Measurement Challenges in Atmospheric Chemistry - ACS Publications

13 Measurement of Personal Exposure to Air Pollution: Status and Needs

Downloaded by TUFTS UNIV on June 3, 2018 | https://pubs.acs.org Publication Date: June 1, 1993 | doi: 10.1021/ba-1993-0232.ch013

Paul J. L i o y Environmental and Occupational Health Sciences Institute, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, 681 Frelinghuysen Road, Piscataway, NJ 08854

Research on air pollution monitoring has expanded its scope of inquiry from characterization of the ambient atmosphere and identification of its chemical and aerosol constituents to determination of an individual's total indoor and outdoor air pollution exposure. (Exposure is the integral of a time-varying concentration over a specified interval of contact.) This new emphasis has spurred the development and evaluation of personal air monitors for applications within populations at risk to high exposure and within the general population. The types of pollutants presently requiring or being considered for personal monitoring are discussed. The associated technological issues and problems are described and illustrated by examples. The criteria for a design of a personal monitor are reviewed, as are the scientific approaches currently being used for personal monitoring and plausible approaches for the future. Activity logs, which are needed to ensure proper allocation of the sources of significant exposure, are briefly discussed.

PERSONAL MONITORING IS A RELATIVELY NEW CONCEPT

i n c o m m u n i t y air p o l l u t i o n m e a s u r e m e n t research (1-3). T h i s fact is not s u r p r i s i n g because most air p o l l u t i o n investigations have b e e n d i r e c t e d t o w a r d the characterization o f the a m b i e n t atmosphere, the observation of p o l l u t a n t t r e n d s , the acquisition o f data o n c h e m i c a l k i n e t i c parameters a n d o n the p h y s i c a l p r o p erties o f aerosols, a n d the d e t e r m i n a t i o n of c o m p l i a n c e to n a t i o n a l a n d o t h e r standards (4). Before the late 1970s, research o n p e r s o n a l m o n i t o r s was p r i m a r i l y c o n d u c t e d i n i n d u s t r i a l settings (5, 6) because A m e r i c a n C o n f e r 0065-2393/93/0232-0373$06.00/0 © 1993 American Chemical Society

Newman; Measurement Challenges in Atmospheric Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1993.


374

M E A S U R E M E N T C H A L L E N G E S IN A T M O S P H E R I C C H E M I S T R Y

ence 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 ( A C G I H ) g u i d e l i n e s a n d O c cupational Safety a n d H e a l t h A d m i n i s t r a t i o n ( O S H A ) standards for w o r k p l a c e contaminants are an 8-h t i m e - w e i g h t e d average or the peak c o n c e n t r a t i o n of a p a r t i c u l a r p o l l u t a n t or m i x t u r e of pollutants (7, 8). T h e c o n c e n t r a t i o n o f w o r k p l a c e contaminants may b e associated w i t h m o r e t h a n one area a n d m a y not vary p r e d i c t a b l y w i t h distance f r o m a source; therefore, area m o n i t o r s have b e e n k n o w n to u n d e r e s t i m a t e exposures i n the w o r k p l a c e that can cause k n o w n h e a l t h effects. C o n s e q u e n t l y , the h y g i e n i s t uses p e r s o n a l m o n itors. O c c u p a t i o n a l exposures are usually associated w i t h r e l a t i v e l y h i g h c o n centrations. I n fact, the concentration of m a n y substances (but not ozone) exceeds a m b i e n t air concentrations b y 2 to 3 orders of m a g n i t u d e . A m u l t i t u d e of samplers are u s e d to detect the i n o r g a n i c or organic c o m p o u n d s e n c o u n t e r e d i n i n d u s t r i a l settings, b u t these samplers collect m a t e r i a l p r i m a r i l y to d e t e r m i n e an 8-h t i m e - w e i g h t e d average (5, 6). E v e n w i t h l o n g s a m p l i n g t i m e s , the total quantities of contaminants c o l l e c t e d i n n o n i n d u s trial m i c r o e n v i r o n m e n t s (e.g., a l i v i n g r o o m , a p a r k , o r a library) are s m a l l , so sensitive techniques are n e e d e d (1-3, 9, 10). F r e q u e n t l y , c o m m u n i t y air e n v i r o n m e n t s are c o m p l e x , a n d most o u t d o o r exposures do not occur near the actual source of air contaminants, a situation that is the n o r m for the w o r k p l a c e (4). T h e concentrations i n c o m m u n i t y air are an average of the emissions d i s p e r s e d w i t h i n the a t m o s p h e r e b y a n u m b e r of sources, b y the same source i n a n u m b e r of different locations, or b y a single large [>100 l b / y e a r (>45 kg/year)] or small [ < 5 l b / y e a r ( < 2 . 2 5 kg/year)] source i n one location (11). I n o t h e r situations the a m b i e n t c o n centrations are an average of the secondary products f o r m e d i n a d e f i n e d area or large r e g i o n (12). I n a d d i t i o n , i n d o o r air exposures result f r o m o u t d o o r air p e n e t r a t i n g indoors a n d f r o m emissions b y i n d o o r sources (e.g., tobacco smoke or solvent evaporation). I n d o o r emissions have some features s i m i l a r to occupational settings because the p e r s o n can b e located adjacent to or can pass near the i n d o o r source (J). A s a c o n s e q u e n c e of the needs i n air exposure research, i m p r o v e d i n s t r u m e n t a t i o n for p e r s o n a l m o n i t o r i n g m u s t be. d e v e l o p e d ; this i n s t r u m e n t a t i o n is the focus of this chapter.

Rationale T h e p e r s o n a l m o n i t o r i n g of c o m m u n i t y air pollutants is r e q u i r e d for four basic reasons; these reasons are associated w i t h a n e e d for a m o r e accurate d e s c r i p t i o n o f an i n d i v i d u a l ' s contact w i t h a p o l l u t a n t that can affect h e a l t h . 1. F o r specific air pollutants, e v e n some a i r pollutants i n the N a t i o n a l A m b i e n t A i r Q u a l i t y S t a n d a r d (e.g., n i t r o g e n d i o x i d e and particulate matter), the highest exposures m a y not o c c u r outdoors.


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Measurement of Personal Exposure to Air Pollution

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2. T h e concentration of an air p o l l u t a n t varies f r o m location to location, so a stationary m o n i t o r may not b e representative of the major exposures to m a n y pollutants. 3. A person's activities alter the patterns of exposure to c o n t a m inants t h r o u g h o u t a day.


4. A person's exposure occurs a l l day l o n g ; this situation indicates the n e e d to have the d e v i c e accompany an i n d i v i d u a l t h r o u g h out an e n t i r e day or, for some pollutants, d u r i n g that p o r t i o n of the day w h e n peak exposures may occur. T h e d e v e l o p m e n t of personal m o n i t o r i n g t e c h n i q u e s a n d t h e i r a p p l i cation to a c o m m u n i t y setting are essential i n exposure studies d e s i g n e d for e p i d e m i o l o g y , risk assessment, a n d c l i n i c a l i n t e r v e n t i o n (JO). F u r t h e r , t h e r e is little i n f o r m a t i o n o n the f o r m a t i o n , transformation, a c c u m u l a t i o n , a n d fate of pollutants i n locations w h e r e the p o p u l a t i o n spends its t i m e (e.g., office b u i l d i n g s o r residences). T h u s , studies are r e q u i r e d that c o u p l e m e a s u r e ments of pollutants at levels of e n v i r o n m e n t a l c o n c e r n w i t h the places w h e r e p e o p l e s p e n d t i m e or conduct significant activities. S o m e t r a d i t i o n a l a n d n e w applications of personal m o n i t o r i n g i n c l u d e the f o l l o w i n g (3, 10): 1. O u t d o o r A i r P o l l u t i o n . A p p l i c a t i o n s i n c l u d e m o n i t o r i n g neighborhoods near a s m a l l local source; m u n i c i p a l i n c i n e r a tors; p h o t o c h e m i c a l smog episodes a n d t h e i r i m p a c t o n o u t d o o r athletics a n d r e c r e a t i o n ; u r b a n traffic congestion; a n d dust resuspension from hazardous wastes. 2. I n d o o r A i r P o l l u t i o n . T h i s category i n c l u d e s m o n i t o r i n g h i g h source emissions or u b i q u i t o u s sources; air emissions f r o m c o n t a m i n a t e d water, w h i c h can c o m e from b a t h r o o m showers, basement seepage, or pesticide c o n t a m i n a t i o n ; a n d tight b u i l d i n g s , w h i c h , because of a lack of d i s p e r s a l , m a y have h i g h concentrations of m a n y chemicals. 3. C o m m u t e r T r a n s i t . A p p l i c a t i o n s i n c l u d e m o n i t o r i n g autom o b i l e c a b i n p o l l u t i o n a n d self-service gasoline r e f u e l i n g . E a c h situation r e q u i r e s an evaluation of the hypotheses to b e tested before the personal m o n i t o r can be d e s i g n e d a n d the i d e n t i f i c a t i o n of the types a n d d u r a t i o n of exposure that m a y occur. O n c e i n h a l e d , the c o m p o u n d may be r a p i d l y m e t a b o l i z e d i n the b o d y ; s h o r t - t e r m m e a s u r e m e n t s w o u l d be a p p r o p r i a t e for such processes. T h e c o m p o u n d m a y i n s t e a d have a l o n g residence t i m e at a specific site i n the l u n g or m a y be stored i n an organ or tissue. T h u s , the i n h a l e d c o m p o u n d o r one o r m o r e of its adducts o r m e tabolites c o u l d e v e n t u a l l y d e l i v e r a biologically effective dose to a target organ o r c e l l (13). T h e m o n i t o r m u s t b e d e v e l o p e d w i t h c o n s i d e r a t i o n of the


376


n a t u r e , concentration, t i m e of contact, a n d b i o l o g i c a l effects o f the c o m pound.


Criteria and Techniques O n c e the i n h a l a t i o n exposure questions have b e e n i d e n t i f i e d , the specifications for each personal m o n i t o r m u s t b e d e t e r m i n e d a n d the m o n i t o r m u s t be v a l i d a t e d for the contaminant b e i n g m e a s u r e d . T a b l e I , u p d a t e d f r o m Samet et a l . (14), identifies c u r r e n t l y available personal m o n i t o r s , a n d T a b l e I I , t a k e n from an E n v i r o n m e n t a l P r o t e c t i o n A g e n c y ( E P A ) r e p o r t (15), shows the p r o j e c t e d needs i n the 1990s. T h e r e are a n u m b e r of o p p o r t u n i t i e s for research o n personal m o n i t o r s ; T a b l e I I indicates that r e l a t i v e l y few c o m m e r c i a l units are c u r r e n t l y available for e i t h e r particulate or gas-phase species. F o r c o m p o u n d s such as p o l y c y c l i c aromatic h y d r o c a r b o n s ( P A H s ) , a two-stage s a m p l e r is r e q u i r e d because some P A H s exist s i m u l t a n e o u s l y i n the gaseous a n d particulate phase (16). C o n s e q u e n t l y , research m u s t be r a n k e d w i t h respect to the significance of the air p o l l u t i o n p r o b l e m , a n d the technological d e v e l o p m e n t s r e q u i r e d to p r o v i d e r e l i a b l e samplers m u s t b e defined. A f t e r a personal m o n i t o r is d e v e l o p e d , the first l e v e l of use w o u l d b e w i t h i n a target p o p u l a t i o n p o t e n t i a l l y h a v i n g h i g h exposures, a n d the second l e v e l w o u l d b e the i n t r o d u c t i o n of a s t r e a m l i n e d m o n i t o r i n g package for applications w i t h i n larger segments o f the general p o p u l a t i o n . N e w p e r s o n a l monitors m u s t address these six c r i t e r i a (10): 1. S e n s i t i v i t y . T h e m o n i t o r s h o u l d detect analytes at levels b e l o w those causing adverse h e a l t h effects, b e sensitive to changes that are o n e - t e n t h of the l e v e l of interest, have p r e c i s i o n of ± 5 % , a n d be easy to calibrate accurately. 2. S e l e c t i v i t y .

T h e m o n i t o r s h o u l d have no response to o t h e r

c o m p o u n d s that m i g h t also be present. 3. R a p i d i t y . S a m p l i n g a n d analysis times s h o u l d b e short c o m p a r e d w i t h biological response t i m e s , response t i m e i n 9 0 % of samples s h o u l d b e less than 30 s, a n d o u t p u t s h o u l d b e R S 2 3 2 or the e q u i v a l e n t . 4. C o m p r e h e n s i v e n e s s . T h e m o n i t o r s h o u l d b e sensitive to a l l contaminants that c o u l d result i n adverse h e a l t h effects a n d adaptable to several analytes. 5. P o r t a b i l i t y . T h e s a m p l i n g a n d analysis d e v i c e s h o u l d b e r u g g e d a n d s h o u l d not interfere w i t h the n o r m a l b e h a v i o r of the i n d i v i d u a l . It s h o u l d have l o w p o w e r c o n s u m p t i o n , a s t a b i l i zation t i m e of less than 15 m i n , a t e m p e r a t u r e range of 2 0 -


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40 °C, a n d a h u m i d i t y range of 0 - 1 0 0 % , a n d it s h o u l d b e battery p o w e r e d .


6. C o s t . S a m p l i n g a n d analysis s h o u l d not b e p r o h i b i t i v e l y expensive. T h e m o n i t o r s h o u l d have few c o m p o n e n t s that are c o n s u m e d b y analysis a n d s h o u l d r e q u i r e l i t t l e m a i n t e n a n c e . F i v e o f the c r i t e r i a are n o r m a l l y c o n s i d e r e d w h e n any a i r p o l l u t i o n m o n i t o r is d e s i g n e d ; h o w e v e r , the fifth c r i t e r i o n — p o r t a b i l i t y — i s essential i n a personal m o n i t o r . O b v i o u s l y , this r e q u i r e m e n t has an i m p a c t o n t h e other c r i t e r i a because it establishes a challenge for a c h i e v i n g specificity for a c h e m i c a l or suite of chemicals, for l o w d e t e c t i o n l i m i t s for adequate d e t e r m i n a t i o n of the concentration a n d exposure, a n d for units that are not c o s t - p r o h i b i t i v e . S e n s i t i v i t y of c u r r e n t personal m o n i t o r s is less t h a n that for stationary m o n i t o r i n g techniques. T h u s , e n t i r e l y n e w approaches appear to b e necessary for detection o f a contaminant i n a p e r s o n a l m o n i t o r . T h e c u r r e n t methodologies types (17, 18):

for personal s a m p l i n g i n c l u d e two major

1. Passive S a m p l i n g . T h e s e techniques p r o v i d e for the a c c u m u l a t i o n of a contaminant o n a substrate o n the basis o f the p r i n c i p l e s of diffusion, s e d i m e n t a t i o n , a d s o r p t i o n , o r absorption. 2. A c t i v e S a m p l i n g . T h e s e techniques use the d y n a m i c passage of the s a m p l e d air at a specified rate t h r o u g h a substrate (e.g., a filter), an absorbant (e.g., Tenax ( d i p h e n y l p h e n y l e n e oxide) or activated charcoal), or a detector (e.g., a photometer) that measures a parameter that is p r o p o r t i o n a l to detectable q u a n tities of a contaminant. A p p l i c a t i o n s of different personal monitors have increased o v e r the past 10 years; passive m o n i t o r i n g techniques are u s e d p r i m a r i l y for l o n g - t e r m s a m p l i n g , w h i c h p r o v i d e s data to quantify exposures associated w i t h c h r o n i c h e a l t h effects. O n e of the most w e l l k n o w n passive t e c h n i q u e s is the P a l m e s t u b e , F i g u r e 1 (19). It has b e e n u s e d to study the m a g n i t u d e of i n d o o r n i t r o g e n dioxide exposures for a v a r i e t y of t i m e p e r i o d s , r a n g i n g from a day to greater t h a n a week. O t h e r samplers are n o w available w i t h variations o n this approach, i n c l u d i n g devices that can be r e a d b y an i n d i v i d u a l w h o has a color chart (20). Passive m o n i t o r i n g techniques w e r e c o n s i d e r e d for the first E P A Total E x p o s u r e Assessment M e t h o d o l o g y ( T E A M ) studies for v o l atile organic species; h o w e v e r , T E A M investigations have u s e d active s a m plers because the personal measurements w e r e m a d e o n l y for 12-h durations (21).



2

2

N 0 : Diffusion badge

Mercury vapor (and others) Ozone

2

Environmental Sciences and Physiology, Harvard School of Public Health, Boston, M A 02115 Environmental Sciences and Physiology, Harvard School of Public Health, Boston, M A 02115

Environmental Sciences and Physiology, Harvard School of Public Health, Boston, MA 02115 SKC, Inc., Eighty Four, PA 15330

N 0 and S 0 : Diffusion tubes

2

N 0 : personal and alarm

Du Pont, Applied Technical Division, P.O. Box 110, Kennett Square, PA 19348 3M Corporation, Technical Service Department, Building 260-3-2, 3M Center, St. Paul, M N 55144 M DA Scientific, Lincolnshire, IL 60069

3M Corporation, Technical Service Department, 3M Center, St. Paul, M N 55144

Industrial Scientific Corporation, Oakdale, PA 15071 National Draeger Inc., P.O. Box 120, Pittsburgh, PA 15230

Manufacturing Company

Formaldehyde: Pro-Tek adsorption badge Formaldehyde: diffusion monitor

Organic vapors: hydrocarbon chemical reaction tubes Organic vapors: charcoal badges

Organic vapors

Pollutant Sampler

fl

Approximate Cost

50 ppb/h

$15/badge, research only

NA

NA 0.05 mg/m integrated >25 ppb at 8 h 3

$800/detector; $100/output; $2,075/dosimeter; $l,045/readout unit $10/tube, research only

$37/monitor and $37/analysis

$20/badge; $25$80 for analysis

$10/badge; $50$300 for analysis by G C or G C / M S

$3/tube; $900 for pump and accessories

NA

2-3 ppm; 1/3 TLV; electrochemical cell based 15 min-8 h TWA 500 ppb/h integrated

depends on vapors and sampling times; minimum level, 10 mg 1.6-54 ppm/h up to 7 days or 0.2-6.75 ppm/8 h TWA 0.1 ppm for 8 h

100-3000 ppm for 4-8 h

NA

Sensitivity and Integrating Time

Table I. Representative Monitoring Equipment for Particulate Matter for Indoor A i r Quality Samples


Newman; Measurement Challenges in Atmospheric Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1993. H

Environmental Sciences and Physiology, Harvard School of Public Health, Boston, MA 02115

NA

NOTES: Particles can be measured with a variety of techniques. With cyclone or impactor separators, smaller fractions can be collected on filters. Mass can also be measured by using the optical properties of particles. For the most part, measuring particles requires equipment costing several hundred to a few thousand dollars. Filters must be pre- and post-weighed in a temperature- and humidity-controlled room; TWA, time-weighted average; TLV, threshold limit value; TSP, total suspended particles; and RS»P, respirable particles. NA, not available. "Reference 20. SOURCE: Adapted from reference 14.

and 0 ^; nmol/m

3

>10 μg/m mass concentration; 1.5 L/s

Handheld Aerosol Monitor (HAM), PPM Inc., Knoxville, T N 37922

4

$3,000-$10,000

NA

GCA-Mini-RAM (personal aerosol monitor), G C A Corporation, Bedford, MA 01730

+

NA

6L/m; separates by using filters in series

National Bureau of Standards under EPA contract, U.S. EPA, Research Triangle Park, N C 27711

3

NA

1.7 L / m

$255 for pump and accessories; $3/tube pumps, $200-$700; filters, $2; cyclones, $20-$100

National Draeger Inc., P.O. Box 120, Pittsburgh, PA 15230 Several manufacturers

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T h e obvious advantages of a passive s a m p l e r , as seen i n F i g u r e 1, are its s i m p l i c i t y , total p o r t a b i l i t y , a n d lack of any ancillary e q u i p m e n t n e e d e d to collect the sample. T h e p r i m a r y d r a w b a c k is the necessity to collect an integrated sample o v e r an e x t e n d e d p e r i o d of t i m e . T h i s d r a w b a c k m a y not be i m p o r t a n t i f the response t i m e for a b i o l o g i c a l effect is not significantly shorter than the m i n i m u m s a m p l i n g d u r a t i o n . A c t i v e s a m p l i n g has always b e e n p r e f e r r e d i n t r a d i t i o n a l air p o l l u t i o n studies because a substance can be c o n c e n t r a t e d o n a p a r t i c u l a r substrate a n d because continuous m e a s u r e m e n t s can be t a k e n . T h e s e samplers have b e e n p l a c e d at fixed m o n i t o r i n g sites o n a roof or i n a trailer (4). T h e use of active s a m p l i n g , h o w e v e r , has not b e e n w i t h o u t p r o b l e m s . F o r instance, the use of substrates such as filters a n d sorbents can affect the m e a s u r e d c o n c e n t r a t i o n b y artifact f o r m a t i o n , b r e a k t h r o u g h , a n d blow-off associated w i t h i n d i v i d u a l c o m p o u n d s or classes (22). P e r s o n a l monitors that use active s a m p l i n g have t e c h n i c a l p r o b l e m s that must be addressed d u r i n g the design phase because • there are s m a l l e r c o m p o n e n t parts, • the size of the p u m p is l i m i t e d , • the v o l u m e or surface of the c o l l e c t i o n m e d i u m or detector is reduced, and


382


• the e n e r g y n e e d e d to p o w e r the d e v i c e is f r o m a self-contained


source. E a c h of these considerations must be r e s o l v e d before a p e r s o n a l m o n i t o r can b e a p p l i e d to air p o l l u t i o n research a n d characterization studies. S o m e advances have b e e n m a d e for c a r b o n m o n o x i d e , v o l a t i l e organic c o m p o u n d s , a c i d aerosols, a n d particulate matter ( P M - 1 0 a n d R S P ; these r e p r e s e n t t h e masses of all particles c o l l e c t e d i n samplers w i t h 5 0 % cut sizes o f 10 a n d 25 μιη, respectively) a n d its components (12, 22-31). E a c h advance is still u n d e r g o i n g d e v e l o p m e n t , a n d f u r t h e r advances can b e a n t i c i p a t e d for these as w e l l as for o t h e r pollutants. T h e next generation o f m o n i t o r s w i l l p r o b a b l y i n c l u d e devices for some pollutants that incorporate the use o f microsensors. C u r r e n t l y , microsensors are b e i n g e x a m i n e d for d e t e c t i o n of n i t r o g e n d i o x i d e and ozone, b u t the range o f sensors available suggests that t h e y can b e u s e d for a n u m b e r of c o m p o u n d s (10, 32): • Biosensors • E l e c t r o c h e m i c a l sensors P o t e n t i o m e t r i c devices A m p e r o m e t r i c devices E l e m e n t s sensitive to contact p o t e n t i a l • T h e r m a l sensors T h e r m i s t o r a n d resistance t h e r m o m e t e r e l e m e n t s T h e r m o e l e c t r i c - b o l o m e t r i c sensors S e m i c o n d u c t o r - b a s e d elements E l e m e n t s sensitive to p i e z o e l e c t r i c t h e r m a l oscillation P y r o e l e c t r i c sensors B l a c k - b o d y radiation sensors • Stress a n d pressure sensors Photoacoustic e l e m e n t s Mass-sensitive elements B u l k p i e z o e l e c t r i c elements (thickness monitors) Surface acoustic-wave (SAW) e l e m e n t s P l a t e - m o d e oscillators Interface i m p e d a n c e e l e m e n t s F i b e r o p t i c e l e m e n t s sensitive to elastic constants • E l e c t r o m a g n e t i c sensors: passive Solid-state c o n d u c t i v i t y (chemiresistance) sensors D i e l e e t r o m e t r i e sensors D i e l e c t r i c sensors Absorptivity elements Index of refraction elements Phase-shift a n d interface i m p e d a n c e (e.g., e l l i p s o m e t r y ) elements Spectral " f i n g e r p r i n t " e l e m e n t s Surface-enhanced R a m a n spectrometers


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• E l e c t r o m a g n e t i c sensors: active Nonlinear behavior, including frequency doubling, elements F l u o r e s c e n c e elements E a c h o f the passive a n d active samplers m e n t i o n e d has a specific s a m p l i n g rate. H o w e v e r , t h e y do not reflect the r e s p i r a t i o n rate o f an i n d i v i d u a l . F o r an estimate o f the dose this r e s p i r a t i o n rate m u s t b e e s t i m a t e d f r o m literature values or collection devices.


Example of Personal Monitor Development and Application T h e difficulties e n c o u n t e r e d i n attempts to a p p l y p e r s o n a l m o n i t o r i n g can b e i l l u s t r a t e d b y the d e v e l o p m e n t s r e q u i r e d to collect P M - 1 0 samples d u r i n g the T o t a l H u m a n E n v i r o n m e n t a l E x p o s u r e S t u d y ( T H E E S ) (25). T h e results of the T H E E S are d e s c r i b e d i n a n u m b e r o f research articles (25, 33-36). T h e f o l l o w i n g is a synopsis of the approach u s e d to collect d a i l y samples from i n d i v i d u a l s for 2 weeks a year o v e r the course o f 2 years (a total o f 28 days). A major p r o b l e m w i t h the c o l l e c t i o n o f particulate m a t t e r is the size of the p u m p . T h e p u m p needs to p r o v i d e a sufficient flow rate to e n s u r e that the i n l e t a n d c o l l e c t i o n m e d i u m c o m p o n e n t s are o p e r a t i n g efficiently (e.g., correct cut size m u s t be p r o v i d e d ) a n d that the system can o b t a i n a large e n o u g h sample to achieve the d e t e c t i o n l i m i t s for the m e a s u r e m e n t o f the c o m p o u n d i n q u e s t i o n . I n T H E E S the target c h e m i c a l was b e n z o [ a ] p y r e n e , w h i c h h a d a l o w e r d e t e c t i o n l i m i t of 0.1 n g / m . A f t e r a series o f laboratory e x p e r i m e n t s it was d e t e r m i n e d that a P M - 1 0 s a m p l e r o p e r a t i n g for 24 h w i t h a 4 L / m i n flow rate was r e q u i r e d to collect adequate mass (>0.5 ng) for analysis. A n i m p a c t o r w i t h a sharp cut size at 10 μπι a n d a 2 5 m m filter was d e v e l o p e d b y V . M a r p l e a n d u s e d as the s a m p l e r (37). It was evaluated i n m y laboratories for c o l l e c t i o n efficiency i n an i n t e r c o m p a r i s o n w i t h a dichotomous s a m p l e r a n d a stationary i n d o o r air s a m p l i n g i m p a c t o r (IASI) (38). T h e results o f the study w e r e excellent for a l l samplers; a slope of 1.0 a n d 1.08 was f o u n d for the regression b e t w e e n mass c o l l e c t e d b y I A S I a n d b y the dichotomous sampler, respectively. T h e i m p a c t o r was adequate for o u r needs; unfortunately, the o n l y p u m p available that o p e r a t e d at the correct flow rate a n d h a d a flow c o n t r o l l e r was d e s i g n e d for occupational h y g i e n e (28). T h e p u m p p r e s e n t e d t h r e e logistical p r o b l e m s . T h e first was a b u l k y d e s i g n that was unresolvable because of insufficient t i m e to r e d e s i g n the u n i t . A s t u r d y s h o u l d e r harness was c o n s t r u c t e d to facilitate c a r r y i n g o f the m o n i t o r b y the participants; h o w e v e r , the p u m p e v e n t u a l l y s h o u l d b e separated into a battery a n d a p u m p assembly. T h i s setup was tested i n the particle T E A M investigations, a l t h o u g h the system was still b u l k y (39). 3

T h e second p r o b l e m was p u m p noise. A w o r k e r m a y not have the same sensitivities about w e a r i n g a p u m p a n d collector as w o u l d a m e m b e r o f the general p u b l i c . F o r the general p u b l i c , the noise levels of greater t h a n 72 d B generated b y a t y p i c a l p u m p are i n t o l e r a b l e , especially w h e n the p u m p


384



is w o r n for 14 days. A t such noise levels relaxation or conversation is not possible (40). A s o u n d c o n t r o l package was constructed to m i n i m i z e t h e noise l e v e l ; the p u m p was h o u s e d i n a box w i t h attenuation m a t e r i a l , a n d t h e p u m p mounts w e r e muffled. T h e noise was r e d u c e d to a p p r o x i m a t e l y 50 d B , w h i c h was f o u n d to b e a reasonable value for a l l participants. T h e t h i r d c o n c e r n was that the p u m p batteries o n l y o p e r a t e d for 12 h . T h e r e f o r e , i t was essential to devise a s a m p l i n g strategy that a l l o w e d for t h e c h a n g i n g t h e batteries halfway t h r o u g h a s a m p l i n g p e r i o d . T h i s situation l e d to a 6 - 8 p . m . start t i m e for t h e samples a n d a 6 - 8 a . m . battery change for each 2 4 - h sample. O b v i o u s l y , a battery that maintains a charge for greater than 24 h is n e e d e d for future exposure studies. T h e final p e r s o n a l m o n i t o r i n g system u s e d is s h o w n i n F i g u r e 2. T h e approach w o r k e d ; w e successfully c o l l e c t e d greater than 9 5 % o f the personal samples, a n d no p o t e n t i a l p a r ticipant refused to wear t h e sampler. D u r i n g t h e day the participants w o r e t h e sampler attached to t h e l a p e l of a n article of c l o t h i n g , b u t at night this was not feasible. T h e r e f o r e , at n i g h t it was p l a c e d i n a convenient location near t h e s l e e p i n g participant. Participants c o u l d not wear t h e sampler d u r i n g specific types o f exercise, a n d they w e r e i n s t r u c t e d to place i t i n a c o n v e n i e n t location at s u c h t i m e s .

Figure 2. Monitoring system used in THEES.



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O b v i o u s l y the methodology was not o p t i m a l , a n d m o r e research is r e q u i r e d o n P M - 1 0 a n d other particle samplers to p r o d u c e a m o r e compact a n d efficiently operated system for consistent use i n large populations. T h e technological p r o b l e m s w i l l be the most d i r e c t to resolve. H o w e v e r , a l o n g t e r m c o n c e r n is w h e t h e r the participants are a l t e r i n g u s u a l activities because they are w e a r i n g a personal m o n i t o r . I n the T H E E S this situation d i d not h a p p e n often because the participants w e r e t o l d that i n such circumstances the d e v i c e s h o u l d be r e m o v e d a n d p l a c e d i n a c o n v e n i e n t location. F u r t h e r m o r e , each p e r s o n was p r o v i d e d w i t h a sports bag i n w h i c h to place the p u m p , a l l o w i n g each p e r s o n to carry the personal s a m p l e r w h e n he or she p a r t i c i p a t e d i n social functions. I n the strict terms of i n d u s t r i a l h y g i e n e practice, the approach used d i d not result i n a l l s a m p l i n g t i m e s b e i n g associated w i t h b r e a t h i n g zone air. T h e logistics w e r e p h y s i c a l l y i m p o s s i b l e and not reasonable because the participants c o u l d not w e a r the samplers to b e d . F u t u r e attempts at m i n i a t u r i z a t i o n or the use of a continuous sensor may solve some of these methodological issues. H o w e v e r , p e r s o n a l monitors w i l l p r o b a b l y c o n t i n u e to sample w i t h i n the personal zone of an i n d i v i d u a l b u t not w i t h i n the b r e a t h i n g zone. T h e T H E E S conclusions i n d i c a t e d the i m p o r t a n c e of p e r s o n a l samplers. Results i l l u s t r a t e d i n F i g u r e 3 show that estimates of the b e n z o [ a ] p y r e n e

Frequency

Daily BaP Dose (no) Figure 3. Benzo[a]pyrene dose for all participants in THEES; CXT estimates from indoor and outdoor measurements (solid bars) and personal air measurements (cross-hatched bars) are shown. (Reproduced with permission from reference 36. Copyright 1991.)


386



inhalation dose f r o m t i m e - w e i g h t e d i n d o o r a n d o u t d o o r e n v i r o n m e n t a l s a m ples was not e q u i v a l e n t to the exposures m e a s u r e d b y the p e r s o n a l samples (36). T h e estimated exposures w e r e s i m i l a r for the m e a n values, b u t the t i m e - w e i g h t e d approach m i s s e d the highest exposures i n the d i s t r i b u t i o n . I n T H E E S most participants w e r e n o n s m o k e r s , so the i n d o o r levels w e r e p r i m a r i l y caused b y the outdoor air a n d i n d i c a t e d that the p e r s o n a l activities c o n t r i b u t e d p r i m a r i l y to the extreme values. T h e i m p o r t a n c e of personal activities was v e r i f i e d b y a d a i l y activity l o g that was filled out b y each participant. T h e l o g was d e s i g n e d to ensure that sources of b e n z o [ a ] p y r e n e c o u l d be accounted for; specific questions o n location a n d o p e r a t i o n of the source a n d passive contact w i t h sources w e r e u s e d . F o r smokers, the personal m e a n values for particulate matter, i n this instance respirable particle concentrations, w e r e d r i v e n b y the i n d o o r air passive smoke (23). T h e studies s u m m a r i z e d i n T a b l e I I I show s i m i l a r i n formation for o t h e r pollutants, a n d for m a n y the outdoor levels are m u c h l o w e r than the i n d o o r levels that result from the presence of specific i n d o o r sources or activities (40).

Discussion T h e types of samplers r e q u i r e d for personal air m o n i t o r i n g i n the future w i l l use a m i x of passive a n d active techniques because not a l l situations l e n d themselves to the use of b o t h a n d because the biological eifect b e i n g s t u d i e d m a y r e q u i r e one s a m p l i n g protocol i n favor of another. I n the case o f o z o n e , w h i c h is one of the major outdoor p o l l u t a n t p r o b l e m s i n the U n i t e d States (41), exposure is estimated f r o m the results from continuous monitors located at stationary sites away f r o m sources of scavenging c o m p o u n d s l i k e N 0 . T h e s e types of sites have p r o v i d e d adequate i n f o r m a t i o n for h u m a n h e a l t h effects field studies because the d a i l y peak or o t h e r d a y t i m e average c o n centrations i n places away f r o m these sources are c o r r e l a t e d w i t h decreases i n l u n g f u n c t i o n . H o w e v e r , to obtain d e t a i l e d i n f o r m a t i o n o n exposure p r o files for i n d i v i d u a l s p a r t i c i p a t i n g i n outdoor activity, an investigator needs a personal device that can r e c o r d the d a i l y m a x i m u m or integrate over a n u m b e r of hours b e t w e e n 10 a . m . a n d 9 p . m . T h u s , a continuous m o n i t o r w o u l d be most desirable. A passive m o n i t o r to d e t e r m i n e i n t e g r a t e d exposure m i g h t w o r k , b u t it m u s t b e capable of at least p r o v i d i n g a n 8-h average for the concentration range of 20 to > 2 0 0 parts p e r b i l l i o n (ppb) (42). C o n c u r r e n t l y , it m a y b e c o m e necessary to m o n i t o r p e r s o n a l exposure to o t h e r smog constituents such as f o r m a l d e h y d e a n d f u e l constituents s u c h as m e t h anol i f the U n i t e d States promotes the use of alternative fuels to operate a large fraction of m o t o r vehicles i n m e t r o p o l i t a n areas (43). Because of the lack of i n f o r m a t i o n o n the c h e m i c a l constituents of alternative fuels (or t h e i r emissions), there c o u l d b e an o p p o r t u n i t y for c h e m i c a l characterization a n d exposure research to l i n k a n d enhance efforts to i d e n t i f y the i m p a c t of toxic c o m p o u n d s o n segments of the p o p u l a t i o n . 2


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Table I U . Summary of Selected Personal Monitoring Studies C a r r i e d Out in the United States Reference

Number of Subjects

RSP

44 23 45 46

20 37 48 101

CO

47 48 49 22

66 98 3 1083

50 51

9 350

VOCs

21 30

355

Pb

52

150

PM-10

25

10-18

PM-10

25

9


Pollutant

N0

2

Summary of Findings Personal exposure did not correlate with outdoor measurements; in most cases it was substantially higher than outdoor concentrations would predict. Exposure to passive tobacco smoke was a major determinant of RSP exposure. Time spent in transit was the primary determinant of personal exposure. Highest C O exposures were due primarily to motor vehicle exhaust. Outdoor monitors overestimated exposures for people not exposed to indoor sources but underestimated exposures for people who resided in homes with unvented combustion appliances. Outdoor measurements did not correlate well with personal exposures. Personal exposure and in-home concentrations tended to be higher than outdoor concentrations for many volatile organic compounds. Highest Pb exposures were experienced by taxi drivers. A l l subjects except office workers experienced highest exposures at work. Highest personal exposures were due to individual activities; nonsmokers' exposures correlated to exposure to ambient air. Highest personal exposures were due to personal activities.

SOURCE: Adapted from reference 1.

T h i s discussion also indicates the n e e d for research o n strategies for i m p l e m e n t a t i o n of personal m o n i t o r i n g . T h e c u r r e n t m o n i t o r i n g t e c h n i q u e s are i n a state of e v o l u t i o n , a n d i n some cases the devices are s t i l l p r i m i t i v e . T o o b t a i n conditions favorable for the d e v e l o p m e n t of p e r s o n a l m o n i t o r s , a major effort must be d i r e c t e d t o w a r d d e f i n i n g the strategies that w i l l y i e l d information o n targeted populations o r populations w i t h h i g h exposures. T h e s e definitions can be a c c o m p l i s h e d t h r o u g h p u r p o s e f u l (focused o n a


388


s m a l l n u m b e r of p e o p l e to d e t a i l the feature of air p o l l u t i o n exposure) o r statistically representative s a m p l i n g of segments of the general p u b l i c . C o n c u r r e n t l y , the t i m e - a c t i v i t y logs must be r e f i n e d for the p o l l u t a n t a n d for situations of c o n c e r n to ensure that the personal samples can b e p l a c e d into a m e a n i n g f u l perspective. W o r k is n o w u n d e r w a y to d e v e l o p a h a n d - h e l d microprocessor data logger that can be u s e d b y a p a r t i c i p a n t to s e q u e n t i a l l y r e c o r d each activity, the t i m e spent i n that activity, o r the t i m e spent i n contact w i t h a source or a type of p o l l u t i o n (e.g., smog).


Summary T h e technological advances i n the i n s t r u m e n t a t i o n r e q u i r e d to c o n d u c t p e r sonal m o n i t o r i n g i n the general p o p u l a t i o n are o c c u r r i n g b u t at a r e l a t i v e l y slow rate. T h e reasons for the delays are not associated w i t h a lack of i m portant questions to be addressed b u t w i t h the n e e d for a m o r e systematic approach to a n s w e r i n g the questions. T h i s approach w i l l p r o v i d e the r e q u i r e d m a r k e t for manufacturers to invest d e v e l o p m e n t costs i n a n i n s t r u m e n t . T h e net result w i l l be better integration o f the c r i t e r i a for p e r s o n a l m o n i t o r s w i t h the i n s t r u m e n t a t i o n needs of a p a r t i c u l a r study. I n the past e q u i p m e n t not o r i g i n a l l y s u i t e d for personal monitors was m o d i f i e d to address exposure a n d e x p o s u r e - h e a l t h effects p r o b l e m s . M a n y of the m o d i f i e d units w e r e successfully u s e d ; h o w e v e r , for future air p o l l u t i o n exposure assessments, basic research o n passive a n d active monitors for a r a n k e d set of chemicals s h o u l d be c o m p l e t e d before the design of a study. T h i s foundation w i l l l e a d to the availability of monitors as the research a n d assessment needs arise. O n e m a i n r e q u i r e m e n t associated w i t h future research is that the investigators d e v e l o p i n g e q u i p m e n t must recognize that the devices are to be w o r n b y p e o p l e a n d that the m o n i t o r must be tested to ensure that the participants i n an exposure study can w e a r it comfortably. I n a d d i t i o n , a i r p o l l u t i o n exposure research must be integrated w i t h research o n the characterization of the atmospheres i n various i n d o o r a n d o u t d o o r e n v i r o n m e n t s . T h i s i n tegration w i l l p r o v i d e a basis for selecting air pollutants or m i x t u r e s w i t h b i o l o g i c a l significance.

Acknowledgment I thank M a l t i P a t e l for w o r k i n p r e p a r i n g the final m a n u s c r i p t . T h i s effort was c o m p l e t e d as part of the N a t i o n a l Institute of E n v i r o n m e n t a l H e a l t h Sciences C e n t e r of E x c e l l e n c e A w a r d E S O S 0 2 2 .

References 1. Sexton, K . ; Ryan, P. B. Assessment of Human Exposure to Air Pollution: Methods, Measurements and Models; A i r Pollution, the Automobile and Public Health; Health Effects Institute, National Academy Press: Washington, DC, 1988; pp 207-238.



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for review March 20, 1991.

ACCEPTED

revised manuscript August 10,


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