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Heavy metal speciation in sediments of Cochin estuary determined using chemical extraction techniques
The Science of the Total Environment, 102 (1991) 113 128 Elsevier Science Publishers B.V., Amsterdam
113
HEAVY METAL SPECIATION IN S E D I M E N T S OF COCHIN E S T U A R Y D E T E R M I N E D USING CHEMICAL EXTRACTION TECHNIQUES
C.K. NAIR, A.N. BALCHAND and P.N.K. NAMBISAN*
Chemical Oceanography Dwision, Cochin University of Science and TechnoZogy, Cochin 682 016, India (Recei :ed October 30th, 1989; accepted January 25th, 1990)
ABSTRACT Sequentiai extraction waz used to characterise ~he various forms of cadmium, copper, lend and zinc in the sediments of Cochin estuary, southwest India, a typical positive tropical estuary. The forms determined were exchangeable cations, carbonate bound, easily reducible (combined with F e M n oxides), organic/sulphide phases and residual fractions. The concentrations determined indicated selective accumulation of the various metals in the different phases of the sediments, with spatial variability. The speciation pattern varies widely for different metals in the freshwater zone, through the estuarine reaches, before being preferentially accumulated in esoteric fractions at the seaward end. The influence of natural estuarine processes in modifying the anthropogenic inputs and in the selective enrichment of quasi.stable metal species is highlighted. The paper also discusses interspecies relationships in the sediments of this coastal region and compares the metal levels with those from other regions.
INTRODUCTION
The speciation of heavy metals in the aquatic environment has received considerable attention recently (Cben et ai., 1976; Hong and Forstner, 1984; Rapin, 1984). These studies throw ligh~ on two aspects: their levels in the environment and their fractionation in different phases. The investigations provide information on the mobility o~' the metal and bioavailability factors, and also highlight the role of processev such as sorption, diffusion and mobilisation in controlling the concentratiorL of metals in sediments (Calmano and Forstner, 1983). Rapin (1984) comments that sequential extraction procedures would provide information on the history of metal inputs, diagenetic transformation within the sediments and the reactivity of heavy metal species of both natural and anthropogenic origin. Earlier studies on heavy metals in sediments were confined to the partitioning of metals into detrital and non-detrital fractions (Hirst and Nicholls, 1958; Gad and Lerich, 1966). Further development was in the direction of a chemical extraction procedure for the separation of metals associated with ferromanganese minerals, carbonate minerals and adsorbed trace elements from * Author to whom all correspondence should be addressed. 0048-9697/91/$03.50
~') 1991 - - Elsevier Science Publishers B.V.
114
pelagic sediments (Chester and Hughes, 1967; Nissenbaum, 1972). Sequential extraction is recognised as a useful methodology for gaining information on the origin, manner of occurrence, bioavailability, mobilisation and transport of heavy metals, despite the poor selectivity (Chao, 1972; Engler et al., 1974; Reuther et al., 1981). In spite of many limitations, partitioning gives valuable htfgrmation about the relative differences in metal association for two environments differing in metal quality (Patchineelam and Forstner, 1984). A five-step sequential extraction technique was introduced by Tessier et al. (1979) and later modified by Forstner (1982). This scheme facilitated the distinction between exchangeable, easily reducible, moderately reducible, organically bound and residual metal fractions. The chemical technique was based on the three groups of components occurring in fluvial systems potentially able to enrich the metals in sediments: (i) detrital solids, coated with oxides and/or o:ganics; (ii) endogenic fractions, transitory in nature, mostly due to in-situ p zocesses; and (iii) diagenetic fractions occurring within sediments (Calmano and Forstner, 1983). This paper discusses the speciation of cadmium, copper, lead and zinc in the sediments of two river reaches of the Cochin estuary as well as within the estuary. An attempt is made to identify anthropogenic sources and enrichment factors, in addition to understanding the importance of selective accumulative phases for this region. MATERIALS A N D M E T H O D S
Study area
The area of study, Cochin estuary (09°40'-10°10'N; 76°15'-76°30'E), was surveyed on 29 and 30 November 1988 at 12 stations (Fig. 1). The survey extended into the two adjoining rivers, Periyar in the north and Muvattupuzha in the south. Stations 1 and 12 are located in freshwater reaches on either side of the barmouth (Station 5). Station 2 in the Periyar River and Station 11 in the Muvattupuzha River receive ettiuents from chemical factories (fertiliser plant, zinc smelter, catalysts, chemicals, etc.~ and a pulp-paper mill, respectively. The fluvial dynamics of this water body are influenced by the riverine discharge from these two rivers and the tidal influence from the Arabian Sea acting through the Cochin barmouth. As for other equatorial regions the west coast of India is characterised by a monsoonal period of high rainfall (JuneSeptember), a post-monsoonal period of moderate rains (October-January) and a pre-monsoonal period of dry weather (February-May). During the monsoon, alluvial laterite is transported as suspended solids from high ground and settles in the shallow coastal sedimentary plains (Mallik and Suchindan, 1984). Sedimentary bedload movements as well as increased transport of suspended solids (particulates) also occur largely during the monsoon season (Paul and Pillai, 1983; Nair, 1987). This facilitates the flushing of previously deposited and mobilised sedimentary material. The survey was timed to account for
115 N
0
1
100
sd
7 6°
1o'
20"
30" E
Fig. 1. M a p of Cochin estuary showing location of sampling stations.
sediments of very recent origin derived by natural processes as well as to detect newly introduced anthropogenic sources. Details of the hydrographic setting and other environmental features of this estuarine system are available elsewhere (Gopinathan and Qasim, 1971; Joseph, 1974; Lakshmanan et al.,1982, 1987; Sankaranarayanan et al., 1986).
Collection and analysis of samples A stainless steel, plastic-lined van-Veen grab was used to collect sediments, and the top 5 cm layer was carefully skimmed, homo?.enised and stored at 5°C. Aliquots of the sample (20 g) (wet weight) were subjected to sequential chemical analysis as detailed below (Fig. 2). After extraction, the phases were separated by centrifugation at 6000 rpm for 5 min. A Perkin-Elmer Model 2380 atomic absorption spectrophotometer was used for the determination of the metals in the various fractions. Stock standard solutions (1000 ppm) of different metals were prepared and used in the preparation of secondary standards. All care was taken in the preparation of reagents and pre-cleaning of glass and plastic ware. Blank corrections were applied where necessary. The analyses were performed in triplicate and the values determined varied within 10% of the computed mean. All values are expressed in microgrammes per gram wet weight. -
116 I
Extractant
I ' Sample 1 M NH4OAc - pH 7 ( 30% ) I
Metal spec£es .I --1
2 hours
I Resldue
I -----~ Ext-*ct
L
. . . . . .
L__R:_,_~Ea uo _ ] 0.1 M NH2OH. ttCl + 0.01 M HNO3 -
Extract
[
pH 2 - 12 hours (30°C) I
1 Res£due
Exchangeable cation fraction
t-
~"I E x t r a c t
(30°c) -
j - ~
J
1 M NaOAC - pH 5 - 12 hours
--
_]
Carbona te bound , . ,
1
f Eas£1y zeduc~ble f r a c t t o n (metals combined with Fe-Mn oxyhydrltes)
]
(30~ v/v) H202 ÷ 0.01 M HNO3 - pH 3 hours (85oc) extracted w£th 1 M NH40AC - 24 hours (30°C)
(.;onc. HNO3 - 4-6 hours (,1800C)
2-J
!
I Ext.ctj Extract
J
i
Or"°""=ludl.g'°ct"" 41 ~ sulfldes
~
Res£dual f : a c t l o n 1
Fig. 2. Sequential extraction scheme.
RESULTS
Cadmium
Figure 3(a) depicts the distribution (#gg-' wet weight) vis-a-vis the percentage of cadmium species in the sediments of Cochin estuary. The maximum variabilitywas observed in the cadmium fraction bound to organic/ sulphides, ranging from 0.22 to 1.47/~gg- '.The two arms of the estuary exhibit distinctive behaviour in the relative abundance of cadmium species. The northern parts, the Periyar River and its lower estuarine reaches, show varying proportions of all five species studied. Exchangeable cations predominate in the freshwater zone (Station 1, 0.15/~gg-', 53.5%) and gradually decr~as~ in content with increasing salinity (0.05/~g g-', 2.3%, at Station 4). Station 2, the recipient of efliuent discharges, and Station 3, in the vicinity, are dominated by carbonate-bound fractions. At all these locations, the organic/ sulphide and residual fractions are comparatively low in concentration, highlighting the authigenic association of cadmium with riverine sandy sediments. The two downstream estuarine stations, 4 and 5, exhibit very strong associ-
117
0.61 Cadmium
"r=~.o.z°"4
0 1 ,_
_ ~4\-
~= o-, 2
3
4"
8_ Copper
1
2
5,4
3
4
5
6 A
6
7" 8 ,4
7
9-1"0-1~1 - 1 ~
/1//~
8
//~
9
(3b)
•
10 11 12
STATIONS Fig. 3. Distribution of cadmium and copper species in the sediments of Cochin estuary. (x axis), Stations ] ]2; (y axis), concentration (/lg g =wet wt); (z axis), percentage, a, Exchangeable cation fraction; b, carbonate.bound; c, easily reducible fraction; d, organic fraction; and e, residual fraction. ation of cadmium w i t h organic/sulphide phases. The content of this cadmium fraction is extremely high (0.74-1.47/xgg -1, i.e. 50-68%), together with appreciable amounts of the detrita] fraction. The downstream trend points to a relative increase in the carbonate-bound fraction. The northern arm of the
estuary shows the results of two influencing factors: riverine processes maintaining near-proportionality between the five species in the upstream reaches, and the downstream area dominated by anthropogenic activities resulting in the selective enrichment of cadmium within the organic and residual phases. The vast expanse of the southern parts of the estuary exhibits a constant ratio, but varying amounts, of the residual cadmium fraction. This feature is accompanied by the absence of exchangeable cadmium. The upper river reaches, composed of silt and sand, contain 30% of the carbonate, easily reducible and organic/sulphide-bound metal. The relative proportions of these three fractions remain more or less unchanged within the riverine environment (between Stations 8 and 12). The residual fraction, thought to be of terrestrial origin, varies from 0.18 to 0.31/xgg 1 in sandy as well as silty-clay environments. The sediments collected from locations marked by saline conditions (Stations 6 and 7) show the tendency of cadmium to associate with carbonates, Fe-Mn oxides and organic/sulphide phases, in equal proportions. The build-up of cadmium within both of the lower estuarine arms of Cochin estuary reflects the assimilative capacity of silty clay sediments subjected to diagenetic processes. The detrital fraction, occupying a major portion of the sediment free from diagenetic processes, acts equally in regulating the fractional distribution of the non-detrital species. Moderate to low saline waters in both arms of the estuary (Stations 2, 3, 6 and 7) exhibited increasing concentrations of cadmium species of the Fe-Mn easily reducible type. It is also noted that authigenic carbonates become increasingly in, olved in the redistribution of Cd species, especially in the southern parts of Cochin estuary
118
Copper Analytical results [Fig. 3(b)] for samples from the northern parts, Stations 1, 2 and 3 (upper and middle estuary), show simila,c concentrations of exchangeable, carbonate-bound and easily reducible, Fe-Mn species. The levels of two other species, organic/sulphide-bound and residual, in the cleaner, upstream stations show progressively increasing concentrations downestuary. This enhancement in concentration is accompanied by a corresponding decrease in the level of the other three species (see Stations 4 and 5). The change in speciation may be associated with biological production in the vicinity of the barmouth. However, unlike cadmium, the mobility of copper is more related to the detrital fraction, via mineralisation. As observed for Station 1 on the Periyar River, Station 12 on the Muvattupuzha River also exhibits proportionally divided metal species of exchangeable, carbonate-bound, easily reducible and organic/sulphide-bound fractions. A significant change is noted at Station 11, the location of the efliuent outfall from the pulp-paper mill where organic/sulphide fractions contribute substantially to the increased levels of copper detected. At other downstream stations also, enhanced levels of organic/sulphide forms of copper are present in comparison with other non-residual frac*ions. The residual fraction downstream of the outfall shows consistently higher values, particularly at Station 10 (deep pool) and Station 8 ( -~ 10.5 ~g g- ~). Further downstream, in mid and lower estuarine reaches, this fraction does not exhibit any significant variability. A distinct feature observed in copper speciation is the increased levels of organic-bound copper in the southern parts, probably associated with suspended solids of the organic wastes discharged from the pulp-paper mills which sediment along the river bed as well as on the estuarine floor. The proportions of the various copper species vary between stations, indicating the ability of copper species to interchange under different environmental conditions. Lead
Figure 4(a) illustrates the distribution of the various species of lead, including percentage proportions. The lead concentration varies from 0.34 to 8.31/~gg-~ in this waterbody. The lead level is higher in the southern parts (composed mainly of the residual fraction) than in the northern parts. Lead does not exist in detectable levels in exchangeable form or bound to organic/ sulphides. The Periyar riverine reaches (Stations 1 and 2) do not contain the carbonate-bound fraction. About 80% of the lead is found in the residual fraction, while the remainder is associated with the Fe-Mn oxide phase. The middle and lower estuary (Stations 3 and 4) contain a carbonate-bound lead fraction derived largely from the residual form. Notably, the concentration of detrital lead is 6.74-7.68#g g-~ in the vicinity of the barmouth. The southern parts of Cochin estuary are also devoid of organic/sulphide-bound lead species
119 /
._
(4a)
J'~
OC
1
_
2
3
4
s
~'
Zin
'=
40
7
8
/ I A
....
9
10
.
,ul
"
11 12~
c4bl .
. .
0 1
2
3
4
5
6
?
8
9
10
11 12
STATIONS
Fig. 4. Distribution of lead and zinc species in the sediments of Cochin estuary. (x axis), Stations 1-12; (y axis),concentration (/~gg-I wet wt); (z axis), percentage, a, Exchangeable cation fraction; b, carbonate-bound; c, easily reducible fraction; d, organic fraction; and e, residual fraction.
in concentrations that can be detected with the methods used. The Muvattupuzha River reaches show the association of this metal with the carbonate phase (0.34-2.36/~gg-~). The deep pool at Station 10 and the river mouth (Station ~3)have large amounts of the residual metal fraction.The predominant residual t.'actionappears to be a contributing factor in controlling speciation in southern parts, unlike its distribution in the northern regions. Locations of high siltand clay content (Stations 5, 6, 7, 8 and 10) were found to contain high amounts of residual lead, indicating a close relationship of this species with the textural class of the sediments. The levelsof residual fraction in the leastsaline regions of the estuary are comparable, but the mid-estuarine enrichment is one order higher. All along the estuary the presence of carbonate-bound lead is persistently noted, highlighting the role of interspecies transformation between residual and carbonate-bound lead. Thus lead speciation is invariably controlled by the sedimentary processes involving the above two species. Zinc
The various fractions of zinc are widely distributed in Cochin estuary [Fig. 4(b)]. Of the five fractions estimated, residual zinc far exceeds the concentrations of other species determined, the range of values being 0.61-63.54/~gg at the various stations. Exchangeable zinc was present at Stations 1, 2 and 3 together with all the other four fractions, in decreasing proportions indicative of species transformation. The carbonate and organic/sulphide-bound fractions show enhanced values in the vicinity of the zinc smelter (Station 2), and the effect is reflected also at ~he downstream stations. The barmouth region is again highly enriched by the various zinc fractions other than the exchange-
120
able fraction. Apart from the abundant level of residual zinc, zinc is associated in decreasing order with the organic/sulphide phase, the carbonate-bound phase followed by the easily reducible Fe-Mn oxide phase. The southern parts of the estuary are also dominated by residual zinc of terrestrial origin, which gradually increased in concentration downestuary. The stations located on the Muvattupuzha River (Stations 9-12) contain insignificant levels of exchangeable zinc, but this trend is altered in the midestuarine region (Station~ 6-8) with detectable levels of exchangeable as well as carbonate-bound zinc. Zinc is also associated with organic/sulphides in increasing amounts proceeding towards the barmouth. DISCUSSION
The ability to accumulate metal species selectively in sediments greatly depends on particle/grain size, composition of the sediment and external conditions of pH, Eh, salinity, and concentrations of organic and inorganic complexing agents (Calmano and Forstner, 1983). Particles of detrital and anthropogenic origin and inorganic minerals coated with hydrous Fe-Mn oxides affect the interaction processes (Forstner, 1976; Jones and Bowser, 1978). In Cochin estuary, variation in bio-productivity, transitory in nature, may also influence the endogenic fractions of metals, thereby redistributing the metal species in the estuary. By applying a sequential extraction procedure, relative bonding strengths were determined and the ability of the metal species to form quasi-stable binding phases with organic material was also established in the lower reaches of these tropical rivers. The three-fold mechanism of metal-organics binaing depicted by Cooper and Harris (1974) and De Groot et al. (1976) also appears to have a significant application in our study. Nevertheless, under the rapidly changing environmental conditions characteristic of the tropics, metal speciation in sedimentary environments comprising regions of freshwater to marine conditions presents variable characteristics. A comparison can be made with the reported levels of metals at other geographic locations (Table 1).
Exchangeable cations Estuarine reactivity is such that exchangeable species are subject to severe changes. The freshwater zone is occupied by this species of cadmium, whereas it is below detection limits in the upper estuarine regions in the southern parts, and a gradual increase is noted downestuary. Exchangeable copper is present at all stations in this estuary, but only at low levels, and contributing a low percentage of total copper. The distribution of the species appears to be regulated by the presence of other competing, strongly binding phases. Copper, as an element distinguished by its biological regulation in sediments (Luoma and Jenne, 1977) even under marine conditions, sustains continued bio-removal in this estuary, in high production zones. Lead, generally of low affinity for
0.47
Weser estuary
Cochin estuary
Brockpolder, Rhine River Rotterdam Harbour Neckar River
17.65
11.04
2. i 1
0.09 (0.020.26)
4.74
1.26
0.07 (BDL 0.15)
1.21
0.31
1.22
214.71
1.24
1.12
0.02
29.30
!: ~
b
15.55
Baie de Nice
0.01
2.40
a
Cadmium
Yanaska River St. Francis River Rhine River
Yellow River
Location
0.07 (0.02 0.11)
2.35
1.26
0.02
0.62
32.35
3.78
0.52
7.18
BDL b
c
0.22 (BDL1.47)
2.17
0.47
0.20
1.23
11.77
1.53
BDL
BDL
BDL
d
1.08
1.08
7.18
0.02
0.22 (0.03 0.46)
0.36
0.16
0.09
0.05
14.71
e
Distribution of metal species from various geographical locations (ppm)"
TABLE 1
0.27 (0.07 0.51)
5.73
95.58
0.86
0.27
0.50
5.45
1.98
0.64
0.12
Copper
0.50 (0.23 0.91)
1.91
499.14
0.43
0.27
5.29
19.80
23.10
0.36 (0.20 0.52)
152.80
392.94
33.81
15.22
4.41
2.02
12.80
0.54
5.12
0.36
1.70 (0.14 3.55)
7.64
42.48
3.00
0.27
5.88
30.30
85.80
19.84
2.43
4.81 (0.73 10.84)
24.83
31.86
5.14
10.95
4.12
68.68
ly °
26.24
2.16
(continued)
This study
Calmano and Forstnet, 1983
Rapin, 1984
Hong and Forstner, 1984
Reference
168.96 3.00
2.56
1.50
1.12 (BDL2.36)
1.05
0.35
0.49
1.38
1.38
52.94
0.43 (BDL0.49)
33.00
46.08
16.15
28.29
22.94
1.18
54.39
79.58
0.28
0.48
42.00
2.56
3.86
1.38
7.94
5.90
22.20
32.87
0.07
4.68 (0.998.31)
72.00
38.40
14.04
36.57
8.82
63.72
14.43
29.41
2.10
0.84 (BDL2.25)
154
11.30
6.12
14.00
94.86
7.37
2.71
0.12
666
35.19
157.50
55.88
80.40
63.21
0.40
6.81 (BDL26.31)
2611
b
1.20
3.75 (0.2524.87)
215
418
76.50
133.00
29.41
322.35
130.65
123.41
c
9.60
9.18 (0.3437.54)
30.72
11.30
7.65
10.50
20.59
73.68
20.10
15.05
d
a, Exchangeable cation fraction; b, carbonate-bound; c, easily reducible fraction; d, organic fraction; e, residual fraction. b BDL, below detection limit.
Cochin estuary
Weser estuary Brockpolder, Rhine River Rotterdam Harbour Neckar River
1.59
19.98
BDL
Baie de Nice
31.14
1.12
BDL
1.77
0.02
Yanaska River St. Francis River Rhine River
Yellow River
e
a
d
a
c
Lead
Location
b
Zinc
(continued)
TABLE 1
(0.6163.54)
17.77
61.44
33.90
27.54
42.00
14.71
119.73
97.15
99.33
20.40
This study
Calmano and Forstner, 1983
Rapin 1984
Hong and Forstner, 1984
Reference
123
sediment in the exchangeable form, has not been found in this state in Cochin estuary. Zinc is yet another metal which is found sparingly in the exchangeable form, even in the clayey-silt ~ediments of the estuarine environment.
Carbonate-bound Of the four metals considered in this study, lead does not show any association with this phase in the northern freshwater parts, whereas other metals exhibit varying affinity. The selective build-up of this fraction is observed on either side of the barmouth for cadmium and zinc. Copper in the carbonatebound form is present at all stations in this estuary, but the amounts are very low. With regard to cadmium associated with the carbonate-bound phase, the effluent outfall regions on both arms of the estuary indicate general enhancement in levels. Comparing stations, cadmium carbonate is found in largest concentration at the barmouth, occupied by saline waters. This reflects the phase selective enrichment of cadmium in tropical estuaries. The distribution of lead species bound to carbonates was observed to be closely related to the textural nature of sediments or locations where pollutants are introduced into the estuary. The highest concentration of carbonate-bound lead was found in the vicinity of the barmouth. In the southern parts, clayey-silt sediments contained lead species of this type and more so in the deep pools of the Muvattupuzha River. The absence of large variations in concentration of the lead carbonate fraction, even in the presence of large amounts of residual lead, is especially noted in this estuary. The barr.aouth region, however, containing large amounts of organics, contained zinc in the carbonate-bound form, similar to other metals. Enrichment at the barmouth may also be due to previously deposited zinc, accumulated in sediments at upstream locations, being transported via bedload movement during the monsoon period and relocated at the barmouth, a divergent field for siltation. The zinc smelter on the bank of the Periyar River, a constant external source, showed a strong contribution of zinc (at Station 2), the content being divided between the carbonate and organic] sulphide phases.
Easily reducible phases The metal concentrations associated with this phase are of comparatively low magnitude; however, the whole of the estuary indicates the presence, in varying amounts, of all the metals investigated. Except for the high zinc content of estuarine regions, near the barmouth, all metals are uniformly distributed in the Fe-Mn oxides phase, irrespective of aquatic environmental differences. Although no definite conclusions can be drawn as to why uniform metal levels are maintained within this phase, the role of adsorption on Fe-Mn flocs determines metal behavior under the oxidising conditions of this tropical estuary. Nevertheless, neither changing environmental conditions from freshwater to marine conditions through the estuarine reaches, nor the
124
changing bed grain size from sandy to clayey silt, has any influence on the level of this metal fraction. It can also be noted that anthropogenic effects are not readily reflected in the easily reducible phases alone. Gupta and Chen (1975) have expressed the view that, under oxidising environments, the relative variations in the fractionation of metals in sediments exhibit only minor changes in the level of this species, found in marginal abundance. Cadmium shows moderately increasing content downestuary (Stations 4-7) compared with upstream stations, coupled with the general trend of enhancement in all fractions, and it may be subjected to processes of interspecies transformation. Copper and lead show no noticeable change in content of this species in this estuary. An exception to this is the trace amounts of lead at three locations (Stations 7, 8 and 9) in the southern parts, for which no specific reason could be found. Zinc bound to the easily reducible phase exhibits an isoplethic value in mid and upstream sediments compared with enhanced values downestuary.
Organics~sulphide-bound These metal species are known to vary widely in distribution and content in aquatic environments. They also reflect the status of the sedimentary processes that influence metal behavior and reveal the natural levels as well as those superimposed by external stresses. The attempt to quantify the enrichment factors has indicated selective cadmium accumulation at locations in the vicinity of the barmouth, an area covered with fine clay and silt (Table 2). It seems that the processes occurring in the marine conditions downestuary and the biogeochemical processes of autochthonous n~ture in the upper estuary, compete with bio-production prevailing in the region of interest. Cadmium intake during periods of high production is known to exceed that at norms l grazing and, upon decay, detritussettlingon the estuarine bed stores the metal in the organic/sulphide phase (Forstner, 1980). This appears to be a very selective process for this part of the waterway. However, in the l;.ght of speciation studies, cadmium exhibits progressive changes in species concentration with increasing association with the organic/sulphide-bound fraction. Copper and zinc also show enhancement in the organic/sulphide-bound fraction downestuary. These metals are also known for their affinity for detrital bio-matter on sediment beds, especially the clay-silt type° The Muvattupuzha River exhibits copper accumulation in the organic/sulphide phase and the Periyar River exhibits zinc accumulation in this phase. Lead is fairly nolo. existent in this form in this estuary, irrespective of geological or biolof:ical processes and the textural or detrital content of the sediment. Similar instances of metal-organic association excluding an element are, as yet, not well documented. The atypical behavior of lead compared with copper, cadmium and zirLc demonstrates its low tendency for incorporation within the facies of existiag sediment types, highlighting the role of heavy metal speciation studies.
125 TABLE 2 Enrichment of metal species Species a
Northern estuary b
Southern estuary b
1
2
3
4
5
1
2
3
Cadmium a b c d e
0.15 0.05 0.03 BDL c 0.05
0.05 0.10 0.05 0.02 0.10
0.05 0.17 0.12 !11 0.39
0.33 2.00 1.67
0.33 3.40 4.90
2.00
Copper a b c d e
0.33 0.75 0.42 0.25 1.17
0.18 0.62 0.36 0.27 1.26
0.24 0.33 0.43 3.30 5.45
0.55 0.83 0.84 1.08 1.08
Lead a b c d e
BDL BDL 0.41 BDL 1.81
BDL 0.38 0.38 BDL 1.15
BDL 1.53 0.45 BDL 7.20
Zinc a b c d e
1.40 0.84 0.41 2.04 3.00
1.10 4.51 1.87 7.16 7.00
0.26 22.8 17.7 36.8 62.6
4
5
BDL 0.15 0.11 0.13 0.25
BDL 0.26 0.11 0.74 0.32
7.50 2.75 6.50 1.39
13.0 2.75 37.0
7.80
BDL 0.02 0.04 0.02 0.18
0.73 0.44 1.02 13.2 4.66
0.15 0.29 0.29 0.15 1.30
0.41 0.69 0.36 1.58 6.67
0.31 0.31 0.41 3.55 5.37
2.74 2.34 1.24 10.5 5.13
2.07 1.07 1.41 23.7 4.14
0.93
1.10
BDL 1.45 0.48 BDL 6.74
4.27 1.41
3.98
BDL 0.97 0.48 BDL 7.02
2.85 1.41
0.64
BDL 0.34 0.34 BDL 1.03
6.82
6.54
0.79 5.30 4.56 3.51 2.34
0.19 27.1 43.2 16.7 20.9
BDL BDL 0.25 0.34 3.50
1.14 3.60 1.10 6.90 22.8
0.26 19.3 10.6 37.5 62.0
4.40 20.3 6.50
}.78
42.2 110 17.7
"a, Exchangeable cation fraction; b, carbonate-bound; c, easily reducible fraction; d, organic fraction; e, residual fraction. b 1, Upestuary values; 2, midestuary values; 3, downestuary values; 4, midestuary enrichment; 5, downestuary enrichment. '~BDL, below detection limit.
Residual fraction As reported elsewhere residual fraction content prominent in the absence enhancement in c o n t e n t show maximised residual site dominated
( P a u l a n d P i l l a i , 1983), a l l t h e m e t a l s h a v e a l a r g e i n t h i s e s t u a r y . T h e r e s i d u a l f r a c t i o n o f l e a d is of other species of lead. Copper and cadmium show a t t w o l o c a t i o n s ( S t a t i o n s 8 a n d 9). A l l f o u r m e t a l s ,deposition at the barmouth and its near vicinity, a
by sa]ilie conditions
of overlying
waters.
126
Enrichment of metals Table 2 shows mid- and downestuary enrichment in species of cadmium, copper, lead and zinc in the northern and southern parts of Cochin estuary. It is evident from the table that the easily reducible and the residual fractions of cadmium at downstream locations in the northern part of the estuary and the organic/sulphide-bound fractions at mid- and downstream locations in the southern parts of the estuary, show considerable enrichment. The other species also exhibit accumulation, with the exception of exchangeable cations. Conversely, copper is depleted in the nor~hern parts of the estuary, excluding the organic/sulphide and residual species downestuary. However, in the southern estuary, all copper fractions exhibit enhancement, especially the organic/sulphide-bound species. For all metals, the general trend is an increase in the enrichment factor proceeding downestuary. Lead was detected or~ly in the easily reducible and residual fractions, and while the mid-estuarine region appears depleted in content, the enrichment factor for the residual fraction increased four-fold downestuary in the northern estuary. In the southern estuary, lead was also enriched in downstream reaches, the residual fraction being considerably increased in comparison with the carbonate or easily reducible species. Zinc exhibited varying enrichment factors: 3.51-43.2 in the northern estuary and 4.40-42.2 in the southern estuary. Although exchangeable zinc is depleted, the mid-estuarine region in both the north and the south indicate a 2-6-fold increase in content of all species except the organic/sulphide.bound fraction in the southern estuary (20.3-fold increase). Compared with background, the downstream accumulation of zinc is 15-40 times for many of the fractions, a factor of considerable importance in the light of the transport and fate of zinc in the sediments of Cochin estuary. The presence of silt and clay in higher proportions in the downstream reaches may also favor incorporation of this metal, which is mostly derived from anthropogenic inputs.
Interspecies relationship T w o sets of relationships have been derived using correlation analysis. The sum of the concentrations of all species of a metal are regressed versus each metal fraction to provide an understanding of interspecies relationships, and values for total and residual iron (cognate data) are statisticallycomputed versus respective values of the four metals (Table 3).The analysis reveals that: (i)cadmium and copper are poorly correlated (except for residual copper); (ii) detectable lead species are well correlated; and (iii)zinc shows significant correlation (except for exchangeable cations). It appears that natural processes control the estuarine sediment levels of cadmium and copper, whereas zinc is controlled by anthropogenic (external) inputs. The behavior of lead species varies, and is unresolved in the light of limited speciation of this metal. Compared with variations in total and residual iron, zinc does not show a close relationship, nor does the total cadmium. However, residual cadmium, copper
127 TABLE
3
Interspecies relationships (r values)
~ ( a - e ) vs
aa b c d e
Fe(e) vs (c) Fe(f) vs (f)
Cadmium
Copper
Lead
Zinc
ND b 0.40 0.44 - 0.006
0.18 0.16 - 0.10 0.42 0.98
ND 0.79 0.59 ND 0.99
- 0.099 0.98 0.93 0.99 0.98
0.89 0.89
0.93 0.93
0.42 0.35
0.21
0.68 - 0.16
a a, Exchangeable cation fi'action;b, carbonate-bound; c, easily reducible; d, organic fraction; e, residual fraction; f, total. b ND, not determined. n = 12.
a n d l e a d ( t o t a l a n d r e s i d u a l ) f r a c t i o n s a r e w e l l r e l a t e d to c h a n g e s o f i r o n i n t h i s estuary. ACKNOWLEDGEMENT T h e a u t h o r s t h a n k C o c h i n U n i v e r s i t y o f S c i e n c e a n d T e c h n o l o g y for u s e o f f a c i l i t i e s ; A N B t h a n k s U G C ( I n d i a ) for f i n a n c i a l a s s i s t a n c e . REFERENCES Calmano, W. and U. FSrstner, 1983. Chemical extraction of heavy metals in polluted river sediments in Central Eu :r:. ~ i . Total Environ., 28:77 90. Chao, L.L., 1972. Selective di~ ~oluti, a of manganese oxides from soils and sediments with acidified hydroxylamine hydrochlonde. Soil Sci. Soc. Am. Proc., 36: 764-768. Chen, K.Y., S.K. Gupta, A.Z. Sycip, C.S. Lu, M. Knezevic and W.W. Choi, 1976. The effect of dispersion settling and resedimentation on migration of chemical constituents during open water disposal of dredged material. Contract Rep., U.S. Army Engineers Waterways Experimental Station, Vicksburg, pp. 221. Chester, R. and M.J. Hughes, 1967. A chemical technique for the separation of ferro-manganese minerals, carbonate minerals and adsorbed trace elements from pelagic sediments. Chem. Geol., 2: 249-262. Cooper, B.S. and R.C. Harris, 1974. Heavy metals in organic phases of river and estuarine sediment. Mar. Pollut. Bull., 5: 24-26. De Groot, A.J., W. Salomons and E. Allersma, 1976. Processes affecting heavy metals in estuarine sediments. In: J.D. Burton and P.S. Liss (Eds), Estuarine Chemistry. Academic Press, London, pp. 131-157. Engler, R.M., J.M. Brannon and J. Rose, 1974. A practical selective extraction procedure for sediment characterization. In: Proc. 168th ACS Meet. Atlantic City. American Chemical Society, Washington DC. Forstner, U., 1976. Lake sediments as indicators of heavy metal pollution. Naturwissenschaften, 63: 465-470.
128 Forstner, U., 1980. Cadmium in polluted sediments. In: J.O. Nriagu (Ed.),Cadmium in the Environment, Part I. John Wiley & Sons, N e w York, pp. 305-363. Forstner, U., 1982. Accumulative phases for heavy metals in limnic sediments. Hydrobiologia, 91: 269-284. Gad, M.A. and H.H. LeRiche, 1966. A method for separating the detrital and nondetrital fractions of trace elements in reduced sediments. Geochim. Cosmochim. Acta, 30: 841-846. Gopinathan, C.K. and S.Z. Qasim, 1971. Silting in navigational channels of the Cochin harbour area. J. Mar. Biol. Assoc. India, 13: 14-26. Gupta, S.K. and K.Y. Chen, 1975. Partitioning of trace metals in selective chemical fractions of nearshore sediments. Environ. Lett., 10: 129-158. Hirst, D.W. and G,D. Nicholls, 1958. Techniques in sedimentary goechemistry. 1. Separation of the detrital and non.detrital fractions of limestone. J. Sediment. Petrol., 28: 461-468. Hong, Y.T. and U, Forstner, 1984. Speciation of heavy metals in Yellow River sediment. In: Proc. Syrup, Heavy Metals in the Environment, Heidelberg. C E P Consultants, Edinburgh, pp.872875. Jones, B.F. and C.J. Bowser, 1978. The mineralogy and related chemistry of lake sediments. In: A. Lerman (Ed.), Lakes -- Chemistry, Geology and Physics. Springer, New York, pp. 179-235. Joseph, P.S., 1974, Nutrient distribution in the Cochin harbour and in its vicinity. Indian J. Mar. Sci., 3:20 32. Lakshmanan, P.T., C.S. Shynamma, A.N. Balchand, P.G. Kurup and P.N.K. Nambisan, 1982. Distribution and seasonal variation of temperature and salinity in Cochin backwaters. Indian J. Mar. Sci., ll: 170-172. Lakshmanan, P.T, C.S. Shynamma, A.N. Balchand and P.N.K. Nambisan, 1987. Distribution and variability of nutrients in Cochin backwaters, southwest coast of India. Indian J. Mar. Sci., 16: 99102. Luoma, S.N. and E.A. Jenne, 1977. Estimating bioavailability of sediment bound metals with chemical extractions. In: D.D. Hemphill (Ed.), Trace Substances in Environmental Health. University of Missouri Press, Columbia, MO, Vol. 10, pp. 343-351. Mallik, T.K. and G.K. Suchindan, 1984. Some sedimentological aspects of Vembanad lake, Kerala, west coast of India. Indian J. Mar. Sci., 13: 159-163. Nair, M.M., 1987. Coastal geomorphology of Kerala. J. Geol. Soc. India, 29: 450458. Nissenbaum, A., 1972. Distribution of several metals in chemical fractions of sediment core from the Sea of Okhotsk. Isr. J, Earth. Sci., 21: 143-154. Patchineelam, S.R. and U. Forstner, 1984, Sequential chemical extractions on polluted sediments from the Subae River, Brazil. In: Proc. Syrup. Heavy Metals in the Environment, Heidelberg. CEP Consultants, Edinburgh, pp. 86ff 863. Paul, A.C. and K.C, Pillai, 1983. Trace metals in a tropical river environment -- Distribution. Water, Air Soil Pollut., 19: 63-73. Rapin, F., 1984. Speciation of heavy metals in a sediment core from Baie de Nice (Mediterranean Sea). In: Proc. Syrup. Heavy Metals in the Environment, Heidelberg. CEP Consultants, Edinburgh, pp. 1005-1008. Reuther, R., R.F. Wright and U. Forstner, 1981. Distribution and chemical forms of heavy metals in sediment cores from two Norwegian lakes affected by acid precipitation. In: Proc. Symp. Heavy Metals in the Environment, Amsterdam. CEP Consultants, Edinburgh, pp. 318321. Sankaranarayanan, V.N., P. Udayavarma, K.K. Balachandran, A, Pylee and T. Joseph, 1986. Estuarine characteristics of the lower reaches of the river Periyar (Cochin Backwater). Indian J. Mar. Sci., 15: 166-170. Tessier, A., P.G.C. Campbell and M. Bisson, 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem., 51: 844851.
113
HEAVY METAL SPECIATION IN S E D I M E N T S OF COCHIN E S T U A R Y D E T E R M I N E D USING CHEMICAL EXTRACTION TECHNIQUES
C.K. NAIR, A.N. BALCHAND and P.N.K. NAMBISAN*
Chemical Oceanography Dwision, Cochin University of Science and TechnoZogy, Cochin 682 016, India (Recei :ed October 30th, 1989; accepted January 25th, 1990)
ABSTRACT Sequentiai extraction waz used to characterise ~he various forms of cadmium, copper, lend and zinc in the sediments of Cochin estuary, southwest India, a typical positive tropical estuary. The forms determined were exchangeable cations, carbonate bound, easily reducible (combined with F e M n oxides), organic/sulphide phases and residual fractions. The concentrations determined indicated selective accumulation of the various metals in the different phases of the sediments, with spatial variability. The speciation pattern varies widely for different metals in the freshwater zone, through the estuarine reaches, before being preferentially accumulated in esoteric fractions at the seaward end. The influence of natural estuarine processes in modifying the anthropogenic inputs and in the selective enrichment of quasi.stable metal species is highlighted. The paper also discusses interspecies relationships in the sediments of this coastal region and compares the metal levels with those from other regions.
INTRODUCTION
The speciation of heavy metals in the aquatic environment has received considerable attention recently (Cben et ai., 1976; Hong and Forstner, 1984; Rapin, 1984). These studies throw ligh~ on two aspects: their levels in the environment and their fractionation in different phases. The investigations provide information on the mobility o~' the metal and bioavailability factors, and also highlight the role of processev such as sorption, diffusion and mobilisation in controlling the concentratiorL of metals in sediments (Calmano and Forstner, 1983). Rapin (1984) comments that sequential extraction procedures would provide information on the history of metal inputs, diagenetic transformation within the sediments and the reactivity of heavy metal species of both natural and anthropogenic origin. Earlier studies on heavy metals in sediments were confined to the partitioning of metals into detrital and non-detrital fractions (Hirst and Nicholls, 1958; Gad and Lerich, 1966). Further development was in the direction of a chemical extraction procedure for the separation of metals associated with ferromanganese minerals, carbonate minerals and adsorbed trace elements from * Author to whom all correspondence should be addressed. 0048-9697/91/$03.50
~') 1991 - - Elsevier Science Publishers B.V.
114
pelagic sediments (Chester and Hughes, 1967; Nissenbaum, 1972). Sequential extraction is recognised as a useful methodology for gaining information on the origin, manner of occurrence, bioavailability, mobilisation and transport of heavy metals, despite the poor selectivity (Chao, 1972; Engler et al., 1974; Reuther et al., 1981). In spite of many limitations, partitioning gives valuable htfgrmation about the relative differences in metal association for two environments differing in metal quality (Patchineelam and Forstner, 1984). A five-step sequential extraction technique was introduced by Tessier et al. (1979) and later modified by Forstner (1982). This scheme facilitated the distinction between exchangeable, easily reducible, moderately reducible, organically bound and residual metal fractions. The chemical technique was based on the three groups of components occurring in fluvial systems potentially able to enrich the metals in sediments: (i) detrital solids, coated with oxides and/or o:ganics; (ii) endogenic fractions, transitory in nature, mostly due to in-situ p zocesses; and (iii) diagenetic fractions occurring within sediments (Calmano and Forstner, 1983). This paper discusses the speciation of cadmium, copper, lead and zinc in the sediments of two river reaches of the Cochin estuary as well as within the estuary. An attempt is made to identify anthropogenic sources and enrichment factors, in addition to understanding the importance of selective accumulative phases for this region. MATERIALS A N D M E T H O D S
Study area
The area of study, Cochin estuary (09°40'-10°10'N; 76°15'-76°30'E), was surveyed on 29 and 30 November 1988 at 12 stations (Fig. 1). The survey extended into the two adjoining rivers, Periyar in the north and Muvattupuzha in the south. Stations 1 and 12 are located in freshwater reaches on either side of the barmouth (Station 5). Station 2 in the Periyar River and Station 11 in the Muvattupuzha River receive ettiuents from chemical factories (fertiliser plant, zinc smelter, catalysts, chemicals, etc.~ and a pulp-paper mill, respectively. The fluvial dynamics of this water body are influenced by the riverine discharge from these two rivers and the tidal influence from the Arabian Sea acting through the Cochin barmouth. As for other equatorial regions the west coast of India is characterised by a monsoonal period of high rainfall (JuneSeptember), a post-monsoonal period of moderate rains (October-January) and a pre-monsoonal period of dry weather (February-May). During the monsoon, alluvial laterite is transported as suspended solids from high ground and settles in the shallow coastal sedimentary plains (Mallik and Suchindan, 1984). Sedimentary bedload movements as well as increased transport of suspended solids (particulates) also occur largely during the monsoon season (Paul and Pillai, 1983; Nair, 1987). This facilitates the flushing of previously deposited and mobilised sedimentary material. The survey was timed to account for
115 N
0
1
100
sd
7 6°
1o'
20"
30" E
Fig. 1. M a p of Cochin estuary showing location of sampling stations.
sediments of very recent origin derived by natural processes as well as to detect newly introduced anthropogenic sources. Details of the hydrographic setting and other environmental features of this estuarine system are available elsewhere (Gopinathan and Qasim, 1971; Joseph, 1974; Lakshmanan et al.,1982, 1987; Sankaranarayanan et al., 1986).
Collection and analysis of samples A stainless steel, plastic-lined van-Veen grab was used to collect sediments, and the top 5 cm layer was carefully skimmed, homo?.enised and stored at 5°C. Aliquots of the sample (20 g) (wet weight) were subjected to sequential chemical analysis as detailed below (Fig. 2). After extraction, the phases were separated by centrifugation at 6000 rpm for 5 min. A Perkin-Elmer Model 2380 atomic absorption spectrophotometer was used for the determination of the metals in the various fractions. Stock standard solutions (1000 ppm) of different metals were prepared and used in the preparation of secondary standards. All care was taken in the preparation of reagents and pre-cleaning of glass and plastic ware. Blank corrections were applied where necessary. The analyses were performed in triplicate and the values determined varied within 10% of the computed mean. All values are expressed in microgrammes per gram wet weight. -
116 I
Extractant
I ' Sample 1 M NH4OAc - pH 7 ( 30% ) I
Metal spec£es .I --1
2 hours
I Resldue
I -----~ Ext-*ct
L
. . . . . .
L__R:_,_~Ea uo _ ] 0.1 M NH2OH. ttCl + 0.01 M HNO3 -
Extract
[
pH 2 - 12 hours (30°C) I
1 Res£due
Exchangeable cation fraction
t-
~"I E x t r a c t
(30°c) -
j - ~
J
1 M NaOAC - pH 5 - 12 hours
--
_]
Carbona te bound , . ,
1
f Eas£1y zeduc~ble f r a c t t o n (metals combined with Fe-Mn oxyhydrltes)
]
(30~ v/v) H202 ÷ 0.01 M HNO3 - pH 3 hours (85oc) extracted w£th 1 M NH40AC - 24 hours (30°C)
(.;onc. HNO3 - 4-6 hours (,1800C)
2-J
!
I Ext.ctj Extract
J
i
Or"°""=ludl.g'°ct"" 41 ~ sulfldes
~
Res£dual f : a c t l o n 1
Fig. 2. Sequential extraction scheme.
RESULTS
Cadmium
Figure 3(a) depicts the distribution (#gg-' wet weight) vis-a-vis the percentage of cadmium species in the sediments of Cochin estuary. The maximum variabilitywas observed in the cadmium fraction bound to organic/ sulphides, ranging from 0.22 to 1.47/~gg- '.The two arms of the estuary exhibit distinctive behaviour in the relative abundance of cadmium species. The northern parts, the Periyar River and its lower estuarine reaches, show varying proportions of all five species studied. Exchangeable cations predominate in the freshwater zone (Station 1, 0.15/~gg-', 53.5%) and gradually decr~as~ in content with increasing salinity (0.05/~g g-', 2.3%, at Station 4). Station 2, the recipient of efliuent discharges, and Station 3, in the vicinity, are dominated by carbonate-bound fractions. At all these locations, the organic/ sulphide and residual fractions are comparatively low in concentration, highlighting the authigenic association of cadmium with riverine sandy sediments. The two downstream estuarine stations, 4 and 5, exhibit very strong associ-
117
0.61 Cadmium
"r=~.o.z°"4
0 1 ,_
_ ~4\-
~= o-, 2
3
4"
8_ Copper
1
2
5,4
3
4
5
6 A
6
7" 8 ,4
7
9-1"0-1~1 - 1 ~
/1//~
8
//~
9
(3b)
•
10 11 12
STATIONS Fig. 3. Distribution of cadmium and copper species in the sediments of Cochin estuary. (x axis), Stations ] ]2; (y axis), concentration (/lg g =wet wt); (z axis), percentage, a, Exchangeable cation fraction; b, carbonate.bound; c, easily reducible fraction; d, organic fraction; and e, residual fraction. ation of cadmium w i t h organic/sulphide phases. The content of this cadmium fraction is extremely high (0.74-1.47/xgg -1, i.e. 50-68%), together with appreciable amounts of the detrita] fraction. The downstream trend points to a relative increase in the carbonate-bound fraction. The northern arm of the
estuary shows the results of two influencing factors: riverine processes maintaining near-proportionality between the five species in the upstream reaches, and the downstream area dominated by anthropogenic activities resulting in the selective enrichment of cadmium within the organic and residual phases. The vast expanse of the southern parts of the estuary exhibits a constant ratio, but varying amounts, of the residual cadmium fraction. This feature is accompanied by the absence of exchangeable cadmium. The upper river reaches, composed of silt and sand, contain 30% of the carbonate, easily reducible and organic/sulphide-bound metal. The relative proportions of these three fractions remain more or less unchanged within the riverine environment (between Stations 8 and 12). The residual fraction, thought to be of terrestrial origin, varies from 0.18 to 0.31/xgg 1 in sandy as well as silty-clay environments. The sediments collected from locations marked by saline conditions (Stations 6 and 7) show the tendency of cadmium to associate with carbonates, Fe-Mn oxides and organic/sulphide phases, in equal proportions. The build-up of cadmium within both of the lower estuarine arms of Cochin estuary reflects the assimilative capacity of silty clay sediments subjected to diagenetic processes. The detrital fraction, occupying a major portion of the sediment free from diagenetic processes, acts equally in regulating the fractional distribution of the non-detrital species. Moderate to low saline waters in both arms of the estuary (Stations 2, 3, 6 and 7) exhibited increasing concentrations of cadmium species of the Fe-Mn easily reducible type. It is also noted that authigenic carbonates become increasingly in, olved in the redistribution of Cd species, especially in the southern parts of Cochin estuary
118
Copper Analytical results [Fig. 3(b)] for samples from the northern parts, Stations 1, 2 and 3 (upper and middle estuary), show simila,c concentrations of exchangeable, carbonate-bound and easily reducible, Fe-Mn species. The levels of two other species, organic/sulphide-bound and residual, in the cleaner, upstream stations show progressively increasing concentrations downestuary. This enhancement in concentration is accompanied by a corresponding decrease in the level of the other three species (see Stations 4 and 5). The change in speciation may be associated with biological production in the vicinity of the barmouth. However, unlike cadmium, the mobility of copper is more related to the detrital fraction, via mineralisation. As observed for Station 1 on the Periyar River, Station 12 on the Muvattupuzha River also exhibits proportionally divided metal species of exchangeable, carbonate-bound, easily reducible and organic/sulphide-bound fractions. A significant change is noted at Station 11, the location of the efliuent outfall from the pulp-paper mill where organic/sulphide fractions contribute substantially to the increased levels of copper detected. At other downstream stations also, enhanced levels of organic/sulphide forms of copper are present in comparison with other non-residual frac*ions. The residual fraction downstream of the outfall shows consistently higher values, particularly at Station 10 (deep pool) and Station 8 ( -~ 10.5 ~g g- ~). Further downstream, in mid and lower estuarine reaches, this fraction does not exhibit any significant variability. A distinct feature observed in copper speciation is the increased levels of organic-bound copper in the southern parts, probably associated with suspended solids of the organic wastes discharged from the pulp-paper mills which sediment along the river bed as well as on the estuarine floor. The proportions of the various copper species vary between stations, indicating the ability of copper species to interchange under different environmental conditions. Lead
Figure 4(a) illustrates the distribution of the various species of lead, including percentage proportions. The lead concentration varies from 0.34 to 8.31/~gg-~ in this waterbody. The lead level is higher in the southern parts (composed mainly of the residual fraction) than in the northern parts. Lead does not exist in detectable levels in exchangeable form or bound to organic/ sulphides. The Periyar riverine reaches (Stations 1 and 2) do not contain the carbonate-bound fraction. About 80% of the lead is found in the residual fraction, while the remainder is associated with the Fe-Mn oxide phase. The middle and lower estuary (Stations 3 and 4) contain a carbonate-bound lead fraction derived largely from the residual form. Notably, the concentration of detrital lead is 6.74-7.68#g g-~ in the vicinity of the barmouth. The southern parts of Cochin estuary are also devoid of organic/sulphide-bound lead species
119 /
._
(4a)
J'~
OC
1
_
2
3
4
s
~'
Zin
'=
40
7
8
/ I A
....
9
10
.
,ul
"
11 12~
c4bl .
. .
0 1
2
3
4
5
6
?
8
9
10
11 12
STATIONS
Fig. 4. Distribution of lead and zinc species in the sediments of Cochin estuary. (x axis), Stations 1-12; (y axis),concentration (/~gg-I wet wt); (z axis), percentage, a, Exchangeable cation fraction; b, carbonate-bound; c, easily reducible fraction; d, organic fraction; and e, residual fraction.
in concentrations that can be detected with the methods used. The Muvattupuzha River reaches show the association of this metal with the carbonate phase (0.34-2.36/~gg-~). The deep pool at Station 10 and the river mouth (Station ~3)have large amounts of the residual metal fraction.The predominant residual t.'actionappears to be a contributing factor in controlling speciation in southern parts, unlike its distribution in the northern regions. Locations of high siltand clay content (Stations 5, 6, 7, 8 and 10) were found to contain high amounts of residual lead, indicating a close relationship of this species with the textural class of the sediments. The levelsof residual fraction in the leastsaline regions of the estuary are comparable, but the mid-estuarine enrichment is one order higher. All along the estuary the presence of carbonate-bound lead is persistently noted, highlighting the role of interspecies transformation between residual and carbonate-bound lead. Thus lead speciation is invariably controlled by the sedimentary processes involving the above two species. Zinc
The various fractions of zinc are widely distributed in Cochin estuary [Fig. 4(b)]. Of the five fractions estimated, residual zinc far exceeds the concentrations of other species determined, the range of values being 0.61-63.54/~gg at the various stations. Exchangeable zinc was present at Stations 1, 2 and 3 together with all the other four fractions, in decreasing proportions indicative of species transformation. The carbonate and organic/sulphide-bound fractions show enhanced values in the vicinity of the zinc smelter (Station 2), and the effect is reflected also at ~he downstream stations. The barmouth region is again highly enriched by the various zinc fractions other than the exchange-
120
able fraction. Apart from the abundant level of residual zinc, zinc is associated in decreasing order with the organic/sulphide phase, the carbonate-bound phase followed by the easily reducible Fe-Mn oxide phase. The southern parts of the estuary are also dominated by residual zinc of terrestrial origin, which gradually increased in concentration downestuary. The stations located on the Muvattupuzha River (Stations 9-12) contain insignificant levels of exchangeable zinc, but this trend is altered in the midestuarine region (Station~ 6-8) with detectable levels of exchangeable as well as carbonate-bound zinc. Zinc is also associated with organic/sulphides in increasing amounts proceeding towards the barmouth. DISCUSSION
The ability to accumulate metal species selectively in sediments greatly depends on particle/grain size, composition of the sediment and external conditions of pH, Eh, salinity, and concentrations of organic and inorganic complexing agents (Calmano and Forstner, 1983). Particles of detrital and anthropogenic origin and inorganic minerals coated with hydrous Fe-Mn oxides affect the interaction processes (Forstner, 1976; Jones and Bowser, 1978). In Cochin estuary, variation in bio-productivity, transitory in nature, may also influence the endogenic fractions of metals, thereby redistributing the metal species in the estuary. By applying a sequential extraction procedure, relative bonding strengths were determined and the ability of the metal species to form quasi-stable binding phases with organic material was also established in the lower reaches of these tropical rivers. The three-fold mechanism of metal-organics binaing depicted by Cooper and Harris (1974) and De Groot et al. (1976) also appears to have a significant application in our study. Nevertheless, under the rapidly changing environmental conditions characteristic of the tropics, metal speciation in sedimentary environments comprising regions of freshwater to marine conditions presents variable characteristics. A comparison can be made with the reported levels of metals at other geographic locations (Table 1).
Exchangeable cations Estuarine reactivity is such that exchangeable species are subject to severe changes. The freshwater zone is occupied by this species of cadmium, whereas it is below detection limits in the upper estuarine regions in the southern parts, and a gradual increase is noted downestuary. Exchangeable copper is present at all stations in this estuary, but only at low levels, and contributing a low percentage of total copper. The distribution of the species appears to be regulated by the presence of other competing, strongly binding phases. Copper, as an element distinguished by its biological regulation in sediments (Luoma and Jenne, 1977) even under marine conditions, sustains continued bio-removal in this estuary, in high production zones. Lead, generally of low affinity for
0.47
Weser estuary
Cochin estuary
Brockpolder, Rhine River Rotterdam Harbour Neckar River
17.65
11.04
2. i 1
0.09 (0.020.26)
4.74
1.26
0.07 (BDL 0.15)
1.21
0.31
1.22
214.71
1.24
1.12
0.02
29.30
!: ~
b
15.55
Baie de Nice
0.01
2.40
a
Cadmium
Yanaska River St. Francis River Rhine River
Yellow River
Location
0.07 (0.02 0.11)
2.35
1.26
0.02
0.62
32.35
3.78
0.52
7.18
BDL b
c
0.22 (BDL1.47)
2.17
0.47
0.20
1.23
11.77
1.53
BDL
BDL
BDL
d
1.08
1.08
7.18
0.02
0.22 (0.03 0.46)
0.36
0.16
0.09
0.05
14.71
e
Distribution of metal species from various geographical locations (ppm)"
TABLE 1
0.27 (0.07 0.51)
5.73
95.58
0.86
0.27
0.50
5.45
1.98
0.64
0.12
Copper
0.50 (0.23 0.91)
1.91
499.14
0.43
0.27
5.29
19.80
23.10
0.36 (0.20 0.52)
152.80
392.94
33.81
15.22
4.41
2.02
12.80
0.54
5.12
0.36
1.70 (0.14 3.55)
7.64
42.48
3.00
0.27
5.88
30.30
85.80
19.84
2.43
4.81 (0.73 10.84)
24.83
31.86
5.14
10.95
4.12
68.68
ly °
26.24
2.16
(continued)
This study
Calmano and Forstnet, 1983
Rapin, 1984
Hong and Forstner, 1984
Reference
168.96 3.00
2.56
1.50
1.12 (BDL2.36)
1.05
0.35
0.49
1.38
1.38
52.94
0.43 (BDL0.49)
33.00
46.08
16.15
28.29
22.94
1.18
54.39
79.58
0.28
0.48
42.00
2.56
3.86
1.38
7.94
5.90
22.20
32.87
0.07
4.68 (0.998.31)
72.00
38.40
14.04
36.57
8.82
63.72
14.43
29.41
2.10
0.84 (BDL2.25)
154
11.30
6.12
14.00
94.86
7.37
2.71
0.12
666
35.19
157.50
55.88
80.40
63.21
0.40
6.81 (BDL26.31)
2611
b
1.20
3.75 (0.2524.87)
215
418
76.50
133.00
29.41
322.35
130.65
123.41
c
9.60
9.18 (0.3437.54)
30.72
11.30
7.65
10.50
20.59
73.68
20.10
15.05
d
a, Exchangeable cation fraction; b, carbonate-bound; c, easily reducible fraction; d, organic fraction; e, residual fraction. b BDL, below detection limit.
Cochin estuary
Weser estuary Brockpolder, Rhine River Rotterdam Harbour Neckar River
1.59
19.98
BDL
Baie de Nice
31.14
1.12
BDL
1.77
0.02
Yanaska River St. Francis River Rhine River
Yellow River
e
a
d
a
c
Lead
Location
b
Zinc
(continued)
TABLE 1
(0.6163.54)
17.77
61.44
33.90
27.54
42.00
14.71
119.73
97.15
99.33
20.40
This study
Calmano and Forstner, 1983
Rapin 1984
Hong and Forstner, 1984
Reference
123
sediment in the exchangeable form, has not been found in this state in Cochin estuary. Zinc is yet another metal which is found sparingly in the exchangeable form, even in the clayey-silt ~ediments of the estuarine environment.
Carbonate-bound Of the four metals considered in this study, lead does not show any association with this phase in the northern freshwater parts, whereas other metals exhibit varying affinity. The selective build-up of this fraction is observed on either side of the barmouth for cadmium and zinc. Copper in the carbonatebound form is present at all stations in this estuary, but the amounts are very low. With regard to cadmium associated with the carbonate-bound phase, the effluent outfall regions on both arms of the estuary indicate general enhancement in levels. Comparing stations, cadmium carbonate is found in largest concentration at the barmouth, occupied by saline waters. This reflects the phase selective enrichment of cadmium in tropical estuaries. The distribution of lead species bound to carbonates was observed to be closely related to the textural nature of sediments or locations where pollutants are introduced into the estuary. The highest concentration of carbonate-bound lead was found in the vicinity of the barmouth. In the southern parts, clayey-silt sediments contained lead species of this type and more so in the deep pools of the Muvattupuzha River. The absence of large variations in concentration of the lead carbonate fraction, even in the presence of large amounts of residual lead, is especially noted in this estuary. The barr.aouth region, however, containing large amounts of organics, contained zinc in the carbonate-bound form, similar to other metals. Enrichment at the barmouth may also be due to previously deposited zinc, accumulated in sediments at upstream locations, being transported via bedload movement during the monsoon period and relocated at the barmouth, a divergent field for siltation. The zinc smelter on the bank of the Periyar River, a constant external source, showed a strong contribution of zinc (at Station 2), the content being divided between the carbonate and organic] sulphide phases.
Easily reducible phases The metal concentrations associated with this phase are of comparatively low magnitude; however, the whole of the estuary indicates the presence, in varying amounts, of all the metals investigated. Except for the high zinc content of estuarine regions, near the barmouth, all metals are uniformly distributed in the Fe-Mn oxides phase, irrespective of aquatic environmental differences. Although no definite conclusions can be drawn as to why uniform metal levels are maintained within this phase, the role of adsorption on Fe-Mn flocs determines metal behavior under the oxidising conditions of this tropical estuary. Nevertheless, neither changing environmental conditions from freshwater to marine conditions through the estuarine reaches, nor the
124
changing bed grain size from sandy to clayey silt, has any influence on the level of this metal fraction. It can also be noted that anthropogenic effects are not readily reflected in the easily reducible phases alone. Gupta and Chen (1975) have expressed the view that, under oxidising environments, the relative variations in the fractionation of metals in sediments exhibit only minor changes in the level of this species, found in marginal abundance. Cadmium shows moderately increasing content downestuary (Stations 4-7) compared with upstream stations, coupled with the general trend of enhancement in all fractions, and it may be subjected to processes of interspecies transformation. Copper and lead show no noticeable change in content of this species in this estuary. An exception to this is the trace amounts of lead at three locations (Stations 7, 8 and 9) in the southern parts, for which no specific reason could be found. Zinc bound to the easily reducible phase exhibits an isoplethic value in mid and upstream sediments compared with enhanced values downestuary.
Organics~sulphide-bound These metal species are known to vary widely in distribution and content in aquatic environments. They also reflect the status of the sedimentary processes that influence metal behavior and reveal the natural levels as well as those superimposed by external stresses. The attempt to quantify the enrichment factors has indicated selective cadmium accumulation at locations in the vicinity of the barmouth, an area covered with fine clay and silt (Table 2). It seems that the processes occurring in the marine conditions downestuary and the biogeochemical processes of autochthonous n~ture in the upper estuary, compete with bio-production prevailing in the region of interest. Cadmium intake during periods of high production is known to exceed that at norms l grazing and, upon decay, detritussettlingon the estuarine bed stores the metal in the organic/sulphide phase (Forstner, 1980). This appears to be a very selective process for this part of the waterway. However, in the l;.ght of speciation studies, cadmium exhibits progressive changes in species concentration with increasing association with the organic/sulphide-bound fraction. Copper and zinc also show enhancement in the organic/sulphide-bound fraction downestuary. These metals are also known for their affinity for detrital bio-matter on sediment beds, especially the clay-silt type° The Muvattupuzha River exhibits copper accumulation in the organic/sulphide phase and the Periyar River exhibits zinc accumulation in this phase. Lead is fairly nolo. existent in this form in this estuary, irrespective of geological or biolof:ical processes and the textural or detrital content of the sediment. Similar instances of metal-organic association excluding an element are, as yet, not well documented. The atypical behavior of lead compared with copper, cadmium and zirLc demonstrates its low tendency for incorporation within the facies of existiag sediment types, highlighting the role of heavy metal speciation studies.
125 TABLE 2 Enrichment of metal species Species a
Northern estuary b
Southern estuary b
1
2
3
4
5
1
2
3
Cadmium a b c d e
0.15 0.05 0.03 BDL c 0.05
0.05 0.10 0.05 0.02 0.10
0.05 0.17 0.12 !11 0.39
0.33 2.00 1.67
0.33 3.40 4.90
2.00
Copper a b c d e
0.33 0.75 0.42 0.25 1.17
0.18 0.62 0.36 0.27 1.26
0.24 0.33 0.43 3.30 5.45
0.55 0.83 0.84 1.08 1.08
Lead a b c d e
BDL BDL 0.41 BDL 1.81
BDL 0.38 0.38 BDL 1.15
BDL 1.53 0.45 BDL 7.20
Zinc a b c d e
1.40 0.84 0.41 2.04 3.00
1.10 4.51 1.87 7.16 7.00
0.26 22.8 17.7 36.8 62.6
4
5
BDL 0.15 0.11 0.13 0.25
BDL 0.26 0.11 0.74 0.32
7.50 2.75 6.50 1.39
13.0 2.75 37.0
7.80
BDL 0.02 0.04 0.02 0.18
0.73 0.44 1.02 13.2 4.66
0.15 0.29 0.29 0.15 1.30
0.41 0.69 0.36 1.58 6.67
0.31 0.31 0.41 3.55 5.37
2.74 2.34 1.24 10.5 5.13
2.07 1.07 1.41 23.7 4.14
0.93
1.10
BDL 1.45 0.48 BDL 6.74
4.27 1.41
3.98
BDL 0.97 0.48 BDL 7.02
2.85 1.41
0.64
BDL 0.34 0.34 BDL 1.03
6.82
6.54
0.79 5.30 4.56 3.51 2.34
0.19 27.1 43.2 16.7 20.9
BDL BDL 0.25 0.34 3.50
1.14 3.60 1.10 6.90 22.8
0.26 19.3 10.6 37.5 62.0
4.40 20.3 6.50
}.78
42.2 110 17.7
"a, Exchangeable cation fraction; b, carbonate-bound; c, easily reducible fraction; d, organic fraction; e, residual fraction. b 1, Upestuary values; 2, midestuary values; 3, downestuary values; 4, midestuary enrichment; 5, downestuary enrichment. '~BDL, below detection limit.
Residual fraction As reported elsewhere residual fraction content prominent in the absence enhancement in c o n t e n t show maximised residual site dominated
( P a u l a n d P i l l a i , 1983), a l l t h e m e t a l s h a v e a l a r g e i n t h i s e s t u a r y . T h e r e s i d u a l f r a c t i o n o f l e a d is of other species of lead. Copper and cadmium show a t t w o l o c a t i o n s ( S t a t i o n s 8 a n d 9). A l l f o u r m e t a l s ,deposition at the barmouth and its near vicinity, a
by sa]ilie conditions
of overlying
waters.
126
Enrichment of metals Table 2 shows mid- and downestuary enrichment in species of cadmium, copper, lead and zinc in the northern and southern parts of Cochin estuary. It is evident from the table that the easily reducible and the residual fractions of cadmium at downstream locations in the northern part of the estuary and the organic/sulphide-bound fractions at mid- and downstream locations in the southern parts of the estuary, show considerable enrichment. The other species also exhibit accumulation, with the exception of exchangeable cations. Conversely, copper is depleted in the nor~hern parts of the estuary, excluding the organic/sulphide and residual species downestuary. However, in the southern estuary, all copper fractions exhibit enhancement, especially the organic/sulphide-bound species. For all metals, the general trend is an increase in the enrichment factor proceeding downestuary. Lead was detected or~ly in the easily reducible and residual fractions, and while the mid-estuarine region appears depleted in content, the enrichment factor for the residual fraction increased four-fold downestuary in the northern estuary. In the southern estuary, lead was also enriched in downstream reaches, the residual fraction being considerably increased in comparison with the carbonate or easily reducible species. Zinc exhibited varying enrichment factors: 3.51-43.2 in the northern estuary and 4.40-42.2 in the southern estuary. Although exchangeable zinc is depleted, the mid-estuarine region in both the north and the south indicate a 2-6-fold increase in content of all species except the organic/sulphide.bound fraction in the southern estuary (20.3-fold increase). Compared with background, the downstream accumulation of zinc is 15-40 times for many of the fractions, a factor of considerable importance in the light of the transport and fate of zinc in the sediments of Cochin estuary. The presence of silt and clay in higher proportions in the downstream reaches may also favor incorporation of this metal, which is mostly derived from anthropogenic inputs.
Interspecies relationship T w o sets of relationships have been derived using correlation analysis. The sum of the concentrations of all species of a metal are regressed versus each metal fraction to provide an understanding of interspecies relationships, and values for total and residual iron (cognate data) are statisticallycomputed versus respective values of the four metals (Table 3).The analysis reveals that: (i)cadmium and copper are poorly correlated (except for residual copper); (ii) detectable lead species are well correlated; and (iii)zinc shows significant correlation (except for exchangeable cations). It appears that natural processes control the estuarine sediment levels of cadmium and copper, whereas zinc is controlled by anthropogenic (external) inputs. The behavior of lead species varies, and is unresolved in the light of limited speciation of this metal. Compared with variations in total and residual iron, zinc does not show a close relationship, nor does the total cadmium. However, residual cadmium, copper
127 TABLE
3
Interspecies relationships (r values)
~ ( a - e ) vs
aa b c d e
Fe(e) vs (c) Fe(f) vs (f)
Cadmium
Copper
Lead
Zinc
ND b 0.40 0.44 - 0.006
0.18 0.16 - 0.10 0.42 0.98
ND 0.79 0.59 ND 0.99
- 0.099 0.98 0.93 0.99 0.98
0.89 0.89
0.93 0.93
0.42 0.35
0.21
0.68 - 0.16
a a, Exchangeable cation fi'action;b, carbonate-bound; c, easily reducible; d, organic fraction; e, residual fraction; f, total. b ND, not determined. n = 12.
a n d l e a d ( t o t a l a n d r e s i d u a l ) f r a c t i o n s a r e w e l l r e l a t e d to c h a n g e s o f i r o n i n t h i s estuary. ACKNOWLEDGEMENT T h e a u t h o r s t h a n k C o c h i n U n i v e r s i t y o f S c i e n c e a n d T e c h n o l o g y for u s e o f f a c i l i t i e s ; A N B t h a n k s U G C ( I n d i a ) for f i n a n c i a l a s s i s t a n c e . REFERENCES Calmano, W. and U. FSrstner, 1983. Chemical extraction of heavy metals in polluted river sediments in Central Eu :r:. ~ i . Total Environ., 28:77 90. Chao, L.L., 1972. Selective di~ ~oluti, a of manganese oxides from soils and sediments with acidified hydroxylamine hydrochlonde. Soil Sci. Soc. Am. Proc., 36: 764-768. Chen, K.Y., S.K. Gupta, A.Z. Sycip, C.S. Lu, M. Knezevic and W.W. Choi, 1976. The effect of dispersion settling and resedimentation on migration of chemical constituents during open water disposal of dredged material. Contract Rep., U.S. Army Engineers Waterways Experimental Station, Vicksburg, pp. 221. Chester, R. and M.J. Hughes, 1967. A chemical technique for the separation of ferro-manganese minerals, carbonate minerals and adsorbed trace elements from pelagic sediments. Chem. Geol., 2: 249-262. Cooper, B.S. and R.C. Harris, 1974. Heavy metals in organic phases of river and estuarine sediment. Mar. Pollut. Bull., 5: 24-26. De Groot, A.J., W. Salomons and E. Allersma, 1976. Processes affecting heavy metals in estuarine sediments. In: J.D. Burton and P.S. Liss (Eds), Estuarine Chemistry. Academic Press, London, pp. 131-157. Engler, R.M., J.M. Brannon and J. Rose, 1974. A practical selective extraction procedure for sediment characterization. In: Proc. 168th ACS Meet. Atlantic City. American Chemical Society, Washington DC. Forstner, U., 1976. Lake sediments as indicators of heavy metal pollution. Naturwissenschaften, 63: 465-470.
128 Forstner, U., 1980. Cadmium in polluted sediments. In: J.O. Nriagu (Ed.),Cadmium in the Environment, Part I. John Wiley & Sons, N e w York, pp. 305-363. Forstner, U., 1982. Accumulative phases for heavy metals in limnic sediments. Hydrobiologia, 91: 269-284. Gad, M.A. and H.H. LeRiche, 1966. A method for separating the detrital and nondetrital fractions of trace elements in reduced sediments. Geochim. Cosmochim. Acta, 30: 841-846. Gopinathan, C.K. and S.Z. Qasim, 1971. Silting in navigational channels of the Cochin harbour area. J. Mar. Biol. Assoc. India, 13: 14-26. Gupta, S.K. and K.Y. Chen, 1975. Partitioning of trace metals in selective chemical fractions of nearshore sediments. Environ. Lett., 10: 129-158. Hirst, D.W. and G,D. Nicholls, 1958. Techniques in sedimentary goechemistry. 1. Separation of the detrital and non.detrital fractions of limestone. J. Sediment. Petrol., 28: 461-468. Hong, Y.T. and U, Forstner, 1984. Speciation of heavy metals in Yellow River sediment. In: Proc. Syrup, Heavy Metals in the Environment, Heidelberg. C E P Consultants, Edinburgh, pp.872875. Jones, B.F. and C.J. Bowser, 1978. The mineralogy and related chemistry of lake sediments. In: A. Lerman (Ed.), Lakes -- Chemistry, Geology and Physics. Springer, New York, pp. 179-235. Joseph, P.S., 1974, Nutrient distribution in the Cochin harbour and in its vicinity. Indian J. Mar. Sci., 3:20 32. Lakshmanan, P.T., C.S. Shynamma, A.N. Balchand, P.G. Kurup and P.N.K. Nambisan, 1982. Distribution and seasonal variation of temperature and salinity in Cochin backwaters. Indian J. Mar. Sci., ll: 170-172. Lakshmanan, P.T, C.S. Shynamma, A.N. Balchand and P.N.K. Nambisan, 1987. Distribution and variability of nutrients in Cochin backwaters, southwest coast of India. Indian J. Mar. Sci., 16: 99102. Luoma, S.N. and E.A. Jenne, 1977. Estimating bioavailability of sediment bound metals with chemical extractions. In: D.D. Hemphill (Ed.), Trace Substances in Environmental Health. University of Missouri Press, Columbia, MO, Vol. 10, pp. 343-351. Mallik, T.K. and G.K. Suchindan, 1984. Some sedimentological aspects of Vembanad lake, Kerala, west coast of India. Indian J. Mar. Sci., 13: 159-163. Nair, M.M., 1987. Coastal geomorphology of Kerala. J. Geol. Soc. India, 29: 450458. Nissenbaum, A., 1972. Distribution of several metals in chemical fractions of sediment core from the Sea of Okhotsk. Isr. J, Earth. Sci., 21: 143-154. Patchineelam, S.R. and U. Forstner, 1984, Sequential chemical extractions on polluted sediments from the Subae River, Brazil. In: Proc. Syrup. Heavy Metals in the Environment, Heidelberg. CEP Consultants, Edinburgh, pp. 86ff 863. Paul, A.C. and K.C, Pillai, 1983. Trace metals in a tropical river environment -- Distribution. Water, Air Soil Pollut., 19: 63-73. Rapin, F., 1984. Speciation of heavy metals in a sediment core from Baie de Nice (Mediterranean Sea). In: Proc. Syrup. Heavy Metals in the Environment, Heidelberg. CEP Consultants, Edinburgh, pp. 1005-1008. Reuther, R., R.F. Wright and U. Forstner, 1981. Distribution and chemical forms of heavy metals in sediment cores from two Norwegian lakes affected by acid precipitation. In: Proc. Symp. Heavy Metals in the Environment, Amsterdam. CEP Consultants, Edinburgh, pp. 318321. Sankaranarayanan, V.N., P. Udayavarma, K.K. Balachandran, A, Pylee and T. Joseph, 1986. Estuarine characteristics of the lower reaches of the river Periyar (Cochin Backwater). Indian J. Mar. Sci., 15: 166-170. Tessier, A., P.G.C. Campbell and M. Bisson, 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem., 51: 844851.