Document g2mOyJwQzyxZMk0Ya1GB0pvDL

^flBVMMF': * P'li 31 ::< ]?i I'l CE f~ \l pf *? ii5f' * ~f i|ft*i > ' !rL : ::,( j:f * I- Ii A STATISTiCAL ASSESSMENT OF THE QUANTITATIVE UPTAKE OF VINYL CHLORIDE MONOMER FROM AQUEOUS SOLUTION - Jim R. Withey I Foods Directorate, Bureau of Chemical Safety, Toxicology Division, Ottawa, Canada i Brian T. Collins __ Foods Directorate, Division of Food Statistics and Operational Planning, Ottawa, Canada j .. .~ ? : 77k presence of vinyl chloride monomer (VCMJ In foodstuffs and to demonstrated carcinogenic potential when administered by the oral route has raised questions 'T\.' concerning the quantitative estimation of the safety of the use of food packaging fabricated from rigid polyvinyl chloride. A statistical model, which was tested by curve-fitting data obtained from an oral uptake study, has been demonstrated to be of predictive vNue. Ninety-five percent confidence limits were- also calculated, and the data from this study were compared with those from a previous gas phase exposure study. It was concluded that If the total dally liquid intake contained 20 ppm of "f VCM then the area generated under the blood level-time curve, for rats, would bo equivalent to an Inhalation exposure ot about 2 ppm for 24 " INTRODUCTION Recent work in our own laboratories and elsewhere (Fuchs et al.,*r 1975; Williams and Miles, 1975) has demonstrated the presence of VCM in ' * foodstuffs. Pharmacokinetic and uptake studies (Withey, 1976) illustrated that uptake from aqueous and lipid solutions containing VCM was extremely rapid and complicated. Since the variability of the uptake of ^ VCM in aqueous solution from the Gl tract did not allow a complete > pharmacokinetic analysis of observed blood level data, it appeared that a -..quantitative measure of uptake was possible only from a statistical analysis of the area under the blood level-time curves (AUC), which could be obtained after dosing. A similar approach has been frequently used for the - assessment of the bioavailability of oral drug dosage forms (Wagner, 1971). it is a pleasure to acknowledge the skill and dedication of Peter Collins, who assisted with the - analytical work, and of Henry James, who surgically prepared the animals that were used In this -StUdy. . /' - ; Requests for reprints should be sent to Jim R. Withey, Foods Directorate, Bureau of Chemical Safety, Toxicology Division, Tunney's Pasture, Ottawa K1A 0L2 Canada. ~ ` ' _ 311 - Journal of Toxicology and Environmental Health, 2:311-321, 1976 Copyright C 1976 by Hemisphere Publishing Corporation > * DTH 000018316 - After an examination of data from a pilot study of the uptake of VCM from aqueous solution when administered intragastrically, an experimental design was conceived in which uptake was assessed for rats of two different body weight groups at five .different dose levels for each. The dose levels ranged from 2 to 25 mg, the lower dose level being limited by the analytical sensitivity, for VCM in blood and the upper dose level by the solubility of VCM in water. The dose-reponse curve data, in terms of the AUC against dose, was then curve-fitted to two model equations and statistically analyzed. The models were studied for goodness of fit to the data and both were found to provide an adequate fit for the data obtained from the 200-g animals. The two models were then extrapolated to predict the uptake for aqueous solutions of VCM pf lower concentrations than those used in the experiment. Results of this study were compared with those from a previous study in which uptake of VCM from gas phase exposures was measured. METHODS AND EXPERIMENTAL DESIGN ^; Sixty male Sprague-Dawley rats, equally divided into two weight groups of approximately 200 and 400 g, were surgically prepared with an indwelling cannula 48 hr prior to dosing. Six animals from each weight group were dosed intragastrically by means of a flexible cannula at each of five dose levels of 2, 4, 8, 16, and 25 mg of VCM, contained in 5 mi of -water. A simple factorial dosing experiment was selected so as to allow the 'effects of animal body weight, dose,.and their interaction to be.assessed.. The order of dosing was then derived by randomly assigning doses and .animal weight combinations with the restriction that two animals could be ^dosed daily.-The animals were deprived of food and water..1.6 hr prior to dosing since these were known, from preliminary studies, to perturb the rate and extent of VCM uptake. Immediately after the removal of food and water, .each animal was dosed by stomach intubation, with 5 ml of water so as to reduce desiccation and excessive overnight weight loss. Animals were weighed prior to the deprivation of food and again prior to dosing. -r-V: ; ' -- - - - Aqueous solutions of VCM were prepared and analyzed just prior to dosing by methods which have been described previously (Withey, 1976). Blood samples (0.1 ml) were taken at 2, 4, 8, 12, 16, and 20 min after dosing and then every 10 min up to 2 hr or until levels of VCM were undetectable.:''>'`--i-;-;` ' \-'v'" :_ . RESULTS - V--.;-.;' \ ' . . ` " The area under each blood level-time curve was calculated, using the trapezoidal rule, from the equation . - _ AND B-T. COLLINS VINYL CHLORIDE UPTAKE FROM SOLUTION 313 f the uptake of ragastrically, an assessed for rats j levels for each, /el being limited >cr dose level by 'ata, in terms of -I equations and :ss of fit to the ie data obtained lated to predict entrations than compared with from gas phase 'o two weight epared with an m each weight .nula at each of ned in 5 ml of as to allow the to be assessed. saing doses and dmals could be --16 hr prior tO' to~ perturb the 1 4moval of food ' -.with 5 ml of v._ ' t weight loss. again prior to* I just prior to ^.Vithey, 1976). : 20 min after of VCM were ted, using the " ;> AUC = ----- t,]iC,*y (1) /o . where C, was the concentration of VCM in the blood at time t, and there were n observations. It was assumed that the blood concentration was zero at time t0 *0. - The AUC for each animal, the actual dose administered, and the weight of the animal just prior to dosing are given in Table la and b. TABLE 1. Actual Body Weights of Animals, Administered Dote, and Area under Curv^ Required - dote BW, AD, . - - ---------- (mb) and AUC* 1 2 3 4 5 6 Mean SO CV - ; (a) Light group (-- 200* body weight) V - , -. .v: 2., BW 205 234 191 223 215 190 209.7 . 17.64 .008 i* AD ; - 128 128 1.95 131 --123 120 121 0133 006 -auc 63JO -4034 38.81 25.76 5024 65.11 44.36 1539 033 4 -- BW 214 210 .198 235 225 219 _ 216.8 -1173 006 AD -- 421 -- 411 427 4.31 -411-4.11 4.19 0090 002 AUC - 75.89 76.18 9016 108.6 . 68.45 1010 86.87 1004 0185 BW 193 209 8 AO 7.96 735 ' -> AUC ' 137.3 355.8 .'- w. - --a* . ;' , ?~BW 4IK-204 221 16 - - y`AD -16.66 16.05 AUC 403.1 327.5 228 235 213 222 7.64 734 . 737 8.31 3211 2601 "1113 203J 213 "f 217 ' 204 ' 222 ' 16.02 16.84 ,1536 "1023 227.0 6113 308.7 .. 2933 216.7 732 231.9 2116 1019 361.9 15.00 007 0283 004 9030 042 r- , - - -- - 021 004 -. 0526 003 134.8 - 037 v BW "~2ir hi -^zoo ,25 ? AD ,, 25.2S . 25.84 25.99 25J3 ' 3'AUC '654.7 610.2 696.7 .8405 . 1131 006' >0645 003 '108.0 016 w -f, -.- .: ` (b) Heavy group (-400* bogy weight) ; 16 * 25 r: BW 405 998 '.387 354 381 ,3*4 AO -a-vlIS 7.118 'H.J9 1.95 -23t f 123 AUC 15.14 "23.75 1056 18.81 14.40 1735 - . . es a " . - - > i.. .7 ' -i BW v 387 352 381 "368 '372 ' 381 AD 4.21 4.43 . 431 425 4.25 401 AUC ,-5336- 3735 29.64 -41.14 -49.11 - 48.92 19.58 -02)5 0141 007 " 447 027 1157 003 0138 003 "8JI2 021 BW - --422 427 - .333 "..363 :-3Sl .` 384 AD 8.08 7.88 .036 .8.15 015 8.34 ..7, AUC .124.7 114.9 392.8 131.2 " 95.92 107.9 -38.28 OIO -0177 002 1141 .071 BW t- t 390 -351 360 - -340 ~3S5 V-3S8 359.0 ' 1076 005 - AO : 1035 . . 15.36 1014 1023 1078 15.39 1004 0561 003 - AUC 295.6 3002 469.9 .215.4 3700 -219.3 -311.7 - 9057 OJI BW AD - AUC 383 - 380 377 ' >53 " 363 _377 .3712 11.63 003 24.34 25.42 -2188 2475 2464 24.64 24.61 0507 002 511.2 4312 394.2- 3917 - 3806 519.4 .438.6 ' 61.95 014 *BW it the actual body weight (g); AD the actual dote admmittcrcd; AUC it the measured area under the Mood cum (minitg/ml); CV is the coeffkicni of variation. V*-** ^ r - *. :* ^ * -V < ^ " -*V DTH 000018318 r 314 ). R. WITHEY AND B. T. COLLINS ,jLrV- eoo 5^ 00 5? 200 G. ANIMALS a) . * 800 b) coo |?40 * 4 1 200 - - V 400 200 OE f '? . Q02 oo aio ai4 002 OOSE/WT. (MG/GM) OOfi 200 6. ANIMALS - Is * cK .oil*00 - 400 & ANIMALS 00 d) ^ 400 :3|= O* 2 0 O *-400 -400 -> * i5 -oo --A 400 1200 2000 "-eoo -. 400 1200 2000 - -- -- TRANSFORMED PREDICTED VALUE 1/tG-MIN/ML) (MG g7* - <00 O UJ , I -- m*4 1200 200 OO -- O 400 xjgo - - 0 jV -400 -00 .-JR; *,*-- CUMULATIVE NORMAU PROBABILITY FIGURE U Cun**fittfng analysis for model L (a) and (b) Area under curve against dose for 200-g and .-&+$***<S*- -ri~''400-gnitnls.'(e) and (d) Seated transformed residuals: againsttransformed predicted values of yea f under curve, (e) Cumulative normal probability plot of the transformed scaled residuals for all animals - Lv- .'***' = * v- -^ANALYSIS OM>ATA'?>t^ ;r-^33*3EcJ' "" ............. ... ` ^ _ Plots of the AUC against the actual administered dose,.Tn mg/kg, were ~ made for the two animal weight classes used in the experiment and are : presented in Fig. 1 a and b. A weighted regression was then performed for 7 the sets of data according to the model equations (model I) below: " .. (AUC)/ * a + at (DJW), + e, for animals weighing about 200 g (2a) and (AUC)/ =00 +0t (DtW), +/ , for animals weighing about 400 g (2b) >. * where (AUC)/ was the calculated area under the blood level-time curve for animal / in the 200-g or 400-g weight class. The ars and 0's were unknown coefficients that were required to be estimated, (D/W)j was the actual dose - DTH 000018319 C id -^:r* t .-AS *ii ?-&r. 1 e eH >r T ) :-- 0 r n .e an VINYLCHL'JI'MI. IN TAKE FROM SOLUTION 315 in mg divide I by the weight of the animal in grams for animal /, and e, was the random error associated with each animal. The values of c, were assumed to have an average of zero and a variance equal to ol()/K,)/> where o2 is an unknown parameter common to both weight classes. After the regression was performed the residuals were transformed (Draper and Smith, 1966) because a weighted regression was performed. The residuals were also sealed to have equal variances (Timm and Carlcson, 1974). A plot of transformed scaled residuals against predicted values of AUC for each animal weight class and a cumulative normal probability plot of the transformed scaled residuals (Daniel and Wood, 1971) were made. It was apparent from an inspection of these graphs that one point in the 400-g weight class was an outlier. This observation was obtained for animal 3, which had received a dose of 8.36 mg but which had yielded an AUC more consistent with those that received a 16-mg dose. This observation was therefore rejected and the analysis was. repeated. No -further outliers were observed after the second regression. 'j 'r An F test and a Scheffe's F projection test (Miller, 1966) on the AUC and (DfW) data showed that the data may pass through the origin for the 200-g weight class but that they did not for the 400-g weight class. Since it was known that the relationship must pass through the origin it was concluded that either the model or the observed data must be in error for the 400-g weight class. Since the AUC was assumed to be zero after VCM blood levels became-undetectable the observed dataf may be biased low* '^Thus. there may be a significant contribution to the values of AUC from the- terminal phase of the blood level-time cun^ especially at low-values of i-'- {D/W). g tz. --O.-y -The*coefficients, estimated after setting~a0 = 0, are shown In-Table 2. & This regression allowed a reduction in the sum of squares (r1) of-76%. The J: plots of scaled transformed residuals against transformed predicted value v and a cumulative normal probability plot of the scaled residuals are shown in Fig. 1, c, d, and e. An approximately equal number of points He above' and below the baseline in Fig. 1, c and d, as would be expected if the -.model is correct. From Fig. Id it was observed that for the 400-g class the `^variance appeared to increase with predicted value, again indicating that the model may not be appropriate. - _ -:V-. l . 1 7?. *<\ -TABLE 2. Coefficients for the Fitted Eqs. (2a) and (2b), -Model 1, After Setting i,b0 and Elimination of the Outlier - Coefficient Estimated value \ .""SE ''-C i 0. 0, .. ,5215 ' 27.55 ' 714S - 1246.8 O'-' > .9.370 tT -viO456.0 f: 0 Si -f:- zz I# f & & DTH 000018320 vyr*"" 7?' r 316 r J. K. WIIIII.Y AND It. I.COI.MN.S Since model I appeared not to pass through the origin for the 400-g weight class, alternative regressions were examined. After some preliminary plots of the data were made, the model (model II) given in Eq. (3) was chosen for further study and a least-squares regression was applied to the data. log(AUC), = 70 + Ti (log weight)/ +y2 (log dose)/ + 73 (log weight)/ (log dose}/ + 6j '-r (3) where log(AUC)/ was log10 of the measured AUC for animal /, (log weighty was logl0 of the actual body weight for animal /, (log dose)/ was log|0 of the actual dose administered to animal /, the y's were coefficients to be estimated, and 6, was a random deviation associated with the ;th animal. The values of 5/ were assumed to follow a normal distribution with an average of zero, a variance of o2,,and all 5's were assumed independent. --.'C*^. /v. ' The residuals were scaled to have equal variance, and a plot of scaled residuals against predicted value, a cumulative normal probability plot, and plots of partial residuals (Larsen and McCleary, 1972) were made. An assessment of these graphs was made and it was decided that animal 3 in the 400-g class was an outlier for this model as well as for model I. The -coefficients y from model II were reestimated after exclusion of the outlier and are shown in Table 3. This regression allowed a reduction in " the- sum of squares (r2) of 94%. Revised plots of scaled residuals against* ; predicted value, partial residual plots, and a revised cumulative normal_ - probability plot were made,*as shown" in Fig. 32, a,'b, c, d. and e, respec-" tesr of the "significance ofincluding the* coefficient in'the model-.was also performed (Draper and Smith, 1966). The hypothesis that v o3 = 0 was rejected {p <0 05), indicating that a3 was a necessary term in * - Confidence regions were calculated For the'regression "surfaces of -models L and II (Miller, 1966). Figure 3 illustrates plots of the AUC /against dose, in mg after rejection of the outlier together with their ^estimated confidence bands for animals weighing exactly 200 and 400 g. jr* .. ' V `i,' . TABLE J. Coefficicnti for the Fitted Eq. (3), Model U Coefficient \ - Calculated value SS-'SE 7, ; -r. 7, . 5.954 -Z006 -1.643 ' 1.169 0.7688 'V . _ 0.3134 .7 - :.V 0.7964 0.3251 DTH 000018323 I } -<* as to the (3) /, (log c)j was ficients the /th ibution issumed f scaled lot, and `ade. An mal 3 in H I . The .`of .the action in -s against -jg. normal^ -j?, respec-O % in the j 4hes>s that . 4y term in '- j. - Effaces of the AUC ^with their md 400 g. ,,nyl chloride ortrre TM" "LUT," i *4r o) a b) 1-4.2- r I o.zY . S <4 . V ***'.! -*> a01r-."" * ji, . I* 2 -o.i v . *sL -44 I -4a O *tKti -5.0 -*z -v & 8tL -a*r1 -O.SK . . 1.0 * 2.2 t iHtebicrco u>io ,AUC* 4 -9.4 It--1--*- 1 Jr*1 oe * 5 2 2.4 2- U>6 (WEIGHT) ^*a4r' 5 t* c) *-o*|- - V 4.2 U PTH 0000]8322 r. 3)8 J. R. WlTHEY AND a T. COLLINS 200 6. ANIMALS 400 Gl ANIMALS .i 4.v<^5| 4 12 20 DOSE (MO.) - -- 4 12 20 OOSE (MO.) 400 & ANIMALS " ... -- . 4- .12 20 OOSE (M6.) / . - .. <0.-12 - 20 'OOSE (MO.) -7<r - : *--' r*. *. . v-*-~ r .V FIGURE 3. Area under curve'against dose with estimated confidence bands. Parts (a) and (b) are for--^- ^Figure 3, c and d; were calculated. from'modelrirtjn which. the: <fcrjved;''^^^w^^: -^equations were, as follows: - 'v-Fbr a 200-g animal !> 4~ -- v? Jog AUC = 1.3378 +1.0458 log(dose) Vv:^^i*r'(6) V _\J -and for 400-g animal - <-; ; -ir * isk*W'?1t,jiry -ee^aSwweLrf ^.ees_ r-rr' **;-*-.eat-syj*nra. veeLSsat;- Ic^AUC-0.7339 * O^lHogfe -taSS*V-, rr-= W;.*r -' j.-ii; V.''c2`K'v7'~~L\rV.~--v3."73*C-~i .4.1 `J..* , '-- : DISCUSSION r'-.. ' -r:- --- --.- .. -.-. -- ,:T^'-, ? i'!::: -ss-^Jsr'> .*..vr.-- .---*. **'*..--Cr^-v:^^:,^-' *. The expected linear relationship between the administcrcd dosc. on S- dose-weight basis, and the evoked response, in terms of the. generated AUC - V. (i.c., model I), appeared to be followed reasonably, well by the data for' the 200-g weight class. For the 400-g class,. however/ equation did not pass through the origin and inspection of the scaled' ?<"' ~'' ":' - ' TH.'. DTH 000018323 VINYI. Clli.OKim: DIM AKt I'KOM SOLUIION 319 transformed residual plots showed some inadequacies in the fit of the data. Since model I was inadequate to fit the data for the 400-g class, an alternate model (model II) was examined and the data appeared to fit model II very well. The plots of scaled residuals against predicted value, scaled residuals against cumulative normal probability, and the partial probability plots were all observed to appear as expected. The linearity of the relationship between log AUC and the factors log(dosc) and log(wcight) X log(dosc) was visually confirmed by inspection of the partial residual plots. However, since only two weight classes were observed it was not possible to ascertain whether a linear relationship existed between r log(AUC) and weight. Hence, even although it was possible to interpolate or extrapolate model II to weights other than 200 or 400 g, it was not considered reliable to do so. A precise relationship of AUC to animal body weight for a given dose may be difficult to establish owing to the factors - which affect the elimination of VCM from the blood compartment. It has been shown (Schaumann, * 1934) that more than 82% of VCM_that is absorbed into the blood compartment is excreted by way of the - pulmonary route, and lung tidal volumes with body weights, for rats, has been reported to vary as the 0.67 power of the body weight (Lcong et al., -1964). The tidal volume and breathing rate would influence the r ^elimination rate for VCM,. and the latter has been shown to influence the ii V- jp. v* u* AUC where first-order kinetic processes are involved (Wagner, 1971)- -lb' ^ The carcinogenic potential of VCM has now been demonstrated at very u .c/jp 31^:.low levels of'chronic gas phase exposure. Moreover, the variety of tumors _ ^ _ ^3^|^^^that''airvnow;. be associated -with- yCM exposure (Maltoni and Lcfeminej-^ryji^^ V '. me.' '-rzr 974^.Thomas et al.,,(l975; Viola et al.,"i 971) has established that tumors ^ ^ ^ T ^^^|l^ve appeared" in any:"organ that is. provided with k good blood suppl r ~.^-Jhus**the^yCM.. blood conccntration-time curve for an animal may be ^ ^considcrccTasVuscful; toxicological parameter in assessing the carcinogenic ^ risk arising from the uptake of VCM from any route of ingestion. %-_ - ? ' * Early findings by "the U.S. ^Food and Drug"Administration (Fed. ^ - Regist., 1975) of up to 20 ppm of VCM in alcoholic beverages,.led to the "V - :&*r ' withdrawal of the prior sanctioned use of rigid polyvinyl chloride as a f ---food-packaging material. More extensive analysis of foods packaged in this < 1:- material (van Esch and van Logtcn,' 1975; Williams and Miles, 1975) >-revealed the presence of VCM at up to 10 ppm of VCM, although manufacturers now claim to have reduced the VCM content of the rigid * - Hr**'-.- * * plastic (Food Chem. News, 1975). It has been reported that a rat of 200-g body weight consumes about - 45 ml of water per day, so that if this total liquid, intake contained 20 ppm of VCM, then the ingested dose would be 0.9 mg of VCM. When the ' dose response curves expressed as Eqs. (4) and (6) were extrapolated to a ' dose of 0.9 mg the predicted AUC's were 23 j and 19.5 min-Mg/ml, - respectively.'While it is appreciated that extrapolation of experimental I r 320 |. R. WITHEY AND B.T. COLLINS results must always be used with reservation, this extrapolation is not very far beyond the lower limit of the experimental dose range (2-25 mg) and the dose response equation appeared to fit reasonably well over the entire experimental range for the animals of 200-g body weight. Since the two predicted values were quite similar either may be used in the following - discussion; for example, let the predicted AUC of 19.5 min-pg/ml be used. - It has been demonstrated (Withey, 1976) that when a rat of any weight was exposed to a constant concentration of VCM in the gas phase, ' the blood compartment rapidly equilibrated to give a plateau or equilibrium blood concentration of VCM which was directly proportional " to the exposure concentration. This relationship was found to obey the linear equation y -- 0.3832*, where y was the exposure concentration in yg/ml and x was the equilibrium blood concentration of VCM in Mg/ml. " This relationship was found to be independent of the body weight. Thus a . blood equilibrium concentration of 19.50 Mg/ml would be predicted for a rat exposed to a constant atmospheric concentration of.VCM of 7.471 pg/ml, which is equivalent to 2834 ppm. If the AUC can be considered as a parameter that is directly proportional to the toxicological effect (i.e., the induction of tumors), then it should be possiblejo equate equivalent values.of AUC ho matter whether these were generated as a:consequence of an exposure to' VCM in the gas phase or after the administration of an ihtragastric dose-Ja the case of VCM an AUC of 19.5Q min-pg/ml would be generated in m atmosphere of 2834 ppm- for T. min. or 1.97 ppm for 24 hr/'Tand this^wouldMepresent an exposure hazard'equivalent to the ingestion orO.9 mg: of VCM by a 200-g rat. These conclusions were based *' .t-r*- . jc * oa_aacomparisort~of,two.fitted equationsand should..therefore, be . i considered-as only approximate; however, it.would appear that the hazards St* - presented by"tbe'pr*ence of VCM in foodstuffs ^concentrations near 20 -CV - . - ppni -foulctexceed thosir in the industriaf world place-forwhich limits have ~ ~ --- t y. ' .7K- REFERENCES r. v . ' . a ~ _' SW'-'V. -i-- -'V Vr Anonymous.- 1974. Occupational Safety and Health Association to issue permanent and temporary vinyl chloride standards. Pesticide Chem. News 2(27 March): 17.. . -t - Daniel. C and Wood, F. S. 1971. Fitting equations to dbm.New York: Wiley.^^TJiSr.^ '-'' . .ri tT? Oraper, N. R. and Smith, H. 1966. Applied regression analysis. New York: Wiley.. v*' Fed. Regist. 1975. Vinyl chloride polymers in contact with food, notice of proposed rule making. *: ^*'-5Tg^Ki40tdS29-WS37. : - -rr- Food Gbem-Mmo-22 December 1975, p. 36. . L. ,j*. -v-~- ...- --, :- :r\' v Fuchs, G-, Gawell, B. M., Aibanus, L. and Siorach, S. 1975. Fbnkomst ar vinylkloridmonomer I - : matfett. Ver Foda. 27(3):t34-145. - . `cO - ' - Larsen, W. A. and Mcdcary, S. J. 1972 Partial residual plots and regression analysis. 1,; ' Vt- '~'f " ,7>eAoefrte 14:761-790. : -r - . v - v - Leong, K. |,, Dowd, G. F. and MacFarland, H. N. 1964. Can. /. Physiol Pharmacol. 42:189-198. Maltoni, C. and Lefemine, G- 1974. Carcinogenicity bioassays of rinyl chloride. Environ. Res. . 7:387-405. -*rii'wr"'t >. ' ' rr. t * > ; -i'* TV- wJS rVhio -Am, DTH 000018325 c*) ( VINYI. CIILOKIUL UP IAKC Of SOLUTION 321 Miller, R. G. 1966. Simultaneous statistical Inference. Toronto: McGraw-Hill. Schaumann, O. 1934. Abiorption, fats and excretion of vinyl chloride. Med. Chcm. {Leverkusen, Ger.) 2:139-147. Thomas, L. B., Popper, H., Berk, P. D., Selikoff, L J. and Falk. H. 1975. Vinyl chloride induced liver disease. N. Engl. /-Med. 292:17-22. Timm, N. H. and Carlcson, J. E. 1972. Lectures on the analysis and interpretation of cell designs . - with unequal cell frequencies. College of Education, University of Pittsburgh, Pennsylvania. - van Each, G. |. and van Logten, M. J. 1975. Vinyl chloride: A report of a European assessment. ~ Food Cosmet. Toxicol 13:121-139. ; Viola, P. Z-, Bigotti, A. and Caputo, A. 1971. Oncogenic response of rat skin, lungs and bones to - vinyl chloride. Owscer Acs. 31:516-522. - -<' .r- ' Wagner, ). G. 1971. Bktphermaceutks and Relevant Pharmacokinetics, chap. 25. Hamilton, Illinois: Drug Intelligence Publications. Williams, 0. T. and Miles, W. F. 1975. Gas-liquid chromatographic determination of vinyl chloride ,r. - in alcoholic beverages, vegetable oils and vinegars. ). Assoc. Offlc. Anal. Cham. 51:272-275. ... Withey, R.). 1976. The pharmacodynamics and uptake of vinyl chloride monomer administered by ' various routes to rats. /. Toxicol. Environ. Health 1:381-394. V-'- ~ '.r~- ; `X " -' ' : Received April 26, 1976 ' - >-- Accepted July 14, 1976 - M T#W- rtssr ' 5 a. - - *'; * . * ->>- - . .~-:y , - - v- IT- led -- -: , ."li ' , V-'i'li' ,3'i.5T - *- ** 4"ja*. .......J J- - '. I- .ssi r1"' - V > jjp-.ee-r - _ ... r *r,ev;^je4.7^irc.- e* . ...-fcs ' ifT'^<Sev-3J-ET< W-Sf-o." ,w;- r1 ' ^ .f*/'/' . . -r. -- 1A,. ; ........ ..; '-V . ai-^-T `pi" *>v. . V .'* - -- ::^v; ... W-L &:**b. *--v +V>* 0; :s - DTH 000018326