Document 7Mq0y4vNMMq31avzOXa4rMzw6

Hyg. ASMK:J 47( 1):3740 (1986) thod for Repeated Evaluation of Benzene Uptake in Rats and Mice During a Six Hour Inhalation Period K EUTERMOSER." GEORGE M. RUSCH,B ROBERT A. KUNAF JOSEPH OGRODNICKDand WILLIAM E. RINEHARTB mics, Im., Mettkrs Road, East Millstone, NJ 08873; *Allied Chemical Corporation, Morristown, NJ 07960; 'Exxon Corporation, rch and Environmental Health Division, East Millstone, NJ 08873; DAmericanHoechst Corporation, Somerville, NJ 08876 measurementsandrespiratory minute volume (RMV)were assessed in rats and mice duringa (-hour inhalatiw exposureto .The next prediction allowed adjustments for changesin R M V during exposure. Tbc uptake ch.racteristies of benzene in both species were different from the aging R M V .ndfrom each other.Tbcgreateat differtnce w s seenin rats where the hhtm the predictions, nor was the data sufficient to suggest whether the rat or the mouse was a suitable model of benzene uptake in hRans. LIrdwtion haiayl studies often are used to establish various relation- exposure; and (2) if such changes were observed, whether or tbip ktween chemical exposure and animal response. In not the rates of benzene and ether uptake were influenced in #rd"nr which use inhalation exposures, a "concentration- 5 a similar manner. !?sc* relationship, rather than a "dose-response"rela- W p , is most often established."' This is because the t - 'concentration of the chemical is measurable more ExPfiment.1 I------ in the exposure chamber (and the workplace) than is Chemicals tor Testhg tlal amount of the chemical entering the exposed *. Commercial grade benzene, supplied by the Chemical Manufacturers Association, and diethyl ether (Mallinkrodt) TIN principle that an exposure effect (E)is proportional to were used for the study. tbe exposure concentration (C) multiplied by the exposure duntion (T), E 0: CT, Inhalaffon Exposum to Benzene Benzene was flash evaporated at 35C in a three-neck, round-bottom flask. Glass tubing was used to deliver the frapuently used to evaluate animal response to inhaled che&ak. One need only incorporate a chemical uptake W m r , such as respiratory minute volume (RMV), into a relationship to determine an expected maximum lnlukddose for a given exposure period."' benzene into the flash evaporator and to conduct the benzene vapor-laden air into the exposure chamber. Vaporladen air was drawn into a one-cubic meter, stainless steel and glass exposure chamber, where it was diluted with room air to reach the desired exposure concentration (300 ppm). ORBdifficulty with application of the CT relationship is tbM apray chemicals have been shown to alter respiratory W h m x during inhalation exposure."' If airborne CbeariCrlE alter RMV, they also would affect the rate of The exposure chambers were operated dynamically at an airflow rate of 205 L/min. A vented glove box provided access to the chamber. The chamber atmosphere was monitored continuously rrp6.t6of tbt chemical during exposure. Further, if the uwof a n airborne chemical also can be affected by during the exposure with a MIRANQ I A Ambient Air Analyzer. Infrared absorbance readings were recorded and com- prOCC8scs other than respiratory performance (e.g., altera- pared to a calibration curve to determine the exposure tiomb blood/gas transfer, etc.), the actual inhaled dose concentration 8given period could be overestimated considerably by sttnithtforward CT relationship. Exporuff and Tstffng Reglmen nd Hatch'3' and Rinehart and Hatch"' have dem- a method of measuring R M V using diethyl ether. s method, net uptake measurements of diethyl MV)and benzene (for the test chemical) were and compared to assess: (1) whether or not net or ether uptake changed during a 6-hr inhalation Inhalation exposure to benzene vapor was continuous hr. Measurements of net benzene uptake and R M V performed prior to benzene exposure after 1hr, 3 hr a of benzene exposure. The time that the animals spc uptake measurements (approximately 20 min per mea ment) was not included in the total exposure time. hooc J (47) January. 1986 Copyright 1906 Amariurr Induslnal liygmne Association 37 was a n uptake mte factor (in mL/min) for 1W orgiuupof aSictdwinga specifxexjmsnre UD 3br,ere.); y c "the~exposureconccn- m -w wIE-(*y m-cm mL);a d 7"was theduration of the exposure 5 t" MlcE-SI 'K" depended upon the inhaled dose model . W k n the theoretical model was calculated, 'K" Epr nJ as equal to the precxposure value for ether b " (= RMV). When the theoretical model, influ- E m ng RMV was calculated, "K"was an average rateduring a specific interval (e.g.. 1 hr t o 3 hr). retical model, influenced by benzene uptake r20 10 "K"was the average uptake rate for benzene 0 12 34 5C Exmsu?OuUTIor. I n u R 5 ! Figure 1 - Cumulative inhaled benzene dose in rats and mice, as influenced by theory, changing RMV. and changing D'Qkrrnces in benzene uptake rates and RMV between prPcrOosed and exposure intervals were analyzed by a Ran- benzene uptake rate. All values are normalized as percentages of the total expected dose. dd#hhcd Block Design'5' with the animals as blocks and the tiat#esiods as treatments. Duncan's Multiple Range Test'" .rprlladto determine which time periods (exposed)differed Prior to benzene exposure, the mice exhibited a mean net uptake rate for benzene of 188 mL/ min, and a mean RMV of frea control (preexposed). 189 mL/ min. The pretest uptake rates for benzene and ether m b n c e s between benzene uptake rates and RMV, at (for RMV) had no significant statistical difference. ere analyzed by a Paired Difference T-test'5' After 1 hr of exposure, the mean net uptake rate for Is as pairing elements and ether and benzene benzene decreased with statistical significance to 65% of the . Statistical analyses were perfoimd sepa- mean pretest value in the mice, but it did not continue to kand mice at each time period (preexposure; ;3-hr exposure; and 6-hr exposure). decline during the remainder of the exposure. After 3 and 6 hrs of exposure, the mean benzene uptake rates were more stable, at 76 and 81% of the pretest value, r e s p e c t i v m RMV values for these same intervals were decreased with Expourfw and Uptake Measurements statistical significance to 96,84 and 69% of the pretest value, respectively, but were statistically different from corres- tul tats receive exposure to a mean benzene concen- ppm (s.d. = 10 ppm) during the 6-hr dosing ponding benzene uptake rates only at the I-hr (lower) and 6-hr (higher) intervals. uptake data for the rats are summarized in The mean, cumulative, inhaled benzene dose for the mice, calculated by each of the three prediction models, is pre- e exposure, the rats exhibited a mean net sented in Table 11. The observed benzene inhaled dose was ene of 152 mL/ min,and a mean RMV of 73% of the theoretical inhaled dose, and 89% of the predic- The pretest uptake rates of benzene and ether no significant, statistical difference. tion which was adjusted for changing RMV. Figure 1 is a graphic representation of the build-up of and 6 hr of continuous benzene exposure, the rates for benzene had decreased with statis- inhaled dose over time, as predicted by each of the three models: theory; theory - adjusted for changing RMV; and to 33, 22 and 9% of the pretest value. The theory -adjusted for benzene uptake rate. The values plotted es at these same intervals had decreased are normalized as percentages of the dose expected by the gnificance to 85,78 and 66% of the pretest unadjusted theoretical model. It was clear from the figure statistical significant difference from the that the inhaled doses of rats and mice, as adjusted for benzene uptake values. changing RMV, were lower than the unadjusted theoretical umulative, inhaled benzene dose for the rats, by each of the three prediction models, is pre- dose, and that the inhaled doses, as adjusted for benzene uptake rate, were lower still. -.b Table 11. The observed benzene inhaled dose was he theoretical inhaled dose. and 36% of the Discussion was adjusted for changing RMV. Benzene was selected for the stud) because of its wide indus- Expowre and Uptake Meerurements trial use and interest. There have been many investigations into the toxicit) of benzene ('"'' Thus, there was interest to received exposure to a mean chamber determine whether or not benzene uptake was constant or 10 ppm (s.d. = 10 ppm) during the 6-hr variable during inhalation exposure. The 300 ppm exposure apor uptake data for mice are summarized level was selected because it was a level which could be experienced during an accidental worker exposure, and yet January 1986 39 vas below the level at which one would expect to observe overt signs of narcotic effects."2' the incorporation of an appropriate rate factor (volume per unit time). The present study demonstrafed that the most appropriate factor was the one related to benzene, the test material. The method used to determine the rate factor for this study was simple and enabled the determination of benzene uptake and R M V at rest, during exposure, without causing undue distress to the ani mal^.'^' The mean pre-exposed R M V values for rats and mice compared well to published value^,"^' which suggested that the uptake method accurately might monitor changes in the RMV duringexposure. It was not known, however, if expo- gave a much different picture than RMV-adjusted, model. The data responsible for alterations In benzene Uptake, sufficient to determine whether the m o w 01 suitable model for benzene uptake in h u m Acknowledgment The authors wish to thank M ~ C.athy Hoffma assistance in performing the exposures. References lung, especially during the time course of the exposure in the study.('-I ') The results from this study presented other points to consider. The cumulative inhaled doses plotted in Figure I clearly demonstrated a dramatic difference in benzene uptake characteristics between ratsand mice. The findings in the rat were similar to those reported by Anderson et ~ f . , " ~ ' using I, Idichloroethylene. They reported that the uptake @ curve was biphasic, possessing a rapid phase that was essentially complete within the first 60-80 minutes. This appeared to represent tissue equilibration and was Independent of concentr;ttic;urlPuel. The second phase, a slower uptake rate, appeared to be related to metabolism.'"' (1966). 3. Long, J.E. and T.F. Hatch: A siological Impairment Produ Pulmonary Irritants.Am. Ind 4. Rlnehart, W.E. and T. F. Hal& C o r n uct (CT)as an Expression of Dose in to Phosgene. Am. Ind. Hyg. Assoc. J 5. Snedecor, G.W. and W.G. CochmS 6. Duncan, D.B.: Multiple Range and MultipleFT rrcs 71'1-42 (1955) The findings ip the mouse suggested that the first phase of benzene uptake m y have been completed within a shorter time frame than in the rat. A comparison of the ratio of RMV to animal volume suggested that the ratio for the mouse was approximately double that for the rat. Thus, the 8. R p c h , o.M.,B.K.J. Lwng .ndS. li8m. J. Torrcol. Envrron. Health 10. Bergman, K-: Whole-BodY Auto Tracer Techniques in Distribution of SomeOrganic Solvents.Scand. Suppl. 7 :1-263 (1979). mg, kg basis, might similarly be attributed to the higher rate of metabolism in the mouse, when compared to the Depression of RMV during the course of dosing was apparent, but there was no clear correlation between RMV and benzene uptake rate in either rats or mice. Thus, the reduction of benzene uptake during exposure must have been related to some other process. It also was reported that the benzene uptake in the mice was statistically significant, it was not considered to have been biologically significant, being related more to analyti- cal variability than to animal response. If anything, ether uptake wouid be expectedto be higher than be- bearlrse of the greater water solubility of ether. Furthennore, ether uptake b s previously been shown to provide a good esti- mate of RMV. In summary, this study demonstrated that predicting inhaled dose from measured uptake rates of a test material bo 15. And.rron, ME., Determination o