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Trace metal concentrations in marine macroalgae from different biotopes in the Aegean Sea
Environment International 27 (2001) 43 ± 47
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Trace metal concentrations in marine macroalgae from different biotopes in the Aegean Sea T. Sawidisa,*, M.T. Brownb, G. Zachariadisc, I. Sratisc a
Department of Botany, University of Thessaloniki, GR-54006 Thessaloniki, Greece Department of Biological Sciences, University of Plymouth, Plymouth PL4 8AA, UK c Laboratory of Analytical Chemistry, University of Thessaloniki, GR-54006 Thessaloniki, Greece b
Received 15 September 2000; accepted 5 April 2001
Abstract The commonest species of red, brown, and green macroalgae were sampled from a range of biotopes in the Aegean Sea and analysed for five different trace metals. Significant differences in metal concentrations were found among different seaweed species from the same biotope. The concentrations of metals in the various seaweed species may reflect their morphology, with those having a larger surface area having a greater internal content. Different species of seaweed have different affinities for different heavy metals. This may reflect competition between metals for binding or uptake sites in the seaweed. Comparing metal concentrations in algae among the studied sampling stations clearly indicates that the degree of accumulation depends not only on human activities but also on the geology of the specific area. While seaweed can be used successfully to assess the levels of heavy metals in the marine environment, not all elevated concentrations of heavy metals necessarily reflect increased levels of pollution. Indeed, the high concentrations of certain metals, e.g., Ni, found in our seaweed samples reflected the metaliferrous nature of the rock. It is therefore important to take account of a region's geology before attempting to interpret the data. D 2001 Elsevier Science Ltd. All rights reserved. Keywords: Algae; Heavy metals; Aegean Sea; Monitoring
1. Introduction Marine macroalgae, which contribute significantly to the primary production of near-shore and estuarine ecosystems, readily accumulate trace metals from solution, and for this reason, have been used extensively as biomonitors of metal contamination of seawater (Brown and Depledge, 1998). Despite recognition of the fact that various intrinsic and extrinsic factors can influence metal uptake, determination of the metal concentrations in seaweed is still considered to provide useful information about the levels of metal contamination and environmental quality of an area, albeit of a qualitative nature (Lobban and Harrison, 1994). Moreover, many macroalgae have a relatively long life span and can therefore integrate short-term temporal fluctuations in environmental concentrations (see review by Phillips, 1994).
* Corresponding author. Faculty of Biology, Institute of Botany, Aristotle University of Thessaloniki, Macedonia, Greece. Tel.: +30-31998294; fax: +30-31-998389.
Within the Mediterranean Sea, there have been several studies using seaweed to assess the degree of metal pollution in different regions, e.g., the northern Adriatic Sea (e.g., Munda and Hudnik, 1991) and Lebanon (e.g., Shiber, 1980). However, the coastlines of Greece have been only sporadically investigated and these studies are usually limited to just a few sites, e.g., the Gulf of Thermaikos (Sawidis and Voulgaropoulos, 1986; Djingova et al., 1987; Fytianos et al., 1997; Haritonidis and Malea, 1995, 1999), Pylos, Ionian Sea (Haritonidis and Nikolaidis, 1989, 1990), and the Gulf of Antikyra (Malea et al., 1992, 1994, 1995). Industrialisation, urbanisation, and mining activity around the coastlines of the Aegean Sea can all negatively impact on fisheries, water resources, and human health of the region. Tourism, too, while of positive benefit economically, may also adversely affect the marine environment which tourists have come to enjoy. In addition to these anthropogenically derived sources of contamination, the geology of some areas surrounding the Aegean Sea has resulted in naturally elevated levels of trace metals. Thus, such sources of trace metals must be distinguished from
0160-4120/01/$ ± see front matter D 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 1 6 0 - 4 1 2 0 ( 0 1 ) 0 0 0 5 2 - 6
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T. Sawidis et al. / Environment International 27 (2001) 43±47
human influences before any assessment of the extent of the pollution problem can be made. Here, we present the results of the most extensive baseline survey of trace metal concentrations in marine macroalgae so far carried out in the Aegean Sea. Commonly occurring seaweed species, belonging to the three classes of Chlorophyceae, Rhodophyceae, and Phaeophyceae, were collected from 14 sites and analysed for concentrations of five different trace metals. 2. Materials and methods 2.1. Study area and sampling stations The sampling network comprised a wide spectrum of biotopes within the Aegean Sea (Fig. 1). (1) Chalkidiki. A peninsula in the north Aegean Sea, located in a region with polymetallic (Pb± Zn ±Au) sulphide deposits which have been mined since ancient times and still continues today. Three stations were sampled: Nea Fokaea, Paliouri, and Kalandra.
(2) Gulf of Thermaikos. Situated in the northeast Aegean, this area is dominated by Thessaloniki, a city of more than 1,200,000 inhabitants. It has been estimated that over 120,000 m3 per day of partially treated (40 m3 per day) domestic sewage and 30,000 m3 per day of industrial wastewater are discharged from the city and its environs into the inner part of the Gulf (Fytianos et al., 1997). The Gulf of Thermaikos is a shallow (max. depth of the inner part is 28 m) wind-stirred bay characterised by weak tidal mixing (tidal range is less than 50 cm) and so there is little dilution of the contamination by seawater from the open sea. Three stations were sampled: A. Trias, situated at the entrance to the Gulf, 10 km from Thessaloniki; N. Krini, a site affected mainly by the municipal wastes from Thessaloniki; Kalochori, situated near the industrialized zone of the city and affected mainly by industrial wastes from an oil refinery, a fertilizer plant, a steel-processing plant, an antiknock compounds factory, and a chlor-alkali plant. (3) Gulf of Pagasitikos. An enclosed gulf in the region of Thessalia and dominated by the city of Volos with c. 80,000 inhabitants. The harbour of Volos is the main export centre of the region. Three stations were sampled: Pefka, situated close to Volos and affected by its industrial and domestic discharges; Alykes, situated west of Volos; Lehonia, situated southeast of Volos. (4) Thira Island. This is the largest of the five islands comprising the volcanic Santorini Island complex in the southeast Aegean. The present-day crescent-shaped island is a consequence of volcanic activity in prehistoric times. The last major eruption dates back 3600 years, to the late Bronze Age and is connected with the myth of lost island of Atlantis. Three stations, Monolithos, Perivolos, and Akrotiri, located on the outer coast of the island, were sampled. (5) Crete. The fifth largest island in the Mediterranean Sea and the largest of the islands forming part of modern Greece. Located in the south Aegean Sea, Crete is a popular tourist destination. Agriculture is the economic mainstay of the island. The sea around Crete forms the deepest part of the Aegean Sea (3294 m). Three stations were sampled: Heraklion, the capital of the island with c. 200,000 inhabitants and which can increase significantly during the summer period; Chania west of Heraklion with a population of 100,000; A. Nicolaos east of Heraklion with a population of 50,000. 2.2. Sampling procedures
Fig. 1. Map of Greece showing the location of studied biotopes. (1) Chalkidiki (N. Fokaea, Paliouri, Kalandra); (2) Thermaikos Gulf (A. Trias, N. Krini, Kalochori); (3) Pagasiticos Gulf (Pefka, Alykes, Lehonia); (4) Thira Is. (Monolithos, Perivolos); (5) Crete Is. (Heraklion, Chania, A. Nikolaos).
A minimum of three samples of the most commonly occurring seaweed were collected from each station. All thalli were thoroughly cleaned with seawater, followed by running distilled water to remove adhering particulate matter and epiphytes. Material was oven-dried at 30°C to constant weight and then pulverised to ensure uniform distribution of metals in the samples.
T. Sawidis et al. / Environment International 27 (2001) 43±47
2.3. Analytical methods for sample pretreatment Accurately weighed portions of each sample (about 1 g dry weight, DW) were digested in 8 ml of concentrated HNO3 (Merck, Proanalysis). The solutions were filtered through Whatman type 589/2 filters and diluted accurately to 25 ml volume with double deionised water. These solutions were then analysed for metal concentrations using a Perkin Elmer 2380 Atomic Absorption Spectrophotometer coupled to an HGA-400 Graphite Furnace controller. In the majority of cases, the determination of Cu, Mn, Ni, and Zn was carried out in flame mode while Cd and Pb, and the determinations of the other metals, were carried out in a graphite furnace. All samples were analysed three times. For all determinations, pyrocoated graphite tubes were used. Two plant material NBS standards (National Bureau of Standards, USA), number 1573 (tomato leaves) and 1575 (pine needles), were also analysed following the procedures used for the seaweeds. Recoveries were 95.5% for copper, 97.5% for zinc, 94.2% for lead, 99.0% for manganese, 97.5% for cadmium, and 98.4% for nickel of the expected values and therefore the procedures employed are considered appropriate. All concentrations are presented as milligram per kilogram dry weight (mg kg 1 DW), and the quoted values are means. 3. Results and discussion The algal species collected from each biotope and their trace metal content are listed in Table 1. The concentrations of metals are expressed as the mean value obtained from the specimens collected during their growing season. Significant differences in metal concentrations were found among different seaweed species from the same biotope. For example, the zinc concentration in Cladophora (57.9 mg kg 1), collected from Kalochori is significantly less than the zinc concentration in Gracilaria (155.3 mg kg 1) collected from the same site. A similar trend is found for manganese in these two seaweed species from Kalochori but not for nickel and copper. There are several possible reasons for such differences in the accumulation of metals by different species. The concentrations of metals in the various seaweed species may reflect their morphology, with those having a larger surface area having a greater internal content. Long-lived species (e.g., perennials vs. annuals) will have the opportunity to accumulate metals to a greater degree. Growth rates too can affect accumulation patterns, with faster growing material appearing to have lower concentrations. The results obtained in this study also indicate that different species of seaweed have different affinities for different heavy metals. This may reflect competition between metals for binding or uptake sites in the seaweed (Lobban and Harrison, 1994). The foregoing discussion highlights some of the problems associated with this type of biomonitoring programme. Pollution levels at various locations should be compared by
45
using the same species at each site. Furthermore, a strict protocol should be adhered to including: using material of the same age, collected at the same time of year (similar growth rates?).Table 2 provides a comparison of heavy metal concentrations at the various sites using the metal concentrations in the brown seaweed Cystoseira barbata and the green seaweed Ulva lactuca and Enteromorpha linza. From these results we can see that, for example, the levels of nickel are highest at Chalkidiki, reflecting the metalliferous nature of the area. Comparing metal concentrations in algae among the studied sampling stations clearly indicates that the degree of accumulation depends not only on the human activities but also on the geology of the specific area. For example, cadmium and nickel concentrations in the Thermaikos Gulf, an area of high human activity, are significantly less than from Chalkidiki, Pagasitikos Gulf, Crete, or Thira. In these latter areas, polymetallic sulphide deposits, which contains Cd and/or Ni, exist. In Chalkidiki, the ultrabasic rocks are the main Ni source whereas in the Pagasitikos Gulf the Ni concentration is partly influenced by the laterite deposits of the area. In the case of copper, the concentrations reflect human activities rather than geological deposits, although copper ores on the eastern side of Chalkidiki may influence the results. Thus, the increased concentrations near the industrial areas of both Thessaloniki and Volos are most likely the result of municipal sludge and industrial wastes. The same is also true for Mn where increased concentrations observed in the Thermaikos Gulf (Kalochori-industrial zone) reflect the discharges of wastewaters from dye-houses, a steel mill, and an electrolytic manganese dioxide factory. The relatively high levels of Cu and other metals at Krini and A. Triada on the opposite side of the industrial zone (Kalochori) could be attributed to the local sea currents carrying metal-rich industrial sewage towards these stations. Similarly, the variability of trace metal concentrations among the 14 stations examined is affected by the dynamic current regime of the Aegean Sea. Water circulation in the north Aegean Sea is dominated by the BSW current that flows westward or southward after passing the Dardanelles. The complex geometry of the north Aegean with respect to the main axis of the direction of the current results in the formation of small-scale cyclonic and anticyclonic flow regions along the general direction of movement. Finally, a very diluted BSW current flows through the northwest passages of the Cyclades plateau, towards the south Aegean Sea (Zodiatis, 1993). Direct comparisons with other published works are fraught with problems, including those associated with sample handling and processing (Gledhill et al., 1998). Ulva and Enteromorpha are two of the most widely used seaweed biomonitors of trace metal pollution. From studies undertaken in various parts of the world, it is possible to obtain an estimate of the expected range of concentrations within these seaweed species from sites varying in metal contam-
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T. Sawidis et al. / Environment International 27 (2001) 43±47
Table 1 The mean concentration (mg kg
1
) of heavy metals in samples of the most common seaweed species collected from sites in the Aegean Sea, Greece
Region
Site
Species
Cu
Zn
Cd
Pb
Mn
Ni
Chalkidiki
N. Fokaea
C. barbata Padina pavonica Laurencia obdusca Halimeda tuna Ceramium rubrum Gigartina tendii Cladophora sp. E. linza C. barbata Acetabularia mediterranea C. barbata Gracilaria verrucosa Codium vulgarae Gra. verrucosa G. tendii L. obdusca E. linza U. lactuca Posidonia oceanica Petalonia fascia Cer. rubrum Gra. verrucosa Polysiphonia deusta Cladophora sp. E. linza U. lactuca Cer. rubrum E. linza C. barbata Cer. rubrum U. lactuca C. barbata U. lactuca C. barbata P. pavonica Cer. rubrum C. barbata Sargassum sp. Cladophora sp. C. barbata Gra. verrucosa U. lactuca C. barbata U. lactuca Corralina officinalis
6.1 3.7 7.1 4.5 10.6 2.0 29.3 3.4 8.8 2.1 1.7 2.1 0.7 3.4 17.8 3.6 6.7 7.4 8.8 3.8 17.1 7.9 13.3 6.8 9.8 11.1 9.9 9.7 2.1 5.4 8.3 3.2 9.0 2.7 3.0 2.0 0.7 2.1 2.2 3.8 14.9 7.0 1.7 14.5 0.85
22.3 19.3 25.4 14.6 27.2 23.4 51.8 45.0 16.4 6.5 29.8 38.0 11.2 50.0 135.0 34.7 67.5 43.7 119.3 43.8 107.0 155.3 64.3 57.9 121.3 88.0 83.3 47.9 18.7 71.6 49.3 58.1 79.9 17.2 26.3 22.3 8.8 18.7 7.0 14.2 43.6 16.4 27.5 56.3 37.5
0.47 1.6 1.2 2.3 1.8 1.1 0.95 0.77 0.83 2.7 0.06 0.06 0.09 0.88 1.45 0.79 0.61 0.42 1.6 0.5 0.84 0.9 0.24 0.32 0.47 0.76 1.6 0.6 0.4 0.74 0.24 2.6 0.54 0.4 1.2 1.4 1.4 0.07 1.0 1.1 0.21 0.42 2.7 1.1 2.9
2.1 2.1 0.02 0.02 8.5 0.02 24.7 0.02 2.5 7.0 0.02 0.02 0.02 0.02 15.7 0.02 0.02 0.02 0.02 0.02 9.9 14.7 17.7 13.0 0.02 0.02 21.5 12.4 0.02 4.1 2.8 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02
70.5 202.5 79.8 71.3 210.8 11.8 416.0 31.5 40.5 6.3 22.2 27.0 30.9 79.3 303.0 61.8 59.7 33.3 530.3 36.4 353.8 909.0 277.5 200.0 94.3 132.3 93.0 77.4 30.9 93.0 100.6 181.3 182.0 47.0 180.5 86.2 7.9 38.0 19.0 5.6 31.3 25.3 34.0 137.0 42.0
8.7 32.3 17.5 21.9 27.5 4.6 32.0 6.9 14.2 17.5 9.7 8.0 9.1 4.6 43.6 4.4 10.3 9.2 N.D. 11.5 18.3 7.5 9.2 8.0 13.7 5.1 13.1 31.8 4.3 N.D. N.D. 28.5 52.6 14.6 18.3 18.3 6.8 13.7 10.3 4.3 15.8 8.7 16.0 13.7 18.3
Paliouri
Kalandra Thermaikos
A. Trias N. Krini
Kalochori
Pagastikos
Pefka Alykes Lehonia
Thira Is.
Monolithos Perivolos
Crete
Heraklion Chania A. Nikolaos
Cu = copper; Zn = zinc; Cd = cadmium; Pb = lead; Mn = manganese; Ni = nickel; N.D. = not detected.
ination. Copper concentrations from contaminated sites range from 20 to 70 mg kg 1 DW and 14 to 134 mg kg 1 DW for Enteromorpha and Ulva, respectively (e.g., Seeliger and Edwards, 1987; Ho, 1990, Phillips, 1990; Brown et al., 1999). For zinc the values for Enteromorpha and Ulva are 95± 130 mg kg 1 and 42 ± 160 mg kg 1, respectively (e.g., Wong et al, 1982; Ho 1987, 1990; Brown et al, 1999). Of the other metals analysed, published values for Cd, Mn, Ni, and Pb in Enteromorpha and Ulva range from < 1.0 ±1200, 5 ±1700, 4 ±50, and 6± 300 mg kg 1, respectively (Brown and Depledge, 1998). In conclusion, the results obtained in this investigation do indicate that seaweed can be used successfully to assess the
levels of heavy metals in the marine environment. However, this preliminary study has also highlighted some of the difficulties associated with this type of `passive' biomonitoring programme. For example, the selection of specific species of seaweed must be considered carefully, since different species appear to accumulate metals to differing levels. Information on the physiology and metal-handling capacity of a range of species is required before such a selection can be made. Biomonitors may reflect the levels of metals in the environment, but they do not provide information on the source of the elevated concentrations, natural or anthropogenic. The results from this study clearly illustrate that not all
T. Sawidis et al. / Environment International 27 (2001) 43±47 Table 2 The mean concentration (mg kg-1) of heavy metals in samples C. barbata and Ulva/Enteromorpha collected from sites in the Aegean Sea, Greece Region
Site
Chalkidiki
N. Fokaea Kalandra Paliouri Thermaikos A. Trias
Species
C. barbata C. barbata E. linza C. barbata E. linza U. lactuca Kalochori E. linza U. lactuca Pagasitikos Alykes C. barbata U. lactuca Lehonia C. barbata U. lactuca Pefka E. linza Thira Is. Monolithos C. barbata Perivolos C. barbata Crete Is. Heraklion C. barbata U. lactuca Chania U. lactuca
Cu
Zn
Cd
Pb
Mn
Ni
6.1 8.8 3.4 1.7 6.7 7.4 9.8 11.1 2.1 8.3 3.2 9.0 9.7 2.7 0.7 3.8 7.0 14.5
22.3 16.4 45.0 29.8 67.5 43.7 121.3 88.0 18.7 49.3 58.1 79.9 47.9 17.2 8.8 14.2 16.4 56.3
0.47 0.83 0.77 0.06 0.61 0.42 0.47 0.76 0.4 0.24 2.6 0.54 0.6 0.4 1.4 1.1 0.42 1.1
2.1 2.5 0.02 0.02 0.02 0.02 0.02 0.02 0.02 2.8 0.02 0.02 12.4 0.02 0.02 0.02 0.02 0.02
70.5 40.5 31.5 22.2 59.7 33.3 94.3 132.3 30.9 100.6 181.3 182.0 77.4 47.0 7.9 5.6 25.3 137.0
8.7 14.2 6.9 9.7 10.3 9.2 13.7 5.1 4.3 N.D. 28.5 52.6 31.8 14.6 6.8 4.3 8.7 13.7
elevated concentrations of heavy metals in the marine environment necessarily reflect increased levels of pollution. Indeed, the high concentrations of certain metals, e.g., Ni, found in our seaweed samples reflected the metaliferrous nature of the rock. It is therefore important to take account of a region's geology before attempting to interpret the data. References Brown MT, Depledge MH. Determinants of trace metal concentrations in marine organisms. In: Langston WJ, Bebianno MJ, editors. Metal metabolism in aquatic environments. London: Chapman & Hall, 1998. pp. 185 ± 217. Brown MT, Hodgkinson WM, Hurd CL. Spatial and temporal variations in the copper and zinc concentrations of two green seaweeds from Otago Harbour, New Zealand. Mar Environ Res 1999;47:175 ± 84. Djingova R, Kuleff I, Arpadjan S, Voulgaropoulos A, Sawidis T, Alexandrov S. Neutron activation and atomic absorption analysis of Ulva lactuca and Gracilaria verrucosa from Thermaicos Gulf, Greece. Toxicol Environ Chem 1987;15:149 ± 57. Fytianos K, Haritonidis S, Albanis T, Konstantinou I, Seferlis M. Bioaccumulation of PCB congeners in different species of macroalgae from Thermaicos Gulf, Greece. J Environ Sci Health 1997;A32:333 ± 45.
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Gledhill M, Brown MT, Nimmo M, Moate R, Hill SJ. Comparison of techniques for removal of particulate material from seaweed tissue. Mar Environ Res 1998;45:295 ± 307. Haritonidis S, Malea P. Seasonal and local variation of Cr, Ni, and Co concentrations in Ulva rigida C. Agardh and Enteromorpha linza (Linnaeus) from Thermaikos Gulf, Greece. Environ Pollut 1995;89:319 ± 27. Haritonidis S, Malea P. Bioaccumulation of metals by the green alga Ulva rigida from Thermaikos Gulf, Greece. Environ Pollut 1999;104:365 ± 72. Haritonidis S, Nikolaidis G. Pb accumulation in macrophyceae of the coasts Kavala (Aegean Sea) and of Pylos (Ionian Sea), Greece. Toxicol Environ Chem 1989;20 ± 21:261 ± 5. Haritonidis S, Nikolaidis G. Cd and Zn uptake in macrophyceae from Greek coasts. Biol Met 1990;2:235 ± 8. Ho YB. Metals in 19 intertidal macroalgae in Hong Kong waters. Mar Pollut Bull 1987;18:564 ± 6. Ho Y. Ulva lactuca as bioindicator of metal contamination in intertidal waters in Hong Kong. Hydrobiologia 1990;203:73 ± 81. Lobban CS, Harrison PJ. Seaweed ecology and physiology Cambridge: Cambridge Univ. Press, 1994 (366 pp.). Malea P. Accumulation of metals in marine phanerogams and macroalgae in the Antikyra Gulf (Viotia, Greece). PhD Thesis, Thessaloniki, Greece. 475 pp., in Greek with English summary, 1992. Malea P, Haritonidis S, Stratis I. Bioaccumulation of metals by Rhodophyta species at Antikyra Gulf (Greece) near an aluminium factory. Bot Mar 1994;37:505 ± 13. Malea P, Haritonidis S, Kevrekidis T. Metal content of some green and brown seaweeds from Antikyra Gulf (Greece). Hydrobiologia 1995;310:19 ± 31. Munda JM, Hudnik V. Trace metal content in some seaweeds from the Northern Adriatic. Bot Mar 1991;34:241 ± 9. Phillips DJH. Use of macroalgae and invertebrates as monitors of metal levels in estuaries and coastal waters. In: Furness RW, Rainbow PS, editors. Heavy metals in the marine environment. Boca Raton, FL: CRC Press, 1990. pp. 81 ± 99. Phillips DJH. Macrophytes as biomonitors of trace metals. In: Kramer KJM, editor. Biomonitoring of coastal waters and estuaries. Boca Raton, FL: CRC Press, 1994. pp. 85 ± 103. Sawidis T, Voulgaropoulos N. Seasonal bioaccumulation of iron, cobalt, copper in marine algae from Thermaikos Gulf of the Northern Aegean Sea, Greece. Mar Environ Res 1986;19:39 ± 47. Seeliger U, Edwards P. Correlation coefficients and concentration factors of copper and lead in seawater and benthic algae. Mar Pollut Bull 1987;8:16 ± 9. Shiber JG. Trace metals with seasonal considerations in coastal algae and molluscs from Beirut, Lebanon. Hydrobiologia 1980;69:147 ± 62. Wong MH, Kwok TT, Ho CF. Heavy metals in Ulva lactuca collected within Tolo Harbour, an almost landlocked sea. Hydrobiol Bull 1982;16:223 ± 30. Zodiatis G. Circulation of the waters in the Aegean Sea. Proc. 4th Natl. Symp. Oceanogr. Fish., Rhodos (Greece). 1993;43 ± 6.
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Trace metal concentrations in marine macroalgae from different biotopes in the Aegean Sea T. Sawidisa,*, M.T. Brownb, G. Zachariadisc, I. Sratisc a
Department of Botany, University of Thessaloniki, GR-54006 Thessaloniki, Greece Department of Biological Sciences, University of Plymouth, Plymouth PL4 8AA, UK c Laboratory of Analytical Chemistry, University of Thessaloniki, GR-54006 Thessaloniki, Greece b
Received 15 September 2000; accepted 5 April 2001
Abstract The commonest species of red, brown, and green macroalgae were sampled from a range of biotopes in the Aegean Sea and analysed for five different trace metals. Significant differences in metal concentrations were found among different seaweed species from the same biotope. The concentrations of metals in the various seaweed species may reflect their morphology, with those having a larger surface area having a greater internal content. Different species of seaweed have different affinities for different heavy metals. This may reflect competition between metals for binding or uptake sites in the seaweed. Comparing metal concentrations in algae among the studied sampling stations clearly indicates that the degree of accumulation depends not only on human activities but also on the geology of the specific area. While seaweed can be used successfully to assess the levels of heavy metals in the marine environment, not all elevated concentrations of heavy metals necessarily reflect increased levels of pollution. Indeed, the high concentrations of certain metals, e.g., Ni, found in our seaweed samples reflected the metaliferrous nature of the rock. It is therefore important to take account of a region's geology before attempting to interpret the data. D 2001 Elsevier Science Ltd. All rights reserved. Keywords: Algae; Heavy metals; Aegean Sea; Monitoring
1. Introduction Marine macroalgae, which contribute significantly to the primary production of near-shore and estuarine ecosystems, readily accumulate trace metals from solution, and for this reason, have been used extensively as biomonitors of metal contamination of seawater (Brown and Depledge, 1998). Despite recognition of the fact that various intrinsic and extrinsic factors can influence metal uptake, determination of the metal concentrations in seaweed is still considered to provide useful information about the levels of metal contamination and environmental quality of an area, albeit of a qualitative nature (Lobban and Harrison, 1994). Moreover, many macroalgae have a relatively long life span and can therefore integrate short-term temporal fluctuations in environmental concentrations (see review by Phillips, 1994).
* Corresponding author. Faculty of Biology, Institute of Botany, Aristotle University of Thessaloniki, Macedonia, Greece. Tel.: +30-31998294; fax: +30-31-998389.
Within the Mediterranean Sea, there have been several studies using seaweed to assess the degree of metal pollution in different regions, e.g., the northern Adriatic Sea (e.g., Munda and Hudnik, 1991) and Lebanon (e.g., Shiber, 1980). However, the coastlines of Greece have been only sporadically investigated and these studies are usually limited to just a few sites, e.g., the Gulf of Thermaikos (Sawidis and Voulgaropoulos, 1986; Djingova et al., 1987; Fytianos et al., 1997; Haritonidis and Malea, 1995, 1999), Pylos, Ionian Sea (Haritonidis and Nikolaidis, 1989, 1990), and the Gulf of Antikyra (Malea et al., 1992, 1994, 1995). Industrialisation, urbanisation, and mining activity around the coastlines of the Aegean Sea can all negatively impact on fisheries, water resources, and human health of the region. Tourism, too, while of positive benefit economically, may also adversely affect the marine environment which tourists have come to enjoy. In addition to these anthropogenically derived sources of contamination, the geology of some areas surrounding the Aegean Sea has resulted in naturally elevated levels of trace metals. Thus, such sources of trace metals must be distinguished from
0160-4120/01/$ ± see front matter D 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 1 6 0 - 4 1 2 0 ( 0 1 ) 0 0 0 5 2 - 6
44
T. Sawidis et al. / Environment International 27 (2001) 43±47
human influences before any assessment of the extent of the pollution problem can be made. Here, we present the results of the most extensive baseline survey of trace metal concentrations in marine macroalgae so far carried out in the Aegean Sea. Commonly occurring seaweed species, belonging to the three classes of Chlorophyceae, Rhodophyceae, and Phaeophyceae, were collected from 14 sites and analysed for concentrations of five different trace metals. 2. Materials and methods 2.1. Study area and sampling stations The sampling network comprised a wide spectrum of biotopes within the Aegean Sea (Fig. 1). (1) Chalkidiki. A peninsula in the north Aegean Sea, located in a region with polymetallic (Pb± Zn ±Au) sulphide deposits which have been mined since ancient times and still continues today. Three stations were sampled: Nea Fokaea, Paliouri, and Kalandra.
(2) Gulf of Thermaikos. Situated in the northeast Aegean, this area is dominated by Thessaloniki, a city of more than 1,200,000 inhabitants. It has been estimated that over 120,000 m3 per day of partially treated (40 m3 per day) domestic sewage and 30,000 m3 per day of industrial wastewater are discharged from the city and its environs into the inner part of the Gulf (Fytianos et al., 1997). The Gulf of Thermaikos is a shallow (max. depth of the inner part is 28 m) wind-stirred bay characterised by weak tidal mixing (tidal range is less than 50 cm) and so there is little dilution of the contamination by seawater from the open sea. Three stations were sampled: A. Trias, situated at the entrance to the Gulf, 10 km from Thessaloniki; N. Krini, a site affected mainly by the municipal wastes from Thessaloniki; Kalochori, situated near the industrialized zone of the city and affected mainly by industrial wastes from an oil refinery, a fertilizer plant, a steel-processing plant, an antiknock compounds factory, and a chlor-alkali plant. (3) Gulf of Pagasitikos. An enclosed gulf in the region of Thessalia and dominated by the city of Volos with c. 80,000 inhabitants. The harbour of Volos is the main export centre of the region. Three stations were sampled: Pefka, situated close to Volos and affected by its industrial and domestic discharges; Alykes, situated west of Volos; Lehonia, situated southeast of Volos. (4) Thira Island. This is the largest of the five islands comprising the volcanic Santorini Island complex in the southeast Aegean. The present-day crescent-shaped island is a consequence of volcanic activity in prehistoric times. The last major eruption dates back 3600 years, to the late Bronze Age and is connected with the myth of lost island of Atlantis. Three stations, Monolithos, Perivolos, and Akrotiri, located on the outer coast of the island, were sampled. (5) Crete. The fifth largest island in the Mediterranean Sea and the largest of the islands forming part of modern Greece. Located in the south Aegean Sea, Crete is a popular tourist destination. Agriculture is the economic mainstay of the island. The sea around Crete forms the deepest part of the Aegean Sea (3294 m). Three stations were sampled: Heraklion, the capital of the island with c. 200,000 inhabitants and which can increase significantly during the summer period; Chania west of Heraklion with a population of 100,000; A. Nicolaos east of Heraklion with a population of 50,000. 2.2. Sampling procedures
Fig. 1. Map of Greece showing the location of studied biotopes. (1) Chalkidiki (N. Fokaea, Paliouri, Kalandra); (2) Thermaikos Gulf (A. Trias, N. Krini, Kalochori); (3) Pagasiticos Gulf (Pefka, Alykes, Lehonia); (4) Thira Is. (Monolithos, Perivolos); (5) Crete Is. (Heraklion, Chania, A. Nikolaos).
A minimum of three samples of the most commonly occurring seaweed were collected from each station. All thalli were thoroughly cleaned with seawater, followed by running distilled water to remove adhering particulate matter and epiphytes. Material was oven-dried at 30°C to constant weight and then pulverised to ensure uniform distribution of metals in the samples.
T. Sawidis et al. / Environment International 27 (2001) 43±47
2.3. Analytical methods for sample pretreatment Accurately weighed portions of each sample (about 1 g dry weight, DW) were digested in 8 ml of concentrated HNO3 (Merck, Proanalysis). The solutions were filtered through Whatman type 589/2 filters and diluted accurately to 25 ml volume with double deionised water. These solutions were then analysed for metal concentrations using a Perkin Elmer 2380 Atomic Absorption Spectrophotometer coupled to an HGA-400 Graphite Furnace controller. In the majority of cases, the determination of Cu, Mn, Ni, and Zn was carried out in flame mode while Cd and Pb, and the determinations of the other metals, were carried out in a graphite furnace. All samples were analysed three times. For all determinations, pyrocoated graphite tubes were used. Two plant material NBS standards (National Bureau of Standards, USA), number 1573 (tomato leaves) and 1575 (pine needles), were also analysed following the procedures used for the seaweeds. Recoveries were 95.5% for copper, 97.5% for zinc, 94.2% for lead, 99.0% for manganese, 97.5% for cadmium, and 98.4% for nickel of the expected values and therefore the procedures employed are considered appropriate. All concentrations are presented as milligram per kilogram dry weight (mg kg 1 DW), and the quoted values are means. 3. Results and discussion The algal species collected from each biotope and their trace metal content are listed in Table 1. The concentrations of metals are expressed as the mean value obtained from the specimens collected during their growing season. Significant differences in metal concentrations were found among different seaweed species from the same biotope. For example, the zinc concentration in Cladophora (57.9 mg kg 1), collected from Kalochori is significantly less than the zinc concentration in Gracilaria (155.3 mg kg 1) collected from the same site. A similar trend is found for manganese in these two seaweed species from Kalochori but not for nickel and copper. There are several possible reasons for such differences in the accumulation of metals by different species. The concentrations of metals in the various seaweed species may reflect their morphology, with those having a larger surface area having a greater internal content. Long-lived species (e.g., perennials vs. annuals) will have the opportunity to accumulate metals to a greater degree. Growth rates too can affect accumulation patterns, with faster growing material appearing to have lower concentrations. The results obtained in this study also indicate that different species of seaweed have different affinities for different heavy metals. This may reflect competition between metals for binding or uptake sites in the seaweed (Lobban and Harrison, 1994). The foregoing discussion highlights some of the problems associated with this type of biomonitoring programme. Pollution levels at various locations should be compared by
45
using the same species at each site. Furthermore, a strict protocol should be adhered to including: using material of the same age, collected at the same time of year (similar growth rates?).Table 2 provides a comparison of heavy metal concentrations at the various sites using the metal concentrations in the brown seaweed Cystoseira barbata and the green seaweed Ulva lactuca and Enteromorpha linza. From these results we can see that, for example, the levels of nickel are highest at Chalkidiki, reflecting the metalliferous nature of the area. Comparing metal concentrations in algae among the studied sampling stations clearly indicates that the degree of accumulation depends not only on the human activities but also on the geology of the specific area. For example, cadmium and nickel concentrations in the Thermaikos Gulf, an area of high human activity, are significantly less than from Chalkidiki, Pagasitikos Gulf, Crete, or Thira. In these latter areas, polymetallic sulphide deposits, which contains Cd and/or Ni, exist. In Chalkidiki, the ultrabasic rocks are the main Ni source whereas in the Pagasitikos Gulf the Ni concentration is partly influenced by the laterite deposits of the area. In the case of copper, the concentrations reflect human activities rather than geological deposits, although copper ores on the eastern side of Chalkidiki may influence the results. Thus, the increased concentrations near the industrial areas of both Thessaloniki and Volos are most likely the result of municipal sludge and industrial wastes. The same is also true for Mn where increased concentrations observed in the Thermaikos Gulf (Kalochori-industrial zone) reflect the discharges of wastewaters from dye-houses, a steel mill, and an electrolytic manganese dioxide factory. The relatively high levels of Cu and other metals at Krini and A. Triada on the opposite side of the industrial zone (Kalochori) could be attributed to the local sea currents carrying metal-rich industrial sewage towards these stations. Similarly, the variability of trace metal concentrations among the 14 stations examined is affected by the dynamic current regime of the Aegean Sea. Water circulation in the north Aegean Sea is dominated by the BSW current that flows westward or southward after passing the Dardanelles. The complex geometry of the north Aegean with respect to the main axis of the direction of the current results in the formation of small-scale cyclonic and anticyclonic flow regions along the general direction of movement. Finally, a very diluted BSW current flows through the northwest passages of the Cyclades plateau, towards the south Aegean Sea (Zodiatis, 1993). Direct comparisons with other published works are fraught with problems, including those associated with sample handling and processing (Gledhill et al., 1998). Ulva and Enteromorpha are two of the most widely used seaweed biomonitors of trace metal pollution. From studies undertaken in various parts of the world, it is possible to obtain an estimate of the expected range of concentrations within these seaweed species from sites varying in metal contam-
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T. Sawidis et al. / Environment International 27 (2001) 43±47
Table 1 The mean concentration (mg kg
1
) of heavy metals in samples of the most common seaweed species collected from sites in the Aegean Sea, Greece
Region
Site
Species
Cu
Zn
Cd
Pb
Mn
Ni
Chalkidiki
N. Fokaea
C. barbata Padina pavonica Laurencia obdusca Halimeda tuna Ceramium rubrum Gigartina tendii Cladophora sp. E. linza C. barbata Acetabularia mediterranea C. barbata Gracilaria verrucosa Codium vulgarae Gra. verrucosa G. tendii L. obdusca E. linza U. lactuca Posidonia oceanica Petalonia fascia Cer. rubrum Gra. verrucosa Polysiphonia deusta Cladophora sp. E. linza U. lactuca Cer. rubrum E. linza C. barbata Cer. rubrum U. lactuca C. barbata U. lactuca C. barbata P. pavonica Cer. rubrum C. barbata Sargassum sp. Cladophora sp. C. barbata Gra. verrucosa U. lactuca C. barbata U. lactuca Corralina officinalis
6.1 3.7 7.1 4.5 10.6 2.0 29.3 3.4 8.8 2.1 1.7 2.1 0.7 3.4 17.8 3.6 6.7 7.4 8.8 3.8 17.1 7.9 13.3 6.8 9.8 11.1 9.9 9.7 2.1 5.4 8.3 3.2 9.0 2.7 3.0 2.0 0.7 2.1 2.2 3.8 14.9 7.0 1.7 14.5 0.85
22.3 19.3 25.4 14.6 27.2 23.4 51.8 45.0 16.4 6.5 29.8 38.0 11.2 50.0 135.0 34.7 67.5 43.7 119.3 43.8 107.0 155.3 64.3 57.9 121.3 88.0 83.3 47.9 18.7 71.6 49.3 58.1 79.9 17.2 26.3 22.3 8.8 18.7 7.0 14.2 43.6 16.4 27.5 56.3 37.5
0.47 1.6 1.2 2.3 1.8 1.1 0.95 0.77 0.83 2.7 0.06 0.06 0.09 0.88 1.45 0.79 0.61 0.42 1.6 0.5 0.84 0.9 0.24 0.32 0.47 0.76 1.6 0.6 0.4 0.74 0.24 2.6 0.54 0.4 1.2 1.4 1.4 0.07 1.0 1.1 0.21 0.42 2.7 1.1 2.9
2.1 2.1 0.02 0.02 8.5 0.02 24.7 0.02 2.5 7.0 0.02 0.02 0.02 0.02 15.7 0.02 0.02 0.02 0.02 0.02 9.9 14.7 17.7 13.0 0.02 0.02 21.5 12.4 0.02 4.1 2.8 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02
70.5 202.5 79.8 71.3 210.8 11.8 416.0 31.5 40.5 6.3 22.2 27.0 30.9 79.3 303.0 61.8 59.7 33.3 530.3 36.4 353.8 909.0 277.5 200.0 94.3 132.3 93.0 77.4 30.9 93.0 100.6 181.3 182.0 47.0 180.5 86.2 7.9 38.0 19.0 5.6 31.3 25.3 34.0 137.0 42.0
8.7 32.3 17.5 21.9 27.5 4.6 32.0 6.9 14.2 17.5 9.7 8.0 9.1 4.6 43.6 4.4 10.3 9.2 N.D. 11.5 18.3 7.5 9.2 8.0 13.7 5.1 13.1 31.8 4.3 N.D. N.D. 28.5 52.6 14.6 18.3 18.3 6.8 13.7 10.3 4.3 15.8 8.7 16.0 13.7 18.3
Paliouri
Kalandra Thermaikos
A. Trias N. Krini
Kalochori
Pagastikos
Pefka Alykes Lehonia
Thira Is.
Monolithos Perivolos
Crete
Heraklion Chania A. Nikolaos
Cu = copper; Zn = zinc; Cd = cadmium; Pb = lead; Mn = manganese; Ni = nickel; N.D. = not detected.
ination. Copper concentrations from contaminated sites range from 20 to 70 mg kg 1 DW and 14 to 134 mg kg 1 DW for Enteromorpha and Ulva, respectively (e.g., Seeliger and Edwards, 1987; Ho, 1990, Phillips, 1990; Brown et al., 1999). For zinc the values for Enteromorpha and Ulva are 95± 130 mg kg 1 and 42 ± 160 mg kg 1, respectively (e.g., Wong et al, 1982; Ho 1987, 1990; Brown et al, 1999). Of the other metals analysed, published values for Cd, Mn, Ni, and Pb in Enteromorpha and Ulva range from < 1.0 ±1200, 5 ±1700, 4 ±50, and 6± 300 mg kg 1, respectively (Brown and Depledge, 1998). In conclusion, the results obtained in this investigation do indicate that seaweed can be used successfully to assess the
levels of heavy metals in the marine environment. However, this preliminary study has also highlighted some of the difficulties associated with this type of `passive' biomonitoring programme. For example, the selection of specific species of seaweed must be considered carefully, since different species appear to accumulate metals to differing levels. Information on the physiology and metal-handling capacity of a range of species is required before such a selection can be made. Biomonitors may reflect the levels of metals in the environment, but they do not provide information on the source of the elevated concentrations, natural or anthropogenic. The results from this study clearly illustrate that not all
T. Sawidis et al. / Environment International 27 (2001) 43±47 Table 2 The mean concentration (mg kg-1) of heavy metals in samples C. barbata and Ulva/Enteromorpha collected from sites in the Aegean Sea, Greece Region
Site
Chalkidiki
N. Fokaea Kalandra Paliouri Thermaikos A. Trias
Species
C. barbata C. barbata E. linza C. barbata E. linza U. lactuca Kalochori E. linza U. lactuca Pagasitikos Alykes C. barbata U. lactuca Lehonia C. barbata U. lactuca Pefka E. linza Thira Is. Monolithos C. barbata Perivolos C. barbata Crete Is. Heraklion C. barbata U. lactuca Chania U. lactuca
Cu
Zn
Cd
Pb
Mn
Ni
6.1 8.8 3.4 1.7 6.7 7.4 9.8 11.1 2.1 8.3 3.2 9.0 9.7 2.7 0.7 3.8 7.0 14.5
22.3 16.4 45.0 29.8 67.5 43.7 121.3 88.0 18.7 49.3 58.1 79.9 47.9 17.2 8.8 14.2 16.4 56.3
0.47 0.83 0.77 0.06 0.61 0.42 0.47 0.76 0.4 0.24 2.6 0.54 0.6 0.4 1.4 1.1 0.42 1.1
2.1 2.5 0.02 0.02 0.02 0.02 0.02 0.02 0.02 2.8 0.02 0.02 12.4 0.02 0.02 0.02 0.02 0.02
70.5 40.5 31.5 22.2 59.7 33.3 94.3 132.3 30.9 100.6 181.3 182.0 77.4 47.0 7.9 5.6 25.3 137.0
8.7 14.2 6.9 9.7 10.3 9.2 13.7 5.1 4.3 N.D. 28.5 52.6 31.8 14.6 6.8 4.3 8.7 13.7
elevated concentrations of heavy metals in the marine environment necessarily reflect increased levels of pollution. Indeed, the high concentrations of certain metals, e.g., Ni, found in our seaweed samples reflected the metaliferrous nature of the rock. It is therefore important to take account of a region's geology before attempting to interpret the data. References Brown MT, Depledge MH. Determinants of trace metal concentrations in marine organisms. In: Langston WJ, Bebianno MJ, editors. Metal metabolism in aquatic environments. London: Chapman & Hall, 1998. pp. 185 ± 217. Brown MT, Hodgkinson WM, Hurd CL. Spatial and temporal variations in the copper and zinc concentrations of two green seaweeds from Otago Harbour, New Zealand. Mar Environ Res 1999;47:175 ± 84. Djingova R, Kuleff I, Arpadjan S, Voulgaropoulos A, Sawidis T, Alexandrov S. Neutron activation and atomic absorption analysis of Ulva lactuca and Gracilaria verrucosa from Thermaicos Gulf, Greece. Toxicol Environ Chem 1987;15:149 ± 57. Fytianos K, Haritonidis S, Albanis T, Konstantinou I, Seferlis M. Bioaccumulation of PCB congeners in different species of macroalgae from Thermaicos Gulf, Greece. J Environ Sci Health 1997;A32:333 ± 45.
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Gledhill M, Brown MT, Nimmo M, Moate R, Hill SJ. Comparison of techniques for removal of particulate material from seaweed tissue. Mar Environ Res 1998;45:295 ± 307. Haritonidis S, Malea P. Seasonal and local variation of Cr, Ni, and Co concentrations in Ulva rigida C. Agardh and Enteromorpha linza (Linnaeus) from Thermaikos Gulf, Greece. Environ Pollut 1995;89:319 ± 27. Haritonidis S, Malea P. Bioaccumulation of metals by the green alga Ulva rigida from Thermaikos Gulf, Greece. Environ Pollut 1999;104:365 ± 72. Haritonidis S, Nikolaidis G. Pb accumulation in macrophyceae of the coasts Kavala (Aegean Sea) and of Pylos (Ionian Sea), Greece. Toxicol Environ Chem 1989;20 ± 21:261 ± 5. Haritonidis S, Nikolaidis G. Cd and Zn uptake in macrophyceae from Greek coasts. Biol Met 1990;2:235 ± 8. Ho YB. Metals in 19 intertidal macroalgae in Hong Kong waters. Mar Pollut Bull 1987;18:564 ± 6. Ho Y. Ulva lactuca as bioindicator of metal contamination in intertidal waters in Hong Kong. Hydrobiologia 1990;203:73 ± 81. Lobban CS, Harrison PJ. Seaweed ecology and physiology Cambridge: Cambridge Univ. Press, 1994 (366 pp.). Malea P. Accumulation of metals in marine phanerogams and macroalgae in the Antikyra Gulf (Viotia, Greece). PhD Thesis, Thessaloniki, Greece. 475 pp., in Greek with English summary, 1992. Malea P, Haritonidis S, Stratis I. Bioaccumulation of metals by Rhodophyta species at Antikyra Gulf (Greece) near an aluminium factory. Bot Mar 1994;37:505 ± 13. Malea P, Haritonidis S, Kevrekidis T. Metal content of some green and brown seaweeds from Antikyra Gulf (Greece). Hydrobiologia 1995;310:19 ± 31. Munda JM, Hudnik V. Trace metal content in some seaweeds from the Northern Adriatic. Bot Mar 1991;34:241 ± 9. Phillips DJH. Use of macroalgae and invertebrates as monitors of metal levels in estuaries and coastal waters. In: Furness RW, Rainbow PS, editors. Heavy metals in the marine environment. Boca Raton, FL: CRC Press, 1990. pp. 81 ± 99. Phillips DJH. Macrophytes as biomonitors of trace metals. In: Kramer KJM, editor. Biomonitoring of coastal waters and estuaries. Boca Raton, FL: CRC Press, 1994. pp. 85 ± 103. Sawidis T, Voulgaropoulos N. Seasonal bioaccumulation of iron, cobalt, copper in marine algae from Thermaikos Gulf of the Northern Aegean Sea, Greece. Mar Environ Res 1986;19:39 ± 47. Seeliger U, Edwards P. Correlation coefficients and concentration factors of copper and lead in seawater and benthic algae. Mar Pollut Bull 1987;8:16 ± 9. Shiber JG. Trace metals with seasonal considerations in coastal algae and molluscs from Beirut, Lebanon. Hydrobiologia 1980;69:147 ± 62. Wong MH, Kwok TT, Ho CF. Heavy metals in Ulva lactuca collected within Tolo Harbour, an almost landlocked sea. Hydrobiol Bull 1982;16:223 ± 30. Zodiatis G. Circulation of the waters in the Aegean Sea. Proc. 4th Natl. Symp. Oceanogr. Fish., Rhodos (Greece). 1993;43 ± 6.