5 Characterization of Particulate Organic Matter From Sediments in the Estuary of the Rhine and from Offshore Dump Sites of Dredging Spoils 1
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Jaap J. Boon , B. Brandt-de Boer , Wim Genuit , Jan Dallinga , and E. Turkstra 1
FOM-Institute for Atomic and Molecular Physics, Kruislaan 407, 1098SJAmsterdam, The Netherlands D. B. W. RIZA, P.O. Box 17, Lelystad, The Netherlands
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Screening of estuarine and marine sediment samples by automated pyrolysis mass spectrometry combined with factor-discriminant analysis leads to a useful classification related to the geographical position and the sources of the organic matter. The mass spectral data give preliminary information about the organic matter composition. Analysis of the characteristic mass peaks m/z=86 and 100 by PMSMS and PGCMS points to bacterial polyalkanoates in the mud fraction of the river sediments. These and other pyrolysis products show that sewage sludge with degraded lignocellulose material and bacterial biomass is an important source of particulate organic matter in river sediment of this heavily populated area in the Netherlands. Extensive sedimentation of particulate matter from fluvial and marine origin takes place in the estuary of the Rhine, particularly in the harbors along the New Waterway, downstream from Rotterdam. Yearly about 20 million m^ of this mud is dredged and dumped into the North Sea (1). As these sediments have trapped organic and inorganic pollutants such as Cr, Cu, Hg, Cd, Pb, Zn and Ni, a considerable pollutant load is imposed on the North Sea ecosystem either directly by the outflowing river water or indirectly by dredging and dumping (2). Detailed knowledge on the molecular level about the fate of the riverine particulate organic matter and its associated pollutant cocktail is still limited. The complex processes which occur in the mixing area between fluvial and marine water in the estuary, result in sediments with characteristics of aquatic and marine origin, mixed up or maybe even reacted with each other in some ways. When these sediments are dredged and dumped offshore, the sedimentary material is exposed to open sea conditions with increased chances of resuspension and resedimentation and consequently a new diagenetic regime for the organic matter. In order to study aspects of the fate of these sediments, we have studied sedimentary particulate matter from sites in the estuary of the Rhine downstream from Rotterdam, from several dredging spoil dumpsites offshore (Loswal Noord), and from sediments of the Flemish 0097-6156/ 86/ 0305-0076$06.00/ 0 © 1986 American Chemical Society
Sohn; Organic Marine Geochemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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Banks i n t h e Southern N o r t h Sea. The o r g a n i c c o m p o s i t i o n o f t h e mud f r a c t i o n from t h e s e sediments was i n v e s t i g a t e d by C u r i e - p o i n t p y r o l y s i s mass s p e c t r o m e t r i e t e c h n i q u e s , whereas m e t a l c o n t e n t , % o r g a n i c c a r b o n , carbon i s o t o p e s , c a r b o n a t e and mud c o n t e n t were determined s e p a r a t e l y on the same sediments. A l t h o u g h t h e a n a l y s i s of e s t u a r i n e p a r t i c u l a t e s f o r t h e l a t t e r c h a r a c t e r i s t i c s i s w i d e l y known, the use f u l n e s s o f p y r o l y s i s methods f o r t h e c h a r a c t e r i z a t i o n of the o r g a n i c m a t t e r f r a c t i o n s has been demonstrated o n l y r e c e n t l y . The f a t e of sewage sludge i n t h e B o s t o n h a r b o r was t r a c e d w i t h t h e r m a l d i s t i l l a t i o n - p y r o l y s i s GCMS ( 3 ) . C o l l o i d a l m a t t e r i n Chesapeake Bay was c h a r a c t e r i z e d by stepwise" p y r o l y s i s GCMS ( 4 ) . The f a t e o f o r g a n i c mate r i a l s and m e t a l s i n t h e r i v e r Rhine delïïâ and i n t h e I J s s e l m e e r was i n v e s t i g a t e d by C u r i e - p o i n t p y r o l y s i s mass s p e c t r o m e t r y and -GCMS ( 5 ) . P y r o l y s i s mass s p e c t r o m e t r y was used f o r the e v a l u a t i o n o f the o r g a n i c m a t t e r i n the e s t u a r i e s of the Ems (6) and G i r o n d e ( 7 ) . These s t u d i e s demonstrated a good c o r r e l a t i o n between PMS d a t a , c a r b o n i s o t o p e s and o t h e r v a r i a b l e s . The p y r o l y s i s methods a p p l i e d i n t h i s study a r e used as a t o o l f o r a g e n e r a l c h a r a c t e r i z a t i o n of the o r g a n i c m a t t e r from the s e d i ments. We d e s c r i b e here the r e s u l t s from s c r e e n i n g of e s t u a r i n e and open sea sediment samples by automated p y r o l y s i s low v o l t a g e mass s p e c t r o m e t r y combined w i t h f a c t o r - d i s c r i m i n a n t a n a l y s i s . C h a r a c t e r i s t i c mass peaks r e s u l t i n g from t h i s procedure were i n v e s t i g a t e d i n more d e t a i l by p y r o l y s i s - t a n d e m mass s p e c t r o m e t r y and p y r o l y s i s p h o t o i o n i z a t i o n GCMS. Experimental Sampling and Sample P r e p a r a t i o n . Samples were c o l l e c t e d by a team from the N e t h e r l a n d s I n s t i t u t e f o r Sea Research ( T e x e l ) and R i j k s w a t e r s t a a t ( t h e M i n i s t r y o f T r a n s p o r t and P u b l i c Works) by a b o x c o r e r ( N o r t h Sea s t a t i o n s ) and Van Veen grab (Rhine s t a t i o n s ) . F i g u r e 1 shows a map w i t h the sample l o c a t i o n s ( f o r d e t a i l s , see ( 8 ) ) . S e d i ment samples were t a k e n from t h e b o x c o r e r o r the grab and i m m e d i a t e l y a f t e r w a r d s resuspended i n f i l t e r e d (0.45 ym) sea o r r i v e r w a t e r ; the s u s p e n s i o n a f t e r s e t t l i n g o f the sand f r a c t i o n was passed over a 50 m i c r o n s i e v e t o a Whatman GFF f i l t e r w i t h a diameter o f 9 cm under g e n t l e s u c t i o n . A f t e r f i l t r a t i o n the f i l t e r e d p a r t i c u l a t e m a t t e r was washed w i t h d e s t i l l e d water t o remove sea s a l t s . The f i l t e r s w i t h t h e i r sediments were s t o r e d i n g l a s s p e t r i e d i s h e s and f r o z e n . Gene r a l l y f i v e b o x c o r e s (coded by l e t t e r ) were t a k e n i n one sampling a r e a (coded by number), whereas i n the Rhine e s t u a r y u s u a l l y t h r e e s e p a r a te samples were grabbed i n d i f f e r e n t p a r t s of the r i v e r bed. Samples from the N o r t h Sea were t a k e n between 22 and 24 November 1983. Sam p l e s i n the New Waterway (Rhine e s t u a r y ) were t a k e n on 2 F e b r u a r y 1984. Samples f o r p y r o l y s i s a n a l y s i s were t a k e n f r o m the f i l t e r s and resuspended i n water immediately b e f o r e a n a l y s i s . A l i q u o t s of these s u s p e n s i o n s (about 50 micrograms of dry m a t t e r ) were t r a n s f e r r e d t o the f e r r o m a g n e t i c sample w i r e s and d r i e d i n vacuo. Samples were ana l y z e d immediately afterwards i n q u a d r u p l i c a t e . P y r o l y s i s Mass Spectrometry and M u l t i v a r i a n t Data A n a l y s i s . The au tomated p y r o l y s i s mass s p e c t r o m e t e r and the m u l t i v a r i a n t d a t a a n a l y s i s by f a c t o r - d i s c r i m i n a n t a n a l y s i s ( f . d . a . ) procedure used have been
Sohn; Organic Marine Geochemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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F i g u r e 1. D i s c r i m i n a n t f u n c t i o n s c o r e map o f t h e p y r o l y s i s mass s p e c t r a of t h e sample s i t e s and t h e i r g e o g r a p h i c a l p o s i t i o n a l o n g the New Waterway (Rhine e s t u a r y ) and i n t h e N o r t h Sea. The numbers i n d i c a t e sampling a r e a s , t h e l e t t e r codes sample s i t e s w i t h i n an area.
Sohn; Organic Marine Geochemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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d e s c r i b e d r e c e n t l y ( 9 ) . The C u r i e - p o i n t temperature of the f e r r o m a g n e t i c sample w i r e s was 510°C.
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P y r o l y s i s Tandem Mass S p e c t r o m e t r y , D e t a i l s of the i n s t r u m e n t have been d e s c r i b e d ( 1 0 ) . P y r o l y s i s c o n d i t i o n s were s i m i l a r t o t h o s e used f o r the PMS i n s t r u m e n t . The p y r o l y s a t e was i o n i z e d a t 70 eV and i o n s of i n t e r e s t were s e l e c t e d i n the f i r s t magnetic s e c t o r ( r e s o l u t i o n 500). These i o n s were d i s s o c i a t e d by c o l l i s i o n w i t h h e l i u m atoms (pres sure 0.9 P a ) , a c c e l e r a t e d a t 15 kV and a n a l y z e d i n a second magnetic s e c t o r . Ions were d e t e c t e d by s i m u l t a n e o u s i o n d e t e c t i o n u s i n g c h a n n e l p l a t e s , a phosphor s c r e e n and a diode a r r a y camera. T o t a l a n a l y s i s time f o r each i o n i s 8 s. P y r o l y s i s P h o t o i o n i z a t i o n GCMS. D e t a i l s of the i n s t r u m e n t have been d e s c r i b e d e a r l i e r ( 1 1 ) . C u r i e p o i n t p y r o l y s i s was performed i n n i t r o gen which a l s o s e r v e d as the c a r r i e r gas. P y r o l y s i s o c c u r r e d d i r e c t l y i n f r o n t of the c a p i l l a r y column, which e x i t s i n t h e p h o t o i o n i z a t i o n chamber of the mass s p e c t r o m e t e r . A 50 m f u s e d s i l i c a column c o a t e d w i t h C P - S i l 5-CB (I.D.=0.32 mm, f i l m t h i c k n e s s : 1 micron) was used f o r the s e p a r a t i o n . The oven was programmed from 80-260 C a f t e r a p e r i o d at room temperature d u r i n g p y r o l y s i s of the sample. Argon I resonance photons (11.6 and 11.8 eV) were used f o r i o n i z a t i o n of the GC e f f l u e n t . I o n source temperature was 150°C, P r e s s u r e i n t h e i o n source was 10~2 T o r r and i n t h e vacuum chamber 10"^ T o r r . The quadrupole was scanned a t 1 scan/s over 30 t o 235 amu. R e s u l t s and D i s c u s s i o n Sampling P l a n and Sediment Workup. A number of c h o i c e s have been made i n d e s i g n o f the sampling program. Samples were t a k e n i n l a t e autumn and w i n t e r i n o r d e r t o m i n i m i z e c o n t r i b u t i o n s o f p h y t o p l a n k t o n to t h e bottom sediments. I t was not p o s s i b l e t o sample a l l m a t e r i a l s i n the same time frame. The open sea samples were t a k e n by b o x c o r i n g to m i n i m i z e l o s s o f s u r f a c e sediments d u r i n g s a m p l i n g . G e n e r a l l y the upper f i v e c e n t i m e t e r s were used f o r the i s o l a t i o n o f t h e f r a c t i o n s m a l l e r t h a n 50 m i c r o n s . Each sample a r e a i n F i g u r e 1 c o n s i s t e d of f i v e i n d i v i d u a l sample s i t e s which were s e p a r a t e d by s e v e r a l m i l e s . T h i s r e p l i c a t i o n was chosen f o r s t a t i s t i c a l reasons i n o r d e r t o e v a l u a t e the r e p r o d u c i b i l i t y i n the c o m p o s i t i o n of the o r g a n i c m a t t e r of the sediments i n one a r e a . Samples i n t h e r i v e r were t a k e n on t h e l e f t s i d e , on the r i g h t s i d e and i n the m i d d l e o f the b e d d i n g f o r t h e same r e a s o n s . The s e p a r a t i o n o f mud and sand was n e c e s s a r y f o r the p y r o l y s i s a n a l y s i s , which i s performed on suspended m a t t e r c o a t e d on a m e t a l w i r e o f 0.5 mm, and because sand p a r t i c l e s do not s t i c k t o t h e s e sample c a r r i e r s . As the samples a r e c o n t i n u o u s l y moved about i n the n a t u r a l environment, a r e s u s p e n s i o n procedure was thought t o be a minor d i s t u r b a n c e o f the o r i g i n a l sediment. The washing p r o c e d u r e , i n which d e s t i l l e d water i s passed o v e r the f i l t e r w i t h p a r t i c u l a t e mat t e r may however r e s u l t i n l o s s of s o l u b l e o r g a n i c m a t t e r t o g e t h e r w i t h t h e sea s a l t s . T h i s measure has been a p p l i e d i n the e a r l i e r p r o f i l l i n g s t u d i e s of e s t u a r i e s (6,7) w i t h PMS and no n e g a t i v e i n f l u e n c e on the r e s u l t s c o u l d be shown. The t e c h n i c a l advantage i s t h a t the HC1 v o l a t i l i z e d from sea s a l t s d u r i n g p y r o l y s i s a n a l y s i s i s m i n i mized and m a t r i x e f f e c t s on the o r g a n i c m a t t e r p y r o l y s i s p a t t e r n s
Sohn; Organic Marine Geochemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
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due t o t h e presence o f s a l t s i s a v o i d e d . I t i s c l e a r t h a t i f d i f f e r ences a r e found i n the c o m p o s i t i o n o f the samples d e s p i t e t h i s work up, t h e o r g a n i c m a t t e r c h a r a c t e r i s t i c s must be v e r y s t a b l e and s t r o n g l y connected t o the p a r t i c u l a t e m a t t e r f r a c t i o n . S c r e e n i n g by Automated P y r o l y s i s Mass S p e c t r o m e t r y . The t o t a l d a t a f i l e a f t e r a n a l y s i s o f a l l samples i n q u a d r u p l i c a t e c o n s i s t e d o f 172 p y r o l y s i s mass s p e c t r a . A l l samples were s i g n i f i c a n t l y d i f f e r e n t from a p r o c e d u r a l b l a n k . I n the t o t a l f i l e o n l y the mud f r a c t i o n from s t a t i o n 7A ( a l l r e p l i c a t e s ) was s t r o n g l y d i f f e r e n t i n p y r o l y s i s mass spectrum from a l l o t h e r s p e c t r a . The p y r o l y s i s spectrum o f 7A was v e r y s i m i l a r t o the spectrum o f c e l l u l o s e . The c e l l u l o s e i n t h i s s e diment may have o r i g i n a t e d from the o u t f a l l sewer o f The Hague c i t y , which e x i t s nearby. The carbon i s o t o p e δ o f -25.44% (8) p o i n t s to a nonmarine o r i g i n . A f t e r removal of t h e 7A a n a l y s e s from the d a t a f i l e , f a c t o r d i s c r i m i n a n t a n a l y s i s was performed a g a i n and a d i s c r i m i nant f u n c t i o n s c o r e map, as shown i n F i g u r e 1, was c a l c u l a t e d . The d i s t a n c e s between the samples i n t h i s map a r e a measure f o r the d i f f e rences i n composition. Discriminant f u n c t i o n s describe a combination of c h e m i c a l s u b s t a n c e s , e x p r e s s e d i n mass peaks, which a r e used f o r a n o p t i m a l d i f f e r e n t i a t i o n . The D-scores can be c o n s i d e r e d as the concen t r a t i o n o f these s u b s t a n c e s . P o s i t i v e and n e g a t i v e v a l u e s a r e o b t a i n ed, because c o n c e n t r a t i o n i s e x p r e s s e d r e l a t i v e t o the average concen t r a t i o n i n a l l samples. About 50% and 15% o f t h e c h a r a c t e r i s t i c v a r i a n ce i n the d a t a f i l e was e x p l a i n e d i n the f i r s t and second d i s c r i m i n a n t f u n c t i o n s r e s p e c t i v e l y . Instrument r e p l i c a t e s g e n e r a l l y f a l l i n t h e c e n t r o i d ( t h e s t a t i o n number) on the map. I f we c o n s i d e r o n l y the f i r s t D - f u n c t i o n , a s t r i k i n g s e p a r a t i o n between most samples from the r i v e r and the marine s t a t i o n s becomes e v i d e n t . Samples 20A, Β and ^ c o l l e c t e d h i g h e s t upstream near R o t t e r dam, were found t o have the h i g h e s t p o s i t i v e Dj s c o r e s , b u t a l l s t a t i o n s a t 19, 18 and two o f the t h r e e s t a t i o n s a t 17 have p o s i t i v e D-j s c o r e s . Most o f t h e s t a t i o n s from 16 a t the mouth o f the New Wa terway near Hoek o f H o l l a n d and a l l open sea s t a t i o n s have n e g a t i v e D^ v a l u e s . The s t a t i o n s w i t h n e g a t i v e D
