Distribution of Trace Organics, Heavy Metals, and Conventional

15 Distribution of Trace Organics, Heavy Metals, and Conventional Pollutants in Lake Pontchartrain, Louisiana 1

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Edward B. Overton , Michael H. Schurtz , Kerry M. St. Pé , and Christian Byrne 1

Institute for Environmental Studies, Louisiana State University, Baton Rouge,LA70803 Louisiana Department of Environmental Quality, Baton Rouge,LA70804 Center for BioOrganic Studies, University of New Orleans, New Orleans,LA70148

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Downloaded by CORNELL UNIV on May 17, 2017 | http://pubs.acs.org Publication Date: April 21, 1986 | doi: 10.1021/bk-1986-0305.ch015

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Polynuclear aromatic hydrocarbons from urban runoff were found at elevated levels in nearshore sediment samples from Lake Pontchartrain. Concentrations decreased with distance from the New Orleans shoreline and approached background levels three to six miles offshore. Quantitative profiles for individual PAH isomers differed significantly between nearshore and offshore sediments. Similar trends were observed with chlorocarbons and lead, but concentrations of other heavy metals did not decrease with distance from the shoreline. Salt water intrusion causes stratification over the southeastern portion of the Lake in the summer. This stratification contributes to and exacerbates bottom anoxic conditions during warm weather months. The objectives of this year long study were twofold and included: (A) determination of the occurrence and distribution of chemicals in Lake Pontchartrain, Louisiana (particularly in the southern portion of the Lake near New Orleans) that resulted from anthropogenic activity; and (B) an overall water quality assessment of the Lake to ascertain any phenomena, in particular urban runoff related water pollution, that may be adversely affecting the ecological balance of the Lake. The strategies developed to address these objectives included: (1) Collection of biota and sediment samples and their analyses for a broad spectrum of chemical substances which included, but were not limited to, those designated as priority pollutants by the U.S. EPA. (2) Examination of the temporal and spatial variation of important estuarine water quality parameters, as well as conventional pollutants, that contribute to nutrient enrichment and other impairments such as increased turbidity and dissolved oxygen depression. 0097-6156/ 86/ 0305-0247S07.00/ 0 © 1986 American Chemical Society American Chemical Society Library 1155 16th St., N.W. Washington, D.C. 20036 Sohn; Organic Marine Geochemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


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O R G A N I C M A R I N E GEOCHEMISTRY

F i e l d and l a b o r a t o r y work was begun i n March of 1982. Field work was u n d e r t a k e n by b i o l o g i s t s w i t h the L o u i s i a n a Department o f E n v i r o n m e n t a l Q u a l i t y . A n a l y s e s of b i o t a and sediment samples f o r a n t h r o p o g e n i c substances were performed at the Center f o r B i o - o r g a n i c S t u d i e s a t the U n i v e r s i t y of New O r l e a n s . Water Q u a l i t y and c o n v e n t i o n a l p o l l u t a n t a n a l y s e s were p r o v i d e d by the l a b o r a t o r y s t a f f of the Department of E n v i r o n m e n t a l Q u a l i t y . Lake P o n t c h a r t r a i n i s a s h a l l o w , open water embayment of a major e s t u a r i n e system i n s o u t h e a s t e r n L o u i s i a n a . I t has a, ^ s u r f a c e area of a p p r o x i m a t e l y 630 square m i l e s (1.60 χ 10 m ) . Depths i n o f f s h o r e areas ( g r e a t e r than one m i l e from shore) range t y p i c a l l y from 12-18 f e e t (4 t o 6 m) w i t h the bottom e x h i b i t i n g a g r a d u a l r e l i e f . L o c a l i z e d d e p r e s s i o n s proximate to t h r e e t i d a l p a s s e s , which connect the l a k e to the G u l f of Mexico, s l o p e to depths up to 40 f e e t (12m). The passes themselves have depths a p p r o a c h i n g 100 f e e t (30m). Lake P o n t c h a r t r a i n r e c e i v e s d r a i n a g e from an area of a p p r o x i m a t e l y 5,000 square m i l e s l o c a t e d m o s t l y to i t s n o r t h . S e v e r a l r i v e r s d r a i n the L o u i s i a n a c o a s t a l p l a i n t e r r a c e s w h i l e two o t h e r r i v e r s d r a i n the former M i s s i s s i p p i R i v e r f l o o d p l a i n southwest and west of the l a k e . From the s o u t h , Lake P o n t c h a r t r a i n r e c e i v e s e x t e n s i v e wetland (marsh and swamp) drainage. The g r e a t e r New Orleans a r e a , which i n c l u d e s J e f f e r s o n and O r l e a n s P a r i s h e s , i s now l e v e e d o f f from the l a k e . However, t h i s m e t r o p o l i t a n a r e a , home f o r over a m i l l i o n p e o p l e , i s d r a i n e d by pumping from an e x t e n s i v e network of man-made c a n a l s i n t o Lake P o n t c h a r t r a i n . I n a d d i t i o n to man-made stormwater d r a i n a g e c a n a l s along the s o u t h e r n s h o r e l i n e , Lake P o n t c h a r t r a i n i s i n f l u e n c e d by a deep d r a f t (12m) channel known as the M i s s i s s i p p i R i v e r G u l f O u t l e t (MRG0). H i g h l y s a l i n e waters are i n t r o d u c e d d i r e c t l y i n t o Lake Pontchartrain via this canal. Because of the c l o s e p r o x i m i t y of the G r e a t e r New Orleans M e t r o p o l i t a n Area to Lake P o n t c h a r t r a i n , w i t h no i n t e r v e n i n g b u f f e r zone, the s o u t h e r n p o r t i o n of the l a k e should l o g i c a l l y be the most a f f e c t e d by a n t h r o p o g e n i c i m p a c t s . As such i t should s e r v e as a "worst c a s e " barometer of the l a k e ' s e n v i r o n m e n t a l h e a l t h . T h e r e f o r e the major focus of t h i s study was d i r e c t e d toward the s o u t h e r n a r e a of Lake P o n t c h a r t r a i n . Sampling S i t e s P r i m a r y sampling s t a t i o n s f o r the study were e s t a b l i s h e d at 16 f i x e d l o c a l i t i e s i n the s o u t h e r n r e g i o n of Lake P o n t c h a r t r a i n . These s t a t i o n s were s e l e c t e d from an approximate 100 square m i l e (2.6 χ 10 m ) g r i d a d j a c e n t to the s o u t h e r n s h o r e l i n e e x t e n d i n g 20 s t a t u t e m i l e s a l o n g J e f f e r s o n and O r l e a n s P a r i s h e s and e x t e n d i n g to s i x m i l e s o f f s h o r e at i t s widest p o i n t (see F i g u r e 1 ) . E i g h t of these s t a t i o n s were l o c a t e d i n the immediate n e a r s h o r e area a d j a c e n t to the mouths of major d r a i n a g e c a n a l s . Each was e s t a b l i s h e d a p p r o x i m a t e l y .23 m i l e s (370m) n o r t h of the r e s p e c t i v e c a n a l ' s mouth. L0RAN C c o o r d i n a t e s f o r each were r e c o r d e d d u r i n g the f i r s t sampling c r u i s e and then used d u r i n g subsequent c r u i s e s to re-occupy the same sampling l o c a l i t y . Ten

Sohn; Organic Marine Geochemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


15.

OVERTON ET AL.

Chemicals in Lake Pontchartrain

Jefferson Parish

Orleans Parish

F i g u r e 1. Map of Lake P o n t c h a r t r a i n showing l o c a t i o n s of the 148 water q u a l i t y sampling s t a t i o n s and the l o c a t i o n s which were a l s o sampled f o r sediments.


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a d d i t i o n a l s t a t i o n s were e s t a b l i s h e d o f f s h o r e w i t h i n the 100 square m i l e s t u d y a r e a . On a monthly b a s i s , March 1982 t o March 1983, f i e l d and l a b o r a t o r y water q u a l i t y a n a l y s e s were taken a t 16 o f t h e p r i m a r y s t a t i o n s . F i e l d WQ r e a d i n g s were taken d u r i n g t h e summer months over t h e e n t i r e area of Lake P o n t c h a r t r a i n a t 148 s a m p l i n g s t a t i o n s ( s e e F i g u r e 1 ) . F i e l d water q u a l i t y measurements were made a t one meter (m) i n t e r v a l s from one meter below the s u r f a c e t o 0.5m above t h e l a k e bottom. Readings were t a k e n w i t h Martek I n s t r u m e n t s , I n c . ( I r v i n e , CA) m u l t i p r o b e analyzers. On a q u a r t e r l y b a s i s between March 1982 and March 1983 l a k e sediment and b i o t a samples were c o l l e c t e d from t e n o f t h e s i x t e e n p r i m a r y s t a t i o n s and a n a l y z e d f o r a n t h r o p o g e n i c o r g a n i c c h e m i c a l s and t r a c e m e t a l s . S t a t i o n s were s e l e c t e d a l t e r n a t e l y so t h a t each was sampled a t l e a s t once d u r i n g the study p e r i o d . Four s t a t i o n s d e s i g n a t e d LP07, LP10,LP11, and LP12, were sampled d u r i n g each q u a r t e r . Sediment samples c o n s i s t e d of t h r e e s e p a r a t e dredge grabs w i t h P e t i t e Ponar samplers ( W i l d l i f e Supply Company). Sediment grabs were composited i n s t a i n l e s s s t e e l b u c k e t s ( 3 g a l l o n ) t h a t were washed and then r i n s e d w i t h nanograde hexane between each sampling s t a t i o n . A l i q u o t s of composited sediments were p l a c e d i n wide-mouth quart j a r s , p r e r i n s e d w i t h nanograde hexane. Nearshore sediments were w e l l s o r t e d f i n e s i l t s w i t h between 1 and 2 p e r c e n t o r g a n i c carbon c o n t e n t . O f f s h o r e sediments were f i n e s i l t s or c l a y s and g e n e r a l l y c o n t a i n e d between 2 and 3 p e r c e n t o r g a n i c carbon content· A n a l y t i c a l Methods A n a l y t i c a l methods were designed t o s c r e e n a r e l a t i v e l y l a r g e number of samples f o r a broad spectrum of o r g a n i c compounds and s e l e c t e d heavy m e t a l s . I n t h e f i e l d , a l l samples were p l a c e d on i c e i m m e d i a t e l y f o l l o w i n g c o l l e c t i o n . Upon d e l i v e r y t o t h e l a b o r a t o r y , samples were f r o z e n and m a i n t a i n e d a t -10 C. J u s t p r i o r t o a n a l y s e s , t h e samples were thawed and t h o r o u g h l y homogenized. The a n a l y t i c a l procedure f o r t r a c e o r g a n i c s i n c l u d e d e x t r a c t i o n of a l l samples, f r a c t i o n a t i o n of the e x t r a c t s by l i q u i d - s o l i d chromatography, and i n s t r u m e n t a l a n a l y s e s of the f r a c t i o n s by f u s e d s i l i c a c a p i l l a r y gas chromatography u s i n g flame i o n i z a t i o n ( g e n e r a l ) d e t e c t i o n , and, f o r some samples, e l e c t r o n c a p t u r e (halogen s p e c i f i c ) d e t e c t i o n . S e l e c t e d f r a c t i o n s were then chosen f o r d e t a i l e d i n s t r u m e n t a l a n a l y s e s u s i n g computerized h i g h r e s o l u t i o n gas chromatography-mass s p e c t r o m e t r y (GCMS) (_1 ) . A l l GCMS d a t a f i l e s were examined w i t h a g e n e r a l s e a r c h procedure developed f o r scanning GCMS d a t a f o r a n t h r o p o g e n i c c h e m i c a l s a t t r a c e l e v e l s . Hard c o p i e s of t h e mass s p e c t r a l data were examined manually t o v e r i f y computer matches and i d e n t i f y compounds not s e l e c t e d by the computer program. Identified compounds were then q u a n t i t a t e d by m u l t i p l y i n g t h e i r peak area w i t h a p p r o p r i a t e response f a c t o r s o b t a i n e d from a n a l y s e s of q u a n t i t a t i v e s t a n d a r d s under i d e n t i c a l i n s t r u m e n t a l tunes and



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c o n d i t i o n s . Standard compounds were not a v a i l a b l e f o r a l l the substances i d e n t i f i e d i n samples. Q u a n t i t a t i v e response f a c t o r s were e s t i m a t e d f o r those compounds not c o n t a i n e d i n a n a l y t i c a l s t a n d a r d s . I t i s i m p o r t a n t to note t h a t the use o f e s t i m a t e d response f a c t o r s g i v e s d a t a t h a t can be compared w i t h e q u i v a l e n t d a t a w i t h i n a g i v e n data base. Comparison of the d a t a w i t h o t h e r r e s u l t s o u t s i d e o f the d a t a base s h o u l d be done w i t h i n the c o n t e x t o f the l i m i t a t i o n s imposed by q u a n t i t a t i v e GCMS a n a l y s e s . I n g e n e r a l , these l i m i t a t i o n s i n the q u a n t i t a t i v e r e s u l t s a r e not s i g n i f i c a n t l y l a r g e when compared w i t h v a r i a b i l i t i e s observed between samples c o l l e c t e d from marine environments. Experience from a n a l y s e s o f many r e p l i c a t e samples and p a r t i c i p a t i o n i n r o u n d - r o b i n type i n t e r l a b o r a t o r y c a l i b r a t i o n programs ( 2 ) has produced d a t a which i n d i c a t e s the a n a l y t i c a l v a r i a b i l i t i e s a r e compound dependent and range from 5% t o 30%. T h i s a n a l y t i c a l v a r i a b i l i t y i s g e n e r a l l y s m a l l when compared to v a r i a b i l i t i e s found between samples c o l l e c t e d i n the marine environment. EPA approved atomic a d s o r p t i o n methods were used i n a l l t r a c e metal a n a l y s e s (3)· Standard q u a l i t y c o n t r o l procedures were f o l l o w e d . These i n c l u d e d : a) c a r e f u l washing o f a l l g l a s s w a r e i n s t r o n g o x i d i z i n g s o l u t i o n s and w i t h Type I water; b) f r e q u e n t a n a l y s e s of g l a s s w a r e and reagent b l a n k s ; c ) a n a l y s e s o f p r o c e d u r a l b l a n k s w i t h each b a t c h o f samples; and d) c a l i b r a t i o n of i n s t r u m e n t s b e f o r e each s e t o f a n a l y s e s by a n a l y z i n g s t a n d a r d s o l u t i o n s . A n a l y t i c a l p r o f i c i e n c y i n the a n a l y s i s o f b i o t a and sediment samples have been demonstrated by p a r t i c i p a t i o n i n r o u n d - r o b i n type I n t e r l a b o r a t o r y c a l i b r a t i o n e x e r c i s e s ( 2 ) . Discussion of Results S a l i n i t y . C o n c e n t r a t i o n p r o f i l e s f o r top and bottom s a l i n i t i e s and d i s s o l v e d oxygen c o n c e n t r a t i o n s a t f o u r s e l e c t e d s t a t i o n s a r e shown i n F i g u r e 2. S i m i l a r i t i e s i n s u r f a c e s a l i n i t y a r e a p p a r e n t , but the s u r f a c e d i s s o l v e d oxygen c o n c e n t r a t i o n s v a r i e d a p p r e c i a b l y . The maximum s u r f a c e s a l i n i t y a t a l l f o u r s t a t i o n s o c c u r r e d i n the e a r l y F a l l (September and O c t o b e r , 1982). The minimum s u r f a c e s a l i n i t y a t a l l s t a t i o n s was measured i n F e b r u a r y , 1983. S u r f a c e s a l i n i t y r e a d i n g s ranged from 1.3 p p t ( p a r t s per thousand) a t s t a t i o n s LP10 t o 9.0 p p t a t s t a t i o n LP07. Seasonal s i m i l a r i t i e s i n bottom s a l i n i t i e s between a l l s t a t i o n s were not a p p a r e n t . Bottom s a l i n i t i e s d i f f e r e d a p p r e c i a b l y i n both magnitude and the time a t which I n c r e a s e s began. S i g n i f i c a n t I n c r e a s e s i n bottom s a l i n i t i e s a t the s t a t i o n n e a r e s t t o the MRGO began between A p r i l and May, 1982. T h i s was f o l l o w e d by a marked s a l i n i t y i n c r e a s e a t s t a t i o n s 1.5 and 4.2 m i l e s o f f s h o r e between June and J u l y , 1982. The s t a t i o n 4.1 m i l e s o f f s h o r e i n J e f f e r s o n P a r i s h ( t h e most remote from the MRGO) d i d not e x h i b i t the abrupt bottom s a l i n i t y i n c r e a s e s t h a t were noted a t the o t h e r s t a t i o n s . Bottom s a l i n i t i e s o f 7 t o 9 ppt and up g e n e r a l l y r e s u l t e d i n s t r a t i f i c a t i o n w i t h s i g n i f i c a n t d e c r e a s e s i n bottom d i s s o l v e d oxygen concentrations·



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J u l y 28-29, 1982 Salinity D i s s o l v e d Oxygen

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Salinity

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D i s s o l v e d O x y g e n (mg/L) 3 4 5 6 7 8 9 10

1.5 m i O f f s h o r e O r l e a n s

F i g u r e 2. Top a n d b o t t o m s a l i n i t y a n d d i s s o l v e d o x y g e n p r o f i l e s a t two s t a t i o n s i n L a k e P o n t c h a r t r a i n o v e r a 12 month a n n u a l c y c l e .

Salinity

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D i s s o l v e d O x y g e n (mg/L) 3 4 5 6 7 8 9 10

4.1 m i O f f s h o r e J e f f e r s o n


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F i g u r e 2. Top a n d b o t t o m s a l i n i t y a n d d i s s o l v e d o x y g e n p r o f i l e s a t two s t a t i o n s i n L a k e P o n t c h a r t r a i n o v e r a 12 month a n n u a l c y c l e .



254


Data c o l l e c t e d a t 0.5 m above t h e Lake's bottom, from the 148 l a k e w i d e s t a t i o n s i n J u l y and August 1982, a r e p r e s e n t e d as i s o p l e t h s i n F i g u r e 3. H i g h e s t bottom s a l i n i t i e s i n Lake P o n t c h a r t r a i n , d u r i n g t h e two month sampling p e r i o d , o c c u r r e d a t and near t h e MRGO-Lake c o n n e c t i o n . Much lower s a l i n i t i e s were r e c o r d e d i n the n o r t h e r n s e c t i o n s of the Lake due t o f r e s h w a t e r i n p u t s from n o r t h s h o r e r i v e r s and p a s s e s . Bottom d i s s o l v e d oxygen c o n c e n t r a t i o n s taken i n J u l y were l o w e s t (1.0 ppm) i n t h e s o u t h c e n t r a l a r e a o f the l a k e and 3.0 ppm a l o n g the s o u t h shore and i n m i d - l a k e r e g i o n s . The lowest d i s s o l v e d oxygen r e a d i n g s r e c o r d e d i n August were found t o be c e n t r a l i z e d i n m i d - l a k e a r e a s . I n g e n e r a l , l o w DO r e a d i n g s c l o s e l y f o l l o w r e g i o n s o f s i g n i f i c a n t s t r a t i f i c a t i o n d u r i n g the summer months when m i x i n g of the s h a l l o w l a k e from weather f r o n t s was m i n i m i z e d . E x a m i n a t i o n o f the i s o h a l i n e s shown i n F i g u r e 3 c l e a r l y i n d i c a t e s t h a t the major source o f h i g h l y s a l i n e waters was the MRGO. S a l i n i t i e s a t the mouths o f two n a t u r a l p a s s e s , which a r e a l s o c o n t r i b u t o r s o f s a l t w a t e r i n t o Lake P o n t c h a r t r a i n , a r e not as h i g h as a t t h e mouth of the MRGO. The MRGO complex which p r o v i d e s a d i r e c t man-made c o n n e c t i o n f o r h i g h l y s a l i n e waters from t h e G u l f o f Mexico t o e n t e r Lake P o n t c h a r t r a i n , c o n t r i b u t e s s i g n i f i c a n t l y t o s t r a t i f i c a t i o n . On the o t h e r hand, the two n a t u r a l passes a l l o w i n f l o w o f waters c h a r a c t e r i z e d by s a l i n i t i e s t h a t a r e c l o s e r i n c o n c e n t r a t i o n t o those i n Lake P o n t c h a r t r a i n . Trace O r g a n i c s . High r e s o l u t i o n gas chromatograms from a n a l y s e s of the s a t u r a t e d hydrocarbon f r a c t i o n s of f o u r sediment samples c o l l e c t e d from the l a k e i n J a n u a r y 1983 a r e shown i n F i g u r e 4. The samples c o l l e c t e d o f f J e f f e r s o n P a r i s h c o n t a i n e d s a t u r a t e d h y d r o c a r b o n p r o f i l e s t y p i c a l o f t e r r e s t r i a l b i o g e n i c hydrocarbon i n p u t s (4_) · These i n p u t s a r e c h a r a c t e r i z e d by odd carbon number h y d r o c a r b o n s , i n t h e range of ja-C24 t o ja-C30, and have g r e a t e r abundances than t h e i r even carbon numbered homologs. The samples c o l l e c t e d o f f Orleans P a r i s h c o n t a i n e d l a r g e complex u n r e s o l v e d m i x t u r e s (CUM) which a r e i n d i c a t i v e of weathered p e t r o g e n i c h y d r o c a r b o n s . The source o f the e x t r e m e l y h i g h l e v e l s o f weathered p e t r o g e n i c hydrocarbons i n the nearshore J e f f e r s o n O r l e a n s P a r i s h sample i s u n c l e a r . However, the hydrocarbon l o a d s i n samples from t h i s s t a t i o n were not t y p i c a l o f those found a t any o f the o t h e r sampling s t a t i o n s i n Lake P o n t c h a r t r a i n . C o n s e q u e n t l y , these l e v e l s cannot be a t t r i b u t e d t o the normal t y p e s and l o a d s o f hydrocarbons found i n urban r u n o f f and p r o b a b l y r e s u l t e d from the s p i l l a g e of weathered p e t r o g e n i c hydrocarbons i n t o the d r a i n a g e c a n a l s i t u a t e d near t h i s sampling s t a t i o n . Because the l e v e l s o f p e t r o g e n i c hydrocarbon were so e l e v a t e d a t t h i s s t a t i o n , we have chosen t o c o n s i d e r a l l data from t h i s s t a t i o n as anomalous. C o n s e q u e n t l y , d a t a from t h i s s t a t i o n have been e x c l u d e d from f u r t h e r d i s c u s s i o n s o f the d i s t r i b u t i o n s and sources of o r g a n i c contaminants i n Lake Pontchartrain. F i g u r e s 5 t h r o u g h 7 show c o n c e n t r a t i o n s of s e v e r a l i m p o r t a n t c l a s s e s o f o r g a n i c compounds, as w e l l as s p e c i f i c o r g a n i c s as a f u n c t i o n o f d i s t a n c e o f f s h o r e and date of sample c o l l e c t i o n . The types o f compounds, which a r e r e p r e s e n t e d as s u b - c l a s s e s of the


OVERTON ET AL.



Isohalines (0.5 m off bottom)

DO Isopleths (0.5 m off bottom)

F i g u r e 3· I s o h a l i n e s and d i s s o l v e d oxygen i s o p l e t h s i n Lake P o n t c h a r t r a i n on c o n s e c u t i v e months i n the summer of 1982.



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F i g u r e 4. H i g h r e s o l u t i o n gas chromatograms o f the s a t u r a t e f r a c t i o n s from f o u r sediment samples c o l l e c t e d i n J a n u a r y 1983.

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t o t a l o r g a n i c s found i n mass s p e c t r a d a t a , are shown i n Table I and i n c l u d e : TIC ( t o t a l i d e n t i f i a b l e compounds; PPAH ( p a r e n t p o l y n u c l e a r a r o m a t i c h y d r o c a r b o n s ) ; TAAH ( t o t a l a l k y l a r o m a t i c h y d r o c a r b o n s ) ; C/N ( c h l o r d a n e and n o n a c h l o r ) ; PCB ( p o l y c h l o r i n a t e d b i p h e n y l s ) ; and DDT (sum of the DDT e n v i r o n m e n t a l d e g r a d a t i o n p r o d u c t s ) . T o t a l hydrocarbon c o n c e n t r a t i o n s (THC) were d e r i v e d from GC d a t a . The q u a n t i t i e s of these v a r i o u s substances g e n e r a l l y d e c r e a s e , i n a g e n e r a l e x p o n e n t i a l f a s h i o n , w i t h d i s t a n c e from the southern s h o r e l i n e , r e a c h i n g background l e v e l s at d i s t a n c e s of 3 t o 6 m i l e s o f f s h o r e . T h i s i s as expected s i n c e the m a j o r i t y of o r g a n i c substances found i n these samples have e x t r e m e l y low water s o l u b i l i t y (5)· C o n s e q u e n t l y , they are g e n e r a l l y t r a n s p o r t e d i n the marine environment as p a r t i c u l a t e matter ( 6 , 7 ) . There are s e v e r a l e x c e p t i o n s to t h i s g e n e r a l o b s e r v a t i o n . For example, p e r y l e n e c o n c e n t r a t i o n s showed no downward t r e n d w i t h d i s t a n c e from the shore. T h i s compound i s produced by both h i g h temperature combustion and n a t u r a l d i a g e n e t i c processes (8) · C o n s e q u e n t l y , i t i s not s u r p r i s i n g t h a t no s i g n i f i c a n t trends were observed r e l a t i n g p e r y l e n e c o n c e n t r a t i o n s w i t h d i s t a n c e from s h o r e . The most abundant c l a s s of o r g a n i c s found i n Lake P o n t c h a r t r a i n sediments was the u n s u b s t i t u t e d p o l y n u c l e a r a r o m a t i c hydrocarbon (PPAH). F i g u r e 8 shows the q u a n t i t i e s and r e l a t i v e d i s t r i b u t i o n s of n i n e d i f f e r e n t PAH compounds a t three d i f f e r e n t sampling s t a t i o n s . These s t a t i o n s were chosen to show the PAH d i s t r i b u t i o n s w i t h d i s t a n c e from the southern s h o r e l i n e . As a g e n e r a l r u l e , s i m i l a r d i s t r i b u t i o n s were noted at other sampling s i t e s as a f u n c t i o n of d i s t a n c e o f f s h o r e . O f f s h o r e PAH l e v e l s were c h a r a c t e r i z e d by e l e v a t e d c o n c e n t r a t i o n s of p e r y l e n e w h i l e n e a r - s h o r e samples c o n t a i n e d m o s t l y f o u r r i n g PAH compounds. Table I I shows the c o n c e n t r a t i o n s of s e l e c t e d t r a c e o r g a n i c s i n b i o t a samples examined d u r i n g t h i s study. In g e n e r a l , h i g h e s t c o n c e n t r a t i o n s were observed i n the s p r i n g . Chlorocarbon c o n c e n t r a t i o n s were comparable to o t h e r areas a l o n g the G u l f Coast and g e n e r a l l y lower than commonly encountered a l o n g the e a s t e r n seaboard ( 9 ) . Heavy M e t a l s . The c o n c e n t r a t i o n s of Barium, Lead and Cadmium, w i t h d i s t a n c e from the s h o r e l i n e , are shown i n F i g u r e 9. Lead c o n c e n t r a t i o n s g e n e r a l l y decreased w i t h d i s t a n c e from the s h o r e l i n e but t h e r e was c o n s i d e r a b l e v a r i a b i l i t y i n t h i s t r e n d . Lead i s t r a n s p o r t e d as p a r t i c u l a t e matter i n the marine environment (10, 1 1 ) . C o n s e q u e n t l y , lower but h i g h l y v a r i a b l e c o n c e n t r a t i o n s o f f s h o r e are to be expected. Other heavy metals s t u d i e d d i d not e x h i b i t any d e t e c t a b l e t r e n d w i t h d i s t a n c e from the s h o r e l i n e . Even the h i g h l y i n s o l u b l e heavy m e t a l , Ba, d i d not show s i g n i f i c a n t l y lower c o n c e n t r a t i o n s i n o f f s h o r e a r e a s . Conclusions F a c t o r s which are c u r r e n t l y a f f e c t i n g e n v i r o n m e n t a l q u a l i t y i n Lake P o n t c h a r t r a i n are g e n e r a l l y those r e l a t e d to urban development and urban p o l l u t i o n , a l t e r e d l a n d use p a t t e r n s , and h y d r o l o g i e m o d i f i c a t i o n w i t h i n the l a k e ' s w a t e r s h e d . Paramount



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F i g u r e 5. P l o t s showing the sediment c o n c e n t r a t i o n s o f a) t o t a l i d e n t i f i a b l e compounds and b) p a r e n t p o l y n u c l e a r a r o m a t i c hydrocarbons w i t h d i s t a n c e from the s o u t h e r n s h o r e l i n e o f Lake P o n t c h a r t r a i n . Sedimnet sample c o l l e c t i o n dates a r e : * A p r i l 1982; • J u l y 1982; Ο January 1983 and Δ October 1982.

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