1 7 3
Cad . Saúd e Púb lic a, Rio de Jane iro , 1 4 (Sup. 3):1 7 3-1 7 6, 1 99 8
OPIN IÃO O P I N I O N
Asbestos: current issues related to cancer
and to uses in developing countries
Asb e sto : se u e mp re g o no s p aíse s
e m d e se nvo lvime nto e q ue stõ e s
re lac io nad as ao c ânc e r
1 Fu n d a c e n t ro, D Me / C S T, Min ist ério d o Tra b a l h o. Ru a Cap ote Valen t e 710, Sã o Pa u l o, SP 0 5 4 0 9 - 0 0 2 , Bra z i l . a l g ra n t i @ u s p. b r Ed u a rd o Al g ra n ti 1
Abstract Asb est os is on e of th e m a in occu p a t ion a l carcin ogen s re c o g n i z ed an d st u d ied in t he l i t e ra t u re . It s u ses h ave u n d ergon e m aj or ch a n ges in recen t d eca d es, w ith seve re restriction s on c o m m e rcial am p h ib oles accord in g to differen t p attern s: in dev elop ed cou n tries asb est os is strict-ly con trolled or ban n ed , excep t in Ja p a n , w h ile in d evelop in g cou n tries con su m p tion h as leve l e d off or in cre a s e d . As a n ex a m p l e , Brazil is on e th e seven w orld lead ers in asbestos p rod u ction a n d c o n s u m p t i o n . Alth ou gh th ere is a clea r excess of m esot h eliom as lin k ed t o a m p h ibole ex p o s u re , m ain ly t o cro c i d o l i t e , t h e re is n o eviden ces th at ch rysotile is h arm less to th e p leu ra . Al s o, t he re-la tion sh ip betw een fibrogen esis an d carcin ogen esis is n ot su fficien tly u n d erstood to d efen d the con cep t th at th ere are p ro t e c t i ve ex p o s u re lim it s to both d iseases. “ C o n t rolled u se”p olicy m ay be e f f e c t i v e at th e occu pa tion a l level in a select grou p of com p a n ies, re p resen tin g on ly a fraction of th e exp osed pop u lation . In develop in g cou n t ries su bject to econ om ic p re s s u re s , th ese issu es m erit p rop er d iscu ssion to a void u n n ecessary d isease an d d eath .
Key words As b e s t o s ; Occu p ation al Ex p o s u re ; N e o p l a s m s
Resumo O asbesto é u m d os p rin cip ais ca n cerígen os ocu pa cion ais recon h ecid os e estu da dos n a l i t e ra t u ra cien tífica . A ten d ên cia m u n d ial de u tiliz ação e con su m o sofreu m odificações n as ú ltim as décad as, coltim u ltim a seve ra rest rição ao u so d os an fibólios coltim erciais e segu e p a drões d istin -t o s : em p aíses d esen volvidos su a u -tiliza çã o é ex -t rem am en -te res-tri-ta ou p ro i b i d a , exceção fei-ta ao Ja p ã o, e em u m a série d e p a íses em d esen volv im en to h á u m a t en d ên cia a est ab ilid a d e ou a u -m en t o n a p rod u çã o e u t iliz açã o. O Bra s i l , co-m o exe -m p l o, é u -m d os set e -m a iores p ro d u t o res e c o n s u m i d o res m u n d ia is d e asbesto. Em b o ra h aja u m m aior excesso d e m esoteliom as re l a c i o n a-d os à ex p osição a an fibólios, n otaa-d am en te a cro c i a-d o l i t a , n ão h á evia-dên cia s a-d e q u e a crisotila se-ja in ócu a p ara a p leu ra . Da m esm a form a, as relações en tre a fib rogên ese e a ca rcin ogên ese n ão sã o su ficien tem en te clara s p ara afirm ar- se q u e h a ja l im ites d e ex p osição q u e p roteja m con t ra am b os efeitos, s i m u l t â n e a m e n t e . A p olítica do “u so con tro l a d o”p od e ser efetiva , ap en a s a n íve l o c u p a c i o n a l , n a s gran des em p re s a s , qu e re p resen ta m ap en as u m a fração d os ex p o s t o s . É n eces-sário q u e n os p aíses em desen vo l v i m e n t o, su jeitos a m aiores pressões econ ôm ica s, estas q u estões seja m tratada s com seried ade, p a ra evitar-se d oen ça s e m ortes desn ecessárias.
ALG RANTI, E. 1 7 4
C ad. Saúde Púb lica , Rio de Jane iro , 1 4(Sup . 3):1 7 3-1 7 6, 1 99 8
B a c k g ro u n d
Asb e st o s is a gr ou p o f silica t e fib re s wit h va r y-in g co n t e n t s o f m a gn e siu n a n d iro n . Th e y a re d ivid e d in t w o gro u p s, t h e se rp e n t in e s re p re se n t e d b y c h r yso t ile a n d t h e a m p h ib o le s in c lu d in g cro c i d o l i t e , a m o s it e (b o t h h a vin g in -d u s t ria l a p p licat ion s), t re m o l i t e, a ct in olit e an -d a n to p h yllit e (n on -co m m e rcial fib res). Asb estos u n iq u e n e s s is re fle ct e d in t h e ir p h ys ica l a n d c h e m ic a l ch a ra c t e rist ics wh ic h co n fe r a h igh t en sile st re n gh t, th e rm a l sta b ilit y, che m ical re-sist en cy t o a cid or a lcali agre s s i o n s, d ep en d in g o n t h e fib re t yp e . Th e se p ro p e rt ie s m a ke t h e m a t t ra c t i ve for d iffe re n t in d u st r ial a p p licat io n s like a sb e st o s-c e m e n t (A/ C) p ro d u c t s (b o a rd s, r o o f c o ve r s , w a t e r re s e r vo irs a n d p ip e s), fri c -t io n m a -t e rials (b ra ke sys-t e m s, clu -t ch sys-t e m s) ga sket s an d te xtiles.
Asb e st o s is fo u n d in u lt ra m a fic r o c k s ( c h r yso t ile a n d t h e n o n -c o m m e rcia l a m p h i-b ole s), se rp e n t in ize d lim e s to n e ro cks d e r i ve d f ro m t h e re o r ga n iza t io n o f u lt r a m a fic o r silicified d o lo m it ic ro cks (ch rysot ile ), a n d in Pre -c a m b r ian b a n d e d iron sto n e s (-cro -cid o lit e a n d am osite). Over 95% of th e world asb estos m in ed is chr y s o t i l e. Se ven cou n trie s a ccou n ts for m ost o f th e p r o d u c t io n : Ru ss ia , Ca n a d a , Ka z a kist h an , Ch in a, Bra zil, Sou th Africa a n d Zi m b a b -we. Wo rld p ro d u ct io n e xp e rie n ce d a sh arp ri s e f ro m t h e e n d of t h e Se c o n d Wor ld Wa r u n t il m id 70s (5 m illio n t o n s) wh e n s t a rt e d t o d e -clin e u n t il it le veled in t h e 90s (3 m illio n t o n s). Declin e in p ro d u ctio n pa ralle led t h e d e clin e in co n su m p t ion in d e ve lo p e d cou n t ri e s, excep t in Ja p a n . In co n t ra st , a s b e st o s in d u st r y gre w in d e velop in g coun tri e s, p articu larly in Sou th A m e-rica , So u t h e as t Asia, Mid d le Ea st a n d Ea s t e rn Eu ro p e. Arou n d 85% of t h e cu rren t u ses are for a sb est o s-ce m e n t p ro d u c t s. To d a y, m o st of t h e d e velop e d n a t io n s b an n e d o r seve rely re s t ri c t-e d a sb t-e st o s u st-e s, b a s t-e d o n t t-e c h n ic al an d / o r so cio-p o lit ica l cri t e ri a .
Occu p at ion a l a n d e n vir on m en ta l e xp o su re t o a sb e st o s ar e a ss o c ia t e d wit h fib ro t ic re a c-t io n s in c-t he lu n gs an d p leu ra , an exce ss of lu n g c a n ce r a n d p le u r a l a n d p e rit o n e a l m e s o t h e -l i o m a s. Cau sa -l re-la t io n s w ith -lar yn gea -l ca n cer, c a n ce r o f t h e d ige s t ive a n d u r i n a ry t ra c t a re s t ill a m a t t e r o f d e b a t e . Alt h o u gh it is n o t t h e m a in c au s e o f o ccu p a t io n a l re s p i ra t o r y d is-e asis-es in m a n y o f th is-e d is-evis-e lop in g co u n t ri is-e s, t a k-in g Braz il a s a go od e xa m p le, d a t a o n a sb e st os re la t e d d isea ses is q u ikly risin g. Rec en t Bra z i l-ia n fe d era l la ws a n d re gu lat io n s p e rm it t e d t h e c on t in u at io n of m in in g, t ra n s f o r m a tio n a n d u t iliz a t io n of c h r y s o t i l e. Use of a m p h ib o le s is n o t p e rm i t t e d .
As t h e re st ill re m a in q u e st io n s re la t e d t o t h e e ffe ct s o f c h r yso t ile in h u m a n s, t h e se d e -velo p m e n t s p o in t for a n u rge n t n e ed t o o p en ly d iscu ss re la te d issu es of th e su b je ct .
The question of chrysotile exposure and mesothelioma
In h u m an s all fo rm s o f asb esto s are cau sa lly re -la t e d t o p a re n ch im a l a n d p le u ra l fib ro s i s , b ro n c h o ge n ic ca rc in o m a a n d m eso t h e lio m a s. Clin ical e ffect s sh ow a n in d u st ry-sp e cific va ri-a t io n , wit h st ro n g ri-a sso ciri-at io n s wit h fib re t yp e a n d fib re size d ist rib u t ion , am o n g o t h e rs. T h i s is p a rt icu larly th e ca se fo r m e so th elio m a. Fro m e p id e m io lo gy t h e re is n o d isp u t e t h a t a m p h i-b o le s ca rr y a h igh e r risk in h u m a n s, i-b u t t h e re is n o e vid e n ce t h a t ch r ys o t ile is h a r m le ss t o t h e p le u ra . Re ce n t re a n a lys is o f h is t o r ica l co -h o rt s d o n o t su p p o rt t -h e b e lie f t -h a t c-h r y s o t i l e c a r rie s a lowe r risk t h an a m o s ite in p ro d u c i n g m e s o t h e l i o m a s. In e xp e r im e n t a l a n im a ls, in -ha lat io n a n d p leu ral in ject ion s stu d ie s sh owe d th at a ll t yp e s of a sb e sto s cau se m e soth elio m a s. Fi b re a n a lysis in m e so th e liom a cases (as in ot h e r a s b e s t o s-re lat e d d is e a se s) a re d o n e in lu n g t iss u e . Me t h o d s fo r fib re id e n t ifica t io n a n d co u n t in g in p le u ral t issu e a re t h e sa m e as in lun g tissu e, b u t q u an t it a tive a n a lysis h as n ot b e e n st a n d a rd i ze d u n t il n ow. Sh o rt ch r y s o t i l e f i b re s in t h e p a rie t a l p le u ra h a ve b e e n d e -s c rib ed in va ryin g ca-se-s of a -sb e-sto-s-rela ted d i-s- is-ea se s wit h n o syste m a tic a sso cia tion with lu n g f i b re c o n t e n t . Th e y re p re se n t t h e m a in fib e r typ e en cou n tere d in p leu ral tissu e. T h e re f o re, it is b io lo gically p la u sib le t h at p le u ral fib res p la y a n im p or tan t role in p le u ra l carc i n o g e n e s i s.
Th e q u e st io n of ra p id ch ryso t ile cle a re n c e is a ls o c h a lle n gin g. El e c t r os t a t ic b o n d s b e -t wee n fib rils are re m oved b y -th e le ach in g of Mg i o n s, sp litt in g t h e fib er lo n gitu d in ally in sm a ll-er fib rils t h a t cou ld b e m ore e a sily fra g m e n t e d a n d r e m ove d fr o m t is s u e . At t h e sa m e t im e t h in n er fib rils c a n rem a in u n d e t e ct e d b y e lec -t ron m icro s c o p y a n d p la y a role in fib ro g e n e s i s a n d carcin o m a in d u ct io n .
Cad. Saúde Púb lic a, Rio de Jane iro , 1 4(Sup . 3 ):1 73 -1 76 , 19 9 8 p e ri o d s. Re s u lt s m a y n o t re fle ct t h e fib re s
lin ke d t o th e cascad e o f e ve n t s t h a t t o ok p la c e ye a rs b e fo re . In ra t e xp e r i m e n t s, e xp o su re t o c h r yso t ile o r a m p h ib o le fib re s sh ow sim ilar fi-b ro ge n ic re s p o n s e s, d e sp it e lowe r p u lm o n a r y a ccu m u lat ion o f ch rysot ile a t n e cro p s y.
It is e stim a t ed th a t 6570% o f th e m e so th e -lio m a c a se s a re e xp la in e d b y t h e p re se n ce o f lo n g, t h in a n d d u ra b le a m p h ib o le s fib re s in th e p e ri p h e r y of t h e lun gs. Fo r d e ca d e s, ch ry s o t i l e h a s ac c ou n t e d fo r 95% o f t h e wo rld a sb e st o s p ro d u ction an d con su m e. Hu m an lu n gs, wh ich a re t h e b e st p o s s ib le s am p le r s, a lw a ys sh o w t h e p re sen ce o f am p h ib oles e ven wh en th e ex-p o s u re is co n sid e r e d t o b e a m ex-p h ib o le -fre e. Co n t a m in a t io n o f ch r yso t ile d e p o s it s wit h t rem o lite is alm o st u n iversal. Th e h igh p ro p o r-t io n a l r-t re m o lir-t e c o n r-t e n r-t o f h u m a n s e xp o se d m a in ly t o ch ryso t ile is c o n sid e re d a s t h e m ain e x p l a n a t o r y va r i a b le lin k e d t o m e s o t h e li o m a o c c u r re n c e , b y so m e re s e a rc h e r s. O t h -e r s, t h in k t h at t r-e m o lit -e c o n t -e n t m a y r-e f l -e c t p a st ch r ysotile exp osu re, wit h o u t b e in g n ece s-s a rily im p lica t ed w it h t h e tu m ou r.
In su m m a r y, c h r ys o t ile h a s la r ge ly b e e n t h e m a in fib re typ e m in e d a n d co n su m ed . T h e ra p id c le a re n c e o f ch r yso t ile fib re s fr o m t h e lu n gs d oe s n ot co n vin c in gly ju st ify a “s m a l l ri s k” o f m e so th eliom a . Th e role of sh o rt p leu ra l c h r ysotile fib e rs in p le u ra l tissu e h as n o t b e e n ro u t in e ly a d d re sse d in scie n t ific st u d ie s. Co n t -am in a t io n o f ch rys o t ile b y a m p h ib o le s is a l-m o s t a lwa ys fo u n d a n d la r ge ly u n a vo i d a b l e . Sh o rt d u ratio n exp er im e n t al stu d ie s sh ow t h a t a ll a sb e st o s fib re s are p o te n t c a rc i n o g e n s. To o u r u n d e rst a n d in g ch ryso tile e xp o su re is st ill a p rob le m t h at is fa r fro m se tt le d .
Relat ionship between fibrosis and cancer
In c re a sin g gra d e s o f a sb e st o s is are a sso cia t e d w it h h igh e r risks of b ro n c h o ge n ic ca rc i n o m a . Th e p r o b le m re m a in s in a s b e st o s e xp o se d w o rke rs with o u t a sb e st o sis. Mo st o f t h e p u b lic at io n s t h a t a d d re ss e d t h e su b je lict u se d lico n -ven t ion a l x- ra ys as th e im a ge too l fo r assessin g f i b ro s i s. Me th o d s for d et ect in g a sb e stosis h ave e vo l ve d in t h e las t ye a r s, w it h t h e u se o f h igh re so lu t io n com p u t ed t om o grap h y sca n s, wh ich is co n sid e re d to b e su p e rior t o co n ve n t io n a l x-rays in th e ea rly d iagn o sis o f th e d ise ase. T h e s e d e ve lo p m e n t s ce r t a in ly will lo we r t h e o ft e n ly q u o t e d figu re s o f 20% of c a se s m is se d b y co n -ve n t io n a l im a ge t e ch n iq u e s, a n d will a llo w m o re c o n fid e n ce in a t t rib u t io n o f c ase s t o a s-b e s t o s e xp o s u re . Lu n g fis-b re s-b u rd e n in t h e
ASBESTO S AND CANCER 1 7 5
ra n ge of a sb e st o sis ca se s, co u pled wit h a p ro p -e r la t -en cy tim -e sin c-e first -e xp o su r-e, -e v-e n in th -e a b s e n c e o f a sb e st o s is, is a ls o co n s id e re d b y so m e re s e a rch e rs a s su fficie n t evid e n ce for a t -t rib u -t ion o f lu n g ca n ce r -to a sb es-t os.
T h e re is n o p ro of th at fib ro gen e sis an d ca r-cin o ge n e sis jo in a co m m o n p a t h . Th e y m a y well b e d iffere n t p ro ce sse s t h a t c a n in t e ract in t h e lu n g en viron m en t. Up to n ow, it can n o t b e st a t e d t h a t a sb e st o sis is a p re - re q u is ite for t h e d e ve lo p m en t o f a n a sb esto s relat e d ca n cer. We c e r t ain ly n e e d m o re d a t a t o h e lp u n d e rst a n d -in g t h e q u est ion .
Asbest os and developing countries
Sin ce t h e s e ve n t i e s , d u e t o t h e in cre a sin g sc i-e n t ific i-e vid i-e n ci-e o f c an ci-e r ris k, s t ro n g ri-e s t ri c-t io n s c-t o a sb e sc-t o s h a ve b e e n a d o p c-t e d in d e ve lo p e d n a t ilo n s, ra n gin g flo r llow e r e xp lo su re lim -i t s, a m p h -ib o le s b a n , re s t r -ic t -io n o f a sb e s t o s co n tain in g pro d u ct s an d to ta l b a n . Som e of th e re s t rictio n s h ave b e en b ase d in scien tific facts, o t h e rs in socio -p olitica l willn ess.
In d e ve lo p in g cou n t rie s th e sce n e is d iffe r-e n t . Ta kin g Bra z il as a n r-e xa m p lr-e , p ro d u c t i o n a n d co n su m p t io n ro s e d u rin g t h e e igh t ie s, p e a ke d a n d s t ab ilize d in t h e n in e tie s. At p re -s e n t, a m e a n o f 1,300g/ ye a r o f ch r y-so t ile i-s co n su m ed p e r cap it a . St ra t egie s fo r u t ilizatio n a n d m a r ke t in g o f a sb e st os a n d it s p ro d u c t s va r y: “ligh t , d u rab le a n d ch e ap” fo r A/ C p ro d -u c t s, “re s is t a n t a n d wit h go o d s afe t y p e r f o r-m a n c e” for frictio n r-m a te ria ls an d ga ske ts. All of t h e a b ove q u a lit ie s a re t r u e, b u t t h e re a re a lso d o u b t fu l st ra t e gie s a s “ i t ’s a we ll kn o wn fib re , wh y ch a n ge t o o t h e rs t h a t on e d o e s n o t kn ow t h e effects?”, “c h rysot ile is fa r le ss h a rm fu l th an a m p h i b o l e s” o r “p re se n t low e xp o su re le ve l s a re safe”.
Risk assessm e n t an d co n tro l o f occu p a tion -a l se tt in gs by in d u st ry -a n d gove rn m en t -a re ve ry p o or in Bra zil. In a d d it io n , workers a re n ot su f-fic ien t ly aw are o f t h eir wo rk en viro n m e n t a n d t h eir ri g h t s. In p ra c t i c e , it m a ke s ve r y lit tle d if-f e re n ce t o h a ve low p e rm ite d if-fib re le ve l s, go o d a n d m o d e rn la b o u r la ws wh e n o n e d o e s n o t h a ve m e a n s a n d su p p o rt t o e n fo rc e t h e m . T h e q u e st ion o f asb e st o s u se, a s o th e r carc i n o g e n s, sh o u ld b e d iscu sse d on rea l gro u n d s. Th e con -c ep t o f -co n t r o lle d u se o f a sb e st o s m ay we ll b e ap p lie d in d e ve lo p e d co u n t rie s b u t, fe asib ilit y in d e ve lo p in g c o u n t r ie s is re s t r ic t e d t o a fe w i n d u s t ri e s, n ot a s a ru l e.
i-ALG RANTI, E. 1 7 6
Cad. Saúde Púb lica , Rio de Jane iro , 1 4(Sup . 3 ):1 73 -1 76 , 19 9 8
u m - s i ze p lan t s in t h e e igh t ie s, ca se re p o r t s o f a s b e s t o s i s , ca se re p o rt s o f a s b e s t o s-re l a t e d b ro n ch o ge n ic ca rc in o m a s (3 ca se s) a n d ca s e re p o r t s of a sb e st o s- re la t e d m e s o t h e lio m a s (3 cases). No t m u ch e p id e m iological in fo rm a t i o n is a va ila b le fr o m o t h e r d e ve lo p in g c o u n t ri e s. Th e sm all n u m b e r o f p u b lica t io n s re fle ct t h e lack o f aw are n e ss o f asb e st o s-re lat e d d is ea se s f r o m h e a lt h p ro fe ssio n a ls a n d also, t h e t im in g co u rse o f eve n t s in cou n t rie s wit h m o re re c e n t i n d u s t ria liza t ion . Gi ve n t o t h is p e cu lia r sit u a -t io n i-t d o e s n o -t -t a ke m u c h e ffor -t -t o c o n clu d e t h a t in t h e n e xt ce n t u r y t h e se d ise a se s w ill b e l a rge ly re s t ricte d t o d e velop in g co u n t ri e s.
Pre s e n t glo b a l e co n o m y b r o u gh t fu rt h e r p ro b le m s t o wo rke r s a n d u n io n s b y ch a n gin g t h e fo cu s o f t h e d isc u ssio n fo r p re s e r vat io n o f jo b p o st s. De ve lo p in g co u n t r ies in t h e ir st ru g-gle fo r att ract in g in ve stm en ts an d b u sin ess are m o re p ron e to close t h eir eyes fo r risky a n d u n
-su it a b le t e c h n o lo gie s. In Bra zil, u n io n s a n d u n i o n - rela t ed a ge n cie s h a ve p la ye d an im p o r-t a n r-t ro le in c o n r-t rib u r-t in g r-t o r-t h e kn owle d ge o f t h e r is ks o f e xp o s u re t o d iffe r e n t a ge n t s , a n d t o t h e wo rk e r’s r i g h t s, b u t it is c le a r th a t t h e ir s t ren gh t is fa d in g.
