Document ykxmKVMLv3z2NRz3ZZqqYZG1X

"wrficc of the lung end the pit* RtFon* (their mew Column x they J,< called lu ncrcised Haply over tie tail 10 years. Thee* is general agreement hi mot) industrialized countiiei that theie has been a real increase of Lis form of cancer*. In about SOS of eases there is a history of exposure to asbestos dust al some time in the past. A feature of these lumours is the long interval between first exposures to asbestos dust and the detection of the caneer. it is tareiv less than ^fl years and may be up to 50 or more years. In some instances the exposure to the dust has been short, only a lew months, but the highest incidence of tumours has occurred in those most heavily exposed to asbestos dun. Cigarette smoking seems to play no part in these turnouts.but some research workers think there may be other co-factors present as well as asbestos10. The only other specific injury caused is the formation of asbestos corns on site fingers when the fibres lodge in the skin. The removal of the fibre usually cures the corn and no cancers of the skin (datable to atbestus have been reported. demiological sri'dict of the incidcnet of these lumoun in man for diffeii ypes of fibre, it items probable llial the impartial fibre* ate Bkely to be those which are stiatjhl. small in diameter (up to about | pm) and perhaps 10 pm in length. It is not vet known whether the ultra-fine fibres only visible under the election microscope ate biologically important. Such fibres arc present in luge numben iu the lungs of those who have been exposed to asbestos, but their combined mass is extremely small. Is is too early yel' in use this information to establish with confidence a separate dust standard to prevent the development of these mesotheliomas. This is a field of intensive research at the present. Some of Use new evidence urgent that the sac and shape of die fibre are more important than its chemical composition, provided it is telatively insoluble. It may be that extremely fine 'fibres of many different materials can penetrate cells without immediately killing them, but-onct inside can damage the mechanisms of ceil divisions. An implication cf this view is that caie should be taken to avoid exposure la duns of all types of fibre less than 0 J pm dia meter and tevtril micrometres in Ictigiiu PRACTICAL IMPLICATIONS OF THE BIOLOGICAL EFFECTS OF ASBESTOS Inhalation cf the fibre For all practical purposes the risk from asbestos is limited to inhalation of the fibres Thus control of the airborne dust levels and their monitoring by insuumenis, which will measure that pan of the dun which can pin access to the deeper pans of flic lung, is an essential step in the safe use of all types of asbestos. Although asbestos fibres an he ingested in minute amounts in beverages which have been filtered through asbestos, or water supplies11, there is nu firm evidence that such tiny tracts hare any ill-effects Feeding massive doses of asbestos to animals has so far failed to produce any mesotheliomas ot other cancers Sue and shape ot fibres Recent research hat helped to clarify (he probable influ ence of fibre length and diameter in producing atbestotis and the bronchial cancers. The fibrosis is thought to be mused principally by the fibres between about 5 and 100 pm ir. length. Fibres much larger than this in the esvircurocn! settle out quickly and are not inhaled. Further tile itpcinioii occurs in the air passages, the important - site para.T.cic: being fibre diameter since it is this dimeitton rathe: liun fibre lens lit that governs the falling speed of ihc lines- Thu< fibres gteater in diameter than abmal ' pm (these also tend to be the longest I mostly fall nr impart, in the upper respiratury tract and ire carried away with the sputum. In the nariow airways any long fibres rcmaicmg are deposited by interception and fibres longer than about I0U pm seldom teach the finest bronchioles Tin# mcar.s that for rite control nt'aslicsiusis. and probably hroneluil cancers, `.lie slosr at iilnes between about 5 pm and It)-.!ui length and up to at),tut 2pm m diameter ithe liacti-*:: irl* the Jus! whtcii has ro lie measured. Fo: -hi mex-thi'h.itr.a. the evidence iVnti: the binl-.'giCilii :r.:p-jiia;ii :.:.c is much h-s> ei-.nplere. t'sing . tu-in u:::ic sources, such at the acn-Jyrvaunf hs'h. si.-.:: ! iinc lib:; -, the W.C and simp. s-t fibic* winch aie i.tj.nf..' :r, bugs of and-.ijt- aid man h-llirvu.g c\p.v:ii; n- d.lieien: type- of uehcsios. and ti.e epi Types of asbestos and occupations within the industry The Ian 10 years have shown the importance to health of the type of asbestos inhaled and the occupation of the winkers within the industty. Earlier medical repons did not differentiate between one type of asbestos and another, end most of the surveys were concerned with asbestos textile wuikers. A full assessment of the risks would ideally be based on studies of woikets only exposed to each type of fibre and in ail tire operations within the industry in which litis fibre was used. 'In practice the information is much less complete thin this. Exposures to one type of fibre leave usually occurred only in the mining and fibre separat ing. This work usually lakes place in countries where'the medical records are samy and the labour turnover is rapid. A notable exception is in the dnysoule mines in Quebec where a very comprehensive survey has'just beec com- plettdl,"H. In the manufacturing countries several types of fibre are often mixed together o; have been processed concurrently so that employees hive been exposed to several types of fibre in unknown quantities. Pan records of dustirr'-i are available for relating to the incidence of the diseases. Thus the current assessment of the relative riski in the past (tom different type*c( P.btt and occupa tions is based on information which is far from complete. Use can be nude of experiment* in animals, especially rats, because most uf the diseases seen in man can be produced :n these animals. New inhumation is rapidly accumulating which may give a clearer indicaiiun of the way in which different lyprs of lihestos produce their biolugical effects There is general agreement that asbestovis and bronchial car.cats can he caused by all types of commctcially used 'jshrsu>i(;uiios!tc.inthop!iyflitc. chrysolite, and crocidolite) if the du>t is inhaled in sufficient quantities, but it now -com lively that the risk from dirysonic may be less than with :he oilier tv pcs of fibre. There is also eviJenee that the li-k -is Imvesi in inning and increase* along lire fibre wparjinig and ;r.anaiarming pinc-'-.-rJ. This is llitiuglit to he d ie in lire higlier pnp.nlnin of anKunc i}u*t consnling .11 ahii- lihre* able lv> perielraic into lire deepest pari ti.e l-.mg. In pufiice tins means rlut the cleaner the l:lr ;:ij <!ic i,e-raip-lcidy il is sepniaird mtu is Jividual