Department of Zoology, University of Madras, Life Science Building, Guindy Campus,. Madras 600 025, India. *Post-Graduate Department of Zoology, Jamal ...
J. Biosci., Vol. 17, Number 4, December 1992, pp. 491-427. © Printed in India.
Distribution of natural radionuclide 40K in biotic and abiotic components of the Cauvery river system, Tiruchirapalli, India R ASOKAN† and Ρ SHAHUL HAMEED* Department of Zoology, University of Madras, Life Science Building, Guindy Campus, Madras 600 025, India *Post-Graduate Department of Zoology, Jamal Mohamed College, Tiruchirapalli 620 020, India MS received 1 October 1991; revised 6 April 1992 Abstract. Abiotic components like water and sediment, and biotic components such as mussels, fish and grass collected from Cauvery river at Tiruchirapalli were analysed for 40 K activity. The highest level of 40K activity was found in the sediment (342 mBq g–1 dry weight) and the lowest activity was found in water (2·209 mBq ml–1). In the freshwater mussel Parreysia favidens (Benson) 40K activity was estimated in the total soft tissues and shells of mussels belonging to three different size groups· In all the size groups 40K activity was two times higher in shells (68–39 mBq g–1 fresh weight) than in the total soft tissues (25–17 mBq g–1 fresh weight)· The results indicate that the younger mussels accumulated more 40K than the older ones. The ability of internal organs of mussels belonging to group III to accumulate 40K was in the following order: gills > digestive gland > foot > mantle. The values ranged from 47 to 18 mBq g–1 fresh weight in the various organs. Concentration of 40K in the mussel was distinctly higher than in the grass Echinochloa colonum (J Koenig) (95 mBq g–1 fresh weight), and the concentration of 40K in the bone of the fish Cirrhina cirrhosa (Bloch) (126 mBq g–1 fresh weight) was higher than to that of muscle (113 mBq g–1 fresh weight)· Keywords. Potassium-40; Parreysia favidens.
natural
radionuclide;
Cauvery
river;
freshwater
mussel;
1. Introduction Many aquatic organisms such as crustaceans, molluscs and fishes, an important source of protein among sections of world population, are capable of accumulating considerable quantities of radionuclides though radionuclides are present in trace amounts in the ambient water (Iyengar and Narayana Rao 1990). Among the aquatic organisms mostly marine animals were used for investigations related to uptake, bioaccumulation and redistribution of both natural and artificial radionuclides (Lowman et al 1971; Bowen et al 1971; Iyengar 1983). Information related to the levels of natural radionuclides in freshwater biota of India is limited. The present study provides 40K content of biotic and abiotic components of a section of the Cauvery river system. 2.
Materials and methods
For the present study, water and sediment samples and biological materials were collected from Cauvery river 1 km downstream of the Mukkombu barrage (10°48’ N, 78°42’E), Tiruchirapalli district, Tamil Nadu (figure 1). †
Corresponding author.
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Figure 1. Map showing the sampling site.
Total beta activity, and potassium and 40K content in the water, sediment and in the freshwater mussel Parreysia favidens (Benson), fish Cirrhina cirrhosa (Bloch), plant Echinochloa colonum (J Koenig) were estimated according to the procedures described by Kannan (1983) and Ganapathy (1984). For measurement of 40K in different age groups of P. favidens, total soft tissues and shells of three different size groups (group I, shell length 2–4 cm; group II, 4–5 cm; group III, 5–6 cm) were used. In group I, soft tissues collected from 65 mussels were pooled whereas in groups II and III soft tissues obtained from 30 and 25 mussels respectively were utilized. In addition 40K contents in individual organs (mantle, gills, foot, viscera and digestive glands) of group III mussels were also estimated. 2.1 Preparation of samples 2.1a Sediment: Sediment weighing 250 g was dried in a hot air oven (105° C) and then heated to 500° C in a muffle furnace. The heated sample was homogenized and 1 g of the homogenized sediment was used for the radiochemical analysis (Iyengar 1983). 2.1b Biological materials: Mussels of all sizes were hand picked, brought to laboratory in plastic buckets, and washed in water to remove sand and detritus materials. In the laboratory they were maintained in Cauvery water (salinity 0·55 ppt, pH 7·6, temperature 29° C) and allowed to depurate for 24 h. After depuration different body tissues were dissected using clean scissors. The biological materials were washed, dried at 105°C, weighed, and ashed in a muffle furnace (450° C overnight) as described by AOAC (1975). One part of the ash was used for the measurement of total beta activity, potassium and 40K.
Potassium-40 in Cauvery river system at Tiruchirapalli 2.2
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Measurement of total beta activity
To measure the total beta activity, 500 mg of ashes obtained from sediment and biological materials were uniformly spread over a clean background known aluminium planchet (3 cm dia). A few drops of 1% collodion solution were added to each planchet and kept under infrared lamp for 15 min. Immediately after drying, beta activity was estimated in a indigenously designed low level beta counter (Health Physics Division, Bhabha Atomic Research Centre, Bombay). The background of the counter is 1·5 cpm with a counting efficiency of 40% for 40K beta activity rays (1·31 meV). 2.3 Estimation of potassium content and 40K To estimate the potassium content in water samples, 1 1 of water was acidified with 0·5 ml of HCl and then concentrated to 30 ml by evaporation. The concentrated water samples were used for potassium, estimation (Havlik 1970). Ashes (500 mg) obtained from the sediment and biological materials were digested with HNO3 and H2O2 (1 : 1) till a white residue was obtained. The residue was dissolved in 0·1 Ν HNO3 and filtered through a Whatman 42 filter paper. The filtrate was used for the estimation of potassium content using a Varian Techtron Model 1100 atomic absorption spectrophotometer (Kannan 1983). 40K activity was calculated assuming that 1 g of natural potassium contains 0·0118 g 40K (Robert and Wesast 1973). The following formula was used for the calculation of 40K. Potassium content in the samples:
where S is mg potassium per g fresh weight, A is the concentration of potassium in the solution after subtracting acid blank concentration and applying dilution factor, Q is quantity of ash in grams taken for analysis/volume of water in ml, Β is factor for conversion of ash weight to fresh weight (for water samples Β should not be used). 40
K content in the samples:
3. Results Total beta activity, and potassium and 40K content of the water, the sediment and the biological materials in the area of study are given in table 1. Regarding total beta activity, the highest activity was recorded in the sediment (549 mBq g–1 dry wt). In the biotic components, highest total beta activity was recorded in the shells of the fresh water mussel P. favidens. It is interesting to note that the total beta
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R Asokan and Ρ Shahul Hameed Table 1. Total beta, Κ content and 40K activity in the freshwater mussel P.favidens, the fish C. cirrhosa, the plant E. colonum, the sediment and in the water from Cauvery river system at Tiruchirapalli.
NM not measured
activity increased as the shell size increased. In the shells of the younger mussels (group I, 2–4cm), the total beta activity rocrded was 197 mBq g–1 fresh wt, which increased to 302 mBq g–1 fresh wt in the older shells (group III, 5–6 cm). In contrast, the total beta activity appeared to decrease in the total soft tissues of the P. favidens as the size of the mussel increased. Regarding total beta activity in different body parts of P. favidens the highest activity (51 mBq g–1 fresh wt) was recorded in the gills and the lowest activity (31 mBq g–1 fresh wt) was found in the digestive glands. The total beta activity in the muscle and bone of the fish C. cirrhosa were 117 and 148 mBq g–1 fresh wt respectively. The total beta activity recorded in the grass E. colonum was 127 mBq g–1 fresh wt. The highest potassium content was recorded in the sediment, the concentration being 12·60 mg g–1 dry wt, followed by water (0·08 mg ml–1) . In the biological materials the highest potassium level was recorded in the bone of the fish C. cirrhosa the value being 4·63 mg g–1
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fresh wt In P. favidens, unlike the total beta activity, potassium content decreased from the younger shells to the older ones (i.e. 2–4 cm to 5–6 cm), and the same trend was found in total soft tissues. Among different body tissues of P. favidens, gills showed a value of 1·72 mg g–1 fresh wt while the lowest value was recorded in the foot (0·68 mg–1 fresh wt). As expected from the above results (since 1 g of natural potassium contains 0·0118 g of 40K: Robert and Wesast 1973) the highest activity of 40K was recorded in the sediment (342 mBq g–1 dry wt), followed by water (2·209 mBq ml–1). In P. favidens the highest 40K activity (68 mBq g–1 fresh wt) was recorded in the shells of the size group I (2–4 cm), which decreased to 39 mBq g–1 fresh wt in the shells of the size group III (5–6 cm). Similarly in the total soft tissue, concentration of 40K decreased from the younger mussels to the older ones. Among different body tissues, gills of P. favidens showed the highest level of 40K (47 mBq g–1 fresh wt). Compared to P. favidens, 40K concentration was higher in the bones and muscles of the fish C. cirrhosa, the values being 126 and 113 mBq g–1 fresh wt respectively. The recorded concentration of 40 K in grass E. colonum was 95 mBq g –1 fresh wt
4.
Discussion
The results of the present study provide baseline data on natural radionuclides, particularly on beta emitters, in a section of the Cauvery river system. The total beta activity and 40K activity of the water, sediment and plant observed in the present study are much lower than the values reported by Havlik (1970) in Czechoslovakian streams. According to Havlik (1970), the total beta activity of the sediment of an unpolluted stream was 2516 mBq g–1 whereas the total beta activity of the sediment of the stream which was polluted due to the mining and processing of uranium ore in a nearby area was 7807 mBq g–1. He also reported that the plants of the unpolluted stream had a total activity of 9546 mBq g–1 whereas the same plant species growing in the polluted stream showed a value of 37,370 mBq g–1. The 40K values of the water, sediment and plant reported in the present study are 4 to 7 times lower than the values reported by Havlik (1970). The levels of 40K observed in the biotic and abiotic components of the present study are found to be normal. It is a well known fact that the mussels are used as the indicators of heavy metal and radionuclide pollution in the marine environment (Iyengar 1983; Farrington et al 1983). The concept of using mussels as a bioindicator of pollution is based on the fact that the suspension feeding bivalve molluscs are capable of accumulating contaminants in the body organs to a concentration significantly higher than in the ambient water and thereby facilitating the analysis of the impact of these contaminants on biological systems (Bayne 1989). In the freshwater environment, mussels like Unio mancus and P. favidens are, like their marine counterparts, fixed to the site for easy and repeated observation and remain in the sediment and water interface and accumulate pollutants, including radionuclides (Merlini 1967; Forester 1980; Hameed and Mohanraj 1989). Asokan (1990) demonstrated that soft tissues of P. favidens could be used as an indicator of 210Po since softer tissues of P. favidens are capable of concentrating more 210Po than the shells. The present study shows that the shells accumulated more 40K than the total soft
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tissues in P. favidens. In molluscs, shell development begins with the formation of periostracum, a protein matrix, on to which CaCO3 is deposited. Jodrey and Wilbur (1955) found that calcium from water will be used for the shell development. During the deposition of calcium some amount of potassium is also deposited on the shell matrix which may be the reason for the occurrence of high potassium level (consequently 40K) in the shells than in tissues. However, the concentration of 40K in the shells decreased with the increase in the age of mussels as indicated by the size of the shells. In bivalves, metabolism-size relationship implies higher physiological activities in younger individuals than the older ones. As a result the uptake of ions including potassium (consequently 40K) is more active in younger mussels (Prosser 1973). When compared with the other internal organs, the concentrations of 40K was high in the gills, because in the freshwater mussels, the active Na–K pump takes place in the gills, which lead to the increased level of potassium (consequently 40K) in the gills (Prosser 1973). This seems to be the responsible factor for the occurrence of high concentration of 40K in the gills than in the other internal organs. Hence it is possible to use the shells of the young P. favidens as an indicator of beta emitting radionuclides in general.
Acknowledgements The authors express their gratitude and thanks to Dr Μ A R Iyengar, Head, Environmental Survey Laboratory, Department of Atomic Energy, Kalpakkam, for encouragement and facilities. We are thankful to Mr V Kannan, Senior Officer, Environmental Survey Laboratory, Kalpakkam, for technical assistance and Dr S Thangavelu, Head of the Department of Zoology, Jamal Mohamed College, Tiruchirapalli, for encouragement. References AOAC 1975 Official methods of analysis of the Association of Official Analytical Chemists (New York: McGraw-Hill) p 428 Asokan R 1990 Studies on the bioaccumulation of natural radionuclides in freshwater mussel Parreysia favidens (Benson) from Kaveri river system (Tiruchirappalli, India); M. Phil, thesis, Bharathidasan University, Tiruchirapalli, India Bayne Β L 1989 Measuring the biological effects of pollution: The mussel watch approach; Water Sci. Technol. 21 1089–1100 Bowen V T, Olsen J S, Osterberg C L and Ravera J 1971 Ecological interactions of marine radioactivity. Radioactivity in the marine environment (Washington, DC: US National Academy of Sciences) pp 200–222 Farrington J W, Goldberg Ε D, Risebrough R W, Martin J Η and Bowen V Τ 1983 U.S. “Mussel Watch” 1967–1978. An overview of the trace metal, DDT, PCB, hydrocarbon and artificial radionuclide data; Environ. Sci. Technol. 17 490–496 Forester A J 1980 Monitoring the bioavailability of toxic metals in acid-stressed shield lakes using pelecypod molluscs (clams and Mussels); Proc. Univ. Montana Annu. Conf. on Trace substances and Environmental Health 14 142–147 Ganapathy S 1984 Cycling of trace and major elements in the aquatic ecosystem adjacent to a nuclear complex at Kalpakkam; Ph. D. thesis, University of Bombay, Bombay Hameed Ρ S and Mohanraj A I 1989 Freshwater mussel Lamellidens marginalis (Lamarck) (Molluscs; Bivalvia: Unionidae) as an indicator of river pollution; Chem. Ecol. 4 57–64 Havlik Β 1970 Radioactive pollution of rivers in Czechoslovakia; Health Phys. 19 617–624
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Iyengar M A R 1983 Studies on the distribution of natural radionuclides in the marine organisms; Ph. D. thesis, University of Bombay, Bombay Iyengar M A R and Narayana Rao Κ 1990 The environmental behaviour of radium; International Atomic Energy Agency; Tech. Rep. Series No. 310, pp 467–684 Jodrey L Η and Wilbur Κ Μ 1955 Calcium deposition in oyster shell; Biol. Bull. 108 346–358 Kannan V 1983 Radioactivity and trace elements in marine macrophytes from Kalpakkam; M.Sc. thesis, University of Bombay, Bombay Lowman F G, Rice Τ R and Richards F A 1971 Accumulation and redistribution of radionuclides by marine organisms. Radioactivity in marine environment (Washington, DC: US National Academy of Sciences) pp 161–199 Merlini Μ 1967 The freshwater clam as a biological indicator of radiomanganese; Int. Symp. On radioecological concentration processes (London: Pergamon Press) pp 977–982 Prosser C L 1973 Comparative animal physiology (Philadelphia: W Β Saunders) Vol 1, pp 79–105 Robert C and Wesast Ε D 1973 Handbook of chemistry and physics (Cleveland: Chemical Rubber Company)
