Environmental Geochemistry and Health 1994 16(2) page 70
Pattern of distribution of selected trace elements in the marine brown alga,
filipendula Ag.
Sargassum
from Sri Lanka
Ranjith Jayasekera Department of Botany, University of Kelaniya,Kelaniya, Sri Lanka
Abstract Baseline concentrations together with biological variations of 29 trace elements (Ag, As, Au, Ba, Br, Cd, Ce, Co, Cr, Cs, Eu, Fe, Hf, I, Mn, Mo, Ni, Pb, Rb, Sb, Sc, Se, Sm, Sr, Tb, Th, Yb, Zn and Zr) were investigated in the brown alga, Sargassum filipendula collected from the western coast of Sri Lanka. Several elements (Co, Cr, Fe, Hf, Ni, Sc, Se, Th, Zr and the rare earth elements) were found to be enriched in S. filipendula compared to NIES No. 9 Sargasso reference material. Concentration of strontium in S. filipendula was highest at all sites. Chemical abundance of the rare earth elements decreased approximately linearly with increasing atomic numbers. The pattern of elemental distribution appears to be due to the fact that S. filipendula seems capable of concentrating high levels of trace elements under conditions of their very low availability in sea water. Concentration factors for elements in S. filipendula lie in a higher range compared with those reported in the literaure for brown algae.
Keywords: Brown
algae, concentration factor, Sargassum filipendula, Sri Lanka, trace elements
Introduction
There is abundant information on the mineral element content of marine algae (Bowen, 1979; DeBoer, 1981), but relatively few extensive analyses have been made in the recent past on their trace element content (NIES, 1988; Rossbach, 1992). Apart from that, most of these investigations have been conducted on temperate rather than tropical algae species. Investigations carried out on the elemental composition of marine brown algae indicate that these algae can accumulate certain chemical elements against a concentration gradient (Bowen, 1979; Rai et al., 1981). Some investigators have concerned themselves with the seasonal variation in the concentration of heavy metals in marine brown algae (Stoeppler, 1990; Schladot et al., 1990) growing in the temperate seas and have suggested that these algae can be used for long-term environmental monitoring of heavy metals. Besides the toxic effects of heavy metals, a series of elements in the Periodic Table are essential nutrients for plant and animal life. To be an essential element, three criteria have to be fulfilled (Arnon, 1953), viz. (1) the organism can not complete its life cycle without that element, (2) it can not be wholly replaced by another element and, (3) its effect on the organism is direct. According to Markert (1991), about one third of the elements of the periodic table may be considered essential to some or all living
organisms. Some elements have been classified as essential for plant life, others are considered toxic while the role of many others is not fully understood (Wallace, 1989). Some elements are believed to be beneficial for certain plants. Therefore new lines of research have emerged recently in plant mineral nutrition, for example the role of less-investigated elements in plant nutrition. However, the presence of a particular element in an organism would not provide direct evidence that the element is essential to that organism, because certain elements are absorbed in excess of requirements, while others are absorbed but not utilised. During the past decade or so, there has been a remarkable growth of interest in trace elements in biological and environmental samples. For example, the lanthanides or the rare earth elements which comprise a total of 15 elements occur at ultratrace levels in plant tissues. These elements possess nearly identical chemical and p h y s i c a l p r o p e r t i e s and are b e c o m i n g technologically more and more significant (Markert, 1987 and 1991). As a result, they are released in trace amounts into the environment at increasing rates. The literature surveyed indicated that hardly any investigations on the lanthanide elements have been conducted on biological or environmental matrices originated from Sri Lanka. Brown algae have been frequently employed for coastal monitoring (Schladot et al., 1990; Stoeppler, 1990). They are important ecologically as
71
R. Jayasekera
Table 1 Analytical values of constituent elements for the N1ES No.9 Sargasso certified reference material. Values are m mg k unless otherwise indicated. Figures in parentheses are reference values only (NIES No. 9, 1988). ,
-]
NIES No. 9 Sargasso Element Certified value A~ As Au Ba Br Ca% Ce Co Cr Cs Eu Fe Hf I Mo Na% Ni Rb Sb Sc Se Sm Sr Tb Te Th U Yb Zn Zr
0.31_+0.02 115+9 (270) 1.34_+0.05 0.12±0.01 (0.2) (0.04) 187+6 (520) 1.70_+0.08 24+2 (0.04) (0.09) (0.05) 1,000-!0.003 (0.4) 15.6+1.2 -
,
.
,
Found 0.31 115 0.003 10 269 1.35 0.197 0.11 0.223 0.041 0.006 187 0.155 500 0.344 1.12 24 0 04 0.088 0.048 0.064 960 0.004 0.265 0 004 0.428 0.012 15.6 3.4
they constitute a significant portion of the food chain in coastal waters. However, tropical regions have only a few brown algae, the commonest of them being Sargassum. The marine brown alga, Sargassumfilipendula was selected for this study as a preliminary to studies on the ecophysiological chemistry of trace elements in tropical marine algae. This species was selected because it was sessile in nature and, an abundant macrophytic alga found along the western coast of Sri Lanka. It is also known to accumulate a series of elements from dilute concentrations in sea water (Bowen, 1979). In addition reliable and accurate contents of trace elements can be determined on Sargassum spp., since a suitable reference material with similar matrix type (NIES No. 9 Sargasso) is available from the National Institute of Environmental Studies in Japan. The objectives of this investigation were (1) to determine natural background concentration
levels of a series of less-investigated trace elements in S. filipendula compared to NIES No.9 Sargasso reference material and (2) to assess the magnitude of concentration factors (Jayasekera, 1991) for those elements taken up from sea water by S. filipendula. It is also important to emphasise here that the establishment of baseline trace element concentration levels for S.filipendula on the western coast of Sri Lanka will serve as a point of reference against which future changes can be measured.
Methodology To avoid chemical changes induced by the age and plant organ, whole mature plants of Sargassum filipendula were collected in February 1992 within a distance of about 3 km at four sites distant from river inputs in the Negombo area on the western coast of Sri Lanka. The sampling sites were c o m p a r a t i v e l y u n d i s t u r b e d by l a r g e - s c a l e anthropogenic activities. The alga grows at or near low water mark in the rocky intertidal area where it is subjected to tidal influences. Its sessile nature and macrophytic size enable a relatively easy collection of large quantities of tissue. As attached plants, they can be used to characterise one location over time. The thallus of S. filipendula is primarily composed of richly branched, long laterals on which the leafy short laterals are borne. The plants are attached to the rocky substratum by means of a more or less irregular, warty, solid parenchymatous base. Each sample consisted of ten or more random collections of the mature plants from throughout a sampling site. The s a m p l e s w e r e then c a r e f u l l y and thoroughly washed with sea water, placed in precleaned polyethylene bags and transported to the Botany Department laboratories where they were then placed on plastic colanders and allowed to drip drain. Collanders were then placed directly into a vacuum oven and the material was dried for 48 h at about 60 °C. The dried samples were carefully packed in precleaned polyethylene bags, brought to the Institute of Physical Chemistry of the Research Centre Juelich (KFA) in Germany, and were then ground in an agate mill under contamination-free conditions to pass a 2-mm aperture sieve. After homogenisation, the material was dried again at 80 °C for 24 h. Samples were analysed for 29 trace elements using instrumental neutron activation analysis (INAA), a sensitive nuclear analytical method for multielement analysis. As no chemical treatment of the sample is necessary for INAA, the risk of contamination during analysis is very low. The operation of the instrument, counting conditions, preparation and analysis of reference materials (using NIES Sargasso certified reference material) and sample replicates follow established quality assurance p r o c e d u r e s (Rossbach, 1992). The analytical results obtained along with the certified values for the NIES No. 9 Sargasso reference material are summarised in Table 1. The trace elements detected in this study by INAA were Ag,
Distribution of selected trace elements
72
Table 2 Mean concentrations (with SD) on a dry weight basis of selected trace elements in Sargassum filipendula sampled at four sites from the western coast of Sri Lanka. Element Ag As Au Ba Br Cd Ce Co Cr Cs Eu Fe Hf I Mn Mo Ni Pb Rb Sb Sc Se Sm Sr Tb Th Yb Zn Zr
Concentration in mg kg-1 Site 1 0.45+ 0.09 31.0+_1.9 0.009+-0.003 25.9+-2.8 432.5+-17 0.33 13.1+_4.5 0.848+-0.05 2.74_+0.38 0.054+_0.01 0.06_+0.02 1,389+167 11.9+6.5 314+_75 16.3 0.696 7.69+-4.7 1.09 17.3_+0.35 0.063_+0.005 0.399+0.04 0.35 0.89_+0.3 1,410-2-_28 0.057+-0.02 2.81 +-1.2 0.074+0.04 7.27+_1.5 47.9_+24
Site 2 0.315 59.1_+2.9 0.003_+0.001 24 +_3.4 435_+13 0.48 3.57_+1.3 0.698+0.08 1.85_+0.33 0.046-+0.009 0.033 934+_159 5.92_+0.95 198+55.4 26.9 0.435+-0.03 0.812+_0.18 1.08 25.2+_1.5 0.049+_0.007 0.334+_0.03 0.343+0.17 0.232+-0.02 1,605_+64 0.024+-0.008 0.374+-0.01 0.061+_0.02 7.0-2--2.3 23.4+4.5
As, Au, Ba, Br, Ce, Co, Cr, Cs, Eu, Fe, Hf, I, Mo, Ni, Rb, Sb, Sc, Se, Sin, Sr, Tb, Th, Yb, Zn and Zr. Cadmium, Mn and Pb were determined using inductively coupled plasma - atomic emission spectroscopy (ICP-AES) at the University of Goettingen. It was not possible to analyse the sea water in this study, because of the great difficulties involved in determining the amount of 'available' elements in sea water which is far below the INAA detection limits. Statistical analysis was performed using MINITAB software package (Schaefer and Anderson, 1989; Zar, 1984). Results and Discussion In this study, concentration data for 29 trace e l e m e n t s in Sargassum filipendula o v e r f o u r locations were obtained. The results are summarised in Table 2, which provides an overview of the natural b a c k g r o u n d c o n c e n t r a t i o n s of those elements together with their variability from site to site. Of the 29 trace elements investigated, concentration of strontium was highest in S.
Site 3 0.416 +_0.004 42.3_+ 10.6 0.013_+0.009 23.5 +1.4 481.5 _+19.3 0.44 8.31 +_1.25 0.605-+0.15 2.09_+0.27 0.057_+0.009 0.028_+0.002 956_+124 8.24+2.97 283+_22.6 10.9 0.746_+0.37 1.85+0.46 0.54 19.7+_0.8 0.068_+0.007 0.306-+0.04 0.315_+0.09 0.545_+0.07 1,420_+43 0.028_+0.005 0.889_+0.05 0.064_+0.31 6.64+_1.5 28.1+_5.9
Site 4 0.434_+0.01 40.7_+4.1 0.011 +-0.004 24.2+-2.4 456+-.513.7 0.32 10.3+ 1.96 0.69+-0.09 2.7+20.43 0.057_+0.009 0.046_+0.004 1,310+_52 12.6+-4.3 427+-76 16.1 0.455_+0.005 3.61_+1.9 0.54 21.8_+0.7 0.061_+0.01 0.391_+0.03 0.343+-0.04 0.61-+0.12 1,3302-_40 0.042_+0.009 1.12_+0.24 0.084+_0.03 6.47_+0.9 43.3+15.2
filipendula at all four sites (Table 2). Except for a few cases, chemical variability for a majority of elements appears to be minimum (Table 2). Abundance of more than half of the elements (Ag, As, Ba, Br, Cd, Co, Cr, Cs, Eu, Fe, Hf, I, Mn, Mo, Pb, Rb, Sb, Sc, Se, Sr, Tb, Yb, Zn and Zr) are relatively uniform from site to site, because they differ by a factor of three or less. Differences in chemical concentrations from one site to another s h o w e d no c l e a r p a t t e r n s that i n d i c a t e accumulations of trace elements from anthropogenic sources. In Table 3, mean concentrations of individual elements in S. filipendula, calculated from the values given in Table 2, are presented together with corresponding biological variations (coefficients of variation). As can be seen in Table 3, biological variation of the concentration values for several elements (Au, Ce, Ni, Sm and Th) is quite high, having the highest for nickel (75%). All mean concentrations given in Table 3 are more or less in agreement with the ranges reported by Bowen (1979). It is also interesting to note that several
73
R. Jayasekera Table 3 Mean concentrations of selected trace elements in sea water (after Bowen, 1979) and Sargassum filipendula. Parenthetical figures calculated from the values given in Table 2 indicate biological variation (in %) of the corresponding element among four sites. Concentration factors (CF) for the elements are also given. Element
Sea water (in g L -1)
Sargassum filipendula (in mg kg -1)
Concentration factor (CF)
Ag As Au Ba Br Cd Ce Co Cr Cs Eu Fe Hf I Mn Mo Ni Pb Rb Sb Sc Se Sm Sr Tb Th Yb Zn Zr
0.04 3.7 0.004 13 67,300 0.11 0.0012 0.02 0.3 0.3 0.00013 2 0.007 60 0.2 10 0.56 0.03 120 0.24 0.0006 0.2 0.00045 7,900 0.00014 0.001 0.00082 4.9 0.03
0.404 43.3 0.0092 24.4 451.4 0.39 8.82 0.71 2.35 0.054 0.042 1,147 9.67 306 17.6 0.583 3.49 0.81 21 0.06 0.358 0.338 0.569 1441 0.038 1.30 0.071 6.85 35.7
1.0 x 104 1.2 x 104 2.3 x 103 1.9 x 103 7.0 x 10° 3.5 x 103 7.4 x 106 3.6 x 104 7.8 x 103 1.8 x 102 3.2 x 105 5.7 x 105 1.4 x 106 5.1 x 103 8.8 x 104 5.8 x 101 6.2 x 103 2.7 x 104 1.8 x 102 2.5 x 102 6.0 x 105 1.7 x 103 1.2 x 106 1.8 x 10 2.7 x 105 1.3 x 106 8.7 x 104 1.4 x 103 1.2 x 106
(13) (23) (40) (4) (4) (18) (39) (12) (17) (8) (30) (18) (10) (27) (33) (24) (75) (34) (14) (12) (11) (4) (41) (7) (34) (70) (13) (5) (29)
elements were found to be highly enriched in S. fili~endula from Sri Lanka (Table 3) compared to NIES No. 9 Sargasso reference material (Table 1); they are: Co (6 fold), Cr (11 fold), Fe (6 fold), Hf (62 fold), Ni (3 fold), Sc (4 fold), Se (7 fold), Th (325 fold), Zr (11 fold), and the rare earth elements Ce (45 fold), Eu (7 fold), Sm (9 fold), Tb (10 fold) and Yb (6 fold). In contrast, zinc content was found to be lower (6.85 mg kg -t) by a factor of 2-3 than in NIES No. 9 Sargasso material (15.6 mg kgq). Mean c o n c e n t r a t i o n s of the elements investigated in the sea water were taken from Bowen (1979) for the calculation of concentration factors given in Table 3. The concentration factors given in Table 3 would not be quite reliable, as the sea water concentration values used for the calculations are based on literature data on sea water collected elsewhere. Assuming that the relative amounts of trace elements of unpolluted sea water (without river inputs) remains more or less constant, the concentration factors calculated could be used to study only the pattern of trace element accumulation by S. filipendula. Further studies on individual trace
elements are, however, necessary to confirm the orders of magnitude of the concentration factors given in Table 3. It can be seen that S. filipendula can concentrate a series of trace elements even when they are available in very low amounts in the sea water. On a dry weight basis, concentrations of the 29 trace elements in S. fiIipendula given in Table 3 decrease along the following sequence: Sr > Fe > Br > I > As > Zr > Ba > Rb > Mn > H f > Ce > Zn > Ni > Cr > Th > Pb > Co > Mo > Sm > Ag > Cd > Sc > Se > Yb > Sb > Cs > Eu > Tb > Au. This elemental sequence is interesting as S. filipendula seems to accumulate strontium in substantial amounts in the plant body which is a unique characteristic for brown algae (Bowen, 1979). It has been reported by Bowen (1979) that the Sr/Ca ratio in brown algae is about 0.14 (as against 0.02 in sea water), but in this study a ratio of 0.05 was obtained (concentration of -31,075 mg kg q, not given in Table 3). In addition to Sr, brown algae accumulate arsenic, bromine and iodine as well (Bowen, 1979) which is further supported by the results given in Table 3.
Distribution of selected trace elements The chemical abundance of the rare earth elements (lanthanides) is quite interesting as far as their natural distribution pattern in the environment is concerned. In this study, a total of 5 rare earth elements (Ce, Eu, Sm, Tb and Yb) were detected in S. filipendula. According to the Harkin's rule (Hollemann and Wiberg, 1976), the lanthanide e l e m e n t s of e v e n atomic n u m b e r s are more abundant than those of the adjacent odd atomic numbers (zig-zag distribution); chemical abundance of these elements decreases approximately linearly with increasing atomic numbers which can clearly be seen from Table 3 (concentration of Ce, Sm, Eu, Tb and Yb are 8.82, 0.569, 0.042, 0.038 and 0.071 mg kg q, respectively): ytterbium (Yb) seems to deviate slightly, probably due to the analytical errors. The peculiar zig-zag distribution (Harkin's rule) of the lanthanide elements detected in S. filipendula can not be clearly seen in this study as only 5 elements were detected out of a total of 15. However, the adjacent two elements, Sm and Eu, and Tb seem to follow the rule; this deviation from the Harkin's rule can not be expounded at present without further investigations. No reference values for the concentration of lanthanide elements in marine brown algae have been published for comparison. Concentration factors, i.e. the ratio of the concentration of a particular element in the tissues to that of the external medium (Salisbury and Ross, 1985; Jayasekera, 1991) for the trace elements detected are given in Table 3. All elements seem to accumulate from sea water in S. filipendula with widely varying orders of magnitude. However, care must be taken in interpreting these values, because of the possibility of analytical errors, and also the composition of sea water near the coast does not remain constant. Concentration factors (Table 3) calculated in S. filipendula for most elements lie in a much higher range compared to CF ranges given for brown algae by Bowen (1979). For example Br, Cd, Co, Cs, Fe, Mo, Ni and Sb (2-3 fold higher); As, Ba and Sr (4-6 fold higher); Ag, Mn and Zn (7-9 fold higher); Pb (12 fold higher); Cr (16 fold), Th (17 fold), Sc (18 fold) and Se (34 fold higher), and the concentration factor for Zr in S. filipendula is about 1,000 times higher than the reported value (1,000) by Bowen (1979) for brown algae. Great differences between the CF values calculated in this study and Bowen's (1979) values could also be attributed to the fact that CF values compiled by B o w e n (1979) are m o s t l y based on studies conducted on temperate brown algae. In contrast, CF value for iodine in S. filipendula is lower by a factor of 2, and for Zn by a factor of 9 than the reported values by Bowen (1979). No reference values of concentration factors for the lanthanide elements are available in Bowen (1979), and the CF values decrease as the atomic weight increases from Ce to Yb. Further interpretation of the CF values given in Table 3 is d i f f i c u l t , as the tissue concentration of a particular element depends entirely on the selectivity during absorption
74
(Epstein, 1972). And also no direct relationship exists between the magnitude of concentration factors and essentiality to plants (Bowen, 1979; Jayasekera, 1991). The degree of accumulation is, however, a complex function of numerous factors. It has also been reported that the brown algae (Phaeophyceae) like Sargassum and Fucus are well adapted to grow in n u t r i e n t - p o o r sea water (Bresinsky, 1991). In conclusion, the relationships described above along with the baseline concentrations reported in this study can be compared with samples collected in the future to assess any changes in elemental composition, assuming that the sampling, sample preparation and analysis are performed by methods comparable to those used in the present study. Plant tissues provide samples which represent an integration of the environmental regime to which the organism has been exposed. Intensive studies on different elements that are not now considered essential are necessary for better understanding of the trace element chemistry in plants. It is now easier to determine those elements accurately at ultra trace levels in plant materials by the advanced analytical methods available like multielement techniques.
Acknowledgements I am deeply grateful to Dr. M. Rossbach of the R e s e a r c h Centre Juelich in G e r m a n y whose enthusiasm did much to inspire my interest in this study. I would like to express my sincere thanks to Dr. Rossbach for active cooperation, and to Mr. A.M.W.W. Samarasinghe for assisting in sampling. Thanks are also owed to two anonymous reviewers for their useful comments on the manuscript.
References Arnon, D.I. 1953. Growth and function as criteria in determining the essential nature of inorganic nutrients. In: Truog, E. (ed.), Mineral Nutrition of Plants, pp. 313-341. The University of Wisconsin Press, Madison, Wisconsin. Bowen, H.J.M. 1979. Environmental Chemistry of the Elements. Academic Press, London. Bresinsky, A. 1991. Evolution und Systematik. In: Sitte, P., Ziegler, H., Ehrendorfer, F.and Bresinsky, A (eds.), Strasburger Lehrbuch der Botanik, 33. Auflage, pp. 644-645. Gustav Fischer Verlag, Stuttgart, New York. DeBoer, J.A. 1981. Nutrients. In: Lobban, C.S., and Wynne, M.J. (eds.), The Biology of Seaweeds, pp. 356-367. Blackwell Scientific Publications, Oxford, Boston. Epstein, E. 1972. Mineral Nutrition of Plants: Principles and Perspectives. John Wiley and Sons, Inc., New York, London. Hollemann, A.F. and Wiberg, E. 1976. Lehrbuch der Anorganischen Chemie. de Gruyter, Berlin. Jayasekera, R. 1991. Chemical composition of the mangrove, Rhizophora mangle L. Journal of Plant Physiology, 138, 119-121.
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R. Jayasekera
Markert, B. 1987. The pattern of distribution of lanthanide elements in soils and plants..Phytochemistry, 26 (12), 3167-3170. Markert, B. 1991. Multielement analysis in plant material. In: Esser, E.and Overdieck, D (eds.), Modern Ecology - Basic and Applied Aspects, pp. 275-293. Elsevier, Amsterdam, London, New York, Tokyo. NIES No. 9 Sargasso. 1988. Certificate of analysis. National Institute of Environmental Studies, Japan. Rai, L.C., Gaur, J.P. and Kumar, H.D. 1981. Phycology and heavy metal pollution. Biological Review, 56, 99-151. Rossbach, M. 1992. Prompt gamma activation analysis with cold neutrons for the characterization of specimen bank materials. In: Rossbach, M., Schladot, J.-D and Ostapczuk, P (eds.), Specimen Banking, pp. 225-237. Springer Verlag, Berlin, Heidelberg. Salisbury, F.B. and Ross, C.W. 1985. Plant Physiology, 3rd edn., Wadsworth Publishing Company, Belmont, California. Schaefer, R.L. and Anderson, R.B. 1989. The Student
Edition of MINITAB. User's manual. Addison Wesley Publishing Company, Inc., and Benjamin/Cummings Publishing Company Inc., California, New York. Schladot, J.-D., Stoeppler, M. and Schwuger, M.J. 1990. Umweltprobenbank Juelich - Ein Projekt fuer das naechste Jahrhundert. Jahresbericht des Forschungszentrums Juelich/Germany, Juelich. Stoeppler, M. 1990. Analytik von Metallen und metallorganischen Verbindungen fuer die Umweltprobenbank in der Bundesrepublik Deutschland. GIT Fachz. Lab., 7, 872-878. Wallace, A. 1989. Plant responses to some hardly known trace elements and trace element composition and distribution in plants. Soil Science, 147 (6), 461-464. Zar, J.H. 1984. Biostatistical Analysis, 2rid edn. Prentice-Hall, Inc., Englewood Cliffs, New Jersey.
[Manuscript No.311: received October 5, 1993 and accepted after revision February 7, 1994.]
Pattern of distribution of selected trace elements in the marine brown alga,
filipendula Ag.
Sargassum
from Sri Lanka
Ranjith Jayasekera Department of Botany, University of Kelaniya,Kelaniya, Sri Lanka
Abstract Baseline concentrations together with biological variations of 29 trace elements (Ag, As, Au, Ba, Br, Cd, Ce, Co, Cr, Cs, Eu, Fe, Hf, I, Mn, Mo, Ni, Pb, Rb, Sb, Sc, Se, Sm, Sr, Tb, Th, Yb, Zn and Zr) were investigated in the brown alga, Sargassum filipendula collected from the western coast of Sri Lanka. Several elements (Co, Cr, Fe, Hf, Ni, Sc, Se, Th, Zr and the rare earth elements) were found to be enriched in S. filipendula compared to NIES No. 9 Sargasso reference material. Concentration of strontium in S. filipendula was highest at all sites. Chemical abundance of the rare earth elements decreased approximately linearly with increasing atomic numbers. The pattern of elemental distribution appears to be due to the fact that S. filipendula seems capable of concentrating high levels of trace elements under conditions of their very low availability in sea water. Concentration factors for elements in S. filipendula lie in a higher range compared with those reported in the literaure for brown algae.
Keywords: Brown
algae, concentration factor, Sargassum filipendula, Sri Lanka, trace elements
Introduction
There is abundant information on the mineral element content of marine algae (Bowen, 1979; DeBoer, 1981), but relatively few extensive analyses have been made in the recent past on their trace element content (NIES, 1988; Rossbach, 1992). Apart from that, most of these investigations have been conducted on temperate rather than tropical algae species. Investigations carried out on the elemental composition of marine brown algae indicate that these algae can accumulate certain chemical elements against a concentration gradient (Bowen, 1979; Rai et al., 1981). Some investigators have concerned themselves with the seasonal variation in the concentration of heavy metals in marine brown algae (Stoeppler, 1990; Schladot et al., 1990) growing in the temperate seas and have suggested that these algae can be used for long-term environmental monitoring of heavy metals. Besides the toxic effects of heavy metals, a series of elements in the Periodic Table are essential nutrients for plant and animal life. To be an essential element, three criteria have to be fulfilled (Arnon, 1953), viz. (1) the organism can not complete its life cycle without that element, (2) it can not be wholly replaced by another element and, (3) its effect on the organism is direct. According to Markert (1991), about one third of the elements of the periodic table may be considered essential to some or all living
organisms. Some elements have been classified as essential for plant life, others are considered toxic while the role of many others is not fully understood (Wallace, 1989). Some elements are believed to be beneficial for certain plants. Therefore new lines of research have emerged recently in plant mineral nutrition, for example the role of less-investigated elements in plant nutrition. However, the presence of a particular element in an organism would not provide direct evidence that the element is essential to that organism, because certain elements are absorbed in excess of requirements, while others are absorbed but not utilised. During the past decade or so, there has been a remarkable growth of interest in trace elements in biological and environmental samples. For example, the lanthanides or the rare earth elements which comprise a total of 15 elements occur at ultratrace levels in plant tissues. These elements possess nearly identical chemical and p h y s i c a l p r o p e r t i e s and are b e c o m i n g technologically more and more significant (Markert, 1987 and 1991). As a result, they are released in trace amounts into the environment at increasing rates. The literature surveyed indicated that hardly any investigations on the lanthanide elements have been conducted on biological or environmental matrices originated from Sri Lanka. Brown algae have been frequently employed for coastal monitoring (Schladot et al., 1990; Stoeppler, 1990). They are important ecologically as
71
R. Jayasekera
Table 1 Analytical values of constituent elements for the N1ES No.9 Sargasso certified reference material. Values are m mg k unless otherwise indicated. Figures in parentheses are reference values only (NIES No. 9, 1988). ,
-]
NIES No. 9 Sargasso Element Certified value A~ As Au Ba Br Ca% Ce Co Cr Cs Eu Fe Hf I Mo Na% Ni Rb Sb Sc Se Sm Sr Tb Te Th U Yb Zn Zr
0.31_+0.02 115+9 (270) 1.34_+0.05 0.12±0.01 (0.2) (0.04) 187+6 (520) 1.70_+0.08 24+2 (0.04) (0.09) (0.05) 1,000-!0.003 (0.4) 15.6+1.2 -
,
.
,
Found 0.31 115 0.003 10 269 1.35 0.197 0.11 0.223 0.041 0.006 187 0.155 500 0.344 1.12 24 0 04 0.088 0.048 0.064 960 0.004 0.265 0 004 0.428 0.012 15.6 3.4
they constitute a significant portion of the food chain in coastal waters. However, tropical regions have only a few brown algae, the commonest of them being Sargassum. The marine brown alga, Sargassumfilipendula was selected for this study as a preliminary to studies on the ecophysiological chemistry of trace elements in tropical marine algae. This species was selected because it was sessile in nature and, an abundant macrophytic alga found along the western coast of Sri Lanka. It is also known to accumulate a series of elements from dilute concentrations in sea water (Bowen, 1979). In addition reliable and accurate contents of trace elements can be determined on Sargassum spp., since a suitable reference material with similar matrix type (NIES No. 9 Sargasso) is available from the National Institute of Environmental Studies in Japan. The objectives of this investigation were (1) to determine natural background concentration
levels of a series of less-investigated trace elements in S. filipendula compared to NIES No.9 Sargasso reference material and (2) to assess the magnitude of concentration factors (Jayasekera, 1991) for those elements taken up from sea water by S. filipendula. It is also important to emphasise here that the establishment of baseline trace element concentration levels for S.filipendula on the western coast of Sri Lanka will serve as a point of reference against which future changes can be measured.
Methodology To avoid chemical changes induced by the age and plant organ, whole mature plants of Sargassum filipendula were collected in February 1992 within a distance of about 3 km at four sites distant from river inputs in the Negombo area on the western coast of Sri Lanka. The sampling sites were c o m p a r a t i v e l y u n d i s t u r b e d by l a r g e - s c a l e anthropogenic activities. The alga grows at or near low water mark in the rocky intertidal area where it is subjected to tidal influences. Its sessile nature and macrophytic size enable a relatively easy collection of large quantities of tissue. As attached plants, they can be used to characterise one location over time. The thallus of S. filipendula is primarily composed of richly branched, long laterals on which the leafy short laterals are borne. The plants are attached to the rocky substratum by means of a more or less irregular, warty, solid parenchymatous base. Each sample consisted of ten or more random collections of the mature plants from throughout a sampling site. The s a m p l e s w e r e then c a r e f u l l y and thoroughly washed with sea water, placed in precleaned polyethylene bags and transported to the Botany Department laboratories where they were then placed on plastic colanders and allowed to drip drain. Collanders were then placed directly into a vacuum oven and the material was dried for 48 h at about 60 °C. The dried samples were carefully packed in precleaned polyethylene bags, brought to the Institute of Physical Chemistry of the Research Centre Juelich (KFA) in Germany, and were then ground in an agate mill under contamination-free conditions to pass a 2-mm aperture sieve. After homogenisation, the material was dried again at 80 °C for 24 h. Samples were analysed for 29 trace elements using instrumental neutron activation analysis (INAA), a sensitive nuclear analytical method for multielement analysis. As no chemical treatment of the sample is necessary for INAA, the risk of contamination during analysis is very low. The operation of the instrument, counting conditions, preparation and analysis of reference materials (using NIES Sargasso certified reference material) and sample replicates follow established quality assurance p r o c e d u r e s (Rossbach, 1992). The analytical results obtained along with the certified values for the NIES No. 9 Sargasso reference material are summarised in Table 1. The trace elements detected in this study by INAA were Ag,
Distribution of selected trace elements
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Table 2 Mean concentrations (with SD) on a dry weight basis of selected trace elements in Sargassum filipendula sampled at four sites from the western coast of Sri Lanka. Element Ag As Au Ba Br Cd Ce Co Cr Cs Eu Fe Hf I Mn Mo Ni Pb Rb Sb Sc Se Sm Sr Tb Th Yb Zn Zr
Concentration in mg kg-1 Site 1 0.45+ 0.09 31.0+_1.9 0.009+-0.003 25.9+-2.8 432.5+-17 0.33 13.1+_4.5 0.848+-0.05 2.74_+0.38 0.054+_0.01 0.06_+0.02 1,389+167 11.9+6.5 314+_75 16.3 0.696 7.69+-4.7 1.09 17.3_+0.35 0.063_+0.005 0.399+0.04 0.35 0.89_+0.3 1,410-2-_28 0.057+-0.02 2.81 +-1.2 0.074+0.04 7.27+_1.5 47.9_+24
Site 2 0.315 59.1_+2.9 0.003_+0.001 24 +_3.4 435_+13 0.48 3.57_+1.3 0.698+0.08 1.85_+0.33 0.046-+0.009 0.033 934+_159 5.92_+0.95 198+55.4 26.9 0.435+-0.03 0.812+_0.18 1.08 25.2+_1.5 0.049+_0.007 0.334+_0.03 0.343+0.17 0.232+-0.02 1,605_+64 0.024+-0.008 0.374+-0.01 0.061+_0.02 7.0-2--2.3 23.4+4.5
As, Au, Ba, Br, Ce, Co, Cr, Cs, Eu, Fe, Hf, I, Mo, Ni, Rb, Sb, Sc, Se, Sin, Sr, Tb, Th, Yb, Zn and Zr. Cadmium, Mn and Pb were determined using inductively coupled plasma - atomic emission spectroscopy (ICP-AES) at the University of Goettingen. It was not possible to analyse the sea water in this study, because of the great difficulties involved in determining the amount of 'available' elements in sea water which is far below the INAA detection limits. Statistical analysis was performed using MINITAB software package (Schaefer and Anderson, 1989; Zar, 1984). Results and Discussion In this study, concentration data for 29 trace e l e m e n t s in Sargassum filipendula o v e r f o u r locations were obtained. The results are summarised in Table 2, which provides an overview of the natural b a c k g r o u n d c o n c e n t r a t i o n s of those elements together with their variability from site to site. Of the 29 trace elements investigated, concentration of strontium was highest in S.
Site 3 0.416 +_0.004 42.3_+ 10.6 0.013_+0.009 23.5 +1.4 481.5 _+19.3 0.44 8.31 +_1.25 0.605-+0.15 2.09_+0.27 0.057_+0.009 0.028_+0.002 956_+124 8.24+2.97 283+_22.6 10.9 0.746_+0.37 1.85+0.46 0.54 19.7+_0.8 0.068_+0.007 0.306-+0.04 0.315_+0.09 0.545_+0.07 1,420_+43 0.028_+0.005 0.889_+0.05 0.064_+0.31 6.64+_1.5 28.1+_5.9
Site 4 0.434_+0.01 40.7_+4.1 0.011 +-0.004 24.2+-2.4 456+-.513.7 0.32 10.3+ 1.96 0.69+-0.09 2.7+20.43 0.057_+0.009 0.046_+0.004 1,310+_52 12.6+-4.3 427+-76 16.1 0.455_+0.005 3.61_+1.9 0.54 21.8_+0.7 0.061_+0.01 0.391_+0.03 0.343+-0.04 0.61-+0.12 1,3302-_40 0.042_+0.009 1.12_+0.24 0.084+_0.03 6.47_+0.9 43.3+15.2
filipendula at all four sites (Table 2). Except for a few cases, chemical variability for a majority of elements appears to be minimum (Table 2). Abundance of more than half of the elements (Ag, As, Ba, Br, Cd, Co, Cr, Cs, Eu, Fe, Hf, I, Mn, Mo, Pb, Rb, Sb, Sc, Se, Sr, Tb, Yb, Zn and Zr) are relatively uniform from site to site, because they differ by a factor of three or less. Differences in chemical concentrations from one site to another s h o w e d no c l e a r p a t t e r n s that i n d i c a t e accumulations of trace elements from anthropogenic sources. In Table 3, mean concentrations of individual elements in S. filipendula, calculated from the values given in Table 2, are presented together with corresponding biological variations (coefficients of variation). As can be seen in Table 3, biological variation of the concentration values for several elements (Au, Ce, Ni, Sm and Th) is quite high, having the highest for nickel (75%). All mean concentrations given in Table 3 are more or less in agreement with the ranges reported by Bowen (1979). It is also interesting to note that several
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R. Jayasekera Table 3 Mean concentrations of selected trace elements in sea water (after Bowen, 1979) and Sargassum filipendula. Parenthetical figures calculated from the values given in Table 2 indicate biological variation (in %) of the corresponding element among four sites. Concentration factors (CF) for the elements are also given. Element
Sea water (in g L -1)
Sargassum filipendula (in mg kg -1)
Concentration factor (CF)
Ag As Au Ba Br Cd Ce Co Cr Cs Eu Fe Hf I Mn Mo Ni Pb Rb Sb Sc Se Sm Sr Tb Th Yb Zn Zr
0.04 3.7 0.004 13 67,300 0.11 0.0012 0.02 0.3 0.3 0.00013 2 0.007 60 0.2 10 0.56 0.03 120 0.24 0.0006 0.2 0.00045 7,900 0.00014 0.001 0.00082 4.9 0.03
0.404 43.3 0.0092 24.4 451.4 0.39 8.82 0.71 2.35 0.054 0.042 1,147 9.67 306 17.6 0.583 3.49 0.81 21 0.06 0.358 0.338 0.569 1441 0.038 1.30 0.071 6.85 35.7
1.0 x 104 1.2 x 104 2.3 x 103 1.9 x 103 7.0 x 10° 3.5 x 103 7.4 x 106 3.6 x 104 7.8 x 103 1.8 x 102 3.2 x 105 5.7 x 105 1.4 x 106 5.1 x 103 8.8 x 104 5.8 x 101 6.2 x 103 2.7 x 104 1.8 x 102 2.5 x 102 6.0 x 105 1.7 x 103 1.2 x 106 1.8 x 10 2.7 x 105 1.3 x 106 8.7 x 104 1.4 x 103 1.2 x 106
(13) (23) (40) (4) (4) (18) (39) (12) (17) (8) (30) (18) (10) (27) (33) (24) (75) (34) (14) (12) (11) (4) (41) (7) (34) (70) (13) (5) (29)
elements were found to be highly enriched in S. fili~endula from Sri Lanka (Table 3) compared to NIES No. 9 Sargasso reference material (Table 1); they are: Co (6 fold), Cr (11 fold), Fe (6 fold), Hf (62 fold), Ni (3 fold), Sc (4 fold), Se (7 fold), Th (325 fold), Zr (11 fold), and the rare earth elements Ce (45 fold), Eu (7 fold), Sm (9 fold), Tb (10 fold) and Yb (6 fold). In contrast, zinc content was found to be lower (6.85 mg kg -t) by a factor of 2-3 than in NIES No. 9 Sargasso material (15.6 mg kgq). Mean c o n c e n t r a t i o n s of the elements investigated in the sea water were taken from Bowen (1979) for the calculation of concentration factors given in Table 3. The concentration factors given in Table 3 would not be quite reliable, as the sea water concentration values used for the calculations are based on literature data on sea water collected elsewhere. Assuming that the relative amounts of trace elements of unpolluted sea water (without river inputs) remains more or less constant, the concentration factors calculated could be used to study only the pattern of trace element accumulation by S. filipendula. Further studies on individual trace
elements are, however, necessary to confirm the orders of magnitude of the concentration factors given in Table 3. It can be seen that S. filipendula can concentrate a series of trace elements even when they are available in very low amounts in the sea water. On a dry weight basis, concentrations of the 29 trace elements in S. fiIipendula given in Table 3 decrease along the following sequence: Sr > Fe > Br > I > As > Zr > Ba > Rb > Mn > H f > Ce > Zn > Ni > Cr > Th > Pb > Co > Mo > Sm > Ag > Cd > Sc > Se > Yb > Sb > Cs > Eu > Tb > Au. This elemental sequence is interesting as S. filipendula seems to accumulate strontium in substantial amounts in the plant body which is a unique characteristic for brown algae (Bowen, 1979). It has been reported by Bowen (1979) that the Sr/Ca ratio in brown algae is about 0.14 (as against 0.02 in sea water), but in this study a ratio of 0.05 was obtained (concentration of -31,075 mg kg q, not given in Table 3). In addition to Sr, brown algae accumulate arsenic, bromine and iodine as well (Bowen, 1979) which is further supported by the results given in Table 3.
Distribution of selected trace elements The chemical abundance of the rare earth elements (lanthanides) is quite interesting as far as their natural distribution pattern in the environment is concerned. In this study, a total of 5 rare earth elements (Ce, Eu, Sm, Tb and Yb) were detected in S. filipendula. According to the Harkin's rule (Hollemann and Wiberg, 1976), the lanthanide e l e m e n t s of e v e n atomic n u m b e r s are more abundant than those of the adjacent odd atomic numbers (zig-zag distribution); chemical abundance of these elements decreases approximately linearly with increasing atomic numbers which can clearly be seen from Table 3 (concentration of Ce, Sm, Eu, Tb and Yb are 8.82, 0.569, 0.042, 0.038 and 0.071 mg kg q, respectively): ytterbium (Yb) seems to deviate slightly, probably due to the analytical errors. The peculiar zig-zag distribution (Harkin's rule) of the lanthanide elements detected in S. filipendula can not be clearly seen in this study as only 5 elements were detected out of a total of 15. However, the adjacent two elements, Sm and Eu, and Tb seem to follow the rule; this deviation from the Harkin's rule can not be expounded at present without further investigations. No reference values for the concentration of lanthanide elements in marine brown algae have been published for comparison. Concentration factors, i.e. the ratio of the concentration of a particular element in the tissues to that of the external medium (Salisbury and Ross, 1985; Jayasekera, 1991) for the trace elements detected are given in Table 3. All elements seem to accumulate from sea water in S. filipendula with widely varying orders of magnitude. However, care must be taken in interpreting these values, because of the possibility of analytical errors, and also the composition of sea water near the coast does not remain constant. Concentration factors (Table 3) calculated in S. filipendula for most elements lie in a much higher range compared to CF ranges given for brown algae by Bowen (1979). For example Br, Cd, Co, Cs, Fe, Mo, Ni and Sb (2-3 fold higher); As, Ba and Sr (4-6 fold higher); Ag, Mn and Zn (7-9 fold higher); Pb (12 fold higher); Cr (16 fold), Th (17 fold), Sc (18 fold) and Se (34 fold higher), and the concentration factor for Zr in S. filipendula is about 1,000 times higher than the reported value (1,000) by Bowen (1979) for brown algae. Great differences between the CF values calculated in this study and Bowen's (1979) values could also be attributed to the fact that CF values compiled by B o w e n (1979) are m o s t l y based on studies conducted on temperate brown algae. In contrast, CF value for iodine in S. filipendula is lower by a factor of 2, and for Zn by a factor of 9 than the reported values by Bowen (1979). No reference values of concentration factors for the lanthanide elements are available in Bowen (1979), and the CF values decrease as the atomic weight increases from Ce to Yb. Further interpretation of the CF values given in Table 3 is d i f f i c u l t , as the tissue concentration of a particular element depends entirely on the selectivity during absorption
74
(Epstein, 1972). And also no direct relationship exists between the magnitude of concentration factors and essentiality to plants (Bowen, 1979; Jayasekera, 1991). The degree of accumulation is, however, a complex function of numerous factors. It has also been reported that the brown algae (Phaeophyceae) like Sargassum and Fucus are well adapted to grow in n u t r i e n t - p o o r sea water (Bresinsky, 1991). In conclusion, the relationships described above along with the baseline concentrations reported in this study can be compared with samples collected in the future to assess any changes in elemental composition, assuming that the sampling, sample preparation and analysis are performed by methods comparable to those used in the present study. Plant tissues provide samples which represent an integration of the environmental regime to which the organism has been exposed. Intensive studies on different elements that are not now considered essential are necessary for better understanding of the trace element chemistry in plants. It is now easier to determine those elements accurately at ultra trace levels in plant materials by the advanced analytical methods available like multielement techniques.
Acknowledgements I am deeply grateful to Dr. M. Rossbach of the R e s e a r c h Centre Juelich in G e r m a n y whose enthusiasm did much to inspire my interest in this study. I would like to express my sincere thanks to Dr. Rossbach for active cooperation, and to Mr. A.M.W.W. Samarasinghe for assisting in sampling. Thanks are also owed to two anonymous reviewers for their useful comments on the manuscript.
References Arnon, D.I. 1953. Growth and function as criteria in determining the essential nature of inorganic nutrients. In: Truog, E. (ed.), Mineral Nutrition of Plants, pp. 313-341. The University of Wisconsin Press, Madison, Wisconsin. Bowen, H.J.M. 1979. Environmental Chemistry of the Elements. Academic Press, London. Bresinsky, A. 1991. Evolution und Systematik. In: Sitte, P., Ziegler, H., Ehrendorfer, F.and Bresinsky, A (eds.), Strasburger Lehrbuch der Botanik, 33. Auflage, pp. 644-645. Gustav Fischer Verlag, Stuttgart, New York. DeBoer, J.A. 1981. Nutrients. In: Lobban, C.S., and Wynne, M.J. (eds.), The Biology of Seaweeds, pp. 356-367. Blackwell Scientific Publications, Oxford, Boston. Epstein, E. 1972. Mineral Nutrition of Plants: Principles and Perspectives. John Wiley and Sons, Inc., New York, London. Hollemann, A.F. and Wiberg, E. 1976. Lehrbuch der Anorganischen Chemie. de Gruyter, Berlin. Jayasekera, R. 1991. Chemical composition of the mangrove, Rhizophora mangle L. Journal of Plant Physiology, 138, 119-121.
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Markert, B. 1987. The pattern of distribution of lanthanide elements in soils and plants..Phytochemistry, 26 (12), 3167-3170. Markert, B. 1991. Multielement analysis in plant material. In: Esser, E.and Overdieck, D (eds.), Modern Ecology - Basic and Applied Aspects, pp. 275-293. Elsevier, Amsterdam, London, New York, Tokyo. NIES No. 9 Sargasso. 1988. Certificate of analysis. National Institute of Environmental Studies, Japan. Rai, L.C., Gaur, J.P. and Kumar, H.D. 1981. Phycology and heavy metal pollution. Biological Review, 56, 99-151. Rossbach, M. 1992. Prompt gamma activation analysis with cold neutrons for the characterization of specimen bank materials. In: Rossbach, M., Schladot, J.-D and Ostapczuk, P (eds.), Specimen Banking, pp. 225-237. Springer Verlag, Berlin, Heidelberg. Salisbury, F.B. and Ross, C.W. 1985. Plant Physiology, 3rd edn., Wadsworth Publishing Company, Belmont, California. Schaefer, R.L. and Anderson, R.B. 1989. The Student
Edition of MINITAB. User's manual. Addison Wesley Publishing Company, Inc., and Benjamin/Cummings Publishing Company Inc., California, New York. Schladot, J.-D., Stoeppler, M. and Schwuger, M.J. 1990. Umweltprobenbank Juelich - Ein Projekt fuer das naechste Jahrhundert. Jahresbericht des Forschungszentrums Juelich/Germany, Juelich. Stoeppler, M. 1990. Analytik von Metallen und metallorganischen Verbindungen fuer die Umweltprobenbank in der Bundesrepublik Deutschland. GIT Fachz. Lab., 7, 872-878. Wallace, A. 1989. Plant responses to some hardly known trace elements and trace element composition and distribution in plants. Soil Science, 147 (6), 461-464. Zar, J.H. 1984. Biostatistical Analysis, 2rid edn. Prentice-Hall, Inc., Englewood Cliffs, New Jersey.
[Manuscript No.311: received October 5, 1993 and accepted after revision February 7, 1994.]
