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Sedimentary records of heavy metals in the industrial harbour of Portovesme, Sardinia (Italy)
The Science of the Total Environment 241 Ž1999. 129]141
Sedimentary records of heavy metals in the industrial harbour of Portovesme, Sardinia ž Italy/ Marco Schintu a,U , Sandro Degetto b a
Dipartimento di Igiene e Sanita ` Pubblica, Uni¨ ersita` degli Studi di Cagliari, Via G.T. Porcell 4, 09100 Cagliari, Italy b ICTIMA-CNR, C.so Stati Uniti 4, 35127-Pado¨ a, Italy Received 10 September 1998; accepted 26 July 1999
Abstract The anthropogenic fluxes of Hg, Cd, Pb and Zn were determined in four sediment cores collected in the harbour of Portovesme, Italy, facing an industrial area containing a lead]zinc smelter, an aluminium production plant and a coal-fired power generation plant. The analytical results and the radiodating of sediment cores show extremely high concentrations of Hg and Cd in the sediments that can be ascribed mostly to the discharge of the liquid effluent from the smelter since the late 1960s. Based on the different extractability of metal species, the anthropic origin of metal pollution as well as the risk of remobilisation of the metals into the marine environment is highlighted. Q 1999 Elsevier Science B.V. All rights reserved. Keywords: Marine sediments; Heavy metals; Lead]zinc smelters; Radiodating; Industrial wastes
1. Introduction Sediments are considered a suitable medium to identify sources of heavy metal pollution in the aquatic environment. Dated sediment profiles could provide a reasonable estimation of past
U
Corresponding author. Tel.: q39-70-6758364; fax: q3970-668661. E-mail address: [email protected] ŽM. Schintu.
natural and anthropogenic environmental conditions and of changes in specific areas ŽForstner ¨ and Wittmann, 1979; Degetto et al., 1997; Von Gunten et al., 1997.. The small harbour of Portovesme ŽFig. 1., south-western coast of Sardinia, receives major inputs from industrial discharges, runoff from smelter and mining areas, dusts dispersed in the harbour area during shipping operations, and atmospheric fallout. Industries began to develop and expand at Portovesme in the late 1960s. The
0048-9697r99r$ - see front matter Q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 8 - 9 6 9 7 Ž 9 9 . 0 0 3 3 6 - 8
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industrial area includes a lead]zinc smelter, a coal-fired power generation plant and aluminium production and refining. Mercury and Cd are potentially among the most hazardous elements of trace concentrations in ores imported and processed locally, and in Pb and Zn minerals that were mined locally and shipped from the harbour of Portovesme until a few decades ago. Data and publications on the level and effects of contaminants on the adjacent coastal areas are very limited ŽRiolfatti et al., 1992., although ore smelters are known to be major point sources of heavy metals in land and water environments ŽWard et al., 1984; Batley, 1987; Langlois et al., 1987; Pilgrim and Hughes, 1994; Zachmann and Block, 1994.. Here we present data that were obtained from radiodated sediment cores from the Portovesme harbour with the aim of assessing the contamination sources, the historical evolution of contamination and the fluxes of Hg, Cd, Pb and Zn to the sediments. An evaluation of the metal anthropogenic fraction and, therefore, the potential threat for the coastal environment has also been
obtained through selective leaching of the sediments. 2. Area of investigation The harbour of Portovesme ŽFig. 1. was built in 1870 to ship the ores Žblende, galena and pyrite. mined in the surrounding areas. Though mining activity has now been practically abandoned, ores and products to and from the industrial area are still transported. The mouth of the harbour is 250 m wide and in the centre a dredged canal approximately 13 m deep allows berthing of vessels. In the north-western area of the harbour the water depth ranges between 6 and 9 m, while in the southern area it is shallower Žbathymetry range: 1]3 m.. In 1991, the shipping traffic was estimated at approximately 6 000 000 t. The main industrial plants nearby are the following: v
v
a plant producing alumina from bauxite, operating since 1972; a plant producing aluminium by electrolysis of alumina, operating since 1972;
Fig. 1. Map of the Portovesme area and location of sampling sites.
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
131
a coal-fired power generation plant Ž720 MW. and a smaller oil-fired plant, operating since 1970; and a lead]zinc smelter built in the late 1960s and in full production since 1972, with a yearly production of 154 000 t of metallic lead and zinc, 500 t of cadmium, and 17 t of mercury and sulphuric acid.
Both the samplings and the analyses refer to 1993. The results are being reported now, because the data were used in legal proceedings on the case that were still in progress until recently.
A cleanup of a wide area Ž390 km2 . surrounding the industrial settlement has been planned by the Italian Government and is now ongoing. Emissions to the atmosphere from the Portovesme area have been estimated at 65 000 t of SOx per year, 4000 t of dust per year, 10 t of Pb per year and 100 t of F per year ŽGazzetta Ufficiale, 1993.. The lead]zinc smelter mostly utilises imported sulphide minerals such as sphalerite ŽZnS. and galena ŽPbS.. Sphalerite usually contains between 50 and 67% of Zn and small percentages of Pb, Cu, Cd, Fe, Au, Ag and Hg. Galena, which can contain Pb up to 86%, can also contain minor elements such as Ag, Cd, Ni, Cu, Co, and As. The efficiency of metal removal from the liquid effluent of the smelter was not improved until 1991, when wastewater treatment technologies using both hydroxide and sulphide precipitations were implemented. The drainpipe discharging the liquid effluents of the smelter is also shared by the aluminium production plant and the warm cooling-water effluent from the coal-burning power generation plant ŽFig. 1.. This causes a clockwise water circulation inside the harbour driven by the warm water stream from the power generation plant. Together with the liquid effluents, the stack emission can also be a source of sediment contamination. However, earlier studies in the area showed the highest deposition of metals in the prevailing NW wind direction ŽContu et al., 1986.. Other possible sources of harbour sediment contamination arise from handling of ores and concentrates Žloadingrunloading of trucks, spillage of liquids, and dust dispersion from materials in open piles accumulated on the harbour embankment and subject to the action of the wind., land erosion, and runoff from the mining areas.
Four sediment cores ŽC1, C2, C3, and C4. were collected in January 1993 in the southern part of the harbour of Portovesme from sampling stations approximately 100 m apart, along the circulation path of the harbour currents ŽFig. 1.. In this area navigation of industrial vessels, which only occurs to reach the docks in the western and northern areas of the harbour, is not possible because the waters are too shallow. Moreover, small private boats, which refer to a tourist marina located nearby, are not allowed to enter the industrial harbour. Furthermore, the sediments in this area are generally undisturbed by bioturbation, since the bottom water is nearly anoxic and large burrowing organisms are absent. However, throughout the sampling period tidal scour was insignificant, no storm events were observed, and freshwater inputs can be ruled out. The outfall of the wastewater treatment plant of the smelter is located in this area ŽFig. 1.. The short cores, up to approximately 30 cm in length, were collected by scuba divers in Plexiglas liners Ž6 cm internal diameter. and frozen to prevent mixing during transport to the laboratory. Freezing was done very rapidly to avoid the formation of large disruptive ice crystals during storage. No compaction was observed as a consequence of the coring procedure. After thawing, the cores were extruded and divided into sections of a thickness of 2 cm. Core sectioning was performed rapidly in the air. Sample homogenisation and sub-sampling were carried out in a Glove Box under nitrogen atmosphere to avoid oxidation. Sediment sub-samples for the determination of total element concentrations Žexcept Hg. were dissolved in HNO3rHClO4rHF ŽAgemian and Chau, 1976.. Total Hg determinations were carried out after cold digestion with a mixture of HClO4rH 2 SO4 and further addition of a solution
v
v
3. Experimental
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of KMnO4 . Analytical blanks were prepared using the same reagents. A Perkin]Elmer model 2100 atomic absorption spectrophotometer ŽAAS. in the flame mode was used for the measurement of Cd, Pb, and Zn in the solutions. Mercury was determined by the cold vapour method. Leaching of sediments with 0.5 N HCl was carried out according to the method of Malo Ž1977.. Total concentrations of Al, Si, Ca, Mg, K, Mn, Fe, Ti, V, and S were determined by X-ray fluorescence ŽXRF. after combustion of the samples at 3608C. An ORTEC 6110 tube excited fluorescence analyser equipped with an X-ray tube ŽMo and W anodes. and a 30-mm2 SirLi detector Žresolution of 160 eV at 5.9 keV. was used. The samples, ground to less than 200 mesh, were prepared as powder pellets Ž3 cm diameter. pressed at 20 t cmy2 with a thickness greater than the critical thickness ŽBertin, 1975. for all the elements concerned. A standard reference material from the National Bureau of Standards ŽRiver Sediment 1546. was used to check the accuracy of the results of both AAS and XRF analyses. Analytical reproducibility was better than 5% as determined from five replicate analyses of a bulk sediment for AAS analyses, and better than 12% for XRF analyses. Organic matter expressed as loss on ignition ŽLOI. was estimated by weight differences between 360 and 1108C ŽBattiston et al., 1989.. The fine fraction content of the sediment was determined by sieving the wet samples with a 63-mm ASTM sieve. 3.1. High resolution gamma spectrometries Radioactivity analyses of the core sediment samples Ž70]100 g wet weight. airtight in disk shaped vessels, were performed after at least 30 days to ensure secular equilibrium between 226 Ra and short lived daughters. Radioassay was by high resolution gamma spectrometry using an N-type intrinsic germanium coaxial detector with a relative efficiency of 26% Žpeak to Compton ratio 56r1: FWHM 1.79 keV at 1.33 MeV and 0.843 keV at 122 keV; FWTM 3.45 keV at 1.33 MeV..
Low energy photon emission data were processed for self-absorption correction as previously described ŽDegetto et al., 1995.. Total 210 Pb activity was measured directly through its emission at 46.5 keV. The fraction supported by 226 Ra inside the sediment was determined through 214 Pb Ž352 keV. and 214 Bi Ž609 keV. photon emissions at radioactive equilibrium. The uncertainty in the determination of radionuclides, taking into account statistical counting and calibration uncertainties, was never less than 10% at a 95% confidence level.
4. Results and discussion The analysed sediment sections and their sedimentation rates are given in Table 1. Chronologies were established from profiles of unsupported 210 Pb with the independent control of the 137 Cs spike from weapon test experiments in the atmosphere Žpeak in 1963]1964.. The contribution of recent 137 Cs deposition from the Chernobyl accident does not interfere with this control; in fact Chernobyl-derived radioactivity is a well-separated event dated at 1986. Moreover, the Table 1 Sedimentation rates Žcmryear. for the cores from Portovesme harbour a Section number
Depth Žcm.
C1
C2
C3
C4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0]2 2]4 4]6 6]8 8]10 10]12 12]14 14]16 16]18 18]20 20]22 22]24 24]26 26]28 28]30 30]32
0.69 0.27 0.25 0.19 0.08 n.d. n.d. n.d. n.d. n.d. n.d.
0.32 0.23 0.34 0.28 0.29 0.43 0.62 0.36 0.77 0.24 0.37 0.15 n.d. n.d. n.d. n.d.
0.31 0.18 0.20 0.18 0.12 0.25 0.27 8.00 1.60 0.16 n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
a
n.d., not determined.
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
deposition of that radioactivity in this area was very low Žtotal beta radioactivity in the air, integrated over the period of deposition, May 1986, was approximately 1r6 compared to that observed in North Italy. ŽColacino, 1986.. In these conditions Chernobyl radioactivity, which doubled the 137 Cs inventory in North Italy could here be a difficult fraction to detect in the sediments. The available data allowed a reliable time to depth match down to 10 cm in C1 and 24 cm in C2, whereas in C3 some uncertainty could arise from the 137 Cs profile, which appears to be very disturbed ŽFigs. 2 and 5.. The maximum fallout, however, is nearly at the same depth for all cores, and the observed differences are substantially compatible with the time scale obtained from unsupported 210 Pb ŽFigs. 3]6.. The cores are different, however, and their difference is at best outlined by the fluxes ŽFig. 7.. The sedimentary concentrations of Hg, Cd, Pb, and Zn are shown in Figs. 3]6, while Table 2 shows the major element concentration in selected sections of the cores. Analyses were carried out on the whole sample. Considering the preferential occurrence of the heavy metals in the finest grain-size fractions, we evaluated the - 63mm fraction content of the sediment samples
133
ŽFigs. 3]6.. A significant relationship between the - 63-mm fraction and metal concentrations was observed in the four cores. The strongest positive correlation coefficients were found in C2 Ž n s 16, P- 0.001; for Hg r s 0.762, for Cd r s 0.889, for Pb r s 0.858, and for Zn r s 0.858.. The fine fraction in the surface layer Ž0]2 cm. of C1, C2, C3 and C4 steadily increases from 19% in C1 to 72% in C4, whereas a fairly opposite trend is observed for sediment dry weight: C1 s 71%, C2 s 62%, C3s 61%, and C4s 39%... Sediment enrichment factors ŽSEFs. have frequently been used to quantify enrichment of trace metals in recent sediments ŽKemp et al., 1976; Forstner and Wit¨ tmann, 1979.. However, the changes are usually calculated relating to a ‘conservative’ substance such as Al, which is considered to reflect non-anthropogenic inputs. As shown in Table 2, the extremely high concentration of this element in the sediments of the harbour Žfrom 5 to 32%., very likely of anthropogenic origin, precludes the calculation of SEFs for these sediments as well as the calculation of metalraluminum ratios ŽBruland et al., 1974. to express the variation of the trace metal content in the sediment cores. However, if the deep layers of the core C3 Žsections 11 and 12., where concentrations were relatively
Fig. 2. Time to depth match for cores C1, C2, and C3. Dots indicate mean age of sections.
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Fig. 3. Metal chronologies and depth profiles for C1 sediment core. U Unsupported
constant, are considered to represent background levels Žmean values: Hgs l; Cds 8; Pb s 65; and Zn s 320 mgrg., then the peak concentrations in sediments deposited after the industrial settlement Ž1970. in C1 were 108, 15, 40, and 42 times
210
Pb.
higher for Hg, Cd, Pb, and Zn, respectively, in C2, 14, 5, 20, and 22 times higher; in C3, 8, 7, 20, and 21 times higher. The runoff from the surrounding mining areas, which were very active at that time, and the scattering of dusts during shipping opera-
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
Fig. 4. Metal chronologies for C2 sediment core. U Unsupported
tions of the ores mined locally, could probably have contributed to the relatively higher metal background concentrations found in the sediments of C1, C2 and C3 that settled before 1900]1910.
210
135
Pb.
The organic content in the cores Žas LOI. never reached 2% and is poorly correlated with heavy metal content. From Fig. 7, Hg, Cd, Pb, and Zn appear to be accumulating at higher rates in core C1, the near-
136
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
Fig. 5. Metal chronologies for C3 sediment core. U Unsupported
est to the industrial waste outlet, and at a lower rate in C2 and C3. In C1 ŽFig. 3. the highest Hg concentration was found in section 4 Ždepth: 6]8 cm., corresponding to the sediment deposited in
210
Pb.
1964]1975, while Cd concentrations were highest in section 2 Ždepth: 2]4 cm., deposited in 1983]1990. It should be noted that both Hg and Cd dramatically decrease in the top layer of C1,
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
Fig. 6. Depth profile for C4 sediment core. U Unsupported
which was deposited in 1990]1993. The sedimentation rate of the section 1 of C1 Ždepth: 0]2 cm. was much higher Ž0.69 cmryear. than the deeper layers Žsections 4 and 5, - 0.20 cmryear.. In C2 the sedimentation rate was approximately 0.3 cmryear since 1930, except for a short
210
137
Pb.
increase in the early 1940s and 1950s. The heavy metal concentration in C2 is lower than that in C1, the highest values for Hg, Cd, Pb, and Zn were detected in the first 4 cm of the core Ž1978]1993.. Mercury and Cd concentrations in the sediment deposited before the smelter was
138
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
Fig. 7. Fluxes of metals to the sediment since approximately 1940.
installed in 1970 are quite uniform along the core. The concentrations of Hg, Cd, Pb, and Zn were relatively constant in the deepest sections of the core Ž13, 14, 15, and 16, not represented in Fig. 4.. Hg concentrations ranged from 2.6 to 3.3 Ž xs 3.2.; Cd from 7.5 to 10.2 Ž xs 8.7.; Pb from 115 to 224 Ž xs 182.; and Zn from 1051 to 1287 Ž xs 1100.. In core C3, sedimentation is generally uniform Žapprox. 0.2 cmryear. and lower than in C1 or C2. Mercury concentrations are relatively lower and quite uniform, while the Cd content is higher in the first 8 cm of the core. The extremely high Hg, Cd, Pb, and Zn concentrations observed from 14 to 18 cm depth of core appear to be due to an
extemporaneous event that occurred in the early 1920s. The corresponding peak sedimentation rate is extremely high Ž8.0 cmryear.. On the basis of analytical data this peak may be due to some raw material being dumped during harbour activities as outlined by the sharp difference in sediment composition compared to the immediately adjoining layers. A relative increase in the metal concentration can also be shown in C2 in the sediments deposited in the same time period. The metal concentrations at lower depths of C3, sediments deposited before 1909, were the lowest in the harbour ŽHgs 0.8]l.2; Cds 8.0]11.0; Pb s 63]72; and Zn s 270]372 mgrg d.w... Fig. 6 shows the heavy metal profiles in core
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
C4. Mercury, Cd, Pb and Zn concentrations are relatively uniform along the core. The very high Cd concentration exhibited both in C4 Žrange: 98]159 mgrg dry weight. and in the upper section of C3 suggest that Cd is more mobile than Hg in the harbour. It is interesting to note that the - 63-mm fraction content ranged from 66 to 80%. This finding is significant in that it implies that differences in concentration inside the harbour may result from sediment accumulation. The high radioactivity value of 210 Pb and 137 Cs and its uniformity with depth proves that core C4 represents an area of accumulation of fine-grained sediment, conveyed from the surrounding surface sediment layers. From the profile of the core no reasonable sedimentation rate was evaluated, since complete mixing of the sedimentary layers was observed ŽFig. 6.. Moreover sampling station C4 was located near a small pier at the outlet of the harbour. The complete mixing observed in this core is likely to be due to marine propellers of vessels operating nearby. From Fig. 7 fluxes of Hg, Cd, Pb, and Zn deposited in the sediments after the industrial settlement Žapprox. 1970. appear to be much higher in core C1, which was collected closer to the liquid effluent discharge in the harbour. Considering that these metals are not present in the
139
cycle of Al production, and that they are supposed to be contained only in low concentrations in the water-soluble components of fly-ash from power stations ŽSabbioni and Goetz, 1982.. The main source of Hg, Cd, Pb, and Zn contamination is likely to be liquid effluents from the lead]zinc smelter in the harbour. Metal concentration in the cores decreases with an increase in the distance of the sampling station from the industrial effluent discharge. Furthermore, Hg, Cd, Pb, and Zn fluxes in C1 sharply decreased between 1990 and 1993, very likely reflecting the post-1990 improvement in wastewater treatment at the smelter, more stringent legal regulations and growing public concern about environmental problems. No historical records of either metal-emissions from the smelter or atmospheric deposition of metals in the region are available. Moreover the correlation coefficients between metals indicate a common source Ž P- 0.0005, n s 47: r s 0.496, Hg-Pb; r s 0.643, Hg-Zn; r s 0.729, Cd-Pb; r s 0.627, CdZn; r s 0.89, Pb-Zn. in spite of the lower value for the relation coefficient between Hg and Cd Ž P- 0.05, r s 0.295.. Treatment of sediments with dilute acids ŽHCl, HNO3 . has been used to separate the most mobile fraction of trace metals Žbound to the sediment in adsorbed, precipitated or co-precipitated and complexed forms. from the ‘residual fraction’
Table 2 Major element concentration of selected sediment profiles Core
Section
Depth Žcm.
Al Ž%.
Si Ž%.
Ca Ž%.
S Ž%.
Mg Ž%.
K Ž%.
Mn Ž%.
Fe Ž%.
Ti Ž%.
V Ž%.
C1
1 5 11
0]2 8]10 20]22
11 30 5
25 8 22
3 3 10
0.3 0.8 0.5
3 2 2
1.0 0.8 1.6
0.05 0.06 0.03
1.2 2.6 0.8
0.2 0.4 0.3
0.05 0.17 0.07
C2
1 5 11
0]2 8]10 20]22
23 12 6
12 18 17
8 10 12
0.6 0.3 0.9
1 2 3
0.8 1.2 1.1
0.07 0.03 0.04
2.2 1.3 2.0
0.4 0.2 0.4
0.09 0.07 0.06
C3
1 5 11
0]2 8]10 20]22
32 30 6
7 8 35
5 4 3
1.0 0.7 0.1
1 2 1
0.5 0.5 1.1
0.07 0.05 0.08
2.5 1.3 0.4
0.4 0.3 0.2
0.10 0.09 0.01
C4
1 5
0]2 8]10
15 25
13 8
8 6
1.0 1.4
3 1
0.98 0.7
0.08 0.1
2.2 2.6
0.4 0.5
0.04 0.1
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
140
Table 3 0.5 N HCl soluble content of Hg, Cd, Pb and Zn Ž% of total metal. of selected sediment profilesa Core
Section
Depth Žcm.
Hg Ž%.
Cd Ž%.
Pb Ž%.
Zn Ž%.
C1
1 5 11
0]2 8]10 20]22
11.6 n.d. n.d.
82.4 43.8 26.4
64.9 77.9 18.5
62.8 24.8 47.3
C2
1 5 11
0]2 8]10 20]22
3.2 n.d. n.d.
51 27.8 21.4
69.4 75.5 78.6
39.5 30.5 60.9
C3
1 5 11
0]2 8]10 20]22
2.4 n.d. n.d.
89.1 63.1 14.4
60.9 63.1 41.3
81.3 82.3 34.9
C4
1 5
0]2 8]10
1.8 1.3
31.1 37.4
86.6 82.4
91.6 85.5
a
n.d., not detected.
ŽMalo, 1977; Forstner and Wittmann, 1979; Bryan, ¨ 1984; Kersten and Forstner, 1990.. Furthermore, ¨ Luoma and Bryan Ž1982., in studies of trace metal uptake by benthic organisms, found that 1 M HCl extraction gave better information about metal bioavailability than either the total metal concentration in the sediment or any one of a range of other extractants Žacetic acid, ammonium acetate, ammonia.. In order to identify the risk of remobilisation of high quantities of toxic metals from the sediments to the water column, selected layers of the cores ŽTable 3. were leached with 0.5 M HCl, according to the method of Malo Ž1977.. Portions of Cd ranging from 51 to 92% of the total metal were extracted from the surface layer Ž0]2 cm. of the cores, while in section 11 Ž20]22 cm. these percentages ranged from 14 to 26%. A similar figure was found for Pb and Zn, but lower percentages of the total metal were extracted. Mercury was recovered with 0.5 M HCl only from the surface layer of C1, C2, and C3, in percentages ranging from 2.5 to 11.5 of total Hg. In core C4 the fraction of Hg, Cd, Pb, and Zn leached with dilute acid did not change with depth, confirming the homogeneity of the sediment accumulated in this area as a result of sediment accumulation and mixing.
5. Conclusion Metal concentration in the cores decreases with an increase in distance from the sampling station from the industrial effluent discharge. Besides, metal leaching with HCl, shows the greatest differences between upper and lower sections in station C1, the most exposed to industrial waste effluents. The observed contamination is likely to be due to liquid effluents from the lead]zinc smelter. Hg, Cd, Pb, and Zn fluxes appear to be pertinent to the industrial settlement in the area and to the performance of their waste treatment. Leaching experiments of surface sediments show that metals are largely present in exchangeable or adsorbed forms. References Agemian F, Chau ASY. Evaluation of the extraction techniques for the determination of metals in aquatic sediments. Analyst 1976;101:761]767. Batley GE. Heavy metal speciation in waters, sediments and biota from Lake Maquarie, New South Wales. Aust J Mar Freshwater Res 1987;38:591]606. Battiston G, Degetto S, Gerbasi R, Sbrignadello G. Determination of sediment composition and chronology as a tool for environmental impact investigations. Mar Chem 1989;26:91]100. Bertin PE. Principles and practice of X-ray spectrometric analysis. New York: Plenum Press, 1975. Bruland KW, Bertine K, Koide M, Goldberg ED. History of metal pollution in Southern California coastal zone. Environ Sci Technol 1974;8:425]432. Bryan GW. Pollution due to heavy metal and their compounds. Marine ecology. J Wiley and Sons, 1984:1289]1431. Colacino M. L’incidente di Chernobyl: misure di radioattivita ` nell’aria. Proceedings of A.I.R.P. Conference, Rome, June 1986:65]86. Contu A, Flore C, Schintu M, Spiga G. Piombo e cadmio nel suolo e nei vegetali di un’area industrializzata della Sardegna. Inquinamento 1986;XXVIIIŽ3.:2]6. Degetto S, Sbrignadello G, Cianchi A, Valdarnini F. Un metodo semplice per la correzione geometrica e di autoassorbimento delle attivita ` di emettitori gamma a bassa energia in matrici ambientali. V Convegno sulle metodologie radiochimiche e radiometriche in radioprotezione, 20]22 June 1995, Urbino, Italy. Degetto S, Schintu M, Contu A, Sbrignadello G. Santa Gilla lagoon ŽItaly.: A mercury sediment pollution case study. Contamination assessment and restoration of the site. Sci Total Environ 1997;204:49]56.
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141 Forstner U, Wittmann GTW. Metal pollution in the aquatic ¨ environment. New York: Springer-Verlag, 1979. Gazzetta Ufficiale. Della Repubblica Italiana n. 190 14r8r93. Piano di disinquinamento per il risanamento del territorio del Sulcis-Iglesiente, 1993. Kemp AL, Thomas RL, Dell CI, Jaquet MJ. Cultural impact on the geochemistry of sediments in Lake Erie. J Fish Res Board Can 1976;33:440]462. Kersten M, Forstner U. Speciation of trace metals in sedi¨ ments. In: Batley GE, editor. Trace metal speciation: analytical methods and problems. CRC Press, 1990. Langlois D, Cooper RJ, Clark NH, Ratkowsky DA. The effect of a mercury containment programme at a zinc smelting plant on the mercury content of a sand flathead in the Dervent Estuary. Mar Pollut Bull 1987;18Ž2.:67]70. Luoma SN, Bryan GW. A statistical study of environmental factors controlling concentrations of heavy metals in the burrowing bivalve Scrobicularia plana and the polychaete Nereis di¨ ersicolor. Estuarine Coast Shelf Sci 1982;15: 95]108. Malo BA. Partial extraction of metals from aquatic sediments. Environ Sci Technol 1977;11:277]288.
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Sedimentary records of heavy metals in the industrial harbour of Portovesme, Sardinia ž Italy/ Marco Schintu a,U , Sandro Degetto b a
Dipartimento di Igiene e Sanita ` Pubblica, Uni¨ ersita` degli Studi di Cagliari, Via G.T. Porcell 4, 09100 Cagliari, Italy b ICTIMA-CNR, C.so Stati Uniti 4, 35127-Pado¨ a, Italy Received 10 September 1998; accepted 26 July 1999
Abstract The anthropogenic fluxes of Hg, Cd, Pb and Zn were determined in four sediment cores collected in the harbour of Portovesme, Italy, facing an industrial area containing a lead]zinc smelter, an aluminium production plant and a coal-fired power generation plant. The analytical results and the radiodating of sediment cores show extremely high concentrations of Hg and Cd in the sediments that can be ascribed mostly to the discharge of the liquid effluent from the smelter since the late 1960s. Based on the different extractability of metal species, the anthropic origin of metal pollution as well as the risk of remobilisation of the metals into the marine environment is highlighted. Q 1999 Elsevier Science B.V. All rights reserved. Keywords: Marine sediments; Heavy metals; Lead]zinc smelters; Radiodating; Industrial wastes
1. Introduction Sediments are considered a suitable medium to identify sources of heavy metal pollution in the aquatic environment. Dated sediment profiles could provide a reasonable estimation of past
U
Corresponding author. Tel.: q39-70-6758364; fax: q3970-668661. E-mail address: [email protected] ŽM. Schintu.
natural and anthropogenic environmental conditions and of changes in specific areas ŽForstner ¨ and Wittmann, 1979; Degetto et al., 1997; Von Gunten et al., 1997.. The small harbour of Portovesme ŽFig. 1., south-western coast of Sardinia, receives major inputs from industrial discharges, runoff from smelter and mining areas, dusts dispersed in the harbour area during shipping operations, and atmospheric fallout. Industries began to develop and expand at Portovesme in the late 1960s. The
0048-9697r99r$ - see front matter Q 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 8 - 9 6 9 7 Ž 9 9 . 0 0 3 3 6 - 8
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industrial area includes a lead]zinc smelter, a coal-fired power generation plant and aluminium production and refining. Mercury and Cd are potentially among the most hazardous elements of trace concentrations in ores imported and processed locally, and in Pb and Zn minerals that were mined locally and shipped from the harbour of Portovesme until a few decades ago. Data and publications on the level and effects of contaminants on the adjacent coastal areas are very limited ŽRiolfatti et al., 1992., although ore smelters are known to be major point sources of heavy metals in land and water environments ŽWard et al., 1984; Batley, 1987; Langlois et al., 1987; Pilgrim and Hughes, 1994; Zachmann and Block, 1994.. Here we present data that were obtained from radiodated sediment cores from the Portovesme harbour with the aim of assessing the contamination sources, the historical evolution of contamination and the fluxes of Hg, Cd, Pb and Zn to the sediments. An evaluation of the metal anthropogenic fraction and, therefore, the potential threat for the coastal environment has also been
obtained through selective leaching of the sediments. 2. Area of investigation The harbour of Portovesme ŽFig. 1. was built in 1870 to ship the ores Žblende, galena and pyrite. mined in the surrounding areas. Though mining activity has now been practically abandoned, ores and products to and from the industrial area are still transported. The mouth of the harbour is 250 m wide and in the centre a dredged canal approximately 13 m deep allows berthing of vessels. In the north-western area of the harbour the water depth ranges between 6 and 9 m, while in the southern area it is shallower Žbathymetry range: 1]3 m.. In 1991, the shipping traffic was estimated at approximately 6 000 000 t. The main industrial plants nearby are the following: v
v
a plant producing alumina from bauxite, operating since 1972; a plant producing aluminium by electrolysis of alumina, operating since 1972;
Fig. 1. Map of the Portovesme area and location of sampling sites.
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
131
a coal-fired power generation plant Ž720 MW. and a smaller oil-fired plant, operating since 1970; and a lead]zinc smelter built in the late 1960s and in full production since 1972, with a yearly production of 154 000 t of metallic lead and zinc, 500 t of cadmium, and 17 t of mercury and sulphuric acid.
Both the samplings and the analyses refer to 1993. The results are being reported now, because the data were used in legal proceedings on the case that were still in progress until recently.
A cleanup of a wide area Ž390 km2 . surrounding the industrial settlement has been planned by the Italian Government and is now ongoing. Emissions to the atmosphere from the Portovesme area have been estimated at 65 000 t of SOx per year, 4000 t of dust per year, 10 t of Pb per year and 100 t of F per year ŽGazzetta Ufficiale, 1993.. The lead]zinc smelter mostly utilises imported sulphide minerals such as sphalerite ŽZnS. and galena ŽPbS.. Sphalerite usually contains between 50 and 67% of Zn and small percentages of Pb, Cu, Cd, Fe, Au, Ag and Hg. Galena, which can contain Pb up to 86%, can also contain minor elements such as Ag, Cd, Ni, Cu, Co, and As. The efficiency of metal removal from the liquid effluent of the smelter was not improved until 1991, when wastewater treatment technologies using both hydroxide and sulphide precipitations were implemented. The drainpipe discharging the liquid effluents of the smelter is also shared by the aluminium production plant and the warm cooling-water effluent from the coal-burning power generation plant ŽFig. 1.. This causes a clockwise water circulation inside the harbour driven by the warm water stream from the power generation plant. Together with the liquid effluents, the stack emission can also be a source of sediment contamination. However, earlier studies in the area showed the highest deposition of metals in the prevailing NW wind direction ŽContu et al., 1986.. Other possible sources of harbour sediment contamination arise from handling of ores and concentrates Žloadingrunloading of trucks, spillage of liquids, and dust dispersion from materials in open piles accumulated on the harbour embankment and subject to the action of the wind., land erosion, and runoff from the mining areas.
Four sediment cores ŽC1, C2, C3, and C4. were collected in January 1993 in the southern part of the harbour of Portovesme from sampling stations approximately 100 m apart, along the circulation path of the harbour currents ŽFig. 1.. In this area navigation of industrial vessels, which only occurs to reach the docks in the western and northern areas of the harbour, is not possible because the waters are too shallow. Moreover, small private boats, which refer to a tourist marina located nearby, are not allowed to enter the industrial harbour. Furthermore, the sediments in this area are generally undisturbed by bioturbation, since the bottom water is nearly anoxic and large burrowing organisms are absent. However, throughout the sampling period tidal scour was insignificant, no storm events were observed, and freshwater inputs can be ruled out. The outfall of the wastewater treatment plant of the smelter is located in this area ŽFig. 1.. The short cores, up to approximately 30 cm in length, were collected by scuba divers in Plexiglas liners Ž6 cm internal diameter. and frozen to prevent mixing during transport to the laboratory. Freezing was done very rapidly to avoid the formation of large disruptive ice crystals during storage. No compaction was observed as a consequence of the coring procedure. After thawing, the cores were extruded and divided into sections of a thickness of 2 cm. Core sectioning was performed rapidly in the air. Sample homogenisation and sub-sampling were carried out in a Glove Box under nitrogen atmosphere to avoid oxidation. Sediment sub-samples for the determination of total element concentrations Žexcept Hg. were dissolved in HNO3rHClO4rHF ŽAgemian and Chau, 1976.. Total Hg determinations were carried out after cold digestion with a mixture of HClO4rH 2 SO4 and further addition of a solution
v
v
3. Experimental
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of KMnO4 . Analytical blanks were prepared using the same reagents. A Perkin]Elmer model 2100 atomic absorption spectrophotometer ŽAAS. in the flame mode was used for the measurement of Cd, Pb, and Zn in the solutions. Mercury was determined by the cold vapour method. Leaching of sediments with 0.5 N HCl was carried out according to the method of Malo Ž1977.. Total concentrations of Al, Si, Ca, Mg, K, Mn, Fe, Ti, V, and S were determined by X-ray fluorescence ŽXRF. after combustion of the samples at 3608C. An ORTEC 6110 tube excited fluorescence analyser equipped with an X-ray tube ŽMo and W anodes. and a 30-mm2 SirLi detector Žresolution of 160 eV at 5.9 keV. was used. The samples, ground to less than 200 mesh, were prepared as powder pellets Ž3 cm diameter. pressed at 20 t cmy2 with a thickness greater than the critical thickness ŽBertin, 1975. for all the elements concerned. A standard reference material from the National Bureau of Standards ŽRiver Sediment 1546. was used to check the accuracy of the results of both AAS and XRF analyses. Analytical reproducibility was better than 5% as determined from five replicate analyses of a bulk sediment for AAS analyses, and better than 12% for XRF analyses. Organic matter expressed as loss on ignition ŽLOI. was estimated by weight differences between 360 and 1108C ŽBattiston et al., 1989.. The fine fraction content of the sediment was determined by sieving the wet samples with a 63-mm ASTM sieve. 3.1. High resolution gamma spectrometries Radioactivity analyses of the core sediment samples Ž70]100 g wet weight. airtight in disk shaped vessels, were performed after at least 30 days to ensure secular equilibrium between 226 Ra and short lived daughters. Radioassay was by high resolution gamma spectrometry using an N-type intrinsic germanium coaxial detector with a relative efficiency of 26% Žpeak to Compton ratio 56r1: FWHM 1.79 keV at 1.33 MeV and 0.843 keV at 122 keV; FWTM 3.45 keV at 1.33 MeV..
Low energy photon emission data were processed for self-absorption correction as previously described ŽDegetto et al., 1995.. Total 210 Pb activity was measured directly through its emission at 46.5 keV. The fraction supported by 226 Ra inside the sediment was determined through 214 Pb Ž352 keV. and 214 Bi Ž609 keV. photon emissions at radioactive equilibrium. The uncertainty in the determination of radionuclides, taking into account statistical counting and calibration uncertainties, was never less than 10% at a 95% confidence level.
4. Results and discussion The analysed sediment sections and their sedimentation rates are given in Table 1. Chronologies were established from profiles of unsupported 210 Pb with the independent control of the 137 Cs spike from weapon test experiments in the atmosphere Žpeak in 1963]1964.. The contribution of recent 137 Cs deposition from the Chernobyl accident does not interfere with this control; in fact Chernobyl-derived radioactivity is a well-separated event dated at 1986. Moreover, the Table 1 Sedimentation rates Žcmryear. for the cores from Portovesme harbour a Section number
Depth Žcm.
C1
C2
C3
C4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0]2 2]4 4]6 6]8 8]10 10]12 12]14 14]16 16]18 18]20 20]22 22]24 24]26 26]28 28]30 30]32
0.69 0.27 0.25 0.19 0.08 n.d. n.d. n.d. n.d. n.d. n.d.
0.32 0.23 0.34 0.28 0.29 0.43 0.62 0.36 0.77 0.24 0.37 0.15 n.d. n.d. n.d. n.d.
0.31 0.18 0.20 0.18 0.12 0.25 0.27 8.00 1.60 0.16 n.d. n.d.
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.
a
n.d., not determined.
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
deposition of that radioactivity in this area was very low Žtotal beta radioactivity in the air, integrated over the period of deposition, May 1986, was approximately 1r6 compared to that observed in North Italy. ŽColacino, 1986.. In these conditions Chernobyl radioactivity, which doubled the 137 Cs inventory in North Italy could here be a difficult fraction to detect in the sediments. The available data allowed a reliable time to depth match down to 10 cm in C1 and 24 cm in C2, whereas in C3 some uncertainty could arise from the 137 Cs profile, which appears to be very disturbed ŽFigs. 2 and 5.. The maximum fallout, however, is nearly at the same depth for all cores, and the observed differences are substantially compatible with the time scale obtained from unsupported 210 Pb ŽFigs. 3]6.. The cores are different, however, and their difference is at best outlined by the fluxes ŽFig. 7.. The sedimentary concentrations of Hg, Cd, Pb, and Zn are shown in Figs. 3]6, while Table 2 shows the major element concentration in selected sections of the cores. Analyses were carried out on the whole sample. Considering the preferential occurrence of the heavy metals in the finest grain-size fractions, we evaluated the - 63mm fraction content of the sediment samples
133
ŽFigs. 3]6.. A significant relationship between the - 63-mm fraction and metal concentrations was observed in the four cores. The strongest positive correlation coefficients were found in C2 Ž n s 16, P- 0.001; for Hg r s 0.762, for Cd r s 0.889, for Pb r s 0.858, and for Zn r s 0.858.. The fine fraction in the surface layer Ž0]2 cm. of C1, C2, C3 and C4 steadily increases from 19% in C1 to 72% in C4, whereas a fairly opposite trend is observed for sediment dry weight: C1 s 71%, C2 s 62%, C3s 61%, and C4s 39%... Sediment enrichment factors ŽSEFs. have frequently been used to quantify enrichment of trace metals in recent sediments ŽKemp et al., 1976; Forstner and Wit¨ tmann, 1979.. However, the changes are usually calculated relating to a ‘conservative’ substance such as Al, which is considered to reflect non-anthropogenic inputs. As shown in Table 2, the extremely high concentration of this element in the sediments of the harbour Žfrom 5 to 32%., very likely of anthropogenic origin, precludes the calculation of SEFs for these sediments as well as the calculation of metalraluminum ratios ŽBruland et al., 1974. to express the variation of the trace metal content in the sediment cores. However, if the deep layers of the core C3 Žsections 11 and 12., where concentrations were relatively
Fig. 2. Time to depth match for cores C1, C2, and C3. Dots indicate mean age of sections.
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Fig. 3. Metal chronologies and depth profiles for C1 sediment core. U Unsupported
constant, are considered to represent background levels Žmean values: Hgs l; Cds 8; Pb s 65; and Zn s 320 mgrg., then the peak concentrations in sediments deposited after the industrial settlement Ž1970. in C1 were 108, 15, 40, and 42 times
210
Pb.
higher for Hg, Cd, Pb, and Zn, respectively, in C2, 14, 5, 20, and 22 times higher; in C3, 8, 7, 20, and 21 times higher. The runoff from the surrounding mining areas, which were very active at that time, and the scattering of dusts during shipping opera-
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
Fig. 4. Metal chronologies for C2 sediment core. U Unsupported
tions of the ores mined locally, could probably have contributed to the relatively higher metal background concentrations found in the sediments of C1, C2 and C3 that settled before 1900]1910.
210
135
Pb.
The organic content in the cores Žas LOI. never reached 2% and is poorly correlated with heavy metal content. From Fig. 7, Hg, Cd, Pb, and Zn appear to be accumulating at higher rates in core C1, the near-
136
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Fig. 5. Metal chronologies for C3 sediment core. U Unsupported
est to the industrial waste outlet, and at a lower rate in C2 and C3. In C1 ŽFig. 3. the highest Hg concentration was found in section 4 Ždepth: 6]8 cm., corresponding to the sediment deposited in
210
Pb.
1964]1975, while Cd concentrations were highest in section 2 Ždepth: 2]4 cm., deposited in 1983]1990. It should be noted that both Hg and Cd dramatically decrease in the top layer of C1,
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
Fig. 6. Depth profile for C4 sediment core. U Unsupported
which was deposited in 1990]1993. The sedimentation rate of the section 1 of C1 Ždepth: 0]2 cm. was much higher Ž0.69 cmryear. than the deeper layers Žsections 4 and 5, - 0.20 cmryear.. In C2 the sedimentation rate was approximately 0.3 cmryear since 1930, except for a short
210
137
Pb.
increase in the early 1940s and 1950s. The heavy metal concentration in C2 is lower than that in C1, the highest values for Hg, Cd, Pb, and Zn were detected in the first 4 cm of the core Ž1978]1993.. Mercury and Cd concentrations in the sediment deposited before the smelter was
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M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
Fig. 7. Fluxes of metals to the sediment since approximately 1940.
installed in 1970 are quite uniform along the core. The concentrations of Hg, Cd, Pb, and Zn were relatively constant in the deepest sections of the core Ž13, 14, 15, and 16, not represented in Fig. 4.. Hg concentrations ranged from 2.6 to 3.3 Ž xs 3.2.; Cd from 7.5 to 10.2 Ž xs 8.7.; Pb from 115 to 224 Ž xs 182.; and Zn from 1051 to 1287 Ž xs 1100.. In core C3, sedimentation is generally uniform Žapprox. 0.2 cmryear. and lower than in C1 or C2. Mercury concentrations are relatively lower and quite uniform, while the Cd content is higher in the first 8 cm of the core. The extremely high Hg, Cd, Pb, and Zn concentrations observed from 14 to 18 cm depth of core appear to be due to an
extemporaneous event that occurred in the early 1920s. The corresponding peak sedimentation rate is extremely high Ž8.0 cmryear.. On the basis of analytical data this peak may be due to some raw material being dumped during harbour activities as outlined by the sharp difference in sediment composition compared to the immediately adjoining layers. A relative increase in the metal concentration can also be shown in C2 in the sediments deposited in the same time period. The metal concentrations at lower depths of C3, sediments deposited before 1909, were the lowest in the harbour ŽHgs 0.8]l.2; Cds 8.0]11.0; Pb s 63]72; and Zn s 270]372 mgrg d.w... Fig. 6 shows the heavy metal profiles in core
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
C4. Mercury, Cd, Pb and Zn concentrations are relatively uniform along the core. The very high Cd concentration exhibited both in C4 Žrange: 98]159 mgrg dry weight. and in the upper section of C3 suggest that Cd is more mobile than Hg in the harbour. It is interesting to note that the - 63-mm fraction content ranged from 66 to 80%. This finding is significant in that it implies that differences in concentration inside the harbour may result from sediment accumulation. The high radioactivity value of 210 Pb and 137 Cs and its uniformity with depth proves that core C4 represents an area of accumulation of fine-grained sediment, conveyed from the surrounding surface sediment layers. From the profile of the core no reasonable sedimentation rate was evaluated, since complete mixing of the sedimentary layers was observed ŽFig. 6.. Moreover sampling station C4 was located near a small pier at the outlet of the harbour. The complete mixing observed in this core is likely to be due to marine propellers of vessels operating nearby. From Fig. 7 fluxes of Hg, Cd, Pb, and Zn deposited in the sediments after the industrial settlement Žapprox. 1970. appear to be much higher in core C1, which was collected closer to the liquid effluent discharge in the harbour. Considering that these metals are not present in the
139
cycle of Al production, and that they are supposed to be contained only in low concentrations in the water-soluble components of fly-ash from power stations ŽSabbioni and Goetz, 1982.. The main source of Hg, Cd, Pb, and Zn contamination is likely to be liquid effluents from the lead]zinc smelter in the harbour. Metal concentration in the cores decreases with an increase in the distance of the sampling station from the industrial effluent discharge. Furthermore, Hg, Cd, Pb, and Zn fluxes in C1 sharply decreased between 1990 and 1993, very likely reflecting the post-1990 improvement in wastewater treatment at the smelter, more stringent legal regulations and growing public concern about environmental problems. No historical records of either metal-emissions from the smelter or atmospheric deposition of metals in the region are available. Moreover the correlation coefficients between metals indicate a common source Ž P- 0.0005, n s 47: r s 0.496, Hg-Pb; r s 0.643, Hg-Zn; r s 0.729, Cd-Pb; r s 0.627, CdZn; r s 0.89, Pb-Zn. in spite of the lower value for the relation coefficient between Hg and Cd Ž P- 0.05, r s 0.295.. Treatment of sediments with dilute acids ŽHCl, HNO3 . has been used to separate the most mobile fraction of trace metals Žbound to the sediment in adsorbed, precipitated or co-precipitated and complexed forms. from the ‘residual fraction’
Table 2 Major element concentration of selected sediment profiles Core
Section
Depth Žcm.
Al Ž%.
Si Ž%.
Ca Ž%.
S Ž%.
Mg Ž%.
K Ž%.
Mn Ž%.
Fe Ž%.
Ti Ž%.
V Ž%.
C1
1 5 11
0]2 8]10 20]22
11 30 5
25 8 22
3 3 10
0.3 0.8 0.5
3 2 2
1.0 0.8 1.6
0.05 0.06 0.03
1.2 2.6 0.8
0.2 0.4 0.3
0.05 0.17 0.07
C2
1 5 11
0]2 8]10 20]22
23 12 6
12 18 17
8 10 12
0.6 0.3 0.9
1 2 3
0.8 1.2 1.1
0.07 0.03 0.04
2.2 1.3 2.0
0.4 0.2 0.4
0.09 0.07 0.06
C3
1 5 11
0]2 8]10 20]22
32 30 6
7 8 35
5 4 3
1.0 0.7 0.1
1 2 1
0.5 0.5 1.1
0.07 0.05 0.08
2.5 1.3 0.4
0.4 0.3 0.2
0.10 0.09 0.01
C4
1 5
0]2 8]10
15 25
13 8
8 6
1.0 1.4
3 1
0.98 0.7
0.08 0.1
2.2 2.6
0.4 0.5
0.04 0.1
M. Schintu, S. Degetto r The Science of the Total En¨ ironment 241 (1999) 129]141
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Table 3 0.5 N HCl soluble content of Hg, Cd, Pb and Zn Ž% of total metal. of selected sediment profilesa Core
Section
Depth Žcm.
Hg Ž%.
Cd Ž%.
Pb Ž%.
Zn Ž%.
C1
1 5 11
0]2 8]10 20]22
11.6 n.d. n.d.
82.4 43.8 26.4
64.9 77.9 18.5
62.8 24.8 47.3
C2
1 5 11
0]2 8]10 20]22
3.2 n.d. n.d.
51 27.8 21.4
69.4 75.5 78.6
39.5 30.5 60.9
C3
1 5 11
0]2 8]10 20]22
2.4 n.d. n.d.
89.1 63.1 14.4
60.9 63.1 41.3
81.3 82.3 34.9
C4
1 5
0]2 8]10
1.8 1.3
31.1 37.4
86.6 82.4
91.6 85.5
a
n.d., not detected.
ŽMalo, 1977; Forstner and Wittmann, 1979; Bryan, ¨ 1984; Kersten and Forstner, 1990.. Furthermore, ¨ Luoma and Bryan Ž1982., in studies of trace metal uptake by benthic organisms, found that 1 M HCl extraction gave better information about metal bioavailability than either the total metal concentration in the sediment or any one of a range of other extractants Žacetic acid, ammonium acetate, ammonia.. In order to identify the risk of remobilisation of high quantities of toxic metals from the sediments to the water column, selected layers of the cores ŽTable 3. were leached with 0.5 M HCl, according to the method of Malo Ž1977.. Portions of Cd ranging from 51 to 92% of the total metal were extracted from the surface layer Ž0]2 cm. of the cores, while in section 11 Ž20]22 cm. these percentages ranged from 14 to 26%. A similar figure was found for Pb and Zn, but lower percentages of the total metal were extracted. Mercury was recovered with 0.5 M HCl only from the surface layer of C1, C2, and C3, in percentages ranging from 2.5 to 11.5 of total Hg. In core C4 the fraction of Hg, Cd, Pb, and Zn leached with dilute acid did not change with depth, confirming the homogeneity of the sediment accumulated in this area as a result of sediment accumulation and mixing.
5. Conclusion Metal concentration in the cores decreases with an increase in distance from the sampling station from the industrial effluent discharge. Besides, metal leaching with HCl, shows the greatest differences between upper and lower sections in station C1, the most exposed to industrial waste effluents. The observed contamination is likely to be due to liquid effluents from the lead]zinc smelter. Hg, Cd, Pb, and Zn fluxes appear to be pertinent to the industrial settlement in the area and to the performance of their waste treatment. Leaching experiments of surface sediments show that metals are largely present in exchangeable or adsorbed forms. References Agemian F, Chau ASY. Evaluation of the extraction techniques for the determination of metals in aquatic sediments. Analyst 1976;101:761]767. Batley GE. Heavy metal speciation in waters, sediments and biota from Lake Maquarie, New South Wales. Aust J Mar Freshwater Res 1987;38:591]606. Battiston G, Degetto S, Gerbasi R, Sbrignadello G. Determination of sediment composition and chronology as a tool for environmental impact investigations. Mar Chem 1989;26:91]100. Bertin PE. Principles and practice of X-ray spectrometric analysis. New York: Plenum Press, 1975. Bruland KW, Bertine K, Koide M, Goldberg ED. History of metal pollution in Southern California coastal zone. Environ Sci Technol 1974;8:425]432. Bryan GW. Pollution due to heavy metal and their compounds. Marine ecology. J Wiley and Sons, 1984:1289]1431. Colacino M. L’incidente di Chernobyl: misure di radioattivita ` nell’aria. Proceedings of A.I.R.P. Conference, Rome, June 1986:65]86. Contu A, Flore C, Schintu M, Spiga G. Piombo e cadmio nel suolo e nei vegetali di un’area industrializzata della Sardegna. Inquinamento 1986;XXVIIIŽ3.:2]6. Degetto S, Sbrignadello G, Cianchi A, Valdarnini F. Un metodo semplice per la correzione geometrica e di autoassorbimento delle attivita ` di emettitori gamma a bassa energia in matrici ambientali. V Convegno sulle metodologie radiochimiche e radiometriche in radioprotezione, 20]22 June 1995, Urbino, Italy. Degetto S, Schintu M, Contu A, Sbrignadello G. Santa Gilla lagoon ŽItaly.: A mercury sediment pollution case study. Contamination assessment and restoration of the site. Sci Total Environ 1997;204:49]56.
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