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Distribution of zinc, lead, cadmium and copper between different size fractions of sediments II. The Krka River Estuary and the Kornati Islands (Central Adriatic Sea)
217
The Science of the Total Environment, 95 (1990) 217-225 Elsevier
DISTRIBUTION
OF ZINC, LEAD,
CADMIUM
AND COPPER
BETWEEN DIFFERENT SIZE FRACTIONS OF SEDIMENTS I I . THE K R K A R I V E R E S T U A R Y A N D T H E K O R N A T I I S L A N D S (CENTRAL
ADRIATIC
SEA)
D. MARTIN~IC 1, ~. KWOKAL~ and M. BRANICA1'2 1Center for Marine Research Zagreb, "Rudjer Bogkovid" Institute, POB 1016, 41000 Zagreb, Croatia (Yugoslavia) 21nstitute of Applied Physical Chemistry, Research Center (KFA), POB 1913, D-5170 Ji~lich (F.R.G.)
(Received October 24th, 1989; accepted November 12th, 1989)
ABSTRACT The levels of zinc, cadmium, lead and copper in different grain-size fractions of recent sediments, collected from the Krka River Estuary and the Kornati Islands during October 1983, were determined. The distributional patterns of these metals mainly depended on the textural characteristics of the sediment. The clay]silt size particles contained the highest amounts of zinc, cadmium and lead. Copper exhibited an irregular particle size distribution. In general, the contents of copper in different grain-size fractions and their distribution throughout the area seemed to be influenced by biological activities. In the coastal region, the concentrations of cadmium in the coarse particles ( > 63 #m) appeared to coincide with the quantities of carbonate present in the sediments. A significant enrichment of lead was observed in the lower part of the Krka River Estuary and in coastal regions with intensive ship traffic. Sediment collected near an industrial waste outflow was found to be enriched with zinc, lead and copper of anthropogenic origin.
INTRODUCTION Multidisciplinary investigations of various compartments of the Krka River Estuary and the Kornati Islands with respect to trace metals have been carried o u t s i n c e 1983. S i n c e t h e e s t u a r y is s u b j e c t t o v a r i o u s h u m a n a c t i v i t i e s , t h e determination of the concentrations of trace metals in the sediments helps in a s s e s s i n g t h e e x t e n t t o w h i c h t h e a r e a is p o l l u t e d b y a n t h r o p o g e n i c s o u r c e s . I t should be noted that interpretation of the sediment metal levels based on g r a n u l o m e t r i c c h a r a c t e r i s t i c s a l o n e is s o m e t i m e s i n a d e q u a t e , e s p e c i a l l y i f mineralogical and chemical features are not taken into consideration. In some c a s e s , t h e s e p a r a t i o n o f a d i s t i n c t r a n g e o f g r a i n - s i z e p a r t i c l e s (e.g. c l a y / s i l t f r a c t i o n , < 63 # m ) p r i o r t o e x a m i n a t i o n o f t h e m e t a l d i s t r i b u t i o n s w i t h i n a l l ranges of grain-size, may lead to inaccurate results. For example, MartinSid et al. (1990) h a v e s t u d i e d t h e a s s o c i a t i o n o f m e t a l s w i t h i n d i f f e r e n t g r a i n f r a c t i o n s in sediments of the Limski Kanal, and found that the metals were not primarily
0048-9697/90/$03.50
© 1990 Elsevier Science Publishers B.V.
218 bound to the finest particles. This was attributed to the amount of organic material present in the sediment fractions. The objectives of this work, as part of investigations undertaken in 1983, were: (i) to classify recent sediments from the Krka River Estuary and the Kornati Islands on the basis of grain size; (ii) to determine the levels of metals (Zn, Cd, Pb, Cu) in the size fractions at each sampling site; and (iii) to interpret and compare the data obtained with the mineralogical and chemical composition of the sediments determined by JuraSi6 et al. (1984), Had~ija et al. (1985) and Prohi6 and Jura~i6 (1989). MATERIALS AND METHODS Sampling area
The Krka River Estuary and the Kornati Islands are situated in the eastern Central Adriatic Sea (Fig. 1). The Krka River Estuary forms part of the Outer Dinaric Karst region and is restricted to part of an ancient river valley between the last active tufa barrier (the Skradinski Buk waterfalls) through Prokljan Lake to the ~ibenik Channel for a total length of 22 km. The estuary gradually deepens from 2 m below the waterfalls, to 42 m in ~ibenik Bay. The mineralogical composition of the sediments in the Krka River Estuary indicated sedimentation of terrigenous material in the upper part of the estuary (an enlarged Prokljan basin), whereas more autigenous carbonate
15°30"
15%5"
" . . ~z.~. " ~ 2 "*,,~ ",
i
i
i
i
~
~
16'00"
"1
~
.
N..~.~
Se
J
a
Fig. 1. Sampling sites in the Krka River Estuary and the Kornati Islands.
\+~.",ms+b,,,',+k
l
219
sedimentation has been found in the lower part of the estuary (Prohi5 and JuraSiS, 1989). Carbon-14 dating of recent carbonates from the 30 cm core, from the central part of the Prokljan basin, gave a sedimentation rate of only 0.06 mm year-1. Therefore, even lower sedimentation rates can be expected in the lower part of the estuary. In addition to small towns such as Skradin and Zaton, and villages situated around the upper part of the estuary, the city of ~ibenik (40000 inhabitants), situated in the lower part of the estuary, with its shipping, metal industry and tourism, represents a serious danger to aquatic life by directly discharging wastes into the estuary. The Kornati Islands, situated 15 km from the shore, and not directly subject to human activities, were chosen as a reference area.
Samples and sample pretreatment In October 1983, sediment samples were collected by divers from various sites in the Krka River Estuary (denoted E-1 to E-5), a coastal area (denoted C-1 to C-3) and the Kornati Islands (denoted R-1 and R-2) (Fig. 1). The diver used a simple acrylic glass tube (20 cm long and 6 cm internal diameter). The tube was inserted into the sediment for its total length and plugged with a polyethylene stopper. The sediment samples were immediately protected against contamination by placing them in polyethylene bags and freezing until analysis. Large calcareous debris and rock fragments were removed with stainless steel forceps prior to sieving. The top 0-5 cm of the sediment was fractionated using sieves of different pore sizes (monofilament polyester meshes, Nyb011 Swiss Silk Boating Cloth MFG Co. Ltd, Ziirich). The following sediment fractions were obtained: < 63; 150300; 300-150; 1000-300, and > 1000#m. A wet sieving technique was applied using bottom water taken just above the sediments at each sampling site. Prior to sieving, the meshes were thoroughly cleaned by three successive acid treatments (diluted Suprapure HC1, 10%). They were soaked in hydrochloric acid for 3 weeks. The air-dried (under "clean bench" conditions) sediment fractions ( ~ 0.5 g) were decomposed by a mixture of perchloric (1 ml) and nitric acids (10 ml) in combination with hydrofluoric acid (5-10 ml), in a closed Teflon crucible (35 ml volume) at a temperature of ,-~ 180°C.
Trace metal determination Electrothermal atomic absorption spectrometry was used for Cd, Pb, and Cu determination. The instrumentation used was a Perkin-Elmer atomic absorption spectrophotometer, Model 3030, with a HGA-400, graphite furnace and an AS-1 autosampler system. Zinc was determined by a flame atomic absorption technique using a Perkin-Elmer Model 5000 equipped with an AS-50 autosampler.
220 TABLE 1 A v e r a g e c o n c e n t r a t i o n s of Zn, Cd, Pb and Cu ~ g g - ~ dry sediment) in different sediment size fractions w i t h the p e r c e n t a g e of the grain-size c o n t r i b u t i o n to the total sediment from the K r k a River E s t u a r y and the K o r n a t i I s l a n d s collected in October 1983. The s t a n d a r d deviation of three a n a l y s e s is b e t w e e n 3 and 10% Location
Fraction
%
Zn
Cd
E-1
> 1000 1000-300 300-150 150- 63 < 63
94.0 1.1 0.8 2.0 2.5
18.7 24.1 27.3 117.2 145.7
0.41 0.40 0.35 0.33 0.40
5.0 3.2 3.7 6.9 10.1
23.6 21.8 11.8 17.2 28.1
E-2
> 1000 1000-300 300-150 150- 75 < 63
2.8 2.9 0.4 5.8 89.0
6.2 40.2
0.10 0.17
12.0 28.8
2.5 9.6
> 1000 1000-300 300-150 150- 63 < 63
3.5 0.3 0.5 5.2 91.3
102.8
0.39
33.2
20.9
89.9
0.54
30.5
22.7
E-3
E-4
< 63
Pb
Cu
C-1
> 1000 1000-300 300-150 150- 63 < 63
70.6 14.4 10.2 4.3 0.5
5.5 6.4 8.0 9.0 42.5
0.08 0.12 0.11 0.10 0.97
4.8 8.1 14.2 20.7 34.6
3.5 3.7 6.1 6.2 14.9
C-2
> 1000 1000-300 300-150 150- 63 < 63
56.0 9.1 11.3 20.2 3.7
3.2 4.0 6.6 6.2 53.5
0.04 0.03 0.05 0.05 0.27
13.1 6.6 7.5 8.4 38.1
1.7 10.5 0.8 2.0 16.2
R-1
> 1000 1000-300 300-150 150- 63 < 63
65.0 10.0 15.0 9.0 0.8
4.0 5.2 3.7 4.6 23.0
0.14 0.21 0.18 0.21 0.47
3.2 4.0 4.6 4.4 12.4
12.3 14.2 8.5 9.7 13.7
R-2
> 1000 1000-300 300-150 150- 63 < 63
67.0 9.4 8.3 8.7 6.4
5.4 4.8 7.1 9.7 30.5
0.12 0.06 0.09 0.08 0.43
3.0 2.8 4.6 6.0 12.4
9.2 19.0 15.8 18.9 13.7
C-3 a
> 1000 1000-300 300-150 150- 63 < 63
70.0 12.0 11.0 5.4 2.1
21.0 19.0 33.1 60.7 154.9
0.11 0.12 0.11 0.14 0.37
11.7 8.9 15.4 21.8 101.4
2.9 3.9 7.5 25.8 68.2
a S i t u a t e d at i n d u s t r i a l w a s t e outflow.
221 lOO
£'2
E-2
C-I
R-I
I~-2
oZn E] Pb &Cu • Cd
oi;=
~
0 o~- . . . . . . fraction(~3 {B)3~0-150 (D) >IOOD A {El {A) 150-63 (C) ~
. B
C
D
B
C
D
E
A
B
C
D
E
B
C
D
E
B
C
D
Fig. 2. Distribution ofZn, Pb, Cd and Cu within different grain fractions of sediments from the Krka River Estuary and the Kornati Islands.
The reagents used for the cleaning and digestion of sediment material were of ultrapure quality (Suprapur, Merck). RESULTS AND DISCUSSION
The levels of Zn, Cd, Pb and Cu (mean values with appropriate standard deviations) in different grain-size fractions, together with the granulometric values, are summarized in Table 1 and illustrated in Fig. 2.
Size distribution analysis At the mouth of the Krka River Estuary, a number of travertine (tufa) barriers have formed, resulting in the presence of freshwater lakes. This restricts the input of coarser suspended material (> 63 to 1000 pm) to the estuary. Indeed, in the estuarine region of the Krka River (E-l) (Fig. 1) near the waterfalls, the top sediments were mainly composed of grains > 1000 #m (94%) (see Table 1). The clay/silt particle fraction (< 63#m) contributed only 3% to the whole sediment core. This implies that the main watercourse entering the estuary carries very little fine-grained suspended material which could settle in this region. These results were later confirmed by JuraSi6 et al. (1984), who concluded that the main watercourse entering the estuary was almost free of suspended matter. The granulometric distribution of sediments collected at Stations E-2 (Skradin) and E-3 (the lower part of Prokljan Lake) (see Fig. 1) differed signifi-
222 cantly from those at Station E-1. The sediments were composed of clay/silt sized particles ( ~ 90%), whereas the contribution of the coarser grains was almost negligible. The main source of suspended matter appears to be GuduSa Creek, which enters directly into Prokljan Lake and governs the grain size distribution of sediments collected at Station E-3. JuraSi~ et al. (1984) observed that suspended material carried by GuduSa Creek settled in Prokljan Lake. The contribution of the coarser particles to the sediments gradually increased from Prokljan Lake seawards (see Table 1 and Fig. 2). Small-sized particles (< 63#m) in sediments from the coastal regions (C-1 and C-2) and the Kornati Islands (R-1 and R-2) were present in very low amounts (0.5-5% wt/wt). Metal concentration
In general, the clay/silt fraction (< 63 pm) at all sampling sites contained larger amounts of zinc, cadmium and lead than the other size fractions. Zinc The zinc content of the clay/silt particles decreased from Station E-1 (147 ~g Zn g-1 dry sediment) seawards, reaching a value of ~ 30 #g Zn g- 1 at the Kornati Islands stations. The same feature was observed for zinc by JuraSi5 et al. (1984). An anomalously high zinc concentration ( l l 7 p g g -1) was obtained in the 150~3#m fraction of the sediment at Station E-1. The larger grain-size fractions also exhibited a tendency to accumulate relatively high amounts of zinc, showing a three-fold enrichment as compared with the same size fractions from other sampling sites. The mineralogical and chemical composition of sediments at Station E-1 obtained by Had~ija et al. (1985) reflected the petrographic composition of the drainage area. Carbonates are the prevailing minerals, with calcite predominating (77% wt/wt of the total sediment). Jura~id et al. (1984) observed that zinc was mainly present in the residual and carbonate fractions of sediment from this area. These findings appear to be contradictory because calcium carbonate, being dominant in the coarse grain-size fraction, is usually classified as a relative diluter of trace metals. However, it seems that organic material may play an important role as a mediating factor in determining the concentration of zinc at this site. Indeed, Had~ija et al. (1985) found relatively high quantities of organic material (10% wt/wt) in sediments from the same area, while it gradually decreased seawards. Similar sized grains in sediments from Limski Kanal, situated in the northern part of the west coast of the Istrian peninsula (North Adriatic Sea), contained elevated concentrations of all metals studied, particularly zinc (Martin~id et al., 1990). This observation is relevant to the amount of organic material present in the sediment. Zinc was almost uniformly distributed between the larger grain size fraction (> 63 ttm)
223 at all other sites (with the exception of C-3: industrial waste outflow) (Fig. 2 and Table 1), indicating limited enrichment through anthropogenic sources.
Cadmium In general, the concentrations of cadmium showed the same distribution pattern for all size fractions (with the exception of E-l). A uniform concentration of cadmium in all grain size classes was observed at E-l, a feature which is difficult to explain due to lack of mineralogical and chemical analyses of the fractions studied. The highest cadmium content (0.17-0.47 #g g-l) was found in the clay/silt size fraction at all sites. Comparing the concentration of metal in size fractions between all sampling sites, it is evident that the sediments from the coastal area (C-1 and C-2), particularly R-1 and R-2 (the Kornati Islands), tend to accumulate higher quantities of cadmium than sediments from estuarine regions (Table 1, Fig. 2). Donazzolo et al. (1984) suggested that cadmium concentrations in sediments from the North Adriatic coast (area extending from the Isonzo to the Piave River mouths) increase with increasing percentage of carbonates. In fact, the carbonate content of recent sediments from the Krka River Estuary and the coastal area varied from 55% (Prokljan basin) to 92% (near Zlarin, off the estuary) (Prohid and Jura6iG 1989). Hence, one can speculate that increased concentrations of cadmium in sediments from the coastal area coincide with the percentage of carbonate fraction. As in the case of zinc, sediment fractions containing particles > 63 tLm were capable of binding cadmium in the same quantities at each sampling site. The average cadmium levels in these fractions, however, differed significantly from one site to another. Among all coastal sampling sites, the coarser sediment fractions ( > 63-100 #m) from the Kornati Islands (R-l) contained two- or threefold higher cadmium concentrations than those at sites R-2, C-1 and C-2 (Table 1). Lead The lowest concentrations of lead were obtained in sediment from site E-1 and the Kornati Islands (R-1 and R-2), while a significant enrichment of lead was observed in sediments from locations on the main shipping routes (E-2, E-3, E-4, C-1 and C-2) (see Table 1 and Fig. 2). This was particularly conspicuous in sediments collected at site C-l, where the concentrations of lead increased proportionally with decreasing particle size. Copper In general, copper exhibited an irregular particle size distribution (Table 1, Fig. 2). High concentrations of copper were associated with the 300-1000 pm fraction and probabiy originated from varying contributions of biogenic calcareous debris or other biological components (plankton, microorganisms, fecal pellets, etc.). It seems likely that the overall biological activity at the sampling sites may partly determine the partitioning of copper within the ~ediment fractions and in the whole sediment. Indeed, the sediments collected
224 at the Kornati Islands had a higher proportion of shell debris (and higher copper concentrations) than sediments from other regions. This is in satisfactory agreement with the observations of JuraSi5 et al. (1984) and Had~ija et al. (1985) that the ratio of 20:1 between calcite and aragonite decreased in the seaward direction to 5:1, indicating increased influence of biogenic components towards the open sea. Similar to zinc and cadmium, the highest concentrations of copper were found in sediments from site E-1 (with the exception of site C-3 situated in the vicinity of an industrial outflow).
Metal content of the polluted sediment Sampling station C-3 required special attention because the sediments in this region were loaded with waste materials discharged from industrial activities. The grain-size distribution of recent sediments at site C-3 was typical for coastal deposits (Table 1). The clay/silt grains were particularly enriched in lead and copper. Three/fold higher concentrations of these metals were obtained compared with the same sediment particles at other coastal sites. No significant enrichment of lead and copper in the coarser particles was observed. On the contrary, particles > 63 gm contained elevated concentrations of zinc, similar to those found in sediment at site E-1. The cadmium content decreased in the concentration range obtained at all other sites, indicating that the sediment at site C-3 was not influenced by cadmium discharged by industrial plants. CONCLUSIONS The clay/silt particle-size grains ( < 63 #m) were restricted to the upper part of the Krka River Estuary (Skradin and the lower part of Prokljan Lake), gradually decreasing in the seaward direction, reaching 1 ~ % of the total sediment in coastal areas. The coarser particles were predominant in the lower part of the Krka River Estuary and the Kornati Islands. Zinc, cadmium and lead were, in general, concentrated in the clay/silt size fractions, while copper showed an irregular particle size distribution. Enrichment by anthropogenic lead was observed in the lower part of the Krka River Estuary and coastal regions with intensive shipping traffic. The cadmium content of the coarser particles increased in the seaward direction as the carbonate component of the sediments increased. It seems that copper associated with all fractions strongly depended on the overall biological activity at the sampling sites. Anthropogenic sources influenced the metal concentrations in sediments collected near industrial waste outflows. ACKNOWLEDGEMENTS This study forms part of the joint project "Environmental Research in
225 A q u a t i c S y s t e m s " of the I n s t i t u t e of Applied P h y s i c a l Chemistry, R e s e a r c h C e n t r e (KFA), Jfilich, and the C e n t r e for M a r i n e R e s e a r c h Zagreb, " R u d j e r Bo§kovi~" I n s t i t u t e , Zagreb F i n a n c i a l s u p p o r t from the I n t e r n a t i o n a l B u r e a u of K F A , Jfilich, w i t h i n the f r a m e w o r k of the bilateral a g r e e m e n t b e t w e e n the F e d e r a l Republic of G e r m a n y and Y u g o s l a v i a is g r a t e f u l l y a c k n o w l e d g e d . This s t u d y was p a r t i a l l y s u p p o r t e d by the U.S. N a t i o n a l Science F o u n d a t i o n and Self M a n a g e m e n t C o m m u n i t y for Scientific R e s e a r c h of SR Croatia, t h r o u g h funds made available to the U . S . - Y u g o s l a v J o i n t B o a r d on Scientific and T e c h n i c a l C o o p e r a t i o n u n d e r P r o j e c t J F P 679-NSF. We are grateful to Prof. D r E.D. Goldberg for his i n v a l u a b l e criticism of the manuscript. REFERENCES Donazzolo, R., O. Hieke-Marlin, L. Menegazzo-Vitturi and B. Pavoni, 1984. Heavy metal content and lithological properties of recent sediments in the Northern Adriatic. Mar. Pollut. Bull., 15: 93-101. Had~ija, O., M. Jura~id, M. Luic, M. Tonkovic and B. Jeri~evid, 1985. The carbohydrates in relation to mineralogic and granulometric composition of surface sediments in the karst estuary (River Krka Estuary, Yugoslavia). Estuarine, Coastal Shelf Sci., 21: 701-709. Jura~id, M., E. Prohid and V. Pravdid, 1984. Sediment surface properties and adsorption of heavy metals in a typical karst estuary. ICSEM (IOC) Workshop on Marine Pollution of the Mediterranean, Lucerne, 11-13 October 1984. Martin~id, D., ~. Kwokal and M. Branica, 1990. Distribution of zinc, lead, cadmium and copper between different size fractions of sediments. I. The Limski Kanal (North Adriatic Sea). Sci. Total Environ., 95 (1990) 201-216. Prohid, E. and M. Jura~id, 1989. Heavy metals in sediments - - Problems concerning determination of the anthropogenic influence. Study in the Krka River Estuary, Eastern Adriatic coast, Yugoslavia. Environ. Geol. Water Sci., 13: 145-151.
The Science of the Total Environment, 95 (1990) 217-225 Elsevier
DISTRIBUTION
OF ZINC, LEAD,
CADMIUM
AND COPPER
BETWEEN DIFFERENT SIZE FRACTIONS OF SEDIMENTS I I . THE K R K A R I V E R E S T U A R Y A N D T H E K O R N A T I I S L A N D S (CENTRAL
ADRIATIC
SEA)
D. MARTIN~IC 1, ~. KWOKAL~ and M. BRANICA1'2 1Center for Marine Research Zagreb, "Rudjer Bogkovid" Institute, POB 1016, 41000 Zagreb, Croatia (Yugoslavia) 21nstitute of Applied Physical Chemistry, Research Center (KFA), POB 1913, D-5170 Ji~lich (F.R.G.)
(Received October 24th, 1989; accepted November 12th, 1989)
ABSTRACT The levels of zinc, cadmium, lead and copper in different grain-size fractions of recent sediments, collected from the Krka River Estuary and the Kornati Islands during October 1983, were determined. The distributional patterns of these metals mainly depended on the textural characteristics of the sediment. The clay]silt size particles contained the highest amounts of zinc, cadmium and lead. Copper exhibited an irregular particle size distribution. In general, the contents of copper in different grain-size fractions and their distribution throughout the area seemed to be influenced by biological activities. In the coastal region, the concentrations of cadmium in the coarse particles ( > 63 #m) appeared to coincide with the quantities of carbonate present in the sediments. A significant enrichment of lead was observed in the lower part of the Krka River Estuary and in coastal regions with intensive ship traffic. Sediment collected near an industrial waste outflow was found to be enriched with zinc, lead and copper of anthropogenic origin.
INTRODUCTION Multidisciplinary investigations of various compartments of the Krka River Estuary and the Kornati Islands with respect to trace metals have been carried o u t s i n c e 1983. S i n c e t h e e s t u a r y is s u b j e c t t o v a r i o u s h u m a n a c t i v i t i e s , t h e determination of the concentrations of trace metals in the sediments helps in a s s e s s i n g t h e e x t e n t t o w h i c h t h e a r e a is p o l l u t e d b y a n t h r o p o g e n i c s o u r c e s . I t should be noted that interpretation of the sediment metal levels based on g r a n u l o m e t r i c c h a r a c t e r i s t i c s a l o n e is s o m e t i m e s i n a d e q u a t e , e s p e c i a l l y i f mineralogical and chemical features are not taken into consideration. In some c a s e s , t h e s e p a r a t i o n o f a d i s t i n c t r a n g e o f g r a i n - s i z e p a r t i c l e s (e.g. c l a y / s i l t f r a c t i o n , < 63 # m ) p r i o r t o e x a m i n a t i o n o f t h e m e t a l d i s t r i b u t i o n s w i t h i n a l l ranges of grain-size, may lead to inaccurate results. For example, MartinSid et al. (1990) h a v e s t u d i e d t h e a s s o c i a t i o n o f m e t a l s w i t h i n d i f f e r e n t g r a i n f r a c t i o n s in sediments of the Limski Kanal, and found that the metals were not primarily
0048-9697/90/$03.50
© 1990 Elsevier Science Publishers B.V.
218 bound to the finest particles. This was attributed to the amount of organic material present in the sediment fractions. The objectives of this work, as part of investigations undertaken in 1983, were: (i) to classify recent sediments from the Krka River Estuary and the Kornati Islands on the basis of grain size; (ii) to determine the levels of metals (Zn, Cd, Pb, Cu) in the size fractions at each sampling site; and (iii) to interpret and compare the data obtained with the mineralogical and chemical composition of the sediments determined by JuraSi6 et al. (1984), Had~ija et al. (1985) and Prohi6 and Jura~i6 (1989). MATERIALS AND METHODS Sampling area
The Krka River Estuary and the Kornati Islands are situated in the eastern Central Adriatic Sea (Fig. 1). The Krka River Estuary forms part of the Outer Dinaric Karst region and is restricted to part of an ancient river valley between the last active tufa barrier (the Skradinski Buk waterfalls) through Prokljan Lake to the ~ibenik Channel for a total length of 22 km. The estuary gradually deepens from 2 m below the waterfalls, to 42 m in ~ibenik Bay. The mineralogical composition of the sediments in the Krka River Estuary indicated sedimentation of terrigenous material in the upper part of the estuary (an enlarged Prokljan basin), whereas more autigenous carbonate
15°30"
15%5"
" . . ~z.~. " ~ 2 "*,,~ ",
i
i
i
i
~
~
16'00"
"1
~
.
N..~.~
Se
J
a
Fig. 1. Sampling sites in the Krka River Estuary and the Kornati Islands.
\+~.",ms+b,,,',+k
l
219
sedimentation has been found in the lower part of the estuary (Prohi5 and JuraSiS, 1989). Carbon-14 dating of recent carbonates from the 30 cm core, from the central part of the Prokljan basin, gave a sedimentation rate of only 0.06 mm year-1. Therefore, even lower sedimentation rates can be expected in the lower part of the estuary. In addition to small towns such as Skradin and Zaton, and villages situated around the upper part of the estuary, the city of ~ibenik (40000 inhabitants), situated in the lower part of the estuary, with its shipping, metal industry and tourism, represents a serious danger to aquatic life by directly discharging wastes into the estuary. The Kornati Islands, situated 15 km from the shore, and not directly subject to human activities, were chosen as a reference area.
Samples and sample pretreatment In October 1983, sediment samples were collected by divers from various sites in the Krka River Estuary (denoted E-1 to E-5), a coastal area (denoted C-1 to C-3) and the Kornati Islands (denoted R-1 and R-2) (Fig. 1). The diver used a simple acrylic glass tube (20 cm long and 6 cm internal diameter). The tube was inserted into the sediment for its total length and plugged with a polyethylene stopper. The sediment samples were immediately protected against contamination by placing them in polyethylene bags and freezing until analysis. Large calcareous debris and rock fragments were removed with stainless steel forceps prior to sieving. The top 0-5 cm of the sediment was fractionated using sieves of different pore sizes (monofilament polyester meshes, Nyb011 Swiss Silk Boating Cloth MFG Co. Ltd, Ziirich). The following sediment fractions were obtained: < 63; 150300; 300-150; 1000-300, and > 1000#m. A wet sieving technique was applied using bottom water taken just above the sediments at each sampling site. Prior to sieving, the meshes were thoroughly cleaned by three successive acid treatments (diluted Suprapure HC1, 10%). They were soaked in hydrochloric acid for 3 weeks. The air-dried (under "clean bench" conditions) sediment fractions ( ~ 0.5 g) were decomposed by a mixture of perchloric (1 ml) and nitric acids (10 ml) in combination with hydrofluoric acid (5-10 ml), in a closed Teflon crucible (35 ml volume) at a temperature of ,-~ 180°C.
Trace metal determination Electrothermal atomic absorption spectrometry was used for Cd, Pb, and Cu determination. The instrumentation used was a Perkin-Elmer atomic absorption spectrophotometer, Model 3030, with a HGA-400, graphite furnace and an AS-1 autosampler system. Zinc was determined by a flame atomic absorption technique using a Perkin-Elmer Model 5000 equipped with an AS-50 autosampler.
220 TABLE 1 A v e r a g e c o n c e n t r a t i o n s of Zn, Cd, Pb and Cu ~ g g - ~ dry sediment) in different sediment size fractions w i t h the p e r c e n t a g e of the grain-size c o n t r i b u t i o n to the total sediment from the K r k a River E s t u a r y and the K o r n a t i I s l a n d s collected in October 1983. The s t a n d a r d deviation of three a n a l y s e s is b e t w e e n 3 and 10% Location
Fraction
%
Zn
Cd
E-1
> 1000 1000-300 300-150 150- 63 < 63
94.0 1.1 0.8 2.0 2.5
18.7 24.1 27.3 117.2 145.7
0.41 0.40 0.35 0.33 0.40
5.0 3.2 3.7 6.9 10.1
23.6 21.8 11.8 17.2 28.1
E-2
> 1000 1000-300 300-150 150- 75 < 63
2.8 2.9 0.4 5.8 89.0
6.2 40.2
0.10 0.17
12.0 28.8
2.5 9.6
> 1000 1000-300 300-150 150- 63 < 63
3.5 0.3 0.5 5.2 91.3
102.8
0.39
33.2
20.9
89.9
0.54
30.5
22.7
E-3
E-4
< 63
Pb
Cu
C-1
> 1000 1000-300 300-150 150- 63 < 63
70.6 14.4 10.2 4.3 0.5
5.5 6.4 8.0 9.0 42.5
0.08 0.12 0.11 0.10 0.97
4.8 8.1 14.2 20.7 34.6
3.5 3.7 6.1 6.2 14.9
C-2
> 1000 1000-300 300-150 150- 63 < 63
56.0 9.1 11.3 20.2 3.7
3.2 4.0 6.6 6.2 53.5
0.04 0.03 0.05 0.05 0.27
13.1 6.6 7.5 8.4 38.1
1.7 10.5 0.8 2.0 16.2
R-1
> 1000 1000-300 300-150 150- 63 < 63
65.0 10.0 15.0 9.0 0.8
4.0 5.2 3.7 4.6 23.0
0.14 0.21 0.18 0.21 0.47
3.2 4.0 4.6 4.4 12.4
12.3 14.2 8.5 9.7 13.7
R-2
> 1000 1000-300 300-150 150- 63 < 63
67.0 9.4 8.3 8.7 6.4
5.4 4.8 7.1 9.7 30.5
0.12 0.06 0.09 0.08 0.43
3.0 2.8 4.6 6.0 12.4
9.2 19.0 15.8 18.9 13.7
C-3 a
> 1000 1000-300 300-150 150- 63 < 63
70.0 12.0 11.0 5.4 2.1
21.0 19.0 33.1 60.7 154.9
0.11 0.12 0.11 0.14 0.37
11.7 8.9 15.4 21.8 101.4
2.9 3.9 7.5 25.8 68.2
a S i t u a t e d at i n d u s t r i a l w a s t e outflow.
221 lOO
£'2
E-2
C-I
R-I
I~-2
oZn E] Pb &Cu • Cd
oi;=
~
0 o~- . . . . . . fraction(~3 {B)3~0-150 (D) >IOOD A {El {A) 150-63 (C) ~
. B
C
D
B
C
D
E
A
B
C
D
E
B
C
D
E
B
C
D
Fig. 2. Distribution ofZn, Pb, Cd and Cu within different grain fractions of sediments from the Krka River Estuary and the Kornati Islands.
The reagents used for the cleaning and digestion of sediment material were of ultrapure quality (Suprapur, Merck). RESULTS AND DISCUSSION
The levels of Zn, Cd, Pb and Cu (mean values with appropriate standard deviations) in different grain-size fractions, together with the granulometric values, are summarized in Table 1 and illustrated in Fig. 2.
Size distribution analysis At the mouth of the Krka River Estuary, a number of travertine (tufa) barriers have formed, resulting in the presence of freshwater lakes. This restricts the input of coarser suspended material (> 63 to 1000 pm) to the estuary. Indeed, in the estuarine region of the Krka River (E-l) (Fig. 1) near the waterfalls, the top sediments were mainly composed of grains > 1000 #m (94%) (see Table 1). The clay/silt particle fraction (< 63#m) contributed only 3% to the whole sediment core. This implies that the main watercourse entering the estuary carries very little fine-grained suspended material which could settle in this region. These results were later confirmed by JuraSi6 et al. (1984), who concluded that the main watercourse entering the estuary was almost free of suspended matter. The granulometric distribution of sediments collected at Stations E-2 (Skradin) and E-3 (the lower part of Prokljan Lake) (see Fig. 1) differed signifi-
222 cantly from those at Station E-1. The sediments were composed of clay/silt sized particles ( ~ 90%), whereas the contribution of the coarser grains was almost negligible. The main source of suspended matter appears to be GuduSa Creek, which enters directly into Prokljan Lake and governs the grain size distribution of sediments collected at Station E-3. JuraSi~ et al. (1984) observed that suspended material carried by GuduSa Creek settled in Prokljan Lake. The contribution of the coarser particles to the sediments gradually increased from Prokljan Lake seawards (see Table 1 and Fig. 2). Small-sized particles (< 63#m) in sediments from the coastal regions (C-1 and C-2) and the Kornati Islands (R-1 and R-2) were present in very low amounts (0.5-5% wt/wt). Metal concentration
In general, the clay/silt fraction (< 63 pm) at all sampling sites contained larger amounts of zinc, cadmium and lead than the other size fractions. Zinc The zinc content of the clay/silt particles decreased from Station E-1 (147 ~g Zn g-1 dry sediment) seawards, reaching a value of ~ 30 #g Zn g- 1 at the Kornati Islands stations. The same feature was observed for zinc by JuraSi5 et al. (1984). An anomalously high zinc concentration ( l l 7 p g g -1) was obtained in the 150~3#m fraction of the sediment at Station E-1. The larger grain-size fractions also exhibited a tendency to accumulate relatively high amounts of zinc, showing a three-fold enrichment as compared with the same size fractions from other sampling sites. The mineralogical and chemical composition of sediments at Station E-1 obtained by Had~ija et al. (1985) reflected the petrographic composition of the drainage area. Carbonates are the prevailing minerals, with calcite predominating (77% wt/wt of the total sediment). Jura~id et al. (1984) observed that zinc was mainly present in the residual and carbonate fractions of sediment from this area. These findings appear to be contradictory because calcium carbonate, being dominant in the coarse grain-size fraction, is usually classified as a relative diluter of trace metals. However, it seems that organic material may play an important role as a mediating factor in determining the concentration of zinc at this site. Indeed, Had~ija et al. (1985) found relatively high quantities of organic material (10% wt/wt) in sediments from the same area, while it gradually decreased seawards. Similar sized grains in sediments from Limski Kanal, situated in the northern part of the west coast of the Istrian peninsula (North Adriatic Sea), contained elevated concentrations of all metals studied, particularly zinc (Martin~id et al., 1990). This observation is relevant to the amount of organic material present in the sediment. Zinc was almost uniformly distributed between the larger grain size fraction (> 63 ttm)
223 at all other sites (with the exception of C-3: industrial waste outflow) (Fig. 2 and Table 1), indicating limited enrichment through anthropogenic sources.
Cadmium In general, the concentrations of cadmium showed the same distribution pattern for all size fractions (with the exception of E-l). A uniform concentration of cadmium in all grain size classes was observed at E-l, a feature which is difficult to explain due to lack of mineralogical and chemical analyses of the fractions studied. The highest cadmium content (0.17-0.47 #g g-l) was found in the clay/silt size fraction at all sites. Comparing the concentration of metal in size fractions between all sampling sites, it is evident that the sediments from the coastal area (C-1 and C-2), particularly R-1 and R-2 (the Kornati Islands), tend to accumulate higher quantities of cadmium than sediments from estuarine regions (Table 1, Fig. 2). Donazzolo et al. (1984) suggested that cadmium concentrations in sediments from the North Adriatic coast (area extending from the Isonzo to the Piave River mouths) increase with increasing percentage of carbonates. In fact, the carbonate content of recent sediments from the Krka River Estuary and the coastal area varied from 55% (Prokljan basin) to 92% (near Zlarin, off the estuary) (Prohid and Jura6iG 1989). Hence, one can speculate that increased concentrations of cadmium in sediments from the coastal area coincide with the percentage of carbonate fraction. As in the case of zinc, sediment fractions containing particles > 63 tLm were capable of binding cadmium in the same quantities at each sampling site. The average cadmium levels in these fractions, however, differed significantly from one site to another. Among all coastal sampling sites, the coarser sediment fractions ( > 63-100 #m) from the Kornati Islands (R-l) contained two- or threefold higher cadmium concentrations than those at sites R-2, C-1 and C-2 (Table 1). Lead The lowest concentrations of lead were obtained in sediment from site E-1 and the Kornati Islands (R-1 and R-2), while a significant enrichment of lead was observed in sediments from locations on the main shipping routes (E-2, E-3, E-4, C-1 and C-2) (see Table 1 and Fig. 2). This was particularly conspicuous in sediments collected at site C-l, where the concentrations of lead increased proportionally with decreasing particle size. Copper In general, copper exhibited an irregular particle size distribution (Table 1, Fig. 2). High concentrations of copper were associated with the 300-1000 pm fraction and probabiy originated from varying contributions of biogenic calcareous debris or other biological components (plankton, microorganisms, fecal pellets, etc.). It seems likely that the overall biological activity at the sampling sites may partly determine the partitioning of copper within the ~ediment fractions and in the whole sediment. Indeed, the sediments collected
224 at the Kornati Islands had a higher proportion of shell debris (and higher copper concentrations) than sediments from other regions. This is in satisfactory agreement with the observations of JuraSi5 et al. (1984) and Had~ija et al. (1985) that the ratio of 20:1 between calcite and aragonite decreased in the seaward direction to 5:1, indicating increased influence of biogenic components towards the open sea. Similar to zinc and cadmium, the highest concentrations of copper were found in sediments from site E-1 (with the exception of site C-3 situated in the vicinity of an industrial outflow).
Metal content of the polluted sediment Sampling station C-3 required special attention because the sediments in this region were loaded with waste materials discharged from industrial activities. The grain-size distribution of recent sediments at site C-3 was typical for coastal deposits (Table 1). The clay/silt grains were particularly enriched in lead and copper. Three/fold higher concentrations of these metals were obtained compared with the same sediment particles at other coastal sites. No significant enrichment of lead and copper in the coarser particles was observed. On the contrary, particles > 63 gm contained elevated concentrations of zinc, similar to those found in sediment at site E-1. The cadmium content decreased in the concentration range obtained at all other sites, indicating that the sediment at site C-3 was not influenced by cadmium discharged by industrial plants. CONCLUSIONS The clay/silt particle-size grains ( < 63 #m) were restricted to the upper part of the Krka River Estuary (Skradin and the lower part of Prokljan Lake), gradually decreasing in the seaward direction, reaching 1 ~ % of the total sediment in coastal areas. The coarser particles were predominant in the lower part of the Krka River Estuary and the Kornati Islands. Zinc, cadmium and lead were, in general, concentrated in the clay/silt size fractions, while copper showed an irregular particle size distribution. Enrichment by anthropogenic lead was observed in the lower part of the Krka River Estuary and coastal regions with intensive shipping traffic. The cadmium content of the coarser particles increased in the seaward direction as the carbonate component of the sediments increased. It seems that copper associated with all fractions strongly depended on the overall biological activity at the sampling sites. Anthropogenic sources influenced the metal concentrations in sediments collected near industrial waste outflows. ACKNOWLEDGEMENTS This study forms part of the joint project "Environmental Research in
225 A q u a t i c S y s t e m s " of the I n s t i t u t e of Applied P h y s i c a l Chemistry, R e s e a r c h C e n t r e (KFA), Jfilich, and the C e n t r e for M a r i n e R e s e a r c h Zagreb, " R u d j e r Bo§kovi~" I n s t i t u t e , Zagreb F i n a n c i a l s u p p o r t from the I n t e r n a t i o n a l B u r e a u of K F A , Jfilich, w i t h i n the f r a m e w o r k of the bilateral a g r e e m e n t b e t w e e n the F e d e r a l Republic of G e r m a n y and Y u g o s l a v i a is g r a t e f u l l y a c k n o w l e d g e d . This s t u d y was p a r t i a l l y s u p p o r t e d by the U.S. N a t i o n a l Science F o u n d a t i o n and Self M a n a g e m e n t C o m m u n i t y for Scientific R e s e a r c h of SR Croatia, t h r o u g h funds made available to the U . S . - Y u g o s l a v J o i n t B o a r d on Scientific and T e c h n i c a l C o o p e r a t i o n u n d e r P r o j e c t J F P 679-NSF. We are grateful to Prof. D r E.D. Goldberg for his i n v a l u a b l e criticism of the manuscript. REFERENCES Donazzolo, R., O. Hieke-Marlin, L. Menegazzo-Vitturi and B. Pavoni, 1984. Heavy metal content and lithological properties of recent sediments in the Northern Adriatic. Mar. Pollut. Bull., 15: 93-101. Had~ija, O., M. Jura~id, M. Luic, M. Tonkovic and B. Jeri~evid, 1985. The carbohydrates in relation to mineralogic and granulometric composition of surface sediments in the karst estuary (River Krka Estuary, Yugoslavia). Estuarine, Coastal Shelf Sci., 21: 701-709. Jura~id, M., E. Prohid and V. Pravdid, 1984. Sediment surface properties and adsorption of heavy metals in a typical karst estuary. ICSEM (IOC) Workshop on Marine Pollution of the Mediterranean, Lucerne, 11-13 October 1984. Martin~id, D., ~. Kwokal and M. Branica, 1990. Distribution of zinc, lead, cadmium and copper between different size fractions of sediments. I. The Limski Kanal (North Adriatic Sea). Sci. Total Environ., 95 (1990) 201-216. Prohid, E. and M. Jura~id, 1989. Heavy metals in sediments - - Problems concerning determination of the anthropogenic influence. Study in the Krka River Estuary, Eastern Adriatic coast, Yugoslavia. Environ. Geol. Water Sci., 13: 145-151.