Document G4RB0OLVQMpoLD2Gry6GNjwx

-*-- ' L_ U T\L. Jl.'L 1 W /*/c\ pPi \v. m. :.,iT" Ad hoc l.'orkir. p Croup on Vinyl chloride.- to bo hold .it Lyon on June 24 , 25 ' Scicnt i f i c Knoknround to the ?ruhloin of Mansur in<- Hir-nan Hxnosure to \* i iiy 1 -li j or i tip, in tho working l.nvi ronm-nt1 9, In any consideration of vinyl chloride in the working environment., it may be useful to consider the manufacturing process from ethylene, by succr.srive mi chlorination and dchydrochlor{nation, in terns of 1 ,2~d i chlorocthnr.c storage, of the tlicmo-cracking of thee intermediate, and of the removal of hydrogen chloride end the separation of vinyl chloride from residual 1,2-dichloroothcne. fit! *-- .* ' ' / * <'t /V; -------------a, l XT --m/'^/ rt- 9\ ri *'<5. J r-..u ; * -(&17..:0. 33 R W Standards of industrial and occupational hygiene are good on the two ICX manufacturing sites. The total escape of vinyl chloride from the closed to tn tn 03 4* complex of engineering plant, on the open site, is a very small one. At distances, remote from the chemical plant, but within the confines of each factory, the vinyl chloride- cone::, in the atmosphere never exceeds 1-2 ppm. In close proximity to, and at the time of the 3-m.in. sampling pciiods, the atmospheric concentration ranges up to 50 ppm, and with improved control and greater precautionary measures, this is likely to be lowered to approximately 20 ppm. Slight leakage of vinyl chloride occurs during removal of the Al^O, filters, <? 10 ppm, during plant maintenance, <5 ppm., and during repair-work to the pumps, during Lhe loading of tankers, etc. but in all of these operations, the resulting atmospheric cor.cn, cf vinyl chloride is a very small one. lienee, for marc than 95/1 of the entire operating time (for the chemical plant), the atmospheric c.oncn. of vinyl chloride never exceed:*. 10 ppm anywhere, and it would be described more accurately os epproxiioni ir.g lo 1 ppn. However, it ought to be stateJ, in all fairness, that vinyl chloride is sometimes discharged from leC-ft chimneys in a dilute lip-stream, amoi'ur i ng to 1 2,000m* 1. with a velocity of 100 ft see ; 12 kg h of vinyl chloride tu'ght be discharged in this way. ft* --"> RMty ^'^v* -n < :;,: (tu * 4 uv* . u --> R c% m it (%. <f(i a *' /?-(cv^^;CIt).;,' OthMrU'Cing' C{h> (d-U & " K" > ^',c^ ^ fl' During the peroxide-catalysed industrial polymerization of vinyl chloride, under successive- bitch operating conditions, the (weighted) average exposure level amounts to approxin.ucly'.-ji) ppm for the various ICX plants. Beck ccncent rat i or.s at times, when the plant vac opened for cleaning between the several so.many hatches, viced to be much higher, than tin's fV* / - working aw rage, but they have r.ov been el ii.ii nated^and under tho prevailing code of practice, they are perhaps not very relevant to bur .an exposure. In any case, if the concern ration cxseede 50 ngm, after the reaction autoclaavvec s'V--''.v'-'.. .. tt-.C eyA.'-.d hatU been --v_r.u.u>id. out, each operator wears an cnve-loping gas nusk, equipped with an individual air/O^-supply. l.'orking conditions are- being improved effectively' tliis year, so that Lhe (weighted) average atmospheric, concent ration of vinyl chloride will be reduced to approximately 2G' ppm. By means of a further 114,030,030 investment in additional auxiliary equipment, the Board of ICI aims to reduce substantially the working atmospheric conen. still further, to about 10 ppm, but this will take sene little time and considerable expense to accomplish. )Z i V^ ' fVriif /^-a 1 //?;* S~y . The sensitivity of CC r.-etheds crrpIcy^A, by inLcrr.t ttent peak measuroirer.t, is of the order of 0,05-0. IQ ppm.. J.ower levels are measured by initial concentration on adsorbents, followed by the slow release of adsorbate into the entry port of the chromatogrtph, and accordingly, this represents cumulative measurement. At this stage, nay T refer to two perspectives. (1) On the assumption that some level of human1 exposure to vinyl chloride is almost inescapable for chemical plant operators, it is responsible to ensure that the prevailing1 levels are as small as possible. Even in tho worst situation, in winch minimal background exposure level is punctuated with brief (but small) peak exposures, as in the case of the opening rf the reactor .belonging to the pelymerination process, such exposure for each individual operator is intermictent^and very occasional. This makes allowance, one might expect, for metabolism and for elimination of the body-burden resulting from vinyl chloride, and for a considerable, recovery of the physiological processes of defence and repair against (such brief and small exposures to) vinyl chloride. R&S 135585 3 R&S 135586 (2) Vinyl chloride is degraded in (sunlight) the atmosphere with a value of sow 35 days. l.ct ur- turn now to the human situation. In mammals, one of the major metabolic pathways for vir.vl chloride leads to CO and to, C0? via formaldehyde, and it implicates intermediary metabolism. f/V f ; In the ci.ee.jCC" situation, l.c. exposure to vnlabellcd material, useful results would he unfor;hcomiup f ron r.-.oni tori-.g the natural^physiological metabolites that are concerned. Apart, from this r.etabolic pathway, chloroacetic acid is found, but it \:oul d be difficult to relate the amounts, produced, to the size of human exposure to vinyl chloride.' In this connexion, the pharmacodynamics, after the oral dosing of rats with vinyl chlonca, arc important, because thcy'ef feet ivc pulmonary el imir.nt j on of unchanged vir.yl chloride from mammalian blcoc imposes a limit to the amount, which becomes available for biotransformntion in the liver. This supposition is substantiated (a) by the results of dosing i.p. and i.v., and (b), by the relationship between the size of the dose and the proportion (of the dose) metabolized. Linear functionality is limiting at a comparatively low dosc-levol. Accordingly, in exposed human subjects, it would be instructive to measure the amount of chloroacctic acid in the 24~h urines (and--dospiic-vhe-obvious. UjaiAations..in.interpretation,, possibly . -- --em*boxy'hsomo,l-obi n--i n-secAianmial--blziod--s.'imp4zis.). In our opinion, such_____ 'f i .. orjj r . observations would be qualitative and confirmatory.. Thoj noni tor ir.g of >l *'*'' unchanged vinyl chloride in the exhaled air after exposure is similarly subject to great difficulty and profound limitation (v. T. J Fry, T Taylor A D K Uathway, Archives de Pharmacodyr.air.iQ-, 1972,196,08) Since chc relative size of a dose, which can be metabolized completely in mammals, is small, and since the pulmonary elimination for this unchanged, lipid'soluble and highly volatile gas is very efficient, it wight be argued that the size of the dose or the level of exposure is not entirely ;;t rn.'uu;. However, this viewpoint is really incorrect, because at hip,her dosagos/exposurcr , up to a limiting value, which probably would not be realized in the human situation, more materia] will be metabolized, and pjcsumably, carcinogenic potcnt.'al will he pro aver than at lower dor.apc/cxposuro. Hence, the t.hcst conditions for the operation of rheir.ica), plant (granted that', some love] of. exposure is unavoidable), would correspond to very intermittent (i.e, very 4 occasional) and very low levels of exposure. The outstanding requirement r.ecns to be for a better unders tend i ns of cancer inductive processes, as they relate to vinyl chloride. BY D H HAT) I'. .'AY (1C I CiX.'TTV.l, T OX ICC'LOGY l^bORATORY, /JYDlXUXY TARK, CllbShinU, /dIGI.IITlX'JIK) CO cn cn R&S