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Clay minerals and trace metal association in the Gangolli estuarine Sediments, West Coast of India
Estuarine, Coastal and Shelf Science (1992) 35,363-370
Clay Minerals and Trace Metal Association in the Gangolli Estuarine S e d i m e n t s , West Coast of India
K. Pandarinath
and A. C. Narayana
a
Department of Marine Geology, Mangalore University, Mangalagangotri-5 74 199 India Received 14 May 1991 and in revised form 6 March 1992
Keywords: Gangolli estuary; clay minerals; trace elements; organic matter; calcium X-ray diffraction analysis of the clay fraction of surficial sediments of Gangolli estuary reveals that smectite is the dominant clay mineral followed by kaolinitechlorite and illite. The distribution of clay minerals is almost uniform throughout the estuary. Most of the trace elements, except Cu, Pb, Zn and Ti, do not show any association with clay minerals. This may be due to the desorption of trace elements which normally takes place in high saline estuarine environment. Organic matter and calcium do not show any significant effect on the abundance and distribution of clay minerals. It appears that the detrital source is the dominating factor in influencing the relative abundance of clay minerals in the estuary.
Introduction T h e study of clay mineralogy of estuarine sediments is very significant because the first adjustments of fresh water clays to marine conditions take place in this environment. However, clay mineral studies on estuarine sediments are very few when compared to marine sediments. Griffin and Ingram (1955) have studied the clay minerals of the Neuse estuary and emphasized the role of salinity on clay mineral distribution. Whitehouse et al. (1960) have observed that flocculation and differential settling do not generally influence clay mineral distributions in the estuaries. In the James river, F~uillet and Fleischer (1980) found that the estuarine circulation, causing inward transport of marine sediment, could account for the observed clay mineral gradients. Gallenne (1974) has studied the clay minerals distribution in suspended matter of the Loire estuary. Studies on clay minerals of river sediments (Ehlmann, 1968), deltaic sediments (Weir et al., 1975) and lake sediments (El Sabrouti & Sokkary, 1982) were carried out to evaluate their abundance and diagenesis. There are a few studies on the occurrence of different clay mineral types in the Indian estuaries and deltas (Seralathan & Swamy, 1982; Prakasa Rao & Swamy, 1987; Ramanathan et al., 1988). Also, studies related to the abundance and association of clay minerals with trace elements are very scanty. ~Authorto whom correspondenceshould be sent. 0272-7714/92/100363 + 08 $03.00[0
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Figure I. Sample locations in the Gangolli estuary. Clay minerals are characterized by large surface areas per unit mass, and these are considered to be the major reason for enrichment of heavy metals on clays. T h e estuarine transport of trace metals and other pollutants is strongly influenced by the behaviour of suspended solids/clay minerals. T h e present paper deals with the abundance of clay minerals and their association with trace elements in the Gangolli estuarine environment. Most of the trace elements show higher concentrations in the lagoon and in the northern part of the estuary. Copper, Zn and Ni are particularly concentrated in higher amounts in the marshy area. However, in general, the Gangolli estuary does not show any pollutants. Study area
T h e Gangolli estuary, a confluence of Haladi, Chakra and Kollur rivers at a place called Gangolli, is located north of Coondapur, on the west coast of India (Lat. 13°38'N and Long. 74°41'E; Figure 1). T h e depth of the estuary varies from 1 metre in the central part
Clay minerals and trace metal
365
to about 8 metres in the northern part. T h e estuary has a zonal pattern in the distribution of sediments. T h e northern part consists of silty sand, the central part sand, silty sand to clayey silt dominates in the lagoon and sand is found in marshy area. Some parts of the estuary have acted by-passers whereas others as retainers of fine particles (Narayana & Pandarinath, unpubl.). T h e Gangolli river basin consists of various geological units such as migmatitic gneisses, metamorphosed sediments, volcanics and laterites. These lithonnits range in age from Archean to Recent.
Methods of study Fifty-four surficial sediment samples were collected in different parts of the Gangolli estuary using a Peterson grab. Out of these, eleven samples, representing all subenvironments of the estuary, were selected for clay minerals study (Figure 1). T h e samples were washed free of salts, and calcium carbonate and organic matter were removed by treating with dilute acetic acid and hydrogen peroxide respectively. Sample fraction of < 2-~tm size was scanned using Ni-filtered copper K~ radiation by Philips X - R a y Diffractometer (XRD) (Model - - P W 1840). Identification of clay minerals and determination of their abundance were based on the procedure of Biscaye (1965). T h e standard glycolation test was carried out for the confirmation of smectite. T h e thermal treatment of the samples to differentiate kaolinite and chlorite could not be carried out as the X R D facility was limited. However, since the peak at 25A is prominent and the kaolinite-chlorite peak at 7A is smooth, it can be said that chlorite abundance is negligible in the samples. Organic matter content was estimated based on the titrimetric method of E1 Wakeel and Riley (1957) using chromic acid, ferrous phenonthroline indicator and ferrous a m m o n i u m sulphate solution as reagents. Calcium content was determined using E D T A , N a O H , h y d r o x y l a m m o n i u m chlbride, triethonolamine and Patton and Reeder's indicator as reagents (Vogel, 1978). T h e well powdered sample was digested with H F - H C 104-HNO 3 in a teflon beaker for trace metal analysis. T h e digested samples were used for the determination of trace metal concentrations by Atomic Absorption Spectrophotometer (ModelVarian-SpectAA-30). T h e behaviour and distribution pattern of organic matter, Ca and trace elements in the study area have been discussed elsewhere (Pandarinath & Narayana, 1991a). T h e clay minerals distribution and trace metal associations are discussed in this paper.
Results and discussion Smectite is the most abundant clay mineral in the sediments followed by kaolinite-chlorite and illite (Table 1; Figure 2). Non-clay minerals gibbsite and quartz are also identified. T h e relative abundance of smectite varies from 46 To to 59 %, kaolinite-chlorite from 32 To to 39% and illite from 6% to 15%. Smectite is produced by the weathering of basic igneous rocks and by the leaching of potassium from illite or muscovite. High smectite concentrations in the sediments around Indian coasts have been attributed to the weathering of Deccan T r a p basalts and subsequent fluvial transportation (Goldberg &Gritfin, 1970). T h e chemical weathering of primary silicate rocks may be the major contributing factor for kaolinite content. T h e concentration of kaolinite detritus in the river runoff influences the abundance of kaolinite in the Arabian sea coasts (Windom, 1976). T h e decrease of illite along this coast is caused by the diluting effect of river detritus smectite derived from the Deccan Traps.
5 11 18 24 28 30 35 38 42 46 50
Sample No.
Kaolinitechlorite
37 32 32 37 38 36 35 37 39 39 38
Montmorillonite
57 59 56 53 46 54 56 55 53 54 56
Relative percentages
7 9 12 10 15 10 9 8 9 7 6
Illite
28 51 16 13 29 21 33 15 34 165 156
Cu
5 25 5 6 13 5 36 2 6 5 3
Pb
42 110 23 28 41 28 48 30 53 147 133
Zn
29 36 18 10 36 27 34 19 49 27 21
Ni
5 7 2 4 9 7 8 7 13 5 5
PPM
Co
141 150 82 79 180 174 143 90 212 112 113
Mn
80 135 75 58 118 101 115 68 151 85 79
Cr
48 78 64 103 97 64 136 88 178 93 87
V
TABLE 1. Clay minerals and geochemistry of the Gangolli estuarine sediments, West coast of India
2.68 3.70 1,74 1-60 4-05 3.15 3.62 2,09 4-80 1-57 1-43
Fe
4 5 4 4 5 4 5 3 6 4 4
AI
0.35 0-30 0.27 0.25 0-58 0.67 0.56 0.37 0.71 0-48 0-42
%
Ti
3-12 5.80 3.12 1.32 3.00 2-94 4-40 3.10 4.20 2.48 2.24
Ca
5.62 10-00 5.24 7.97 7.48 4.83 7-00 5-00 10-83 4.93 5.21
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T h e highest smectite content (59%) and a relatively low content (33%) of kaolinitechlorite are encountered in back water lagoon sediments (S. N o . 11). T h e northern part samples (S. No.28 & 30) contain higher contents ofillite (10% & 15%) than the other parts of the estuary. Except for these variations, the distribution of clay minerals is almost uniform throughout the estuary. T h e relative percentages of the clay minerals in the estuarine sediments are almost the same as those of the nearshore sediments off Gangolli (Pandarinath & Narayan'a, 1991 b). Cation adsorption is the c o m m o n process that acts on clay minerals during their transportation from fresh to saline water environments (Weaver, 1959). Clay minerals can change in estuaries because of uptake of potassium from the seawater or by the formation of interlayer hydroxide sheets of aluminium and iron (Eisma, 1988). Clay minerals are believed to be good carriers of trace elements. T h e present study reveals that they act as carriers only for certain elements in the estuary. Factor analysis (Table 2) reveals fairly significant negative loadings in Factor-3 for smectite, Cu and Zn and this explains the adsorption of Cu and Zn by smectite. Heydemarm (1958) explains that the copper is adsorbed by clay minerals and adsorption increases as the concentration of Cu and p H increases. Lindberg et al. (1975) have also observed an increase in particulate mercury concentrations with increasing salinity. Smectite and Pb have strong positive loadings, while kaolinite-chlorite and Ti - - negative loadings in Factor-2. T h e negative loadings of kaolinite-chlorite and Ti suggest the association of Ti with the mineral. T h e substitution of Ti for alnmininm occurs in poorly crystallized kaolinite (Grim, 1968). T h e factor analysis reveals that the other trace e l e m e n t s - - Ni, Co, M n , Cr, V - - do not show any association with the clay minerals. T h e clay minerals in the sediments are mainly detrital in nature and desorption with trace elements takes place on contact with sea water (Murty et al., 1973). Rae and Aston (1982) have observed a decrease in the concentration of mercury in the suspended solids to coincide with an increase in chlorinity and with a decrease in the quantity of suspended matter around high water in the Wyre estuary. As stated by Chandrashekaram and Ushakumari (1987), the deprotonation of the iron hydroxide surfaces of the clays by
368
K. Pandarinath & A. C. Narayana
TABLE2. Varimax rotated R-mode factor loadingmatrix Factor-1 -
0.2854 0-2093 0 " 1 5 0 4
-0-0711 0.4474 0.0789 0.9520 0.9218 0.9059 0.9579 0.7120 0.9242 0-9063 0.7438 0,6236 0.7253 47.5500 47.5500
Factor-2
Factor-3
Variable
0-7631 -0-8738 0-1235 -0-2487 0.6132 0.0246 0-0803 -0.1867 -0.1279 0.2157 --0.1856 0-1339 0.1319 -- 0-4650 0.7247 0.2893 17-6500 65.2000
0.4163 -0.3334 0.7853 -0.8979 0.0419 -0-9122 -0-0689 0-0651 0-0969 0-0059 --0.0632 0-3114 0.0568 0.0129 --0.0298 0.1206 15.9400 81-1400
Montmorillonite Kaolinite-chlorite Illite Cu Pb Zn Ni Co Mn Cr V Fe AI Ti Ca Organicmatter Variance Cumulativevariance
-
sodium chloride present in saline water creates electrostatic repulsion between the trace elements and the clay mineral surfaces. This desorption mechanism may be the reason for the absence of association between some trace elements and clay minerals. Prithviraj and Prakash (1990) also have attributed the same reason for the non-association of clays and trace elements in the innershelf region of Kerala. T h e abundance of Ca and organic matter affects partly the diagenesis of clay minerals in marine/estuarine sediments. Table 2 reveals the strong positive loading of smectite and Ca and strong negative loading of kaolinite-chlorite in Factor-2. T h e strong positive loadings of smectite and Ca in Factor-2 suggest that the availability of Ca is a favourable condition for the formation of smectite as reported by Deer et al. (1966), whereas the strong negative loading of kaolinite-chlorite in the same factor suggests that the presence of Ca is not favourable for the formation of kaolinite (Millot, 1970). Grim et al. (1949) and Grim (1951, 1968) have reported that kaolinite is unstable in highly alkaline waters and it alters to illite in estuarine and marine sediments. However, the relative abundance of the kaolinite-chlorite is nearly 3 to 4 times more than that ofillite in the study area, hence the transformation of kaolinite to illite may not be taking place here. T h e role of organic matter in the formation and transformation of clay minerals has been established by various workers (Hamdi, 1977; E1 Sabrouti & Sokkary, 1982). T h e abundance of smectite over illite in the sediments suggests that part of the smectite might have formed as a result of post-depositional alteration of illite as reported by El Sabrouti and Sokkary (1982). T h e positive loading on illite and negative loading on smectite in Factor-3 (Table 2) also support this transformation in the study area. Such a transformation is also noticed in the alluvial soils of the Nile (Hamdi, 1967). E1 Sabrouti and Sokkary (1982) have reported that the organic matter will aid in transformation ofillite to smectite. Prakash Rao and Swamy (1987) have observed a steady increase in smectite content with organic matter in the sediments of the Godavari delta. T h e surface electrical properties of suspended material and the presence of surface oxide or organic films are matters of prime importance in the estuarine transport of particles (Hunter & Liss, 1982). Hunter (1980)
Clay minerals and trace metal
369
has e s t a b l i s h e d t h a t n a t u r a l l y o c c u r r i n g o r g a n i c surfactants are a d s o r b e d r e a d i l y on to a w i d e variety o f solid surfaces, p r o d u c i n g particles o f u n i f o r m e l e c t r o p h o r e t i c b e h a v i o u r . S u s p e n d e d m a t t e r in e s t u a r i n e waters has a h i g h d e g r e e o f surface u n i f o r m i t y w i t h r e s p e c t to electrical p r o p e r t i e s a n d w i t h r e s p e c t to t h e c h e m i c a l a n d p h y s i c a l factors c o n t r o l l i n g the surface electrical state. T h i s m a y result f r o m t h e f o r m a t i o n o f u b i q u i t o u s surface coatings on s u s p e n d e d particles o f m e t a l oxides, o r g a n i c surface-active m a t t e r , or b o t h . H o w e v e r , t h e factor analysis ( T a b l e 2) does n o t s h o w any relation b e t w e e n clay m i n e r a l s a n d o r g a n i c m a t t e r in the s t u d y area. T h e r e f o r e , it a p p e a r s that o r g a n i c m a t t e r m a y n o t b e h a v i n g a role in t r a n s f o r m a t i o n o f illite to s m e c t i t e in the G a n g o l l i e s t u a r i n e sediments. T h e detrital source m a y be the overall d o m i n a t i n g factor in influencing the o c c u r r e n c e a n d d i s t r i b u t i o n o f clay m i n e r a l s in the s t u d y area.
Conclusions T h e clay m i n e r a l s in the surficial s e d i m e n t s o f t h e G a n g o l l i e s t u a r y are in o r d e r o f a b u n d a n c e smectite, k a o l i n i t e - c h l o r i t e a n d illite. T h e clay m i n e r a l d i s t r i b u t i o n is u n i f o r m t h r o u g h o u t t h e estuary. T h e R - m o d e factor analysis reveals t h a t except for a few trace e l e m e n t s , m o s t o f t h e m do n o t associate w i t h t h e clay m i n e r a l s . T h i s m a y be a t t r i b u t e d to the d e s o r p t i o n m e c h a n i s m t h a t takes place as the fresh r i v e r i n e clays get in c o n t a c t w i t h t h e saline e s t u a r y w a t e r a n d to the effects o f m i x t u r e o f e s t u a r i n e s e d i m e n t s w i t h m a r i n e derived sediments. Although organic matter and calcium support the formation of smectite, it is n o t significant in the p r e s e n t area. I n general, the relative a b u n d a n c e a n d d i s t r i b u t i o n o f clay m i n e r a l s in the s t u d y area m o s t l y d e p e n d on detrital source.
Acknowledgements T h e a u t h o r s t h a n k D r R. R. N a i r a n d D r N . H . H a s h i m i , Scientists, N a t i o n a l I n s t i t u t e o f O c e a n o g r a p h y , G o a for p r o v i d i n g t h e X R D facility a n d for t h e i r v a l u a b l e suggestions. T h e k i n d h e l p o f D r S u r e s h Raj, R e s e a r c h A s s o c i a t e , d u r i n g X R D w o r k is g r a t e f u l l y a c k n o w l e d g e d . T h a n k s are also d u e to D r B. R. J. Rao, G e o l o g i c a l S u r v e y o f I n d i a ( G S I ) for the A A S facility, a n d F. G. F r a n c i s a n d D r R. K r i s h n a m u r t h y , G S I , M a n g a l o r e for their h e l p in trace m e t a l analysis. A u t h o r s g r a t e f u l l y t h a n k D r D . E i s m a , N e t h e r l a n d s I n s t i t u t e for Sea R e s e a r c h a n d to a n o n y m o u s referees for t h e i r v a l u a b l e c o m m e n t s o n t h e earlier draft, w h i c h h e l p e d to i m p r o v e t h e status o f this p a p e r .
References Biscaye, P. E. 1965 Mineralogy and sedimentation of recent deep sea clay in the Atlantic ocean and adjacent seas and oceans. Bulletin Geological Society of America 76, 803-832. Chandrashekaram, D. & Ushakumari, S. 1987 Metal adsorption capacity of laterites and clays. In Proceedings of the National Symposium on Role of Earth Sciences in Environment (Sahu, K. C., ed.). Indian Institute of Technology, Bombay, pp. 203-214. Deer, W. A., Howie, R. A. & Zussman, J. 1966 An introduction to the rock-forming minerals. Longman Publications, London, p. 528 Ehlmann, A. J. 1968 Clay mineralogy of weathered products and of river sediments, Puerto Rico. Journal of Sedimentary Petrology 38, 885-894. Eisma, D. 1988 Transport and deposition of suspended matter in estuaries and nearshore sea. In Physical and Chemical weathering in geochemical cycles (Lerman, Meybeck, M., eds). Klaver Academic Publishers, pp. 273-298. El Sabrouti, M. A. & Sokkary, A. A. 1982 Distribution of clay minerals and their diagenesis in the sediments of lake Edku. Marine Geology 45, M15-M21.
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El Waked, S. K. & Riley, J. P. 1957 The determination of organic carbon in marine muds.Journal Cons. Perm. Int. Explor Mar 22, 180-183. Feuillet, J. P. & Fleischer, P. 1980 Estuarine circulation: Controlling factor of clay mineral distribution in James river estuary, Virginia. Journal of Sedimentary Petrology 50, 267-280. Gallene, B. 1974 Study of fine material in suspension in the estuary of the Loire and its dynamic grading. Estuarine, Coastal and Shelf Science 2, 261-272. Goldberg, E. D. & Griff-m, G. M. 1970 The sediments of the northern Indian ocean. Deep Sea Research 17, 513-537. Griffin, G. M. & Ingram, R. L. 1955 Clay minerals of the Neuse estuary. Journal of Sedimentary Petrology 25, 194-200. Grim, R. E. 1951 The depositional environment of red and green shales. Journal of Sedimentary Petrology 21, 226-232. Grim, R. E. 1968 Clay Mineralogy. McGraw-Hill, New York. p. 600. Grim, R. E., Diem, R. S. & Bradley, W. F. 1949 Clay mineral composition of some sediments from the Pacific Ocean off the California coast and gulf of California. Bulletin Geological Society of America 60, 1785-1808. Hamdi, M. 1977 The mineralogy of the fine fraction of the alluvial soils of Egypt. Journal of Soil Science (U.A.R.) 7, 15--21. Heydemann, A. 1958 Adsorption aus sehr verdunnten kupferlosungen an reinen Tonmineralen. Geochimica et CosmochimicaActa 15, 305-329. Hunter, K. A. 1980 Microe_lectrophoretic properties of natural surface active organic matter in coastal sea water. Limnology and Oceanography. 25, 807-822. Hunter, K. A. & Liss, P. S. 1982 Organic matter and the surface charge of suspended particles in estuarine waters. Limnology and Oceanography 27, 322-335. Lindberg, S. E., Andren, A. W. & Harriss, R. 1975 Geochemistry of mercury in the estuarine environment. In Estuarine Research (Crown, L. E. ed.). Academic Press, New York, pp. 64-108. Millot, G. 1970 Geology of Clays. Springer, New York, p. 429. Murty, P. S. N., Rao, Ch.M. & Reddy, C. V. G. 1973 Partition patterns of iron, manganese, nickel and cobalt in the shelf sediments off west coast of India. Indian Journal of Marine Science 2, 6-12. Pandarinath, K. & Narayana, A. C. 1991a Distribution and Geochemistry of Gangolli estuarine sediments, west coast of India. Vol. of Abstracts, International Symposium on Oceanography of the Indian Ocean, National Institute of Oceanography, Goa, India. p. 42. Pandarinath, K. & Narayana, A. C. 1991b Clay minerals distribution and their association with trace elements, calcium and organic matter in the innershelf sediments of Gangolli, west coast of India. Journal of Coastal Research 7, 981-987. Prakash Rao, M. & Swamy, A. S. R. 1987 Clay mineral distribution in the mangroves of the Godavari delta. Clay Research 6, 81-86. Prithviraj, M. & Prakash, T. N. 1990 Distribution and Geochemical association of clay minerals on the inner shelf of central Kerala, India. Marine Geology 92, 285-290. Rae, J. E. & Aston, S. R. 1982 The role of suspended solids in the estuarine geochemistry of mercury. Water Research 16, 649-654. Ramanathan, V., Subramanian, V. & Vaithyanathan, P. 1988 Chemical and sediment characteristics of the upper reaches of Cauvery estuary, east coast of India. Indian Journal of Marine Sciences 17, 114-120. Seralathan, P. & Seetharamaswamy, A. 1982 Clay minerals in the modern deltaic sediments in the Cauvery river. Indian Journal of Marine Sciences 11, 167-169. Vogel, A. I. 1978 A text book of quantitative inorganic analysis Longman Inc. New York, p. 925. Weaver, C. W. 1959 Clays and clay minerals. Proceedingsof 8th National Conference, Pergamon Press, New York, p. 154. Weir, A. H., Ormerod, E. C. & El Mansey, I. M. 1975 Clay mineralogy of sediments of the western Nile delta. Clay Mineralogy 10. Whitehouse, U. O., Jeffrey, L. M. & Debrecht, J. D. 1960 Differential settling tendencies of clay minerals in saline waters. In Clays and Clay Minerals (Swireeford, A., ed.), Proceedings of 7th National Conference, Pergamon Press, pp. 1-79. Windom, H. E. 1976 Lithogenous material in marine sediments, In Chemical Oceanography (Riley, J. P. & Chester, R., eds). Academic Press, New York, pp. 103-135.
Clay Minerals and Trace Metal Association in the Gangolli Estuarine S e d i m e n t s , West Coast of India
K. Pandarinath
and A. C. Narayana
a
Department of Marine Geology, Mangalore University, Mangalagangotri-5 74 199 India Received 14 May 1991 and in revised form 6 March 1992
Keywords: Gangolli estuary; clay minerals; trace elements; organic matter; calcium X-ray diffraction analysis of the clay fraction of surficial sediments of Gangolli estuary reveals that smectite is the dominant clay mineral followed by kaolinitechlorite and illite. The distribution of clay minerals is almost uniform throughout the estuary. Most of the trace elements, except Cu, Pb, Zn and Ti, do not show any association with clay minerals. This may be due to the desorption of trace elements which normally takes place in high saline estuarine environment. Organic matter and calcium do not show any significant effect on the abundance and distribution of clay minerals. It appears that the detrital source is the dominating factor in influencing the relative abundance of clay minerals in the estuary.
Introduction T h e study of clay mineralogy of estuarine sediments is very significant because the first adjustments of fresh water clays to marine conditions take place in this environment. However, clay mineral studies on estuarine sediments are very few when compared to marine sediments. Griffin and Ingram (1955) have studied the clay minerals of the Neuse estuary and emphasized the role of salinity on clay mineral distribution. Whitehouse et al. (1960) have observed that flocculation and differential settling do not generally influence clay mineral distributions in the estuaries. In the James river, F~uillet and Fleischer (1980) found that the estuarine circulation, causing inward transport of marine sediment, could account for the observed clay mineral gradients. Gallenne (1974) has studied the clay minerals distribution in suspended matter of the Loire estuary. Studies on clay minerals of river sediments (Ehlmann, 1968), deltaic sediments (Weir et al., 1975) and lake sediments (El Sabrouti & Sokkary, 1982) were carried out to evaluate their abundance and diagenesis. There are a few studies on the occurrence of different clay mineral types in the Indian estuaries and deltas (Seralathan & Swamy, 1982; Prakasa Rao & Swamy, 1987; Ramanathan et al., 1988). Also, studies related to the abundance and association of clay minerals with trace elements are very scanty. ~Authorto whom correspondenceshould be sent. 0272-7714/92/100363 + 08 $03.00[0
© 1992AcademicPress Limited
364
K. PandaHnath & A. C. Narayana
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1,2'
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Figure I. Sample locations in the Gangolli estuary. Clay minerals are characterized by large surface areas per unit mass, and these are considered to be the major reason for enrichment of heavy metals on clays. T h e estuarine transport of trace metals and other pollutants is strongly influenced by the behaviour of suspended solids/clay minerals. T h e present paper deals with the abundance of clay minerals and their association with trace elements in the Gangolli estuarine environment. Most of the trace elements show higher concentrations in the lagoon and in the northern part of the estuary. Copper, Zn and Ni are particularly concentrated in higher amounts in the marshy area. However, in general, the Gangolli estuary does not show any pollutants. Study area
T h e Gangolli estuary, a confluence of Haladi, Chakra and Kollur rivers at a place called Gangolli, is located north of Coondapur, on the west coast of India (Lat. 13°38'N and Long. 74°41'E; Figure 1). T h e depth of the estuary varies from 1 metre in the central part
Clay minerals and trace metal
365
to about 8 metres in the northern part. T h e estuary has a zonal pattern in the distribution of sediments. T h e northern part consists of silty sand, the central part sand, silty sand to clayey silt dominates in the lagoon and sand is found in marshy area. Some parts of the estuary have acted by-passers whereas others as retainers of fine particles (Narayana & Pandarinath, unpubl.). T h e Gangolli river basin consists of various geological units such as migmatitic gneisses, metamorphosed sediments, volcanics and laterites. These lithonnits range in age from Archean to Recent.
Methods of study Fifty-four surficial sediment samples were collected in different parts of the Gangolli estuary using a Peterson grab. Out of these, eleven samples, representing all subenvironments of the estuary, were selected for clay minerals study (Figure 1). T h e samples were washed free of salts, and calcium carbonate and organic matter were removed by treating with dilute acetic acid and hydrogen peroxide respectively. Sample fraction of < 2-~tm size was scanned using Ni-filtered copper K~ radiation by Philips X - R a y Diffractometer (XRD) (Model - - P W 1840). Identification of clay minerals and determination of their abundance were based on the procedure of Biscaye (1965). T h e standard glycolation test was carried out for the confirmation of smectite. T h e thermal treatment of the samples to differentiate kaolinite and chlorite could not be carried out as the X R D facility was limited. However, since the peak at 25A is prominent and the kaolinite-chlorite peak at 7A is smooth, it can be said that chlorite abundance is negligible in the samples. Organic matter content was estimated based on the titrimetric method of E1 Wakeel and Riley (1957) using chromic acid, ferrous phenonthroline indicator and ferrous a m m o n i u m sulphate solution as reagents. Calcium content was determined using E D T A , N a O H , h y d r o x y l a m m o n i u m chlbride, triethonolamine and Patton and Reeder's indicator as reagents (Vogel, 1978). T h e well powdered sample was digested with H F - H C 104-HNO 3 in a teflon beaker for trace metal analysis. T h e digested samples were used for the determination of trace metal concentrations by Atomic Absorption Spectrophotometer (ModelVarian-SpectAA-30). T h e behaviour and distribution pattern of organic matter, Ca and trace elements in the study area have been discussed elsewhere (Pandarinath & Narayana, 1991a). T h e clay minerals distribution and trace metal associations are discussed in this paper.
Results and discussion Smectite is the most abundant clay mineral in the sediments followed by kaolinite-chlorite and illite (Table 1; Figure 2). Non-clay minerals gibbsite and quartz are also identified. T h e relative abundance of smectite varies from 46 To to 59 %, kaolinite-chlorite from 32 To to 39% and illite from 6% to 15%. Smectite is produced by the weathering of basic igneous rocks and by the leaching of potassium from illite or muscovite. High smectite concentrations in the sediments around Indian coasts have been attributed to the weathering of Deccan T r a p basalts and subsequent fluvial transportation (Goldberg &Gritfin, 1970). T h e chemical weathering of primary silicate rocks may be the major contributing factor for kaolinite content. T h e concentration of kaolinite detritus in the river runoff influences the abundance of kaolinite in the Arabian sea coasts (Windom, 1976). T h e decrease of illite along this coast is caused by the diluting effect of river detritus smectite derived from the Deccan Traps.
5 11 18 24 28 30 35 38 42 46 50
Sample No.
Kaolinitechlorite
37 32 32 37 38 36 35 37 39 39 38
Montmorillonite
57 59 56 53 46 54 56 55 53 54 56
Relative percentages
7 9 12 10 15 10 9 8 9 7 6
Illite
28 51 16 13 29 21 33 15 34 165 156
Cu
5 25 5 6 13 5 36 2 6 5 3
Pb
42 110 23 28 41 28 48 30 53 147 133
Zn
29 36 18 10 36 27 34 19 49 27 21
Ni
5 7 2 4 9 7 8 7 13 5 5
PPM
Co
141 150 82 79 180 174 143 90 212 112 113
Mn
80 135 75 58 118 101 115 68 151 85 79
Cr
48 78 64 103 97 64 136 88 178 93 87
V
TABLE 1. Clay minerals and geochemistry of the Gangolli estuarine sediments, West coast of India
2.68 3.70 1,74 1-60 4-05 3.15 3.62 2,09 4-80 1-57 1-43
Fe
4 5 4 4 5 4 5 3 6 4 4
AI
0.35 0-30 0.27 0.25 0-58 0.67 0.56 0.37 0.71 0-48 0-42
%
Ti
3-12 5.80 3.12 1.32 3.00 2-94 4-40 3.10 4.20 2.48 2.24
Ca
5.62 10-00 5.24 7.97 7.48 4.83 7-00 5-00 10-83 4.93 5.21
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Clay minerals and trace metal
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T h e highest smectite content (59%) and a relatively low content (33%) of kaolinitechlorite are encountered in back water lagoon sediments (S. N o . 11). T h e northern part samples (S. No.28 & 30) contain higher contents ofillite (10% & 15%) than the other parts of the estuary. Except for these variations, the distribution of clay minerals is almost uniform throughout the estuary. T h e relative percentages of the clay minerals in the estuarine sediments are almost the same as those of the nearshore sediments off Gangolli (Pandarinath & Narayan'a, 1991 b). Cation adsorption is the c o m m o n process that acts on clay minerals during their transportation from fresh to saline water environments (Weaver, 1959). Clay minerals can change in estuaries because of uptake of potassium from the seawater or by the formation of interlayer hydroxide sheets of aluminium and iron (Eisma, 1988). Clay minerals are believed to be good carriers of trace elements. T h e present study reveals that they act as carriers only for certain elements in the estuary. Factor analysis (Table 2) reveals fairly significant negative loadings in Factor-3 for smectite, Cu and Zn and this explains the adsorption of Cu and Zn by smectite. Heydemarm (1958) explains that the copper is adsorbed by clay minerals and adsorption increases as the concentration of Cu and p H increases. Lindberg et al. (1975) have also observed an increase in particulate mercury concentrations with increasing salinity. Smectite and Pb have strong positive loadings, while kaolinite-chlorite and Ti - - negative loadings in Factor-2. T h e negative loadings of kaolinite-chlorite and Ti suggest the association of Ti with the mineral. T h e substitution of Ti for alnmininm occurs in poorly crystallized kaolinite (Grim, 1968). T h e factor analysis reveals that the other trace e l e m e n t s - - Ni, Co, M n , Cr, V - - do not show any association with the clay minerals. T h e clay minerals in the sediments are mainly detrital in nature and desorption with trace elements takes place on contact with sea water (Murty et al., 1973). Rae and Aston (1982) have observed a decrease in the concentration of mercury in the suspended solids to coincide with an increase in chlorinity and with a decrease in the quantity of suspended matter around high water in the Wyre estuary. As stated by Chandrashekaram and Ushakumari (1987), the deprotonation of the iron hydroxide surfaces of the clays by
368
K. Pandarinath & A. C. Narayana
TABLE2. Varimax rotated R-mode factor loadingmatrix Factor-1 -
0.2854 0-2093 0 " 1 5 0 4
-0-0711 0.4474 0.0789 0.9520 0.9218 0.9059 0.9579 0.7120 0.9242 0-9063 0.7438 0,6236 0.7253 47.5500 47.5500
Factor-2
Factor-3
Variable
0-7631 -0-8738 0-1235 -0-2487 0.6132 0.0246 0-0803 -0.1867 -0.1279 0.2157 --0.1856 0-1339 0.1319 -- 0-4650 0.7247 0.2893 17-6500 65.2000
0.4163 -0.3334 0.7853 -0.8979 0.0419 -0-9122 -0-0689 0-0651 0-0969 0-0059 --0.0632 0-3114 0.0568 0.0129 --0.0298 0.1206 15.9400 81-1400
Montmorillonite Kaolinite-chlorite Illite Cu Pb Zn Ni Co Mn Cr V Fe AI Ti Ca Organicmatter Variance Cumulativevariance
-
sodium chloride present in saline water creates electrostatic repulsion between the trace elements and the clay mineral surfaces. This desorption mechanism may be the reason for the absence of association between some trace elements and clay minerals. Prithviraj and Prakash (1990) also have attributed the same reason for the non-association of clays and trace elements in the innershelf region of Kerala. T h e abundance of Ca and organic matter affects partly the diagenesis of clay minerals in marine/estuarine sediments. Table 2 reveals the strong positive loading of smectite and Ca and strong negative loading of kaolinite-chlorite in Factor-2. T h e strong positive loadings of smectite and Ca in Factor-2 suggest that the availability of Ca is a favourable condition for the formation of smectite as reported by Deer et al. (1966), whereas the strong negative loading of kaolinite-chlorite in the same factor suggests that the presence of Ca is not favourable for the formation of kaolinite (Millot, 1970). Grim et al. (1949) and Grim (1951, 1968) have reported that kaolinite is unstable in highly alkaline waters and it alters to illite in estuarine and marine sediments. However, the relative abundance of the kaolinite-chlorite is nearly 3 to 4 times more than that ofillite in the study area, hence the transformation of kaolinite to illite may not be taking place here. T h e role of organic matter in the formation and transformation of clay minerals has been established by various workers (Hamdi, 1977; E1 Sabrouti & Sokkary, 1982). T h e abundance of smectite over illite in the sediments suggests that part of the smectite might have formed as a result of post-depositional alteration of illite as reported by El Sabrouti and Sokkary (1982). T h e positive loading on illite and negative loading on smectite in Factor-3 (Table 2) also support this transformation in the study area. Such a transformation is also noticed in the alluvial soils of the Nile (Hamdi, 1967). E1 Sabrouti and Sokkary (1982) have reported that the organic matter will aid in transformation ofillite to smectite. Prakash Rao and Swamy (1987) have observed a steady increase in smectite content with organic matter in the sediments of the Godavari delta. T h e surface electrical properties of suspended material and the presence of surface oxide or organic films are matters of prime importance in the estuarine transport of particles (Hunter & Liss, 1982). Hunter (1980)
Clay minerals and trace metal
369
has e s t a b l i s h e d t h a t n a t u r a l l y o c c u r r i n g o r g a n i c surfactants are a d s o r b e d r e a d i l y on to a w i d e variety o f solid surfaces, p r o d u c i n g particles o f u n i f o r m e l e c t r o p h o r e t i c b e h a v i o u r . S u s p e n d e d m a t t e r in e s t u a r i n e waters has a h i g h d e g r e e o f surface u n i f o r m i t y w i t h r e s p e c t to electrical p r o p e r t i e s a n d w i t h r e s p e c t to t h e c h e m i c a l a n d p h y s i c a l factors c o n t r o l l i n g the surface electrical state. T h i s m a y result f r o m t h e f o r m a t i o n o f u b i q u i t o u s surface coatings on s u s p e n d e d particles o f m e t a l oxides, o r g a n i c surface-active m a t t e r , or b o t h . H o w e v e r , t h e factor analysis ( T a b l e 2) does n o t s h o w any relation b e t w e e n clay m i n e r a l s a n d o r g a n i c m a t t e r in the s t u d y area. T h e r e f o r e , it a p p e a r s that o r g a n i c m a t t e r m a y n o t b e h a v i n g a role in t r a n s f o r m a t i o n o f illite to s m e c t i t e in the G a n g o l l i e s t u a r i n e sediments. T h e detrital source m a y be the overall d o m i n a t i n g factor in influencing the o c c u r r e n c e a n d d i s t r i b u t i o n o f clay m i n e r a l s in the s t u d y area.
Conclusions T h e clay m i n e r a l s in the surficial s e d i m e n t s o f t h e G a n g o l l i e s t u a r y are in o r d e r o f a b u n d a n c e smectite, k a o l i n i t e - c h l o r i t e a n d illite. T h e clay m i n e r a l d i s t r i b u t i o n is u n i f o r m t h r o u g h o u t t h e estuary. T h e R - m o d e factor analysis reveals t h a t except for a few trace e l e m e n t s , m o s t o f t h e m do n o t associate w i t h t h e clay m i n e r a l s . T h i s m a y be a t t r i b u t e d to the d e s o r p t i o n m e c h a n i s m t h a t takes place as the fresh r i v e r i n e clays get in c o n t a c t w i t h t h e saline e s t u a r y w a t e r a n d to the effects o f m i x t u r e o f e s t u a r i n e s e d i m e n t s w i t h m a r i n e derived sediments. Although organic matter and calcium support the formation of smectite, it is n o t significant in the p r e s e n t area. I n general, the relative a b u n d a n c e a n d d i s t r i b u t i o n o f clay m i n e r a l s in the s t u d y area m o s t l y d e p e n d on detrital source.
Acknowledgements T h e a u t h o r s t h a n k D r R. R. N a i r a n d D r N . H . H a s h i m i , Scientists, N a t i o n a l I n s t i t u t e o f O c e a n o g r a p h y , G o a for p r o v i d i n g t h e X R D facility a n d for t h e i r v a l u a b l e suggestions. T h e k i n d h e l p o f D r S u r e s h Raj, R e s e a r c h A s s o c i a t e , d u r i n g X R D w o r k is g r a t e f u l l y a c k n o w l e d g e d . T h a n k s are also d u e to D r B. R. J. Rao, G e o l o g i c a l S u r v e y o f I n d i a ( G S I ) for the A A S facility, a n d F. G. F r a n c i s a n d D r R. K r i s h n a m u r t h y , G S I , M a n g a l o r e for their h e l p in trace m e t a l analysis. A u t h o r s g r a t e f u l l y t h a n k D r D . E i s m a , N e t h e r l a n d s I n s t i t u t e for Sea R e s e a r c h a n d to a n o n y m o u s referees for t h e i r v a l u a b l e c o m m e n t s o n t h e earlier draft, w h i c h h e l p e d to i m p r o v e t h e status o f this p a p e r .
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