have been assessed for sediment cores collected in the nearshore area of Haifa. Bay in March 1987. The trace metal distributions over whole lengths of the.
Marine Environmental Research 31 (1991) 1-15
Trace Metals and Organic Matter in Nearshore Sediment Cores from the Eastern Mediterranean (Haifa Bay of Israel) B. S. K r u m g a l z & G. F a i n s h t e i n National Institute of Oceanography, Israel Oceanographic and Limnological Research, Tel-Shikmona, POB 8030, Haifa 31080, Israel (Received 6 April 1989; revised version received and accepted 29 July 1990)
ABSTRACT Distribution of six trace metals (cadmium, copper, mercury, lead, zinc and iron), carbonates and total organic matter (definedas loss on ignition - L O I ) have been assessed for sediment cores collected in the nearshore area of Haifa Bay in March 1987. The trace metal distributions over whole lengths of the cores (ca 60-80 cm) were found to be very uniform, and no post-industrial trace metal pollution signals were detected up to 80 cm depth in the nearshore sediments. The uniformity of trace metal distribution over the whole lengths o f the cores in the studied area was explained by active bioturbation of the marine sediment on the continental shelf of the Mediterranean coast of Israel. Strong evidence has been found that there was no anthropogenic trace metal transport )Crom the industrially polluted southern inner part of Haifa Bay to the outer part of the bay.
INTRODUCTION N u m e r o u s studies (Forstner & Wittmann, 1979; Katz & Kaplan, 1981; Salomons & Forstner, 1984) have demonstrated that nearshore sediments from coastal areas near large industrial and urban centers are very often heavily contaminated by trace metals such as mercury, cadmium, lead, zinc and copper. These trace metals are introduced into coastal waters by the intensive development of industries and urbanization. The trace metals are transported by prevailing local currents and are removed from the water by 1
Marine Envinron. Res. 0141-1136/91/$03"50 © 1991 Elsevier Science Publishers Ltd, England.
Printed in Great Britain
2
B.S. Krumgalz, G. Fainshtein
various biological and physico-chemical processes, including their scavenging by sinking particulate or organic matter (Bostrom et al., 1974, 1981; Grimanis et al., 1977). Therefore heavy metal distributions in cores of nearshore sediments reflect the historical development of local pollution. In addition, sediment data can sometimes be used to detect a local source of anthropogenic trace metal impact (Sharp & Nardi, 1987; Krumgalz, 1988b). Haifa Bay, an economically important area on the northern coast of Israel, serves also as a fishing ground for commercial fisheries. A considerable number of chemical plants and other industries discharge their effluents, after some degree of treatment, through the Kishon River (Krumgalz et al., 1989b, 1990) into the bay. The bay also receives wastewater from agricultural runoff and domestic sewage. Such discharges usually contain potentially harmful substances including toxic elements which can be sorbed by particulate matter and assimilated by organisms, eventually reaching the sediments. Thus sediments and benthic organisms are useful indicators of long-term inputs of chemical pollutants. The earlier studies (Hornung et al., 1983, 1985; Krumgalz et al., 1984, 1989a, 1990; Hornung, 1986) demonstrated that the south part of inner Haifa Bay was in some degree contaminated by cadmium, copper, lead, mercury and zinc originating from the Kishon river system (Krumgalz et al., 1989b, 1990). However, it was found (Hornung et al., 1989; Krumgalz et al., 1989a, 1990) that measurable quantities of these trace metals do not reach the northern inner part of Haifa Bay. The remaining question was: does trace metal pollution exist in the outer part of Haifa Bay, and if it does, what is its source or sources? To answer this question, the sediment cores were taken for the first time in the outer part of Haifa Bay and analysed for trace metal and organic matter content. Along with trace metal analysis, the sedimentology of these cores was also studied.
EXPERIMENTAL Sediment cores up to 80 cm long were collected from a calm sea on 31 March 1987 for four stations indicated in Fig. 1 and described in Table 1 from the R / V S h i k m o n a using a hydroplastic gravity corer made by the Geological Survey of Israel after Richards and Keller (1961). Approximately 500 kg of mass was used to drive the corer into the sediment. The inner diameter of the plastic corer was 8"5 cm. After delivery of the corer on board ship, the plastic corer with the core barrel was immediately plugged on both sides by plasticcovered rubber stoppers and maintained in a vertical position during quick freezing at -18°C. Three sampling stations (4c, 5c and 6c) were situated in the outer part of Haifa Bay and station 2c was selected south of the bay at
Trace metals and organic matter in nearshore sediment cores
3
35"00'
ggb;, J
tli plan!
32"50' "2c
/
/ !
'xt$llon river
I
:''.
Fig. 1.
• 2
"'." ""'"
M a p o f sampling locations.
TABLE 1 Description of the Core Sampling Stations
Station number
Coordinates
Water depth o f core sampling
Core length (cm)
(m) 2c
4c 5c 6c
32 ° 49-2' N, 32 ° 52"7' N, 32 ° 54"5' N, 32° 56'5' N,
34 ° 53'5' E 35 ° 00"4' E 35 ° 00.8' E 35° 01-5' E
60 20 32 35
62 82 74 78
4
B.S. Krumgalz, G. Fainshtein
Tel-Shikmona. The latter station was considered apriori as a clean control station, since this area is believed to be unaffected by discharges from any source of trace metals in the study area. Sediments for the four sampled stations were either mud or muddy sand. We were unable to obtain cores of the sandy sediment in the nearshore area of Haifa Bay. After freezing, all cores were sliced horizontally in 2-cm pieces (the upper and bottom pieces were either 4 or 5 cm). All the pieces were cleaned from the outside with a plastic spatula, placed in numbered polyethylene bags and kept again in a deep freezer. The final cleaning of the core pieces was done before their lyophilization. Prior to any sample analysis, the sediment samples were lyophilized, samples were sieved through polyester sieves and only the fraction smaller than 250/~m (fine sand, silt and clay) was taken for analysis. For trace metal determination, samples of the dry sediments were digested for 3 h at 140°C with concentrated nitric acid (65% wt) in Uniseal, teflonlined, high-pressure decomposition vessels. The digested samples were cooled, transferred to either 10-, 25- or 50-ml volumetric flasks and diluted to these volumes with deionized distilled water. The solutions obtained after digestion of these sediments were transparent with various amounts of undissolved silicate. Each sample was analyzed at least in duplicate. Before trace metal determination, each solution was filtered. The concentrations of copper, cadmium, iron, lead and zinc were measured using a flame atomic absorption spectrophotometer (IL951). The concentration of total mercury in solutions obtained after separate sample digestion was measured on a Coleman mercury analyzer (MAS-50). Reagent blanks were obtained by the same digestion procedure without th e sediment. The accuracy of our entire analytical procedure was repeatedly checked by analyzing samples of reference sediment standards (BCSS-1, MESS-l, Standard Reference Materials 1645 river sediment and 1646 estuarine sediment). These standards were treated and analyzed for trace metals in a similar manner to those of the sediments with each batch of sediments studied. The results of these determinations were discussed earlier (Krumgalz & Fainshtein, 1989) and showed good agreement with certified values and results obtained in other laboratories. To give a quantitative illustration of the accuracy of our data, we present (Table 2) heavy metal determination of Standard Reference Material 1645 river sediment. The organic matter was determined by the ignition loss procedure described by Galle and Runnels (1960), and Dean (1974) with slight modifications. Briefly, the procedure consisted of heating a lyophilized sediment sample (predried at 105°C to constant weight) at 500°C for 2 h. The loss of weight by the sediment sample as a result of this heating was assumed to be due to organic matter ignited only. To distinguish the organic matter
b
e
This study"
Certified values a Bettinelli et al. (1986) Bettinelli et al. (1986) Rauret et al. (1988) Rauret et al. (1988) Rauret et al. (1988)
8"9+0"3 (29) 10.2+ 1-5 9"1 +- 0"3 10-0_+0"3
Cd
108.2+4-5 (31) 109+-_ 19 107 +- 9 115+ 14 107 +- 12 114___+17 116-1-6
Cu
723'5+36"8 (29) 714+-,28 737 +- 15 731 +- 16 720 +- 32 789_+90 i 776+60 i
Pb
1 731 + 2 7 (23) 1 720+-- 169 1 685 +- 45
Zn
Trace metal contents (pg/g d.w.)
88-7+8'7 c (37) 113 _+ 12
Fe × 10 -3
6'96+0'29 (l 8)
LOI (%)
4.96+0.01 (3)
Carbonate content (%)
a Precision expressed as 95 % tolerance limits. The estimated uncertainty for the results obtained in this study represents the combined effects of the errors dealing with digestion method, analytical method and material variability for samples of 1.0 g or more. Values given in parentheses are number of determinations. b Direct injection. c The reasons for the discrepancy between our results of iron determinations and the certified values were discussed in Krumgalz and Fainshtein (1989). d The estimated uncertainties for certified values include also systematic errors among various analytical methods in the same laboratory and from other laboratories participating in the element determination (material variability for standard reference sediments for 0.5 g or more). e Complete digestion with acid mixtures containing HF. I Graphite furnace atomic absorption spectroscopy with the L'vov platform. g Atomic absorption spectroscopy, standard addition. h Digestion with H N O 3 + HCI mixture. i It is an erroneous result, we think, since it is impossible that fully digested sediment contains less lead than the same sediment digested only by H N O 3 + HCI mixture.
b,~ b.h g,h
b,e,f ~,I.o
Digestion and determination methods
Reference
TABLE 2 Trace Metal, Total Organic Matter (LOI) and Carbonate Content in Standard Reference Material 1645 River Sediment
~"
~. :~ ~
,2
6
B.S. Krumgalz, G. Fainshtein
determined by the ignition loss method from that determined by other methods, the former will be called 'loss on ignition' (LO1). The carbonate content was determined by adding an excess of HC1 of known concentration close to I'0N to the sediment sample (0" 1-5 g) and then by back titrating the remaining acid by NaOH solution (Anwar & Mohamed, 1970). The endpoint of titration was determined by a digital titration system (Radiometer DTS-833) with a glass electrode (G2040C) and a calomel electrode (K4040). The granulometric analysis was conducted by mechanical sieving of the sediments through a set of polyester sieves. The following particle size fractions were obtained: > 1000#m, 500-1000, 250-500, 105-250, 63-105 and less than 63 ~m. The coarsest particle size fraction (more than 1"0 ram) was represented by rough fragments of carbonate debris of mollusc shells, and was not used in the following stages of chemical analysis.
RESULTS A N D DISCUSSION The results ofgranulometric analysis of the four cores are presented in Table 3, and the corresponding carbonate content of the grain size fraction less than 0"250 mm is illustrated in Fig. 2. The figure shows that the marine sediments of Haifa Bay have a relatively high amount of carbonates, which consist mainly of mollusc shell debris. Core No. 2c, sampled south of and outside Haifa Bay, has a different composition and structure compared to the other cores sampled from the outer part of the bay. This core consists mainly of coarse sand (fraction 0-5-1-0mm) and medium sand (fraction 0.25-0.50 mm), and has a homogeneous granulometric structure over the full core depth, while for the other three cores there is a less homogeneous granulometric structure. This is especially clear for core No. 6c; its upper 5 cm structure is similar to that of core Nos 4c and 5c, while below the upper 5 cm the structure of core No. 6 is similar to that of core No. 2c, consisting mostly of coarse and medium sand. Wet granulometric analysis of the deepest section of core No. 5 gave results generally close to those obtained by dry analysis. However, this technique decreased the percentage of coarse and medium sand while increasing that of fine sand, apparently by breaking up sediment conglomerates formed by fine-grained sediment cemented either by sea salts or by dissolved organic matter under a drying process without prewashing (Krumgalz, 1989). The results obtained for the trace metals, carbonate and organic matter (LOI) content of the sediment fraction with grain size less than 0.250 m m for the four cores are illustrated in Fig. 2. This figure shows that the sediments of core Nos 2c and 6c have considerably higher concentrations of trace metals than do the sediments of core Nos 4c and 5c. Possible reasons for this trace
7
Trace metals and organic matter in nearshore sediment cores
TABLE 3 Granulometric Content (%) of Sediment Cores of Haifa Bay (Dry Analysis)a
Core number
Depth of
Granulometric content (%) of various sediment Jractions
core piece fi'om the surface (cm)
Coarsesand Medium sand Finesand Veryfine sand Silt and clay (0"5 1"0 (0'25-0"50 (0"125~)'250 (0"063-0"125 (
