Bull. Environ. Contam. Toxicol. (1992) 49:325-333
i
9 1992 Spfinger-Verlag New York Inc.
~nvir .or~..
al
Diffusive Personal Sampler for Methyl Acetate Monitoring Tomojiro Yasug~ ~'2 Toshio Kawai, ~ Kazunori Mizunuma, ~'2 and Masayukilkeda ~
1Osaka Occupational Health Service Center, Osaka 550, Japan and 2Department of Public Health, Kyoto University Faculty of Medicine, Kyoto 606-01, Kyoto, Japan
M e t h y l a c e t a t e is an o r g a n i c s o l v e n t present in some industrial materials such as paints and adhessives (Kumai et al., 1983), and to a l e s s e r extent in degreasers (Inoue et al., 1983); e x p e r i e n c e shows a mixture of m e t h a n o l and m e t h y l a c e t a t e is used for removal of s t y r e n e m o n o m e r - c o n t a i n i n g uncured resin from b r u s h e s in f i b e r - r e i n f o r c e d p l a s t i c s p r o d u c t i o n . Furthermore, additional attention has b e e n recently p a i d to this e s t e r as a p o s s i b l e s o u r c e of m e t h a n o l in s n i f f i n g thinner. O g a w a et al. (1988) s t u d i e d a case of acute optic n e u r o p a t h y a f t e r t h i n n e r sniffing, and suspected methyl acetate as a c a u s a t i v e agent in the thinner; one paint t h i n n e r w h i c h the p a t i e n t used to sniff contained this e s t e r by 20% (in addition to methanol by 20%), this e s t e r is m o r e v o l a t i l e with higher vapor pressure at s a t u r a t i o n than methanol, r e a d i l y absorbed, and q u i c k l y h y d r o l y z e d to m e t h a n o l and a c e t a t e w h e n taken into body. I n t e r e s t i n g l y , this ester is not only l i p o p h i l i c as an o r g a n i c solvent, but partly soluble a l s o in water. B e c a u s e of this physico-chemical characteristics, application of c o n v e n t i o n a l p e r s o n a l d i f f u s i v e s a m p l e r s such as those e q u i p p e d w i t h c a r b o n c l o t h ( H i r a y a m a and Ikeda, 1979) or w a t e r (Uchida et al., 1990) as an a b s o r b e n t is associated w i t h d i f f i c u l t i e s due to rapid s p o n t a n e o u s desorption. A n e w d i f f u s i v e s a m p l e r is d e v e l o p e d in the p r e s e n t s t u d y in w h i c h s i l i c a gel is e m p l o y e d as an a b s o r b i n g material. The details are described in this communication. MATERIALS AND METHODS S~lica gel (A gel w i t h a r e l a t i v e s u r f a c e area of 790 m /g, 20-30 mesh; Kida C h e m i c a l s , Tokyo, Japan) was a Request off-print
to:
M.
Ikeda 325
at the a b o v e address.
NONIpERMEABLE SEPTUM
CAP
I
E E
lijsi !i i ~.Z.I..t.l i-~-
I
CD
SEMI-PERMEABLE MEMBRANE
F i g g u r e I. Structure of the s a m p l e r with silica gel as an absorbent
I-
CAP
Silica gel, 1.2 g, in a cylindrical container is e x p o s e d to the ambient air across a semipermeable membrane (Cellpore~ NW-II; S e k i s u i C h e m i c a l Co., Osaka, Japan) to a b s o r b solvent vapor, e.g., m e t h y l acetate. The lower part of an o u t e r c y l i n d e r serves also a w i n d - k i l l e r .
CD C~
]Jill 5.2 mm ! 11 mm kind gift from Komyo-Rikagaku Other reagents were purchased Inc., Kyoto, Japan.
& Co., Tokyo, from Nacalai
Japan. Tesque,
The structure of the newly designed sampler is d e p i c t e d in Fig. i. The m a i n part of the s a m p l e r is a poly-propylene cylinder (25 m m in l e n g t h and 9 mm in inner d i a m e t e r ) c o n t a i n i n g ca. 1.2 g of s i l i c a gel. One end of the c y l i n d e r is a i r - t i g h t l y sealed. The o t h e r end is s e a l e d w ~ t h a s e m i p e r m e a b l e p o l y p r o p y l e n e membrane (Cellpore ~NW-II; Sekisui Chemical Co., Osaka, Japan); the m e m b r a n e allows free p a s s a g e of methyl acetate vapor. The entire cylinder is p r o t e c t e d by a n o t h e r l a r g e r p o l y p r o p y l e n e c y l i n d e r (60 mm in l e n g t h and 13 m m in inner d i a m e t e r ) that serves also as a w i n d - k i l l e r . The s a m p l e r can be used as a personal sampler ( a t t a c h e d to the chest of an e x p o s e d worker) as w e l l as a stationary sampler, keeping s e a l e d end up and w i n d - k i l l e r part d o w n so that the 326
silica gel is in a direct contact with the semipermeable membrane so that m e t h y l acetate vapor a f t e r p a s s i n g t h r o u g h the m e m b r a n e w i l l be a b s o r b e d by the s i l i c a gel. Samplers were tested in a s e r v o - m e c h a n i z e d solvent vapor exposure chamber s y s t e m (Koizumi and Ikeda, 1981; Kumai et al., 1984). The v a p o r c o n c e n t r a t i o n in the c h a m b e r was m e a s u r e d automatically every 13 min, and performance was s u c h that the m e a n of the m e a s u r e d c o n c e n t r a t i o n s was a l m o s t 100% of the n o m i n a l concentration w i t h a c o e f f i c i e n t of v a r i a t i o n of less than 4%. Under standard conditions, i.e., unless otherwise specified, the e x p o s e d s i l i c a gel was q u a n t i t a t i v e l y transferred to a glass container, and shaken vigorously for 10 m i n in the p r e s e n c e of 3 ml of ethanol (spiked w i t h m e t h a n o l b y 0.1%, v/v, as an internal standard). The e x t r a c t was s u b j e c t e d to GC analysis on 30-m D B - W A X c a p i l l a r y c o l u m n at 40~ with flame-ionization detectors as previously described (Kawai et al., 1991a and b). Under the conditions employed, it was p o s s i b l e to c o m p l e t e one a n a l y s i s in 7 min. For c o m p a r i s o n , two o t h e r types of samplers, i.e., the one equipped w i t h c a r b o n c l o t h ( H i r a y a m a and Ikeda, 1979) and the o t h e r w i t h w a t e r (Uchida et al., 1990), w e r e a l s o e x p o s e d to m e t h y l acetate. The procedures of the GC analysis were as previously described (Hirayama and Ikeda, 1979; U c h i d a et al., 1990). Regression analysis and t-test were employed when necessary. RESULTS
AND DISCUSSION
To e x a m i n e the recovery, 1.2 g of s i l i c a gel spiked with 300 p g of m e t h y l a c e t a t e was e x t r a c t e d w i t h 3 ml of e t h a n o l c o n t a i n i n g 0.01% m e t h a n o l for a p e r i o d of 10 min. R e c o v e r y of m e t h y l a c e t a t e was 100.6% (with a coefficient of variation of 0.95% after 5 measurements) b a s e d on GC a n a l y s i s of m e t h y l a c e t a t e in 10 ~i ethanol. Under the conditions studied, m e t h a n o l r e m a i n e d in e t h a n o l and was not lost in air or absorbed by silica gel. Similar recovery experiments w i t h water, carbon disulfide and ethyl acetate in the p l a c e of e t h a n o l disclosed that the recovery was about 38.2• (average• of 5 determinations) with water, and none with carbon disulfide. In the case of e t h y l acetate, a large peak for e t h y l a c e t a t e o v e r - l a p p e d w i t h a small p e a k for methanol in the chromatogram under the GC c o n d i t i o n s employed, w h i c h m a d e it d i f f i c u l t to study 327
b~ O@
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EXPOSURE
DURATION
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F i g u r e 2. Absorption of methyl acetate by silica gel as a function of exposure duration
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F i g u r e 3. Absorption of methyl acetate by silica gel as a function of exposure concentration
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Figure 4. A b s o r p t i o n of m e t h y l a c e t a t e by water as a f u n c t i o n of e x p o s u r e duration
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Figure 5. A b s o r p t i o n of m e t h y l a c e t a t e by carbon cloth as a function of e x p o s u r e duration
~
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recovery.
Silica gel-equipped samplers were exposed to m e t h y l acetate at i00, 200, 400, 800 a n d 1600 p p m f o r i, 2, 4, 6 and 8 h. At e a c h c o n c e n t r a t i o n and exposure duration, 2 to 3 samplers were taken out of the e x p o s u r e c h a m b e r and a n a l y z e d for the a m o u n t of m e t h y l acetate absorbed. The r e s u l t s are d e p i c t e d in Figs. 2 and 3 taking exposure duration and exposure concentration on the h o r i z o n t a l axis, respectively. It is evident f r o m the f i g u r e s that the amount of methyl acetate absorbed is l i n e a r l y r e l a t e d to b o t h the exposure duration up to 8 h and to exposure intensity up to 1600 ppm. It was possible to calculate from the d a t a that the a v e r a g e amount of m e t h y l a c e t a t e a b s o r b e d s h o u l d be 1.354 ~ g / p p m / h . Similar experiments with water-equipped samplers showed that the a m o u n t m e t h y l a c e t a t e absorbed was l i n e a r l y r e l a t e d to the e x p o s u r e d u r a t i o n (the m a x i m a l duration tested; 8 h) and the e x p o s u r e c o n c e n t r a t i o n (the maximal concentration tested; 800 ppm) as s h o w n in Fig. 4. T h e r a t e of m e t h y l a c e t a t e a b s o r p t i o n was 124,7 n g / p p m / h . When carbon-cloth equipped samplers w e r e e x p o s e d to m e t h y l a c e t a t e at up to 800 p p m for up to 8 h, however, a leveling-off in the a m o u n t of methyl acetate was observed after long time exposure at high concentrations; the a m o u n t was no longer proportional to e x p o s u r e t i m e at 8 h at 400 and 800 ppm, w h e r e a s it w a s p r o p o r t i o n a l up to 4 h at 400 and 800 ppm, or up to 8 h at 200 ppm (Fig. 5). The absorption r a t e was 5 . 5 8 1 ~ g / p p m / h w h e n the d a t a w e r e s e l e c t e d w h e r e the l i n e a r i t y w a s held. S e v e r a l s a m p l e r s e q u i p p e d w i t h s i l i c a gel (i.e., the present device), carbon cloth or water were impregnated w i t h m e t h y l a c e t a t e at 1000 p p m for 1 h. They were then kept in f r e s h a i r for 48 h or m o r e a f t e r the t e r m i n a t i o n of the e x p o s u r e ; 3 s a m p l e r s w e r e a n a l y z e d at e a c h t i m e p e r i o d . When l o g a r i t h m of the a m o u n t of m e t h y l a c e t a t e d e t e c t e d in the a b s o r b e n t was graphed a g a i n s t the time in f r e s h air, it w a s f o u n d that m e t h y l a c e t a t e d i s a p p e a r e d s p o n t a n e o u s l y f r o m the absorbent w i t h a h a l f - t i m e of a b o u t ii.0 h a n d 9.6 h for carbon clothand water-equipped samplers, respectively. In c o n t r a s t , e s s e n t i a l l y no d e c a y in the methyl acetate amount was observed during the period of the study (for 84 h) with silica gelequipped samplers; the c a l c u l a t e d h a l f - t i m e w a s 335 h ( T a b l e i). In o r d e r to e x a m i n e if the s i l i c a g e l - e q u i p p e d s a m p l e r has a c a p a c i t y to r e s p o n d q u a n t i t a t i v e l y to a short term peak exposure, 7 samplers were simultaneously 330
Table
i.
S~,pler 1 2 3
D e c a y h a l f - t i m e for m e t h y l types of s a m p l e r s Absorbent Silica gel Carbon cloth Water
acetate
Desorbent
Study duration (h)
Ethanol CS 2
84 48 48
in the 3
Half-time (h) 334.8 11.0 9.6
e x p o s e d to 1600 p p m m e t h y l a c e t a t e for 15 m i n and the amount of m e t h y l a c e t a t e was d e t e r m i n e d . In practice, 590.5• pg (mean• of 10 d e t e r m i n a t i o n s ) methyl acetate was detected. Because the m e a s u r e d m e t h y l a c e t a t e v a p o r c o n c e n t r a t i o n was 1600 ppm, the 15 m i n exposure should result in the a b s o r p t i o n of 544 ug methyl acetate. Thus the r e s p o n s e rate was 108.5• 15.6%; m e a n • S i m i l a r e x p e r i m e n t s w i t h s a m p l e r s of other two types s h o w e d that the r e s p o n s e rate was 116.4% and 130.7% with c a r b o n clothand watere q u i p p e d samplers, r e s p e c t i v e l y . The present study has clearly demonstrated that p e r s o n a l d i f f u s i v e s a m p l i n g can be a p p l i e d to m o n i t o r m e t h y l a c e t a t e exposure, w h e n silica gel w i t h a large relative surface is e m p l o y e d as an absorbent; the amount of m e t h y l a c e t a t e a b s o r b e d is p r o p o r t i o n a l to the e x p o s u r e d u r a t i o n up to 8 h and to the e x p o s u r e concentration up to 1600 p p m (or 8 times the current occupational e x p o s u r e limit of 200 ppm; American C o n f e r e n c e of G o v e r n m e n t a l I n d u s t r i a l H y g i e n i s t s 1991; Deutsche Forschungsgemeinschaft, 1991; Japan A s s o c i a t i o n of I n d u s t r i a l H e a l t h 1991). The r e s p o n s e of the s a m p l e r to a short term p e a k e x p o s u r e is also s a t i s f a c t o r y (i.e., 108.5%). In practice, one of the q u e s t i o n to be s e t t l e d is the choice of the s o l v e n t for e x t r a c t i o n . The solvents present in the working environment or those i n t e r f e r i n g w i t h GC a n a l y s i s m u s t be e x c l u d e d . Carbon disulfide is s e l d o m used in u s u a l s o l v e n t w o r k s h o p s other than rayon industries, but f a i l e d to e x t r a c t m e t h y l a c e t a t e from s i l i c a gel. Extraction with water also gave p o o r r e s u l t s (i.e., ca. 40%) a l t h o u g h the rate was reproducible. Ethanol w i t h an e x t r a c t i o n rate of 100% a p p e a r s to be the solvent of choice because it is present in industrial solvent preparations o n l y on v e r y l i m i t e d o c c a s i o n s (Kumai et al., 1983; Inoue et al., 1983), even though the prevalence might be h i g h e r among home-use products (Saito and Ikeda, 1988).
331
It was also found that s a m p l e r s of b o t h c a r b o n c l o t h (Hirayama and Ikeda, 1979) and w a t e r types (Uchida et al., 1990) can q u a n t i t a t i v e l y a b s o r b m e t h y l a c e t a t e at low concentrations such as 200 p p m (Fig. 4 and 5). The difficulty is associated with rather rapid spontaneous desorption of m e t h y l acetate from the a b s o r b e n t s ; the d e s o r p t i o n h a l f - t i m e was c a l c u l a t e d to be 9.6 h for w a t e r - e q u i p p e d s a m p l e r s and ii.0 h for carbon c l o t h - e q u i p p e d s a m p l e r s (Table i). When an extreme case is assumed such that an extensive e x p o s u r e takes place o n l y at the b e g i n n i n g of an 8-h workshift f o l l o w e d by e s s e n t i a l l y no e x p o s u r e during the rest of the shift, the h a l f - t i m e v a l u e s suggest that about 34% and 40% loss in m e t h y l a c e t a t e in the absorbent w i l l be e x p e c t e d for the f o r m e r and the latter samplers, r e s p e c t i v e l y , b e f o r e the t e r m i n a t i o n of the shift. Acknowledgments. The a u t h o r s are g r a t e f u l to Prof. S. Horiguchi, Osaka Occupational Health Service Center, Osaka 550, Japan, for his i n t e r e s t in this work. This work was supported in part by Grant in Aid for Developmental R e s e a r c h (No. 02557030) given to M.I. from the M i n i s t r y of Education, S c i e n c e and C u l t u r e of the G o v e r n m e n t of Japan. REFERENCES American Conference of Governmental Industrial Hygienists (1991) 1 9 9 0 - 1 9 9 1 T h r e s h o l d Limit V a l u e s for Chemical S u b s t a n c e s and Physical Agents and B i o l o g i c a l E x p o s u r e Indices. ACGIH, C i n c i n n a t i OH, U.S.A. Deutsche Forschungsgemeinschaft (1991) Maximum Concentrations at the Workplace and Biological T o l e r a n c e V a l u e s for W o r k i n g M a t e r i a l s , 1991. VCM, Weinheim, Germany Hirayama T, Ikeda M (1979) A p p l i c a b i l i t y of carbon felt to the d o s i m e t r y of s o l v e n t v a p o r mixture. Am Ind Hyg A s s o c J 4 0 : 1 0 9 1 - 1 0 9 6 Inoue T, T a k e u c h i Y, H i s a n a g a N, Ono Y, Iwata M, Ogata M, Saito K, S a k u r a i H, H a r a I, M a t s u s h i t a T, Ikeda M (1983) A nationwide survey on organic solvent components in various solvent products: Part I. Homogeneous p r o d u c t s such as thinners, degreasers and reagents. Ind H l t h 2 1 : 1 7 5 - 1 8 3 Japan Association of Industrial Health (1991) R e c o m m e n d e d o c c u p a t i o n a l e x p o s u r e limits. Jpn J Ind Hlth 32:381-401 (in Japanese with English translation) K a w a i T, Y a m a o k a K, U c h i d a Y, Ikeda M (1991) Exposure to v a p o r s of b e n z e n e and o t h e r a r o m a t i c s o l v e n t s in tank truck loading and delivery. Bull Environ C o n t a m T o x i c o l 46:1-8 332
Kawai T, M i z u n u m a K, Y a s u g i T, H o r i g u c h i S, Uchida Y, Iwami O, Iguchi H, Ikeda M (1991) U r i n a r y methylhippuric acid isomer levels after occupational exposure to a xylene mixture. Int Arch Occup Environ Hlth 63:69-75 K o i z u m i A, Ikeda M (1981) A s e r v o m e c h a n i s m for v a p o r concentration control in e x p e r i m e n t a l exposure chambers. Am Ind Hyg Assoc J 42:417-425 Kumai M, K o i z u m i A, Saito K, Sakurai H, Inoue T, T a k e u c h i Y, Hara I, Ogata M, M a t s u s h i t a T, Ikeda M (1983) A nationwide survey on organic solvent components in various solvent products: Part II. Heterogeneous products such as paints, inks and adhesives. Ind Hlth 21:185-197 Kumai M, K o i z u m i A, M o r i t a K, Ikeda M (1984) An exposure system for organic solvent vapor. Bull Environ C o n t a m T o x i c o l 32:200-204 Ogawa Y, T a k a t s u k i R, Uema T, Seki Y, H i r a m a t s u K, O k a y a m a A, M o r i m o t o K, Kaneko Z (1988) Acute optic n e u r o p a t h y induced by thinner sniffing: Inhalation of m i x e d organic solvent c o n t a i n i n g m e t h y l alcohol and m e t h y l acetate. Ind Hlth 26:239-244 Saito J, Ikeda M (1988) Solvent constituents in paint, glue and thinner for plastic m i n i a t u r e hobby. Tohoku J Exp Med 155:275-283 Uchida Y, Kawai T, Y a s u g i T, Ikeda M (1990) Personal m o n i t o r i n g s a m p l e r for acetone v a p o r exposure. Bull E n v i r o n C o n t a m T o x i c o l 44:900-904 Received November 5, 1991; accepted March 4, 1992.
333
i
9 1992 Spfinger-Verlag New York Inc.
~nvir .or~..
al
Diffusive Personal Sampler for Methyl Acetate Monitoring Tomojiro Yasug~ ~'2 Toshio Kawai, ~ Kazunori Mizunuma, ~'2 and Masayukilkeda ~
1Osaka Occupational Health Service Center, Osaka 550, Japan and 2Department of Public Health, Kyoto University Faculty of Medicine, Kyoto 606-01, Kyoto, Japan
M e t h y l a c e t a t e is an o r g a n i c s o l v e n t present in some industrial materials such as paints and adhessives (Kumai et al., 1983), and to a l e s s e r extent in degreasers (Inoue et al., 1983); e x p e r i e n c e shows a mixture of m e t h a n o l and m e t h y l a c e t a t e is used for removal of s t y r e n e m o n o m e r - c o n t a i n i n g uncured resin from b r u s h e s in f i b e r - r e i n f o r c e d p l a s t i c s p r o d u c t i o n . Furthermore, additional attention has b e e n recently p a i d to this e s t e r as a p o s s i b l e s o u r c e of m e t h a n o l in s n i f f i n g thinner. O g a w a et al. (1988) s t u d i e d a case of acute optic n e u r o p a t h y a f t e r t h i n n e r sniffing, and suspected methyl acetate as a c a u s a t i v e agent in the thinner; one paint t h i n n e r w h i c h the p a t i e n t used to sniff contained this e s t e r by 20% (in addition to methanol by 20%), this e s t e r is m o r e v o l a t i l e with higher vapor pressure at s a t u r a t i o n than methanol, r e a d i l y absorbed, and q u i c k l y h y d r o l y z e d to m e t h a n o l and a c e t a t e w h e n taken into body. I n t e r e s t i n g l y , this ester is not only l i p o p h i l i c as an o r g a n i c solvent, but partly soluble a l s o in water. B e c a u s e of this physico-chemical characteristics, application of c o n v e n t i o n a l p e r s o n a l d i f f u s i v e s a m p l e r s such as those e q u i p p e d w i t h c a r b o n c l o t h ( H i r a y a m a and Ikeda, 1979) or w a t e r (Uchida et al., 1990) as an a b s o r b e n t is associated w i t h d i f f i c u l t i e s due to rapid s p o n t a n e o u s desorption. A n e w d i f f u s i v e s a m p l e r is d e v e l o p e d in the p r e s e n t s t u d y in w h i c h s i l i c a gel is e m p l o y e d as an a b s o r b i n g material. The details are described in this communication. MATERIALS AND METHODS S~lica gel (A gel w i t h a r e l a t i v e s u r f a c e area of 790 m /g, 20-30 mesh; Kida C h e m i c a l s , Tokyo, Japan) was a Request off-print
to:
M.
Ikeda 325
at the a b o v e address.
NONIpERMEABLE SEPTUM
CAP
I
E E
lijsi !i i ~.Z.I..t.l i-~-
I
CD
SEMI-PERMEABLE MEMBRANE
F i g g u r e I. Structure of the s a m p l e r with silica gel as an absorbent
I-
CAP
Silica gel, 1.2 g, in a cylindrical container is e x p o s e d to the ambient air across a semipermeable membrane (Cellpore~ NW-II; S e k i s u i C h e m i c a l Co., Osaka, Japan) to a b s o r b solvent vapor, e.g., m e t h y l acetate. The lower part of an o u t e r c y l i n d e r serves also a w i n d - k i l l e r .
CD C~
]Jill 5.2 mm ! 11 mm kind gift from Komyo-Rikagaku Other reagents were purchased Inc., Kyoto, Japan.
& Co., Tokyo, from Nacalai
Japan. Tesque,
The structure of the newly designed sampler is d e p i c t e d in Fig. i. The m a i n part of the s a m p l e r is a poly-propylene cylinder (25 m m in l e n g t h and 9 mm in inner d i a m e t e r ) c o n t a i n i n g ca. 1.2 g of s i l i c a gel. One end of the c y l i n d e r is a i r - t i g h t l y sealed. The o t h e r end is s e a l e d w ~ t h a s e m i p e r m e a b l e p o l y p r o p y l e n e membrane (Cellpore ~NW-II; Sekisui Chemical Co., Osaka, Japan); the m e m b r a n e allows free p a s s a g e of methyl acetate vapor. The entire cylinder is p r o t e c t e d by a n o t h e r l a r g e r p o l y p r o p y l e n e c y l i n d e r (60 mm in l e n g t h and 13 m m in inner d i a m e t e r ) that serves also as a w i n d - k i l l e r . The s a m p l e r can be used as a personal sampler ( a t t a c h e d to the chest of an e x p o s e d worker) as w e l l as a stationary sampler, keeping s e a l e d end up and w i n d - k i l l e r part d o w n so that the 326
silica gel is in a direct contact with the semipermeable membrane so that m e t h y l acetate vapor a f t e r p a s s i n g t h r o u g h the m e m b r a n e w i l l be a b s o r b e d by the s i l i c a gel. Samplers were tested in a s e r v o - m e c h a n i z e d solvent vapor exposure chamber s y s t e m (Koizumi and Ikeda, 1981; Kumai et al., 1984). The v a p o r c o n c e n t r a t i o n in the c h a m b e r was m e a s u r e d automatically every 13 min, and performance was s u c h that the m e a n of the m e a s u r e d c o n c e n t r a t i o n s was a l m o s t 100% of the n o m i n a l concentration w i t h a c o e f f i c i e n t of v a r i a t i o n of less than 4%. Under standard conditions, i.e., unless otherwise specified, the e x p o s e d s i l i c a gel was q u a n t i t a t i v e l y transferred to a glass container, and shaken vigorously for 10 m i n in the p r e s e n c e of 3 ml of ethanol (spiked w i t h m e t h a n o l b y 0.1%, v/v, as an internal standard). The e x t r a c t was s u b j e c t e d to GC analysis on 30-m D B - W A X c a p i l l a r y c o l u m n at 40~ with flame-ionization detectors as previously described (Kawai et al., 1991a and b). Under the conditions employed, it was p o s s i b l e to c o m p l e t e one a n a l y s i s in 7 min. For c o m p a r i s o n , two o t h e r types of samplers, i.e., the one equipped w i t h c a r b o n c l o t h ( H i r a y a m a and Ikeda, 1979) and the o t h e r w i t h w a t e r (Uchida et al., 1990), w e r e a l s o e x p o s e d to m e t h y l acetate. The procedures of the GC analysis were as previously described (Hirayama and Ikeda, 1979; U c h i d a et al., 1990). Regression analysis and t-test were employed when necessary. RESULTS
AND DISCUSSION
To e x a m i n e the recovery, 1.2 g of s i l i c a gel spiked with 300 p g of m e t h y l a c e t a t e was e x t r a c t e d w i t h 3 ml of e t h a n o l c o n t a i n i n g 0.01% m e t h a n o l for a p e r i o d of 10 min. R e c o v e r y of m e t h y l a c e t a t e was 100.6% (with a coefficient of variation of 0.95% after 5 measurements) b a s e d on GC a n a l y s i s of m e t h y l a c e t a t e in 10 ~i ethanol. Under the conditions studied, m e t h a n o l r e m a i n e d in e t h a n o l and was not lost in air or absorbed by silica gel. Similar recovery experiments w i t h water, carbon disulfide and ethyl acetate in the p l a c e of e t h a n o l disclosed that the recovery was about 38.2• (average• of 5 determinations) with water, and none with carbon disulfide. In the case of e t h y l acetate, a large peak for e t h y l a c e t a t e o v e r - l a p p e d w i t h a small p e a k for methanol in the chromatogram under the GC c o n d i t i o n s employed, w h i c h m a d e it d i f f i c u l t to study 327
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Figure 4. A b s o r p t i o n of m e t h y l a c e t a t e by water as a f u n c t i o n of e x p o s u r e duration
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Figure 5. A b s o r p t i o n of m e t h y l a c e t a t e by carbon cloth as a function of e x p o s u r e duration
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Silica gel-equipped samplers were exposed to m e t h y l acetate at i00, 200, 400, 800 a n d 1600 p p m f o r i, 2, 4, 6 and 8 h. At e a c h c o n c e n t r a t i o n and exposure duration, 2 to 3 samplers were taken out of the e x p o s u r e c h a m b e r and a n a l y z e d for the a m o u n t of m e t h y l acetate absorbed. The r e s u l t s are d e p i c t e d in Figs. 2 and 3 taking exposure duration and exposure concentration on the h o r i z o n t a l axis, respectively. It is evident f r o m the f i g u r e s that the amount of methyl acetate absorbed is l i n e a r l y r e l a t e d to b o t h the exposure duration up to 8 h and to exposure intensity up to 1600 ppm. It was possible to calculate from the d a t a that the a v e r a g e amount of m e t h y l a c e t a t e a b s o r b e d s h o u l d be 1.354 ~ g / p p m / h . Similar experiments with water-equipped samplers showed that the a m o u n t m e t h y l a c e t a t e absorbed was l i n e a r l y r e l a t e d to the e x p o s u r e d u r a t i o n (the m a x i m a l duration tested; 8 h) and the e x p o s u r e c o n c e n t r a t i o n (the maximal concentration tested; 800 ppm) as s h o w n in Fig. 4. T h e r a t e of m e t h y l a c e t a t e a b s o r p t i o n was 124,7 n g / p p m / h . When carbon-cloth equipped samplers w e r e e x p o s e d to m e t h y l a c e t a t e at up to 800 p p m for up to 8 h, however, a leveling-off in the a m o u n t of methyl acetate was observed after long time exposure at high concentrations; the a m o u n t was no longer proportional to e x p o s u r e t i m e at 8 h at 400 and 800 ppm, w h e r e a s it w a s p r o p o r t i o n a l up to 4 h at 400 and 800 ppm, or up to 8 h at 200 ppm (Fig. 5). The absorption r a t e was 5 . 5 8 1 ~ g / p p m / h w h e n the d a t a w e r e s e l e c t e d w h e r e the l i n e a r i t y w a s held. S e v e r a l s a m p l e r s e q u i p p e d w i t h s i l i c a gel (i.e., the present device), carbon cloth or water were impregnated w i t h m e t h y l a c e t a t e at 1000 p p m for 1 h. They were then kept in f r e s h a i r for 48 h or m o r e a f t e r the t e r m i n a t i o n of the e x p o s u r e ; 3 s a m p l e r s w e r e a n a l y z e d at e a c h t i m e p e r i o d . When l o g a r i t h m of the a m o u n t of m e t h y l a c e t a t e d e t e c t e d in the a b s o r b e n t was graphed a g a i n s t the time in f r e s h air, it w a s f o u n d that m e t h y l a c e t a t e d i s a p p e a r e d s p o n t a n e o u s l y f r o m the absorbent w i t h a h a l f - t i m e of a b o u t ii.0 h a n d 9.6 h for carbon clothand water-equipped samplers, respectively. In c o n t r a s t , e s s e n t i a l l y no d e c a y in the methyl acetate amount was observed during the period of the study (for 84 h) with silica gelequipped samplers; the c a l c u l a t e d h a l f - t i m e w a s 335 h ( T a b l e i). In o r d e r to e x a m i n e if the s i l i c a g e l - e q u i p p e d s a m p l e r has a c a p a c i t y to r e s p o n d q u a n t i t a t i v e l y to a short term peak exposure, 7 samplers were simultaneously 330
Table
i.
S~,pler 1 2 3
D e c a y h a l f - t i m e for m e t h y l types of s a m p l e r s Absorbent Silica gel Carbon cloth Water
acetate
Desorbent
Study duration (h)
Ethanol CS 2
84 48 48
in the 3
Half-time (h) 334.8 11.0 9.6
e x p o s e d to 1600 p p m m e t h y l a c e t a t e for 15 m i n and the amount of m e t h y l a c e t a t e was d e t e r m i n e d . In practice, 590.5• pg (mean• of 10 d e t e r m i n a t i o n s ) methyl acetate was detected. Because the m e a s u r e d m e t h y l a c e t a t e v a p o r c o n c e n t r a t i o n was 1600 ppm, the 15 m i n exposure should result in the a b s o r p t i o n of 544 ug methyl acetate. Thus the r e s p o n s e rate was 108.5• 15.6%; m e a n • S i m i l a r e x p e r i m e n t s w i t h s a m p l e r s of other two types s h o w e d that the r e s p o n s e rate was 116.4% and 130.7% with c a r b o n clothand watere q u i p p e d samplers, r e s p e c t i v e l y . The present study has clearly demonstrated that p e r s o n a l d i f f u s i v e s a m p l i n g can be a p p l i e d to m o n i t o r m e t h y l a c e t a t e exposure, w h e n silica gel w i t h a large relative surface is e m p l o y e d as an absorbent; the amount of m e t h y l a c e t a t e a b s o r b e d is p r o p o r t i o n a l to the e x p o s u r e d u r a t i o n up to 8 h and to the e x p o s u r e concentration up to 1600 p p m (or 8 times the current occupational e x p o s u r e limit of 200 ppm; American C o n f e r e n c e of G o v e r n m e n t a l I n d u s t r i a l H y g i e n i s t s 1991; Deutsche Forschungsgemeinschaft, 1991; Japan A s s o c i a t i o n of I n d u s t r i a l H e a l t h 1991). The r e s p o n s e of the s a m p l e r to a short term p e a k e x p o s u r e is also s a t i s f a c t o r y (i.e., 108.5%). In practice, one of the q u e s t i o n to be s e t t l e d is the choice of the s o l v e n t for e x t r a c t i o n . The solvents present in the working environment or those i n t e r f e r i n g w i t h GC a n a l y s i s m u s t be e x c l u d e d . Carbon disulfide is s e l d o m used in u s u a l s o l v e n t w o r k s h o p s other than rayon industries, but f a i l e d to e x t r a c t m e t h y l a c e t a t e from s i l i c a gel. Extraction with water also gave p o o r r e s u l t s (i.e., ca. 40%) a l t h o u g h the rate was reproducible. Ethanol w i t h an e x t r a c t i o n rate of 100% a p p e a r s to be the solvent of choice because it is present in industrial solvent preparations o n l y on v e r y l i m i t e d o c c a s i o n s (Kumai et al., 1983; Inoue et al., 1983), even though the prevalence might be h i g h e r among home-use products (Saito and Ikeda, 1988).
331
It was also found that s a m p l e r s of b o t h c a r b o n c l o t h (Hirayama and Ikeda, 1979) and w a t e r types (Uchida et al., 1990) can q u a n t i t a t i v e l y a b s o r b m e t h y l a c e t a t e at low concentrations such as 200 p p m (Fig. 4 and 5). The difficulty is associated with rather rapid spontaneous desorption of m e t h y l acetate from the a b s o r b e n t s ; the d e s o r p t i o n h a l f - t i m e was c a l c u l a t e d to be 9.6 h for w a t e r - e q u i p p e d s a m p l e r s and ii.0 h for carbon c l o t h - e q u i p p e d s a m p l e r s (Table i). When an extreme case is assumed such that an extensive e x p o s u r e takes place o n l y at the b e g i n n i n g of an 8-h workshift f o l l o w e d by e s s e n t i a l l y no e x p o s u r e during the rest of the shift, the h a l f - t i m e v a l u e s suggest that about 34% and 40% loss in m e t h y l a c e t a t e in the absorbent w i l l be e x p e c t e d for the f o r m e r and the latter samplers, r e s p e c t i v e l y , b e f o r e the t e r m i n a t i o n of the shift. Acknowledgments. The a u t h o r s are g r a t e f u l to Prof. S. Horiguchi, Osaka Occupational Health Service Center, Osaka 550, Japan, for his i n t e r e s t in this work. This work was supported in part by Grant in Aid for Developmental R e s e a r c h (No. 02557030) given to M.I. from the M i n i s t r y of Education, S c i e n c e and C u l t u r e of the G o v e r n m e n t of Japan. REFERENCES American Conference of Governmental Industrial Hygienists (1991) 1 9 9 0 - 1 9 9 1 T h r e s h o l d Limit V a l u e s for Chemical S u b s t a n c e s and Physical Agents and B i o l o g i c a l E x p o s u r e Indices. ACGIH, C i n c i n n a t i OH, U.S.A. Deutsche Forschungsgemeinschaft (1991) Maximum Concentrations at the Workplace and Biological T o l e r a n c e V a l u e s for W o r k i n g M a t e r i a l s , 1991. VCM, Weinheim, Germany Hirayama T, Ikeda M (1979) A p p l i c a b i l i t y of carbon felt to the d o s i m e t r y of s o l v e n t v a p o r mixture. Am Ind Hyg A s s o c J 4 0 : 1 0 9 1 - 1 0 9 6 Inoue T, T a k e u c h i Y, H i s a n a g a N, Ono Y, Iwata M, Ogata M, Saito K, S a k u r a i H, H a r a I, M a t s u s h i t a T, Ikeda M (1983) A nationwide survey on organic solvent components in various solvent products: Part I. Homogeneous p r o d u c t s such as thinners, degreasers and reagents. Ind H l t h 2 1 : 1 7 5 - 1 8 3 Japan Association of Industrial Health (1991) R e c o m m e n d e d o c c u p a t i o n a l e x p o s u r e limits. Jpn J Ind Hlth 32:381-401 (in Japanese with English translation) K a w a i T, Y a m a o k a K, U c h i d a Y, Ikeda M (1991) Exposure to v a p o r s of b e n z e n e and o t h e r a r o m a t i c s o l v e n t s in tank truck loading and delivery. Bull Environ C o n t a m T o x i c o l 46:1-8 332
Kawai T, M i z u n u m a K, Y a s u g i T, H o r i g u c h i S, Uchida Y, Iwami O, Iguchi H, Ikeda M (1991) U r i n a r y methylhippuric acid isomer levels after occupational exposure to a xylene mixture. Int Arch Occup Environ Hlth 63:69-75 K o i z u m i A, Ikeda M (1981) A s e r v o m e c h a n i s m for v a p o r concentration control in e x p e r i m e n t a l exposure chambers. Am Ind Hyg Assoc J 42:417-425 Kumai M, K o i z u m i A, Saito K, Sakurai H, Inoue T, T a k e u c h i Y, Hara I, Ogata M, M a t s u s h i t a T, Ikeda M (1983) A nationwide survey on organic solvent components in various solvent products: Part II. Heterogeneous products such as paints, inks and adhesives. Ind Hlth 21:185-197 Kumai M, K o i z u m i A, M o r i t a K, Ikeda M (1984) An exposure system for organic solvent vapor. Bull Environ C o n t a m T o x i c o l 32:200-204 Ogawa Y, T a k a t s u k i R, Uema T, Seki Y, H i r a m a t s u K, O k a y a m a A, M o r i m o t o K, Kaneko Z (1988) Acute optic n e u r o p a t h y induced by thinner sniffing: Inhalation of m i x e d organic solvent c o n t a i n i n g m e t h y l alcohol and m e t h y l acetate. Ind Hlth 26:239-244 Saito J, Ikeda M (1988) Solvent constituents in paint, glue and thinner for plastic m i n i a t u r e hobby. Tohoku J Exp Med 155:275-283 Uchida Y, Kawai T, Y a s u g i T, Ikeda M (1990) Personal m o n i t o r i n g s a m p l e r for acetone v a p o r exposure. Bull E n v i r o n C o n t a m T o x i c o l 44:900-904 Received November 5, 1991; accepted March 4, 1992.
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