Convenient Field Sampling Method for Monitoring Volatile

Chapter 5

Convenient Field Sampling Method for Monitoring Volatile Compounds in Exhaled Breath Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on July 12, 2018 at 11:47:55 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Michael S. Morgan, Gary S. Phillips, and Eileen M . Kirkpatrick Department of Environmental Health, University of Washington, Seattle, WA 98195 A modified half-face air purifying respirator was developed as a technique for large-scale monitoring that will be acceptable to workers, simple to apply, and relatively sensitive. Exhaled air was directed through the respirator exhaust port and then through a two-part cartridge. The f i r s t part contained four layers of activated charcoal cloth which adsorbed organic solvent vapors; the cloth was subsequently desorbed for gas chromatographic analysis. The second part contained 70 g of 8-12 mesh molecular sieve whose weight gain (water) was proportional to the volume of air exhaled. The proportionality was determined by independent measurement of volume in subjects while at rest and while exercising. Controlled atmospheres containing toluene at relative humidities near saturation were passed through the cartridge at steady flows equal to resting human ventilatory rates. Toluene recovery was 70% for simulated breath concentrations of 0.75 mg/m to 60 mg/m (0.20 ppm to 16 ppm). Normal adults volunteered to breathe toluene in air at 150 mg/m (40 ppm) or 340 mg/m (90 ppm) for four hours (TLV = 375 mg/m or 100 ppm, 8 hr TWA). About eighteen hours later their breath was sampled, to simulate a worksite measurement at the start of the next shift. Samples of at least 140 liters were taken from each subject, and the mean exhaled concentrations were 344 μg/m and 600 μg/m (0.23% and 0.18% of exposure TWA), respectively, in good agreement with literature reports using more complicated methods not appropriate for field application. The device can be used to collect samples of up to 300 liters in 30 minutes, and i t s sensitivity and selectivity are then limited only by the desorption and analysis of the charcoal adsorbent. The lower limit of quantitation for toluene, with conventional GC analysis, was about 65 μg/m (18 ppb). The technique can be applied to most solvents capable of adsorption on charcoal, and w i l l permit sampling large numbers of workers with minimal job disruption. In a limited f i e l d application, automobile body painters showed levels of toluene in their exhaled breath that could not be 3

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0097-6156/89/0382-0056$06.00/0 ° 1989 American Chemical Society

Wang et al.; Biological Monitoring for Pesticide Exposure ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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MORGAN E T A L .

Volatile Compounds in Exhaled Breath

57

explained by inhalation exposure alone; observations of frequent skin contact with the solvent suggested that important skin absorption also occurred, and the breath levels reflected the workers' total solvent exposure. Among methods available for biological monitoring, exhaled breath analysis offers potential advantages as i t i s less intrusive than drawing blood and often gives a better reflection of blood composition than does urinalysis. The appearance of volatile compounds in exhaled breath after industrial exposure has been demonstrated in several instances (1-7). Table I shows some examples, together with solubility data which suggest means of identifying other compounds as candidates for this form of biological monitoring. However, breath analysis has not become widespread in the workplace because of practical problems in sampling large numbers of workers and in interpreting the results. Because concentrations of contaminants in exhaled air are low and the air is moist, previous research has relied either on elaborate and expensive equipment or on sampling methods subject to moisture-related loss of contaminant. Further, evaluating the results of breath sampling requires consideration of the complex excretion kinetics of most volatile compounds and of the effects of respiratory dead space on the composition of exhaled breath. The last point has led to efforts to sample alveolar air by procedures requiring much cooperation from the worker. This work addresses some of these problems. A portable, simplified breath sampling system has been developed which is suitable for mass screening, is capable of collecting a relatively large sample, and gives good performance in sampling moist air. Table I. Materials Shown to be Present in Exhaled Breath after Industrial Exposure

Compounds

—Partition Coefficients— Found in Blood/Air Fat/Air QU/Ajr Breath 3 t

Benzene Toluene Xylene Methyl Ethyl Ketone Ethylene Oxide Trichloroethylene Chloroform Methylchloroform Carbon Tetrachloride

6-8 10-16 26-38 200 90 8-10 8-10 3 2-6

425 962 140 560-660 280 250 360

492 1470 3700 260 700-940 400-560

A

20 hours 20 hours 20 hours 2 hours 0 hours 20 hours 0 hours 20 hours 6 hours

Ref. 15,24 12 25 26 27 5 28 29 30

& Time measured from the end of the exposure period The primary value in breath sampling lies in the fact that alveolar gas is very nearly in equilibrium with arterial blood (Figure 1). Mixed expired air, however, is not equal in composition to alveolar air, because of the addition of air from the respiratory dead space. Nevertheless, for samples taken over periods of ten minutes or more, such that a l l the expired air i s


58

BIOLOGICAL MONITORING FOR PESTICIDE EXPOSURE

c o l l e c t e d and i t s volume measured, t h e r e i s u s u a l l y a p r e d i c t a b l e r e l a t i o n s h i p between a l v e o l a r and mixed e x p i r e d a i r , so t h a t t h e l a t t e r can s t i l l be used t o make e s t i m a t e s of t h e b l o o d l e v e l s of t r a c e compounds.(1-3) A more s e r i o u s p r o b l e m i n s a m p l i n g e i t h e r a l v e o l a r o r mixed e x p i r e d a i r i s t h e e f f e c t of t h e passage o f t i m e a f t e r exposure has ended. Models and e x p e r i m e n t a l measurements of e x c r e t i o n k i n e t i c s of v o l a t i l e compounds have shown t h a t w i t h i n two t o f o u r hours a f t e r t h e end of exposure, t h e b r e a t h l e v e l s d e c r e a s e r a p i d l y , and are s t r o n g l y c o r r e l a t e d w i t h t h e c o n c e n t r a t i o n i n t h e i n h a l e d a i r a t t h e end of exposure.(4-6) At longer times post-exposure, the breath l e v e l s are l e s s time dependent, and a r e more c l o s e l y p r o p o r t i o n a l t o t h e time w e i g h t e d average exposure, o r body burden, of t h e compound.(H) The use of b r e a t h a n a l y s i s i n m o n i t o r i n g p e s t i c i d e exposure has not y e t been r e p o r t e d , but t h i s g e n e r a l approach has p o t e n t i a l v a l u e f o r c e r t a i n k i n d s of p e s t i c i d e f o r m u l a t i o n s . Table I I p r e s e n t s some examples of p e s t i c i d e components which have p h y s i c o c h e m i c a l p r o p e r t i e s which f a v o r t h e i r e x c r e t i o n , a t l e a s t i n p a r t , i n b r e a t h . S u i t a b l e compounds must be v o l a t i l e , and must have s o l u b i l i t y p r o p e r t i e s i n b l o o d and body f a t t h a t a r e c l o s e t o t h e ranges g i v e n i n Table I . Many of t h e fumigants used i n a g r i c u l t u r e meet t h e s e r e q u i r e m e n t s , and a few have a c t u a l l y been found i n t h e b r e a t h of workers exposed i n e x p e r i m e n t a l o r industrial settings. In a d d i t i o n , many of t h e v e h i c l e s used i n p e s t i c i d e f o r m u l a t i o n s a r e good c a n d i d a t e s f o r b r e a t h m o n i t o r i n g , and examples a r e i n c l u d e d i n Table I I . T a b l e I I . P e s t i c i d e Components w i t h P h y s i c o c h e m i c a l P r o p e r t i e s F a v o r i n g t h e Use of E x h a l e d B r e a t h f o r B i o l o g i c a l M o n i t o r i n g Compound

Volatile

Chloropicrin Methylisocyanate Ethylene D i c h l o r i d e HCN Sulfuryl Fluoride Vapam Dichloropropylene Dichloropropane Methyl Chloroform E t h y l e n e Oxide Naphthalene p-Dichlorobenzene M e t h y l Bromide Methyl Isothiocyanate Diesel fuel Kerosene Methanol Petroleum d i s t i l l a t e s Xylene Toluene

X X X X X X X X X X X X X X X X X X X X

L i p i d Soluble

X

X X X X X X X X X X X X X

B r e a t h Data Available

E^fs.

X

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X X

29 27

X

31

X X

25 12

The g o a l of t h e work d e s c r i b e d here was t o d e s i g n and demonstrate a f i e l d - p o r t a b l e t e c h n i q u e f o r s a m p l i n g mixed e x p i r e d


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MORGAN ETAL.


a i r f o r v o l a t i l e compounds, a t t i m e s l o n g a f t e r exposure when t h e b r e a t h l e v e l i s i n d i c a t i v e of body burden. The use of mixed e x p i r e d a i r r e p r e s e n t s a c o n c e s s i o n t o t h e need f o r s i m p l i c i t y i n s a m p l i n g , but t h e method s h o u l d s t i l l g i v e a r e s u l t u s e f u l i n b i o l o g i c a l monitoring. The s a m p l i n g method was d e m o n s t r a t e d i n human v o l u n t e e r s l o n g a f t e r a r e l a t i v e l y low i n h a l a t i o n exposure (as low as 20% of t h e o c c u p a t i o n a l T h r e s h o l d L i m i t V a l u e , TLV), as a s e v e r e t e s t of performance. R e s u l t s w i l l a l s o be p r e s e n t e d f o r f i e l d s t u d i e s w i t h workers exposed t o s o l v e n t s i n t h e a u t o m o b i l e repair industry. M a t e r i a l s and Methods Sampler D e s i g n and

Performance

The sampler i s based on a h a l f - f a c e , d u a l c a r t r i d g e r e s p i r a t o r whose i n h a l a t i o n p o r t s a r e f i t t e d w i t h s t a n d a r d a i r p u r i f y i n g e l e m e n t s . ( 1 ) On t h e e x h a l a t i o n p o r t i s mounted a s p e c i a l c a r t r i d g e f o r s a m p l i n g e x h a l e d a i r . The o p e r a t i n g p r i n c i p l e o f t h i s c a r t r i d g e i s based on: a.) q u a n t i t a t i v e a d s o r p t i o n of o r g a n i c v a p o r s and subsequent a n a l y s i s by s t a n d a r d methods, and b.) d e t e r m i n a t i o n of t h e a i r volume sampled by t a k i n g advantage of t h e n e a r l y i n v a r i a n t c o n c e n t r a t i o n of water vapor i n e x p i r e d a i r among i n d i v i d u a l s o v e r a wide range of a c t i v i t y l e v e l s . (8 9) The s a m p l i n g c a r t r i d g e i s shown i n cutaway v i e w i n F i g u r e 2. The upper s e c t i o n c o n t a i n s f o u r l a y e r s of a c t i v a t e d c h a r c o a l c l o t h mounted i n p a i r s s e p a r a t e d by t e f l o n g a s k e t s . This adsorbent i s a woven m a t e r i a l ( C h a r c o a l C l o t h L i m i t e d , Maidenhead, U n i t e d Kingdom) h a v i n g p r o p e r t i e s s i m i l a r t o g r a n u l a r c h a r c o a l , e x c e p t t h a t i t s c o l l e c t i o n performance, based on s t u d i e s w i t h v o l a t i l e a n e s t h e t i c s , i s r e p o r t e d t o be much b e t t e r at h i g h w a t e r vapor c o n t e n t . (1Q.) The lower s e c t i o n c o n t a i n s 70 g of 8 - 12 mesh m o l e c u l a r s i e v e of 3 A p o r e s i z e which c o l l e c t s t h e w a t e r vapor (maximum c a p a c i t y 14 g water vapor p e r 100 g a d s o r b e n t ) . The o r g a n i c v a p o r s c o l l e c t e d on t h e c h a r c o a l c l o t h were r e c o v e r e d by d e s o r p t i o n of p a i r e d l a y e r s i n 10 ml carbon d i s u l f i d e f o r one hour. The e l u e n t was a n a l y z e d by gas chromatograph u s i n g a flame i o n i z a t i o n d e t e c t o r f o l l o w i n g recommended p r o c e d u r e s . (JL1) G e n e r a l l y , t h e c l o t h l a y e r p a i r s were a n a l y z e d s e p a r a t e l y t o p e r m i t d e t e c t i o n of b r e a k t h r o u g h p a s t t h e f i r s t p a i r of l a y e r s . The c o l l e c t e d water vapor was d e t e r m i n e d g r a v i m e t r i c a l l y . The c a r t r i d g e was f a b r i c a t e d from p o l y v i n y l c h l o r i d e p i p e w i t h s t a i n l e s s s t e e l screens t o r e t a i n the adsorbents. The l o a d e d c a r t r i d g e weighed about 180 ± 10 g, and t h u s added about 60% t o t h e weight of t h e r e s p i r a t o r . Resistance t o a i r f l o w through the c a r t r i d g e was l e s s t h a n 2 cm H 2 O / L / S a t f l o w r a t e s up t o 1 L/s. The s a m p l i n g c a r t r i d g e was t e s t e d f o r r e c o v e r y e f f i c i e n c y w i t h c o n t r o l l e d atmospheres d e s i g n e d t o s i m u l a t e human b r e a t h cont a i n i n g low l e v e l s of o r g a n i c v a p o r . Toluene was s e l e c t e d f o r t h i s s t u d y as i t i s used i n l a r g e q u a n t i t i e s i n i n d u s t r y and s t u d i e s of i t s t o x i c o k i n e t i c s have been r e p o r t e d by s e v e r a l a u t h o r s . (2 12-15) The atmospheres were g e n e r a t e d i n a 90 l i t e r g l a s s m i x i n g chamber e q u i p p e d w i t h a c o o l e d - m i r r o r dew p o i n t hygrometer and a p h o t o i o n i z a t i o n d e t e c t o r . The d e t e c t o r was c a l i b r a t e d b e f o r e and a f t e r t h e s t u d y u s i n g a c a p i l l a r y d i f f u s i o n tube (1£). Compressed b r e a t h i n g q u a l i t y a i r was p a s s e d t h r o u g h a h i g h e f f i c i e n c y f i l t e r and a bed of g r a n u l a r c h a r c o a l b e f o r e e n t e r i n g t h e chamber a t 40 L/min. Water was a t o m i z e d i n t o the chamber, and l i q u i d t o l u e n e was metered v i a m o t o r - d r i v e n s y r i n g e t h r o u g h a h e a t e d m e t a l t u b e . r

r


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mixed expired air

t

dead s p a c e

xalveolar air:* venous blood

arterial blood

p (arterial) = p (alveolar) arterial content = p (alveolar) x partition coefficient

F i g u r e 1 — Schematic diagram o f t h e r e l a t i o n s h i p among venous b l o o d , a r t e r i a l b l o o d , a l v e o l a r a i r and mixed e x p i r e d a i r , w i t h r e s p e c t t o c o n c e n t r a t i o n o f a v o l a t i l e m a t e r i a l . "p" r e f e r s t o t h e p a r t i a l p r e s s u r e o f t h e v o l a t i l e component o f i n t e r e s t .

F i g u r e 2 — Cutaway view o f t h e b r e a t h s a m p l i n g c a r t r i d g e showing t h e s e c t i o n f o r o r g a n i c s o l v e n t vapor c o l l e c t i o n and t h e s e c t i o n f o r m o i s t u r e c o l l e c t i o n ; t h e two s e c t i o n s nest t i g h t l y t o g e t h e r when i n use. The s o l v e n t s e c t i o n i s t h r e a d e d t o f i t a s t a n d a r d r e s p i r a t o r c a r t r i d g e h o l d e r which i s mounted i n t h e exhaust p o r t o f t h e mask.


5. MORGAN ETAL.

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Both r e l a t i v e h u m i d i t y (RH) and s o l v e n t c o n c e n t r a t i o n were m o n i t o r e d c o n t i n u o u s l y . The g e n e r a t o r was c a p a b l e o f p r o d u c i n g s t a b l e atmospheres a t between 5% and 95% RH and c o n t a i n i n g between 0.38 mg/m (0.1 ppm) and 1500 mg/m (400 ppm) o f t o l u e n e . Recovery d a t a were o b t a i n e d o v e r a range o f RH and a i r t e m p e r a t u r e s , whose s e l e c t i o n was based on p r e l i m i n a r y measurements o f the a i r s t r e a m l e a v i n g r e s p i r a t o r s w h i l e b e i n g worn. C a r t r i d g e s were c h a l l e n g e d w i t h 10 L/min a i r c o n t a i n i n g t o l u e n e a t l e v e l s between 0.75 mg/m (0.20 ppm) and 150 mg/m (40 ppm) f o r 30 minutes based on the r e s u l t s o f t o x i c o k i n e t i c s t u d i e s . To d e t e r m i n e t h e r e l a t i o n s h i p between water vapor c o l l e c t e d and the volume o f e x p i r e d a i r sampled, a group o f s i x v o l u n t e e r s wore t h e r e s p i r a t o r w h i l e a t r e s t o r w h i l e w a l k i n g on a t r e a d m i l l a t v a r i o u s work l e v e l s . The r e s u l t i n g pulmonary v e n t i l a t i o n r a t e s ranged from 4 L/min t o 28 L/min. E x p i r e d a i r was p a s s e d t h r o u g h the sampling c a r t r i d g e i n s e r i e s w i t h a c a l i b r a t e d pneumotachometer. The f l o w s i g n a l from t h e pneumotachometer was i n t e g r a t e d e l e c t r o n i c a l l y t o g i v e an a c c u r a t e measurement o f a i r volume. The weight g a i n o f the m o l e c u l a r s i e v e i n t h e c a r t r i d g e was t h e n compared t o the independent measurement o f volume. The s a m p l i n g p e r i o d s were between f o u r t e e n and twenty m i n u t e s . 3

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Performance i n C o n t r o l l e d Human Exposures As a d e m o n s t r a t i o n o f the d e v i c e under r e a l i s t i c c o n d i t i o n s o f use, h e a l t h y a d u l t male v o l u n t e e r s were r e c r u i t e d f o r a l a b o r a t o r y s t u d y . A f t e r g i v i n g i n f o r m e d c o n s e n t , each s u b j e c t was sampled f o r t h e b a s e l i n e l e v e l o f t o l u e n e i n e x p i r e d b r e a t h . Then a i r a t 50% RH c o n t a i n i n g t o l u e n e a t 150 mg/m (40 ppm) o r 340 mg/m (90 ppm) was p a s s e d t h r o u g h a mask c o v e r i n g t h e s u b j e c t ' s nose and mouth a t 35 L/min, f o r f o u r h o u r s . Between 17 and 20 hours l a t e r , c o r r e s p o n d i n g t o the s t a r t o f t h e next work s h i f t , a b r e a t h sample was t a k e n and a n a l y z e d . The sampling p r o c e d u r e c o n s i s t e d of f i r s t w e a r i n g t h e r e s p i r a t o r w i t h o u t the s p e c i a l s a m p l i n g c a r t r i d g e f o r seven t o t e n minutes t o a l l o w a i r t e m p e r a t u r e and RH i n s i d e t h e mask t o s t a b i l i z e . Then the s a m p l i n g c a r t r i d g e was a t t a c h e d and t h e s u b j e c t c o n t i n u e d t o b r e a t h e a t r e s t f o r 15 t o 20 min. The c a r t r i d g e was t h e n d i s a s s e m b l e d and t h e a d s o r b e n t s were a n a l y z e d w i t h i n one hour. R o u t i n e sampling o f l a b o r a t o r y ambient a i r i n d i c a t e d t h a t t o l u e n e l e v e l s were always l e s s t h a n 10 |ig/m . The o b s e r v e d b r e a t h c o n c e n t r a t i o n s were c o r r e c t e d f o r t h e d i l u t i o n e f f e c t o f t h e r e s p i r a t o r c a v i t y dead space. I n a s e p a r a t e e x p e r i m e n t , the c o r r e c t i o n f a c t o r f o r each s u b j e c t was e s t i m a t e d by measuring the c o n c e n t r a t i o n o f carbon d i o x i d e i n mixed e x p i r e d a i r c o l l e c t e d : a.) a t t h e r e s p i r a t o r o u t l e t p o r t and b.) a t the mouth. I t was assumed t h a t the d i l u t i o n o f e x p i r e d c a r b o n d i o x i d e by the r e s p i r a t o r dead space a p p r o x i m a t e s c l o s e l y the d i l u t i o n o f e x p i r e d t r a c e organics. 3

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Performance i n I n d u s t r i a l S e t t i n g s E l e v e n p a i n t e r s employed i n f i v e a u t o m o b i l e body r e p a i r and r e p a i n t i n g shops were t h e n s t u d i e d , w i t h t h e i n t e n t o f d e t e r m i n i n g whether o r not b r e a t h c o n c e n t r a t i o n s o f t o l u e n e used as a s o l v e n t compared t o t r a d i t i o n a l measurements o f t h e s o l v e n t i n b r e a t h i n g zone ambient a i r . B r e a t h samples were c o l l e c t e d f o r f i f t e e n m i n u t e s b e f o r e the b e g i n n i n g o f each s h i f t f o r f i v e c o n s e c u t i v e days i n each p a i n t e r . D u r i n g t h e s a m p l i n g p e r i o d no p a i n t i n g was done, and s t a n d a r d o r g a n i c vapor c a r t r i d g e s were a t t a c h e d t o t h e


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i n l e t p o r t s o f t h e s a m p l i n g r e s p i r a t o r , t o ensure t h a t no exposure occurred. D u r i n g each s h i f t t o l u e n e c o n c e n t r a t i o n s i n each worker's b r e a t h i n g zone were measured, as t h e 8 hour t i m e - w e i g h t e d average, u s i n g a p a s s i v e d o s i m e t e r i n c o r p o r a t i n g a c t i v a t e d charcoal.(12) Samples were c o l l e c t e d u s i n g t h e Model 530-11 d o s i m e t e r o f SKC I n c . , F u l l e r t o n , CA. The c h a r c o a l elements were d e s o r b e d i n 2.0 m l carbon d i s u l f i d e and t h e e l u e n t a n a l y z e d by t h e procedure c i t e d e a r l i e r . Recovery e f f i c i e n c y f o r d o s i m e t e r s was t a k e n from m a n u f a c t u r e r ' s l i t e r a t u r e . A l l p a i n t e r s were o b s e r v e d d u r i n g a t l e a s t p a r t o f each s h i f t , t o determine t h e use o f g l o v e s and r e s p i r a t o r y p r o t e c t i o n , and t o e s t i m a t e t h e e x t e n t o f s k i n contact with l i q u i d paint solvent. Results O v e r a l l r e c o v e r y o f t o l u e n e from t h e c h a r c o a l c l o t h was c a l c u l a t e d as t h e mass d e t e r m i n e d a f t e r c o l l e c t i o n and d e s o r p t i o n , d i v i d e d by t h e mass p r e s e n t e d t o t h e c h a r c o a l d e t e r m i n e d from a i r volume and toluene c o n c e n t r a t i o n . R e s u l t s o f recovery are presented i n Table III. The r e c o v e r y dropped a t c o n c e n t r a t i o n s above 60 mg/m (16 ppm), presumably due i n p a r t t o b r e a k t h r o u g h . A t 60 mg/m o r l e s s , t h e r e c o v e r y c o e f f i c i e n t of v a r i a t i o n was l e s s t h a n 15%. 3

3

Table I I I O v e r a l l Recovery o f Toluene from Toluene C o n c e n t r a t i o n (mg/m ) 3

Temp

Convenient Field Sampling Method for Monitoring Volatile

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