health, University fpretria Charlme Blignaut, MB ChB, DOH, MMed (CH) Departmmt fcmmunity Health, University fcape Twn Max 0 Bachmann, MB ChB, DOH, MSc, FFCH, MFPHM Jnny Myers, MB ChB, BSc, MD, MFOM In the curse f a case-cntrl study f mesthelima in Suth Africa, detailed expsure infrmatin was btained frm 123 subjects. This expsure infrmatin is f interest in that it shws the cntributin different fibre types (crcidlite, arnsite and chrystile) make t the caselad (the chrystile caselad is f particular interest as chrystile is still mined in Suth Africa), the prprtin f subjects with n recall f asbests expsure, the ccupatins t lk ut fr when taking an ccupatinal histry, the prprtin f cases with exclusively envirnmental expsure (wh are nt eligible fr wrkers' cmpensatin and therefre require special cnsideratin), the imprtance f putative causes ther than asbests, and the danger f incidental expsure (e.g. use f panel heaters r living in asbests-cement structures). Despite decades f asbests mining and the attendant mesthelima epidemic, the abve issues have nt been thrughly studied in this cuntry. Suth African case series have been published but all were frm ne gegraphical regin, ne ccupatin (mining), r a single clinic. The nly incidence study' and the Suth African registry data share the flaw f incmplete expsure data prvided by surrgate infrmants. These limitatins are reduced in large measure by the detailed expsure data presented in this article. The analytical data are reprted elsewhere; this article fcuses n the details f asbests expsure reprted in persn by a relatively large number f subjects. METHODS AND SUBJECTS Study centres and research teams The study was cnducted in the six majr industrial ce~tres f Suth Africa, with each centre including all hspitals within 50 km f the city centre. Greater Blemfntein, Cape Twn, Durban, Jhannesburg, Kimberley, Prt Elizabeth and Pretria were selected as study centres because they are the majr industrial cities and are gegraphically placed s that their tertiary hspitals serve much f Suth Africa, including the asbests mining regins (withut being in asbests mining districts themselves). Durban was later abandned as a study centre as it did nt perate successfully. A research tearn cmprising a c-rdinatr and tw interviewers, between them fluent in English and the predminant vernaculars, was established in each study centre. Each team was trained using a detailed interactive instructin manual as pre-reading, fllwed by a day-lng training sessin. Research tearns perated fr apprximately 16 mnths, frm late 1988 thrugh early Cases Our intentin was t include all cases treated r diagnsed in the study centres ver the study perid. T achieve this all pathlgists, nclgists, cardithracic surgens and respiratry physicians registered in the study centres were invited by mail and telephne t refer new cases t the research

2 -. teams. In additin, t encurage participatin, key practitiners mst likely t encunter cases were visited by research te.ams. All these medical practitiners were reminded regularly f the study and were sent brightly clured reminder cards at intervals fr display in their rms. T increase the specificity f diagnsis, cases were nly entered int the study if a specialist pathlgist diagnsed mesthelima, the histlgical diagnsis was supprted n review by a member f the Suth African Asbests Tumur Reference Panel (a panel f experienced specialist pathlgists established t standardise the histlgical diagnsis f mesthelima), and immunhistchemical staining supprted the diagnsis with a minimum requirement f negative staining fr carcin-embrynic antigen (CEA). Expsure infrmatin Expsure infrmatin was btained directly frm subjects by means f a structured questinnaire after written infrmed cnsent had been btained. The questinnaire was administered in the preferred language f the subject and in a standard manner. The questinnaire included a residential histry (twn and magisterial district); time spent near dckyards, mines, mills, asbests-using factries r stres f asbests; parents' ccupatin; dmestic and leisure-time expsure t dust; and a cmplete ccupatinal histry, with detailed questining regarding asbests expsure. Tw cmpnents f the questinnaire were develped as 'memry jggers' t aid recall f particularly imprtant ptential surces f asbests expsure. One sectin enumerated districts in which asbests had been mined and the ther listed imprtant industries, ccupatins and activities with a knwn risk f asbests expsure. The industry and ccupatin lists were cmpiled by cllating infrmatin frm three surces, namely the literature, cnsultatin with experienced ccupatinal health practitiners, and the patient database f the Occupatinal Medicine Clinic f the Natinal Centre fr Occupatinal Health (NCOH). General references' 'were used t cmpile an initial list. T this was added the imprtant expsure settings reprted by patients wh had attended the clinic, with patients crss-filed accrding t expsure categry. The list was then.refined by tw experienced ccupatinal hygienists wh tgether prduced the final 31 primary memry jggers r ccupatinal risk settings (Appendix 1). Asbests expsure categries Subjects were ~uped accrding t prbability f expsure t asbests (expsure class), the likely fibre type and the nature f this expsure (e.g. ccupatinal r envirnmental). Expsure classes Table I shws the criteria fr allcatin f subjects t definite, prbable, pssible r unlikely asbests expsure classes. Table L Criteria fr asbests expsure classes Definite 1. Direct r indirect ccupatinal expsure reprted 2. Cntact with asbests while spending time in an asbests mining district (cntact included playing n tailings dumps, living near a mine r mill, parent wrking n a mine r mill asbests.fibre cntaminating wrk r dmestic envirnment) 3. Dmestic expsure reprted Prbable : 1. Wrked in high-riskccupatin r activity with n k:an f ccupatinal expsure 2 Spent 12 mnths r lnger in an asbestqs mining district f NW Cape, NE Transvaal r E Transvaal with n reprted cntact with asbests 3. C-resident wrked with asbests prducts injhe residence Pssible 1. Wrked in a risk ccupatin with n recall f ~pati~ expsure - 2. Spent less than 12 mnths in NW Cape, NE Transvaal r E Transvaal district with n recall f cntact 3. Dmestic use f asbests cement prducts r heating panels 4. Lived r wrked in an asbests cement structure 5. Lived r wrked Within 1 km f a dckyard r asbests prduct manufacturing factry 6. Uncertain direct r indirect ccupatinal expsure reprted Unlikely 1. N recall f expsure 2. N risk r high-risk ccupatin r activities 3. Lived in 'ther' district with n reprted cntact The magisterial districts f Suth Africa were divided int five grups: Nrthern Cape and Nrth West (Cape crcidlite mining, previusly the NW Cape asbests fields); Nrthern Prvince (amsite and/r Transvaal crcidlite mining, previusly the NE Transvaal mining regin); Mpumalanga (chrystile mining); 'ther' districts (minr asbests depsitsanthphillite, chrystile r tremlite mined in a small lcality fr a shrt perid in sme districts); and nn-asbests districts (n asbests depsits). The perid spent in any f the asbests districts was recrded fr each subject using the questinnaire data. Living 'near' an asbests mine r mill was nt restricted t a specified distance, since it is well knwn that extensive areas arund mines and mills were cntaminated, particularly in the Nrthern Cape" and Nrthern Prvince. 7 'High-risk' ccupatins r activities are thse fr which asbests expsure was thught t be prbable evenif the subject did nt actually recall expsure. In Appendix I thse wrk activities described in AI, 3, 6, 12, 13, 16, 18, 19, 21 and 22 were labelled high risk, while all ther activities described in A (excluding sugar-eane) and B were labelled 'risk' ccupatins. 'Other' districts mined asbests in limited quantities and in a small sectin f the district, ften nly fr a relatively shrt perid f time. Cnsequently asbests expsure was June 1999, V!. 89, N. 6 sam]

3 cnsidered unlikely in these areas - unless there was als reprted cntact with asbests, in which case the subject wuld be classified as definitely expsed. Nature f expsure Expsure was categrised. as ccupatinal, envirnmental, dmestic, r incidental. The categry'direct ccupatinal' included subjects wh wrked with asbests, while 'indirect ccupatinal' referred t expsure due t the use f asbests by c-wrkers. 'Envirnmental-mining' referred t expsure due t cntaminatin f the general envirnment by asbests mining, milling and related activities, while the categry'envirnmentalther' included thse living within a kilmetre f an asbestsusing factry, stre f asbests r dckyard. Dmestic expsure invlved expsure incurred at hme, either due t cntaminated wrk clthes (dmestic-elthes), r t wrk with asbests prducts (dmestic-use), fr instance hbbies and the servicing f mtr vehicle brakes. Incidental expsure invlved use f asbests cement garden furniture, spending time in asbests cement structures and use f asbests heating panels. RESULTS One hundred and twenty-three cases were accepted int the study. Table IT shws that 94% had pleural mesthelima, and that the mean age fr each regin was in the 50-6-year age grup. Ninety-fur (76%), 14 (11%),.12 (10%) and 5 (4%) cases were classed as definite, prbable, pssible and unlikely expsure, respectively; 17 cases were therefre classed as pssible r unlikely. A fairly cnvincing case culd be made fr asbests expsure even in mst f the pssible cases. One subject had visited the Nrthern Cape twn f Prieska (fr seven I-week visits) and anther Kegas (fr nine 10-day visits). Five subjects had wrked in jbs assciated with asbests expsure: an electrician in a dckyard, a plumber and cnstructin site wrker, a mulder in a fundry, a sailr with ship maintenance experience and wrk n a cnstructin site, and a prductin freman in alchl prductin where filters were made f asbests. Less cnvincing but suggestive histries were btained in 4 f the remaining 5 cases. Here 1 subject was a winch driver n a gldmine (pssible expsure frm brake shes); 1 spent time n cnstructin sites as a pay clerk; 1 had been a shemaker fr 36 mnths, a cnstructin site wrker fr 6 mnths and had wrked in an asbests cement building fr 120 mnths; the 5th, wh had been a metal grinder fr 456 mnths, was fund t have cated fibres in his sputum. The 12th pssible case is intriguing. She had been an ffice wrker in a factry making bdy filler, which has chrystile as a cmpnent. She had had her first cntact with the bdy filler 4 years befre diagnsis, t shrt a latent perid t lend itseli t causal interpretatin. Her nly ther pssible cntact was the use f asbests panel heaters fr an unspecified length f time. Tw f the 5 subjects classed as unlikely prvided infrmatin weakly suggestive f sme asbests cntact. Subject 1 wrked n the nrth-western Cape diamnd fields. It has been suggested that crcidlite fibres may have been carried t these alluvial fields by the Orange River, which passes thrugh the Cape crcidlite fields n its way t the Atlantic Ocean (JCA Davies, NCOH - persnal cmmunicatin). The subject als wrked in a fundry but did nt recall being expsed t asbests, did nt wrk near the fu..-naces and had never wrn heat-prtective clthing. Fr cmpensatin purpses a thrugh expsure histry was btained frm the patient by an experienced ccupatinal Table n. Cbaraderistic:s f 123 Suth African mesthelima cases Site*.Sex Pleura Peritneum Male Female Age (mean (SD» Jhannesburg ;; 55.8 (13) (N =48) Pretria (11) (N = 21) Kimberley (12) (N = 22) Blemfntein (10) (N = 19) Cape Twn (15) (N = 10) Prt Elizabeth ( 7) (N=3) Ttal 115 (94%) 7(6%) 102 (83%) 21 (17%) 55.4 (12) Excludes perica<dium: Jhannesburg = 1 case.

4 medicine physician. 0 additinal evidence t supprt expsure culd be btained and n cated fibres were present in his sputum. Subject 2 reprted that her father wrked at the Kegas asbests mine. She did nt recall having lived in a mining district herself and culd recall n cntaminatin f the hme by wrk clthes; she als did nt knw whether she had been brn befre r after this emplyment. The ther 3 had n recall f asbests expsure, and had been a gldminer, a dmestic wrker and a security guard n a platinum mine, respectively. Fur f these 5 'unlikely' subjects prvided sputum, and n cated fibres (ferruginus bdies) were detected. The nature f asbests expsure is shwn in Table ill. Only 3 cases were categrised 'nne' - these 3 plus the 2 cases categrised 'ther district' make up the 'unlikely' class discussed abve. Fifty-eight per cent f the cases had had ccupatinal expsure t asbests. N subject had been expsed exclusively as a cnsequence f cntaminated wrk clthes (dmestic-clthes), but this was nevertheless an imprtant surce f expsure as 13 subjects (11%) reprted cntact with asbests in this way. All f them had either wrked with asbests r lived in a mining district and were therefre nt allcated t the 'dmestic-clthes' categry. Tw cases had 'dmestic-use' as the majr surce f expsure: ne built his wn huse and cut asbests ceilings, and the ther was expsed while her husband insulated their huse. This wman had anther pssible surce f expsure as she had wrked as a piq clerk and had visited cnstructin sites fr apprximately 30 minutes per week fr many years. Table Ill. Nature f asbests expsure in 123 Suth African cases f mesthelima Cases Female cases Nature N (%) Occupatinal Direct Indirect 9 7 High risk 0 Risk 8 7 Uncertain 2 2 Envirnmental Mining Other 0 + Uncertain ccupatinal Risk 8 6 'Other' district nly 2 2 ~m Dmestic Clthes 0 I Use 2 2 Incidental 0 Nne 3 2 Ttal 123 N (%) Occupatinal asbests expsure Table IV lists all subjects wh reprted ccupatinal asbests expsure next t the industry in which they had wrked and the ccupatin f the expsed subject. These data are presented as they may be useful in taking an expsure histry. Data frm bth cases and cntrls are presented, as the industry r ccupatin in which expsure ccurred in Suth Africa is f interest irrespective f the caseicntrl status f the subject. A number f unexpected ccupatins are represented. Fr example, the pliceman was a detective respnsible fur criminal investigatins n the asbests mines in the district where he wrked. The farmer wrked with asbests cement prducts in building and maintenance n the farm. Of the 123 cases, 23 had wrked n Cape crcidlite mines;3 subjects reprted emplyment at Penge, an amsite mine in the Nrthern Prvince; 3 had wrked in a mixture f,amsite and Transvaal crcidlite mines; and 1 subject had w.rked in a Transvaal crcidlite mine. It is ntable that n subject has wrked n a chrystile mine. District-specific expsure and crcidlite expsure A prprtin f cases had had n asbests expsure ther than that which may have ccurred due t living in r visiting an asbests mining district r frm ccupatinal r thercntact with asbests mined in the particular district. In these individuals asbests fibre type culd be identified cnfidently as the expsure had ccurred exclusively in a mining district. The numbers f such cases were: Cape crcidlite nly - 44, amsite with r withut Nrthern Prvince crcidlite - 7, chrystile - 0, and slight pssibility f expsure t unspecified asbests in 'ther' district - 2. N subject reprted exclusively Mpumalanga expsure, but 1 had spent 369 mnths in chrystile mining districts and nly 3 mnths in Nrthern Prvince mining districts. He was a pliceman wh cnducted criminal investigatins n chrystile mines and n an asbests mine in the Nrthern Prvince (amsite and/r crcidlite). Strng evidence f expsure t crcidlite was reprted in 68 f the 123 cases (55.3%). Clear evidence f expsure t this fibre ccurred in subjects expsed in the Nrthern Cape mining districts, thse with ccupatinal crcidlite mining expsure (Nrthern Cape, except fr 1 Nrthern Prvince ~ase), ccupatinal cntact with large-diameter asbests cement pipes (2 cases), battery casings (2 cases) r as reprted by the subject (l case). Sme cases nt included as crcidlite-expsed may well have had substantial cntact with this agent, fr example 3 subjects mined asbests in the Pietersburg asbests fields and were therefre prbably expsed t bth Transvaal crcidlite and amsite. These cases were nt included in the crcidlite grup in :rder t limit this grup t cases with almst incntestable crcidlite expsure. Exclusively envirnmental expsure Table V shws the expsure details f 22 cases with exclusively June 1999, V!. 89, N. 6 SAM]

5 Table IV. Occupatinal asbests expsure in study subjects accrding t industry and ccupatin Industry Mining r milling Engineering Gldmining asbests Heavy Light Dry cleaning Cnstructin Pwer Agriculture Transprt Battery manufacture Rubber Asbests prduct lllanufacture Asbests cement Frictin materials Flr tiles Fundry Chemical Law enfrcement Fire cntrl Navy Cmmercial. Public service Occupatin (number fsubjects in each ccupatin) Asbests mining and milling Undergrund (l4) General maintenance (2) Surface (12) Mill (6) Office administratr (2) Transprt (3) Biler peratr (2) Fitter and turner (11) Freman (3) Machine peratr (6) Welder (2) Cnstructin Carpenter (5) Labratry supervisr (2) General labur (4) Other (4) Sailr (I) Railway line (I) Steam lcmtive maintenance (I) Driver (4) Furnace masn (I) Bilermaker (4) Factry manager (I) Electrician (4) Turbine maintenance (I) Engineer Marine (l) Unspecified (I) Mtr vehicle mechanic (I) Farmer (I) Uphlsterer (I) TImaker (I) Crane driver (I) Oeaner (I) Building inspectr (I) Pliceman (I) Salesman (I) Painter(l) Streman (I) Missing data (l) envirnmental asbests expsure. Tw subjects (Nrthern Cape N. 5 and Nrthern Prvince N. 1) spent years in asbests cement structures; as the relevance f this cntact is unclear, these 2 cases were categrised as 'exclusively envirnmental'. Fifteen f the 22 cases (68.2%) were dcumented as having expsure beynd mere residence in a district. It is ntable that this was directly related t mining and related activity. Expsure t nn-asbests agents Thirty subjects reprted expsure t nn-asbests agents putatively assciated With mesthelima, namely glass fibre (21 cases), ther manufactured mineral fibres (3 cases), radiactive material (2 cases), nickel (3 cases), and sugar-cane (l case). N subject reprted expsure t X-rays, raditherapy befre current illness r beryllium. Twenty f the 21 subjects with expsure t glass fibre were classed as having had definite r prbable asbests expsure. The remaining subject, wh had wrked n cnstructin sites as a pay clerk fr 54 mnths, was classed as having had pssible expsure. Nine subjects reprted expsure t an agent ther than glass fibre: 8 f them

6 Table V. Twenty-tw cases with exclusively envirnmental expsure Regin Nrthern Cape Nrthern Prvince Mpumalanga + Nrthern Prvince Year f first Case Mnths spent in Nature f asbests cntact entering N. district r ptential cntact district Stayed < 5 km frm Danielskuil mine Nne recalled. 3 visits x 3 weeks each Nne recalled 1?, Stayed < 5 km frm Riries mine. Father a miner " Lived in asbests cement building % Father a miner - clthes cntaminated hme lived < 500 m frm stre f asbests at Prieska statin Farmer: asbests mill n farm bundary Missing infrmatin Spuse a miner. clthes cntaminated hme Brther a miner. clthes cntaminated hme Lived within 1 km f an asbests mine Lived within 5 km f Bretby mine % Lived within 0.5 km f Riries mine Lived near Prieska railway statin Nne recalled Father a miner. Lived within 5 km f an asbests mill Asbests transprted past his hme - brken bags. cntaminated area Mther wrked at Pmfret mine Nne recalled Taught in asbests cement classrms Pliceman - regular trips t asbests mmes 1958 had had definite r prbable asbests expsure, the remaining case was classed as having had pssible asbests. expsure due t nine visits t Kegas, a crcidlite asbests mining district in the Nrthern Cape prvince. Nne f the 5 unlikely asbests expsure cases reprted expsure t ne f the agents listed abve. N subject reprted purely incidental expsure, e.g. use f asbests cement furniture r heating panels. Hwever, 1 subject reprted cntact with chrystile 4 years befre diagnsis (a very shrt perid between expsure and disease - manifestatin), but had used asbests panel healers fr an unspecified length f time. DISCUSSION This study cnfirms that a histry f asbests expsure can be btained in the verwhelming majrity f Suth African mesthelima cases; that envirnmental expsure in the crcidlite mining areas f the Nrthern Cape accunts fr a significant prprtin f cases; that there is a relative paucity f diagnsed cases linked t amsite r chrystile; and that ther causes f mesthelima ccur rarely, if at all, in this cuntry. In the ~ain, limitatins f this study relate t the representativeness f cases. The number f subjects wh culd ptentially have entered the study is nt knwn, but indirect evidence suggests that ascertainment f diagnsed cases was reasnable: the nly incidence study in Suth Africa' registered n average lei9 cases per year fr (This was fr the whle f Suth Africa and histlgical cnfirmatin f the diagnsis was nt necessary.) Mre imprtant, there is evidence that in sme respects the 123 cases ~h entered ur study were nt representative fsuth African cases. Fifty-five per cent f the cases were white, yet this grup nly makes up apprximately 20% f Suth Africa's ppulatin. A likely explanatin is that black Suth Africans have prer access t health care,' but the effect f underrepresentatin f black subjects is nt knwn. N study team was successfully established in Durban (KwaZulu-Natal), but Durban has a majr harbur that exprts asbests (mainly chrystile). The prprtin f cases cllected in Kimberley (22/123) was nt as large as expected, given the histric imprtance f this regin. In summary, althugh it cannt be quantified, it is pssible that this series f cases underrepresents cases with envirnmental June 1999, VL 89, N. 6 'SAMJ

7 expsure t Cape crcidlite and thse with harbur-related expsure. Putative nn-asbests agents This study shwed that putative nn-asbests agents tgether with a pssible backgrund rate culd make a very small cntributin t the mesthelima caselad in Suth Africa. This is imprtant, as an assumptin f asbests expsure is likely t be crrect in the verwhelming majrity f cases. It wuld seem reasnable t prvide sme frm f cmpensatin t all diagnsed cases since the cause is almst certainly direct r indirect industrial activity. The current system f restricting cmpensatin t nly thse peple with a histry f ccupatinal expsure shuld be revised. Envirnmental cases The large prprtin f cases due t purely envirnmental expsure is unique t Suth Africa. Australia is the nly ther cuntry t have mined crcidlite in significant amunts and it is als the nly ther cuntry t have dcumented envirnmental cases in any number. Australia has maintained a mesthelima surveillance prgramme since Fergusn et al." presented expsure data n 726 cases cllected frm 1 January 1980 t 31 December Envirnmental expsure had ccurred in 43 f these cases (6%), but in nly 6 f the 726 (less than 1%) was envirnmental expsure a cnsequence f living in an asbests mining regin (Wittenm, the crcidlite district). This is abut 1 case per year - in sharp cntrast t the findings f ur study. Here 22 cases were fund t have been expsed envirnmentally and a further 8 had experienced envirnmental expsure and had been emplyed in a risk ccupatin with n recall f asbests expsure. Nne f the Suth African envirnmental cases was eligible fr financial cmpensatin r fr payment f medical expenses related t the disease. Fibre-specific data - the relative imprtance f the Nrthern Cape and paucity f chrystile cases The majrity f subjects wh had mined asbests had mined Cape crcidlite, and the majrity f subjects with asbests expsure exclusively in an asbests-mining district had incurred this expsure in the Nrthern Cape prvince. Of the 22 subjects with nly envirnmental expsure, 20 (91%) had been expsed in the Nrthern Cape. Besides a greater risk fllwing crcdilite expsure, explanatins fr the prepnderance f cases with Nrthern Cape mining district experience are that these districts mined much mre asbests than the ther districts; that the nature f the mining peratins led t cntaminatin f a much larger area; and that they generated much mre dust, thereby expsing mre peple t cntaminatin. The first suggestin is difficult t supprt. It was nly in abut 1960 that crcidlite prductin exceeded that f amsite. Amsite and chrystile prductin were substantial thrughut the 1960s and early t mid-1970s. (Given the lng latent perid fr mesthelima mre recent data are nt f real interest.) Twenty-seven, 53 and 100 metric kiltns f chrystile were prduced in 1960, 1970 and 1975, respectively." It is true that Cape crcidlite mining tk place ver a wide gegraphical area, but extensive cntaminatin f the Nrthern Prvince has been well dcumented. 7 Asbests pllutin f surrunding villages and the envirns was extensive, fr example at least nine mills perated in the Mafefe district, each with a large asbests waste dump. Disease due t envirnmental expsure was cmmn in mining areas, fr example 389 f 611 randmly selected adults frm Mafefe had a histry f envirnmental asbests expsure, and 34% f these 389 individuals had pleural disease. Mpumulanga (chrystile) cmmunities have nt been studied, and the extent f envirnmental pllutin experienced by these cmmunities and f asbests-related disease in this area is nt knwn. Dust levels in and arund Nrthern Prvince mines and mills were very high (dust cunts taken in the Penge mill remained well abve 12 fibres / ml until after the secnd half f the 1970s).7 There are very few published studies f fibre levels in Mpumalanga chrystile mines, with the nly readily available d~ta taken frm Slade's 1931 thesis. ID Given the cntaminatin f mining regins in the Nrthern Prvince and the fact that the Nrthern Cape is a sparsely ppulated regin, it is untenable that the prepnderance f Cape crcidlite cases can be explained slely n the basis f a prepnderance f individuals expsed t this fibre. Suth African data suggesting that amsite is less dangerus than Cape crcidlite, at least as far as mesthelima is cncerned, have been presented by Sluis-Cremer and c-wrkers. l1 They fund the incidence f mesthelima per subject-years t be 7.8 and 44.6 fr amsite and crcidlite miners, respectively, and the prprtinal mrtality rati in men fllwed up frm 20 years after first emplyment t be 1.7% and 11.9%, respectively. Paucity f chrystile cases N case with a histry f chrystile mining entered the study, and there was n case invlving exclusively envirnmental expsure t chrystile. Althugh n case culd be said t have shwn gd evidence f exclusively chrystile ccupatinal expsure, 2 subjects reprted having had cntact with this material and little if any cntact with amphibles. One f these subjects spent 369 mnths in chrystile mining districts and 3 mnths n an asbests mine in the Nrthern Prvince, and the ther had been expsed t chrystile nly 4 years befre diagnsis. This is a very shrt latent perid and des nt lend itself t causal interpretatin. The absence f Suth African chrystile cases is nt an

8 islated finding. N mesthelima cases have been recrded frm Suth African ch.rystile mines. 12 One explanatin fr the absence f exclusively ch.rystile cases is that prductin and use f the material in Suth Africa was s limited that nly a small number f individuals were expsed, resulting in very few cases. This seems unlikely. Hart' estimates that ch.rystile prductin cnstituted apprximately 30% f ttal asbests prductin by the end f the 1970s; in the early 60s, prductin was clser t 20%. Substantial numbers f miners wrked in chrystile prductin - frm the 1930s t mid-1980 rughly wrkers were emplyed in chrystile mining at anyne time (RSJ du Tit, NCOH persnal cmmunicatin), and in 1960 there were apprximately wrkers, cnstituting 17% f all asbests miners. Frm these data it seems unlikely that scarcity f expsed wrkers is an adequate explanatin fr the absence f cases. In summary, the great prepnderance f crcidlite cases, fllwed by arnsite and ch.rystile (in this study n cnvincing case was identified), is cnsistent with the view that there is a fibre gradient in mesthelimagenic ptential f Suth African asbests (crcidlite > arnsite > ch.rystile). Dr Erica Jansen was the c-rdinatr f the Prt Elizabeth study centre. Cases were referred t this study by a large number f Suth African practitiners, ntably pathlgists. We thank them fr their gdwill and c-peratin. The Suth African Asbests Tumur Reference Panel members supprted the prject by reviewing the diagnses f mesthelima. Financial supprt came frm the Suth African Medical Research Cuncil, the Angl American and De Beers Chairman's Fund and the Natinal Cancer Assciatin f Suth Africa. The paper is based n a PhD thesis awarded by the UniverSity f Cape Twn. APPENDIX I. MEMORY 'JOGGERS' READ OUT TO STUDY SUBJECTS A. Have yu ever been invlved in any f the fllwing? 1. Insulatin wrk 2. Wrking with furnaces 3. Manufacturing asbests cement prducts 4. Wrking with bilers 5. Wearing heat-prtective clthing 6. Selling asbests 7. Cnstructin site wrk 8. Demlishing buildings 9. Wrking in a factry using asbests 10. Wrking fr the navy/ merchant navy 11. Repairing/servicing mtr vehicles mre thchi nce a mth. 12. Helping manufacture asbests-entaining articles 13. Wrking in a pwer statin 14. Wrking with the manufacture f batteries 15. Wrking in the plastic industry 16. Using asbests rpe r asbests gaskets 17. Wrking in the rubber industry 18. Manufacturing brake linings r clutch plates 19. Transprting asbests 20. Wrking fr a railway cmpany 21. Insulatin f ht-water pipes 22. Wrking with steam lcmtives (train engines) 23. Wrking with sugar-cane References 1. Zwi AB, Reid G, Landau SP. Kielkwski 0, Sitas F. Becklake MR. Mesthelima in Suth Africa, : Incidence and case characteristics.lntjepidemi11989; 18: 32()" Health and Safety Cmmissin. Asbests. Val L Final reprt f the Advisry Cmmittee. Lndn: HMSO,l979. J. Health and Safety Cmmissin. Asbests. VaL 2. Final Reprt f the Advisry Cmmittee. Lndn: HMSO, Michaels L, Chissick SS. Asbests. Vl. I. Prperties, Applicatin and Hazards. Belfast lhn Wuey & Sns, Internatinal Labur Office. Encyclpaedia foccupatinal Health and Safety. 3rd 00. rev. Parmeggiani L, ed.. Geneva: flo, Marchand PE. The discvery f mesthelima in Nrthwestern Cape Prvince in the Republic f Suth Africa. Am I Ind Med 1991;:[9, Felix MA, Leger JP. Ehrlich RI. Three minerals, three epidemics - asbests mining and disease in Suth Africa. In: Mehlam MA, Uptn A, eds. The Identificatin and Cntrl f Envirnmental and Occupatinal Diseases. Princetn: Princetn Scientific Publishing Cmpany, Fergusn DA, Berry G, Jelihvsky T, et al. The Australian mesthelima surveillance prgram Med JAU5tl987; 147, Hart HP. Asbests in Suth Africa. Jurnal f the Suth African Institute f Mining and MetaIIurgy 1988; 88, Slade GF. The incidence f respiratry disability in wrkers emplyed in asbests mining, with special reference t the type f disability caused by the inhalatin f asbests dust. MO thesis, University f the Witwatersrand, Sluis-Cremer GK,. Liddell FDK,. Lgan WPD, Bezuidenhut BN. The mrtality f amphible miner.; in Suth Africa, BO. Br JInd Med 1992; 4'r Wagner le. Mesthelima and mineral libels. Cncer 1986; 57, B. Did yu ever wrk as a 1. Biler maker 2. Fitter and/ r turner 3. Stevedre 4. Marine/civil engineer 5. Plumber/ plumber's assistant 6. Welder/ welder's assistant 7. Building carpenter/building carpenter's assistant 8. Electrician/ electrician's assistant 9. Paint manufacturer AccqJted 15 Nv June 1999, V!. 89, N. 6 SAMJ