Atmospheric Aerosol - ACS Publications - American Chemical Society

10

Sources and Fates of Atmospheric Polycyclic

Atmospheric Aerosol Downloaded from pubs.acs.org by KTH ROYAL INST OF TECHNOLOGY on 12/10/15. For personal use only.

Aromatic Hydrocarbons

RONALD A. HITES School of Public and Environmental Affairs and Department of Chemistry, Indiana University, 400 East Seventh Street, Bloomington, IN 47405 P o l y c y c l i c aromatic hydrocarbons (PAH) are produced by the combustion, under f u e l r i c h c o n d i t i o n s , of almost any f u e l . Although a few PAH with vinylic bridges (such as acenaphthylene) are l o s t , most PAH are q u i t e s t a b l e i n the atmosphere and e v e n t u a l l y accumulate i n environmental sinks such as marine sediments. S p a t i a l and historical measurements of PAH i n sediments i n d i c a t e that these compounds are s t a b l e , conservative markers of man's energy producing activities. I n 1775, P u r s e v i l P o t t f i r s t n o t e d t h a t t h e compounds a s s o c i a t e d w i t h s o o t c a u s e d s c r o t a l c a n c e r i n B r i t i s h chimney sweeps ( 1 ) . N o t h a v i n g modern methods o f i n s t r u m e n t a l a n a l y s i s a v a i l a b l e t o h i m , P o t t was u n a b l e t o s p e c i f y t h e c h e m i c a l s t r u c t u r e s o f t h e s e compounds. I t r e m a i n e d u n t i l 1933 b e f o r e Cook e t a l . i d e n t i f i e d t h e e x a c t s t r u c t u r e o f b e n z o [ a ] p y r e n e and d e m o n s t r a t e d i t s c a r c i n o g e n i c i t y ( 2 ) . Thus, p o l y c y c l i c a r o m a t i c hydrocarbons (PAH) a r e one o f t h e f e w g r o u p s o f compounds w h i c h a r e known t o be c a r c i n o g e n i c t o man. A l t h o u g h t h e r e a r e few chimney sweeps i n b u s i n e s s t o d a y , p e o p l e a r e s t i l l e x p o s e d t o c o n s i d e r a b l e amounts o f p o l y c y c l i c a r o m a t i c h y d r o c a r b o n s . C i g a r e t t e smoking, f o r example, i s a m a j o r s o u r c e o f PAH (3_) ; c o k e p r o d u c t i o n a l s o h a s h i g h PAH emissions ( 4 ) . The e x a c t s y n t h e t i c c h e m i s t r y w h i c h p r o d u c e s PAH i n a f u e l r i c h f l a m e i s n o t w e l l known, e v e n t o d a y . I t i s c l e a r , h o w e v e r , t h a t PAH c a n b e p r o d u c e d f r o m a l m o s t a n y f u e l b u r n e d u n d e r o x y g e n deficient conditions. S i n c e s o o t i s a l s o formed under t h e s e cond i t i o n s , PAH a r e a l m o s t a l w a y s f o u n d a s s o c i a t e d w i t h s o o t . As an example o f t h e PAH a s s e m b l a g e p r o d u c e d b y c o m b u s t i o n s y s t e m s , F i g u r e 1 shows g a s c h r o m a t o g r a p h i c mass s p e c t r o m e t r y (GCMS) d a t a f o r PAH p r o d u c e d b y t h e c o m b u s t i o n o f k e r o s e n e ( 5 ) . The s t r u c t u r e s o f t h e m a j o r compounds a r e a l s o g i v e n i n F i g u r e 1. We draw t h e r e a d e r ' s a t t e n t i o n t o a number o f f e a t u r e s o f t h i s PAH m i x -

0097-6156/81/0167-O187$05.00/0 © 1981 American Chemical Society


00 oo


10.

HiTES

Polycyclic

Aromatic

189

Hydrocarbons

T a b l e I . PAH I d e n t i f i e d b y GCMS ( s e e F i g u r e s 1-3)

2 4 8 10 14 15 18 19 22 23 25 27 30 31

Biphenyl Acenaphthylene Fluorene C H Phenanthrene Anthracene Methylphenanthrene 4H-cyclopenta[def]phenanthrene Fluoranthene Benz[e]acenaphthylene Pyrene ^ Me t h y I f l u o r a n t h e n e Benzo[ghi]fluoranthene CisHiQ(unknown) a

1 4

8

^Probably cyclopent[bc o r f g ] 3

32 33 34 35 37 38 39 40 42 43 44 46 47 48

Cyclopenta[cd]pyrene Benz[a]anthracene Chrysene Methylchrysene Benzofluoranthene Benzo[e]pyrene Benzo[a]pyrene Perylene C21H12(unknown) C21H12(unknown) Ideno[l,2,3-cd]pyrene Dibenz[a,c]anthracene Benzo[ghi]perylene Anthanthrene

acenaphthylene.

C o u l d be methylpyrene.

"Could be m e t h y l b e n z [ a ] a n t h r a c e n e .


190

ATMOSPHERIC AEROSOL

ture. F i r s t , f l u o r a n t h r e n e (peak 22) and p y r e n e (peak 25) a r e p r e s e n t i n about e q u a l abundances. S e c o n d , t h e abundance o f p h e n a n t h r e n e f a r e x c e e d s t h a t o f a n t h r a c e n e (peak 1 5 ) , a l e s s s t a b l e compound. T h i r d , b e n z o [ a ] p y r e n e (peak 39) i s a l w a y s f o u n d w i t h i t s n o n c a r c i n o g e n i c i s o m e r b e n z o [ e ] p y r e n e (peak 3 8 ) . A p a r t i c u l a r l y i n t e r e s t i n g g r o u p o f compounds i n c o m b u s t i o n e f f l u e n t s a r e t h o s e w i t h a v i n y l i c b r i d g e s u c h as a c e n a p h t h y l e n e (peak 4) and c y c l o p e n t e n o [ c d ] p y r e n e (peak 3 2 ) . P e a k 2 3 , a l t h o u g h n o t l a b e l e d , has b e e n p o s i t i v e l y i d e n t i f i e d as a c e p h e n a n t h r y l e n e , a compound w h i c h a l s o has a v i n y l i c b r i d g e . We e m p h a s i z e t h i s s t r u c t u r a l f e a t u r e b e c a u s e o f i t s c h e m i c a l r e a c t i v i t y (compared to t h e f u l l y a r o m a t i c p o r t i o n s o f t h e PAH). We s h a l l s e e l a t e r t h a t t h i s r e a c t i v i t y i s i m p o r t a n t when c o n s i d e r i n g t h e f a t e o f PAH i n t h e a t m o s p h e r e . The PAH shown i n F i g u r e 1 a r e t y p i c a l o f t h o s e p r o d u c e d f r o m the c o m b u s t i o n o f v a r i o u s f u e l s ( 5 ) . W i t h o u t e x c e p t i o n , t h e comb u s t i o n o f a l m o s t any f u e l w i l l p r o d u c e t h e s u i t e o f compounds shown i n F i g u r e 1. The r e l a t i v e a b u n d a n c e s , h o w e v e r , can be s u b s t a n t i a l l y d i f f e r e n t d e p e n d i n g on t h e t e m p e r a t u r e o f c o m b u s t i o n . In f a c t , t h e r e l a t i v e abundance o f t h e a l k y l h o m o l o g s o f PAH, i s h i g h l y dependent on t h e t e m p e r a t u r e a t w h i c h t h e f u e l i s b u r n e d (6). A l t h o u g h F i g u r e 1 shows v e r y modest amounts o f a l k y l homol o g s ( s e e t h e r e g i o n b e t w e e n p e a k s 25 and 3 0 ) , o t h e r f u e l s , b u r n e d u n d e r o t h e r c o n d i t i o n s , c a n show c o n s i d e r a b l y g r e a t e r ab u n d a n c e s o f a l k y l PAH, One c a n , i n f a c t , u s e t h e r e l a t i v e abundance o f t h e a l k y l homologs t o deduce t h e t e m p e r a t u r e a t w h i c h the f u e l was b u r n e d . Once t h e p o l y c y c l i c s a r e r e l e a s e d f r o m t h e c o m b u s t i o n s y s t e m , p r e s u m a b l y a d s o r b e d on s o o t o r f l y a s h , t h e y a r e t h e n e x p o s e d t o p o t e n t i a l a t m o s p h e r i c d e g r e d a t i o n . A s i m p l e way i n w h i c h t o n o t e the r e l a t i v e d e g r a d a t i o n s u s c e p t i b i l i t y o f t h e v a r i o u s PAH i s t o compare t h e GCMS d a t a o f t h e PAH coming f r o m a c o m b u s t i o n s y s t e m (see F i g u r e 1) w i t h t h e PAH p r o f i l e o f a t m o s p h e r i c p a r t i c u l a t e s (see F i g u r e 2) ( 7 ) . We s e e t h a t t h o s e PAH w i t h o u t v i n y l i c b r i d g es a r e s t i l l p r e v a l e n t , t h a t t h e r a t i o o f f l u o r a n t h r e n e t o p y r e n e i s s t i l l a b o u t 1:1, and t h a t t h e r a t i o o f p h e n a n t h r e n e t o a n t h r a cene i s a b o u t 10:1. Those compounds w i t h v i n y l i c b r i d g e s [ a c e n a p h t h y l e n e (peak 1 4 ) , a c e p h e n a n t h r y l e n e (peak 2 3 ) , and c y c l o p e n t e n o [ c d ] p y r e n e (peak 3 2 ) ] h a v e c o m p l e t e l y v a n i s h e d f r o m t h e PAH m i x t u r e found i n the atmosphere. C l e a r l y , the i n c r e a s e d chemical r e a c t i v i t y o f t h e r e l a t i v e l y l o c a l i z e d d o u b l e bond f o u n d i n t h e s e compounds makes them s u s c e p t a b l e t o p h o t o l y t i c o x i d a t i o n . A s s u m i n g most PAH a r e s t a b l e i n t h e a t m o s p h e r e , w h i c h we f e e l i s an e x c e l l e n t a s s u m p t i o n , we a s k what happens t o t h e s e compounds a f t e r t h e y a r e r e l e a s e d f r o m c o m b u s t i o n s y s t e m s t h r o u g h o u t t h e w o r l d . We s u g g e s t t h a t PAH a r e t r a n s p o r t e d t o aq u a t i c s e d i m e n t s e i t h e r by d i r e c t a i r b o r n e t r a n s p o r t o r by s e d i ment r e s u s p e n s i o n and r e d e p o s i t i o n . The b a s i s f o r t h e s e arguments i s e x t e n s i v e a n a l y s e s o f PAH i n s e d i m e n t s w h i c h we h a v e c a r r i e d o u t o v e r t h e l a s t s e v e r a l


HITES

Polycyclic

Aromatic

22

191

Hydrocarbons

38 37 139

25

Ml Temp. (°C) ~ i — 70

90

10

110

20

130

30

150 —ι 40

ι— 170

50

190 — ι — 60

— ι — 210

230

70

80

240 —ι— 90

Time (min.) Analytical Chemistry

Figure 2. Capillary-column gas chromatogram of the total polynuclear hydrocar bon fraction of airârticulate matter (1). Conditions: 11 m X 0.26 mm-Id. glass capillary coated with SE-52 methylphenylsilicone stationary phase; see Table I for peak identities.


192

ATMOSPHERIC AEROSOL

years. The d a t a shown i n F i g u r e 3 a r e among t h e f i r s t we obt a i n e d on s e d i m e n t a r y PAH ( 6 , 8 ) . T h i s i s a GCMS a n a l y s i s o f PAH i n t h e sediment of t h e C h a r l e s R i v e r , a r a t h e r p o l l u t e d body of w a t e r i n B o s t o n . By c o m p a r i n g t h i s f i g u r e w i t h t h e d a t a shown i n F i g u r e 2, one s e e s c o n s i d e r a b l e r e s e m b l a n c e . The r a t i o s o f t h e m a j o r g r o u p s o f compounds a r e t h e same. The PAH w i t h v i n y l i c b r i d g e s a r e m i s s i n g as t h e y w e r e i n t h e a t m o s p h e r e , and t h e a l k y l homologs a r e a b o u t as abundant as one m i g h t e x p e c t . We h a v e obt a i n e d s i m i l a r d a t a , b u t i n a more q u a n t i t a t i v e f a s h i o n , f r o m o v e r 50 s e d i m e n t s a m p l e s f r o m a r o u n d t h e w o r l d ( 9 ) . T h e s e d a t a i n d i c a t e t h a t PAH a r e u b i q u i t o u s and t h a t t h e y a r e f o u n d i n a l most a l l s a m p l e s b o t h n e a r t o and remote f r o m u r b a n a r e a s . The PAH p a t t e r n i n a l l o f t h e s e s a m p l e s , even t h e most remote i s s i m i l a r t o t h a t shown i n F i g u r e 3. Even though the r e l a t i v e d i s t r i b u t i o n remains c o n s t a n t , the t o t a l l e v e l o f PAH d e c r e a s e s d r a m a t i c a l l y w i t h d i s t a n c e f r o m u r ban c e n t e r s . F i g u r e 4 shows a p l o t o f t h e t o t a l PAH abundance i n f i v e m a r i n e s e d i m e n t s a m p l e s t a k e n f r o m M a s s a c h u s e t t s Bay as a f u n c t i o n o f d i s t a n c e f r o m B o s t o n ( 1 0 ) . One can s e e t h a t t h e r e i s a t h r e e o r d e r o f m a g n i t u d e d e c r e a s e i n t h e t o t a l abundance o f PAH w i t h i n 100 k i l o m e t e r s o f B o s t o n . A t t h a t p o i n t , t h e t o t a l PAH l e v e l i s a b o u t 100 ppb; r e m a r k a b l y , t h i s i s what we s e e i n a l m o s t a l l o t h e r remote s a m p l e s . B a s e d on t h e s e and o t h e r measurements o f PAH l e v e l s , we s u g g e s t t h e f o l l o w i n g s c e n a r i o f o r t h e t r a n s p o r t o f PAH. The v a r ious f u e l s which are burned i n m e t r o p o l i t a n areas produce a i r b o r n e p a r t i c u l a t e m a t t e r ( s o o t and f l y a s h ) on w h i c h p o l y c y c l i c a r o m a t i c h y d r o c a r b o n s a r e adsorbed. These p a r t i c l e s a r e t r a n s p o r t e d by t h e p r e v a i l i n g w i n d f o r d i s t a n c e s w h i c h a r e a s t r o n g f u n c t i o n o f t h e p a r t i c l e ' s d i a m e t e r . We s u g g e s t t h a t t h e l o n g r a n g e a i r b o r n e t r a n s p o r t o f s m a l l p a r t i c l e s a c c o u n t s f o r PAH i n deep o c e a n s e d i m e n t s . L a r g e r a i r b o r n e p a r t i c l e s w i l l s e t t l e back onto the urban a r e a ; r a i n t h e n washes them f r o m t h e s t r e e t s and b u i l d i n g s . The PAH i n t h i s u r b a n r u n - o f f e v e n t u a l l y a c c u m u l a t e i n l o c a l s i n k s . We s u g g e s t t h a t t h e s e h i g h l y c o n t a m i n a t e d s e d i m e n t s a r e t h e n s l o w l y t r a n s p o r t e d by r e s u s p e n s i o n and c u r r e n t s t o s e a - w a r d l o c a t i o n s w h e r e t h e s e d i m e n t s a c c u m u l a t e i n b a s i n s o r t h e deep oc e a n . The r a p i d d e c r e a s e i n PAH t o a l e v e l o f 160 ppb w i t h i n 94 km o f B o s t o n ( s e e F i g u r e 4) i n d i c a t e s t h a t t h i s t r a n s p o r t mode i s a r a t h e r s h o r t range e f f e c t (10). The s t a b i l i t y o f PAH i s a l s o a p p a r e n t when one examines s e d i m e n t s a m p l e s t a k e n i n s u c h a way as t o p r e s e r v e t h e h i s t o r i c a l r e c o r d ( 1 1 ) . T h i s can be done by c a r e f u l l y c o r i n g s e d i m e n t s , p a r t i c u l a r l y a t a n o x i c l o c a t i o n s where t h e r e i s l i t t l e b i o t u r b a t i o n , s e g m e n t i n g t h e c o r e i n t o 2-4 cm s e c t i o n s , and a n a l y z i n g e a c h s e c t i o n f o r PAH q u a n t i t a t i v e l y . An example o f s u c h d a t a i s shown i n F i g u r e 5; t h i s r e p r e s e n t s a c o r e f r o m t h e P e t t a q u a m s c u t t R i v e r i n Rhode I s l a n d , a h i g h l y a n o x i c b a s i n ( 1 2 ) . The t o t a l PAH c o n c e n t r a t i o n r a n g e s f r o m 14,000 ppb n e a r t h e s e d i m e n t s u r f a c e t o

l*e] Ι

Figure

3.

High-resolution

gas chromatogram of PAH in Charles River for peak identities.

i4o

sediment (6).

See Table I

Geochimica et Cosmochimica Acta


ATMOSPHERIC AEROSOL

194 Ί

Γ

Ί

Ί

Γ

Γ


10"

J 10

10

L 20

_1_ 30

J 40

L 50

J_ 60

70

DIST FROM BOSTON

_L 80

90

100

(km) Geochimica et Cosmochimica Acta

Figure

4.

Total PAH

1820

concentrations vs. distance from Boston Bay samples (10)

1840

I860

1880 1900 1920 Year of Deposition

1940

I960

for

Massachusetts

1980

Geochimica et Cosmochimica Acta

Figure 5. Total PAH abundance in the various Pettaquamscutt River sediment core sections vs. date of deposition (( Μ λ left scale); benzo[a]pyrene abundance in the Gosser Ploner Sea (14) vs. date of deposition ( ® , right scale) (12).


10.

HiTES

Polycyclic

Aromatic

Hydrocarbons

195

l e s s t h a n 120 ppb a t t h e c o r e b o t t o m . D e s p i t e t h e range o f con c e n t r a t i o n s , t h e r e l a t i v e d i s t r i b u t i o n o f t h e PAH ( e x c l u d i n g r e tene and p e r y l e n e ) i s i n d i c a t i v e o f combustion. F o r example, t h e r a t i o o f t h e CigHô i s o m e r s ( n o n a l k y l a t e d ) t o t h e i r m o n o a l k y l h o m o l o g s (C17H12) i s 3.0 + 0.4. I n no c a s e does t h i s r a t i o become l e s s than u n i t y which would be expected i f t h e s o u r c e were d i r e c t f o s s i l f u e l c o n t a m i n a t i o n . The r a t i o o f t h e CigHô i s o m e r s t o t h e C13H12 i s o m e r s i s 2.7 + 0.3, and t h e r a t i o o f t h e C I I + H I Q i s o mers t o t h e C2 0 12 i s o m e r s i s 0.46 + 0.08. T h e s e r a t i o s a r e c o n s i s t e n t t h r o u g h o u t t h e c o r e and a r e i n d i c a t i v e o f c o m b u s t i o n s o u r c e s ( 6 , 1 1 , 1 2 ) . We, t h e r e f o r e , c o n c l u d e t h a t c o m b u s t i o n g e n e r a t e d PAH p r e d o m i n a t e i n a l l s e c t i o n s o f t h e c o r e . U s i n g t h e 3 mm/yr d e p o s i t i o n r a t e r e p o r t e d b y G o l d b e r g e t a l . ( 1 3 ) a p l o t o f t o t a l PAH ( e x c l u d i n g r e t e n e a n d p e r y l e n e ) i n t h e P e t t a q u a m s c u t t c o r e v s . y e a r o f d e p o s i t i o n was d e v e l o p e d ( s e e F i g u r e 5 ) . F o r comparison, t h e benzo[a]pyrene data r e p o r t e d by Grimmer and Bohnke ( 1 4 ) f o r a c o r e f r o m t h e G r o s s e r P l o n e r S e a a r e a l s o p l o t t e d i n F i g u r e 5. The s i m i l a r i t y b e t w e e n t h e s e two core p r o f i l e s i s q u i t e remarkable. B o t h show r a p i d i n c r e a s e s i n PAH c o n c e n t r a t i o n s b e g i n n i n g a r o u n d 1900. As d i s c u s s e d e l s e w h e r e ( 1 1 , 12) t h i s i n c r e a s e i s c e r t a i n l y due t o t h e h e a v y i n d u s t r i a l i z a t i o n o c c u r r i n g a t t h e t u r n o f t h e c e n t u r y and t h e combustion associated with i t . A s l i g h t d e c r e a s e i n t o t a l PAH a r o u n d 1930 i s p r e s e n t i n b o t h c o r e s (see F i g u r e 5 ) . I t i s i n t r i g u i n g t o s p e c u l a t e t h a t t h i s r e f l e c t s a n e v e n t o c c u r r i n g b o t h i n E u r o p e a n d New E n g l a n d a t t h i s t i m e . The D e p r e s s i o n c o u l d b e s u c h an e v e n t . D u r i n g t h e D e p r e s s i o n , t h e U n i t e d S t a t e s ' t o t a l energy consumption decreased f r o m 25 χ 1 0 BTU i n 1929 t o 18 χ 1 0 BTU i n 1932 b e f o r e r e s u m ing i t s increasing trend (15). The P e t t a q u a m s c u t t d a t a a r e f r o m a s u f f i c i e n t l y deep c o r e t o a l l o w us t o a s s e s s t h e PAH b u r d e n p r i o r t o 1900. The PAH c o n c e n t r a t i o n s a r e a t a l o w a n d c o n s t a n t l e v e l (^200 p p b ) f o r t h e 50 y r p r e v i o u s t o t h e t u r n o f t h e c e n t u r y . T h i s l e v e l may b e i n d i c a t i v e o f PAH f r o m n a t u r a l c o m b u s t i o n p r o c e s s e s s u c h a s f o r e s t fires. C o n t r i b u t i o n s from n a t u r a l p r o c e s s e s appear t o be i n s i g n i f i c a n t i n areas o r periods of high anthropogenic a c t i v i t y . The d e c r e a s e i n PAH l e v e l s a f t e r 1950 i s i n t e r e s t i n g a n d i s s i m i l a r t o that observed a t other l o c a t i o n s (14). I n our case, we t h i n k t h i s r e f l e c t s t h e change f r o m c o a l t o o i l a n d n a t u r a l gas a s home h e a t i n g f u e l s w h i c h o c c u r r e d i n t h e 1950's. During t h e p e r i o d 1944-1961 t h e u s e o f c o a l i n t h e U n i t e d S t a t e s d e c r e a s e d by 40% w h i l e t h e u s e o f o i l and gas i n c r e a s e d by 200% (15). S i n c e c o m b u s t i o n o f c o a l u s u a l l y p r o d u c e s more PAH t h a n o i l and g a s ( 1 6 ) , t h i s change i n f u e l u s a g e w o u l d r e s u l t i n a d e c r e a s e i n PAH p r o d u c t i o n d u r i n g t h e same p e r i o d . We s h o u l d p o i n t out t h a t t h e p o s s i b i l i t y o f r e t u r n i n g t o c o a l as a major energy s o u r c e m i g h t , t h e r e f o r e , h a v e a s i g n i f i c a n t e f f e c t on man's i n p u t o f PAH i n t o t h e s e d i m e n t a r y e n v i r o n m e n t . H

1 5

1 5

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ATMOSPHERIC

AEROSOL

I n summary, we a r e s u g g e s t i n g t h a t most PAH a r e a s t a b l e , c o n s e r v a t i v e m a r k e r o f man's e n e r g y p r o d u c i n g a c t i v i t i e s a n d t h a t t h i s PAH r e c o r d c a n b e r e a d w i t h b o t h s p a t i a l a n d h i s t o r i c a l r e s olution. I n t h i s c o n t e x t , PAH may b e g o o d , l o n g - t e r m i n d i c a t o r s of a i r q u a l i t y .


Acknowledgements We a r e g r a t e f u l t o t h e N a t i o n a l S c i e n c e F o u n d a t i o n ( G r a n t Numbers OCE-77-20252 a n d OCE-80-05997) a n d t h e D e p a r t m e n t o f E n e r g y ( G r a n t Numbers EE-77-S-02-4267 a n d AC02-80EV-10449) f o r t h e i r s u p p o r t o f o u r r e s e a r c h on PAH. The a u t h o r a l s o t h a n k s M i l t L e e , Bob L a f l a m m e , J o h n W i n d s o r , a n d J o h n F a r r i n g t o n f o r t h e i r c o l l a b o r a t i o n on t h e t o p i c s d i s c u s s e d h e r e . Literature Cited 1. P o t t , P. " C h i r u r g i c a l Observations"; Hawkes, C l a r k e , C o l l i n s : London, 1775. 2. Cook, J. W.; Hewett, C. L.; Hieger, I . J . Chem. Soc. 1933, 395. 3. Wynder, E. L.; Hoffman, D. "Tobacco and Tobacco Smoke. Studies i n Experimental Carcinogenesis"; Academic Press: New York, 1967; p. 730. 4. S e a r l , T. D.; Cassidy, F. J . ; King, W. H.; Benson, R. A. Anal. Chem. 1970, 42, 954. 5. Lee, M. L.; Prado, G. P.; Howard, J. B.; H i t e s , R. A. Biomed. Mass Spec. 1977, 4, 182. 6. Laflamme, R. E.; H i t e s , R. A. Geochim. Cosmichim. Acta 1978, 42, 289. 7. Lee, M. L.; Novotny, M.; B a r t l e , K. D. Anal. Chem. 1976, 48, 1566. 8. H i t e s , R. Α.; Biemann, W. G. Adv. Chem. 1975, 147, 188. 9. H i t e s , R. Α.; Laflamme, R. E.; Windsor, J. G. Jr. Adv. Chem. 1980, 185, 289. 10. Windsor, J . G. Jr.; H i t e s , R. A. Geochim. Cosmochim. A c t a . 1979, 43, 27. 11. H i t e s , R. Α.; Laflamme, R. E.; F a r r i n g t o n , J . W. Science. 1977, 198, 829. 12. H i t e s , R. Α.; Laflamme, R. E.; Windsor, J. G. Jr.; F a r r i n g t o n , J . W.; Deuser, W. G. Geochim. Cosmochim. 1980, 44, 873. 13. Goldberg, E. D.; Gamble, E.; Griffin, J . J . ; Koide, M. E s t u a r i n e C o a s t a l Mar. S c i . 1977, 5, 549. 14. Grimmer, G.; Bohnke, H. Cancer L e t t . 1975, 1, 75. 15. H o t t l e , H. C.; Howard, J. B. "New Energy Technology - Some Facts and Assessments"; MIT Press:Cambridge, 1971. 16. N a t i o n a l Academy of Sciences " P a r t i c u l a t e P o l y c y c l i c Organic Matter"; Nat. Acad. Sci.:Washington, D.C., 1972. R E C E I V E D March 10,1981.

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