Sengupta, M. and Dalwani, R. (Editors). 2008.
Proceedings of Taal2007: The 12th World Lake Conference: 329-336
Grain Size Effect on Trace Metals in Contaminated Sediments Along the
Iranian Coast of the Caspian Sea
Abdolhossein Parizanganeh
The laboratory preparation and analysis of the samples were carried out in the Great Lakes Institute for
Environmental Research (GLIER), University of Windsor, Canada and
Department of Geography, Zanjan University, Zanjan- Iran
E-mail :[email protected]
ABSTRACT
Sediments are integral and inseparable parts of the aquatic environments, so any environmental program
concerning water quality would be incomplete without the proper study of its sediments. The elemental
concentration of sediments not only depends on anthropogenic and lithogenic sources, but also upon the
textural characteristic, organic matter content, mineralogical composition and depositional environment
of sediments. The generally accepted opinion is that the smaller the size of the sediment fraction, the
larger the amount of trace metals bound to this fraction, and that trace elements are mainly present in the
clay/silt particles with grain size less than 0.063 mm. In general, this is due to the increase in specific
surface area of the smaller fractions and to the surface properties of clay minerals. Forty two separated
size fractions of the sediments collected from fourteen sampling stations along the southern Caspian Sea
were analyzed employing aquaregia digestion followed by Inductively Coupled Plasma–Optical
Emission Spectroscopy to evaluate the pollution level and the trends in samples collected along the
Iranian coast of the Caspian sea in August 2005. Selective partitioning of the studied contaminants in
sediment fractions was observed, with a minimum content in the very fine sand fractions of grain size
0.075-0.125 mm. Anomalously high concentrations of trace metal content in the medium and coarse
sediment fractions on the seashore direction of the Sea was explained by rapid sea level rise and its
impact in eroding beaches, formation of large agglomerates formed from smaller sediment fraction
particles, and the presence of heavy minerals or coarse fractions of terrigenous origin.
Keywords: Grain size, Accretion, Erosion, Heavy metals, Sediments, Caspian sea, Iran.
INTRODUCTION
Sediments play an important role in the pollution
scheme of the water systems as they are less
susceptible to flow conditions than water. When
effluents meet water, various physico-chemical
reactions take place and a large part of the effluent in
one form or other either settles down, adheres to, or
is adsorbed by the sediments depending upon the
physico-chemical conditions and on the species of
the pollutants, nutrients, or trace metals under
consideration.
Heavy metals are not permanently fixed on
sediments and can be released back to the water
column by changes in environmental conditions,
such as pH, redox potential, and the presence of
organic chelators (Förstner 1987). The elemental
concentration of sediments not only depends on
anthropogenic and lithogenic sources, but also upon
the textural characteristic, organic matter content,
mineralogical
composition
and
depositional
environment of sediments (Presley and others 1980).
It is generally believed that metals are
associated with smaller grain-size particles (Whitney
1975; Gibbs 1977; Filipek and Owen 1979;
Ackermann 1980; Salomons and Förstner 1984;
Martincic and others 1990; Biksham and others
1991). This trend is predominantly attributed to
sorption, co-precipitation and complexing of metals
on particle surfaces and coatings. Smaller particles
have a larger surface area: volume ratio and therefore
contain higher concentration of metals. The specific
surface area of sediments is dependent on
granulometric parameters and mineral composition
(Juracic and others 1980, 1982). Increased
concentration of metals in coarse fractions are also
observed and it is believed that the coarser particles
may better document anthropogenic inputs.
This work was undertaken in order to obtain
more information on the geochemical associations
and the effect of particle size on heavy metal
distributions in sediments.
MATERIALS AND METHODS
Sample collection and size fractionation
In figure 1 the locations of the fourteen sampling
stations (S1 to S14), along the southern Caspian Sea
are shown. The sites were located in the vicinity of
settled areas, with these being Astara (S1), Lisar
(S2), Taze Abad (S3), Hasan Rud (S4), Dastak (S5),
Gaskar mahale (S6), Tonkabon (S7), Hachi Rud
(S8), Vanosh (S9), Siah Kola (S10), Zarinabad (S11),
Amirabad (S12), Gamishtapeh (S13), and
Makhdomgholi (S14). The freshly deposited
sediment samples were collected by scooping with a
plastic spade from the upper 5 cm. The collected
sediment samples were packed and sealed in prewashed polyethylene bags and transferred to the
laboratory within a week, where they were dried at
100˚ C temperature. For determining the relationship
between grain size and metal contents, the sediment
samples were fractionated into ten sizes by a sieve
shaker. The sieves were cleaned thoroughly before
use by several acid treatments (diluted HCl, 10%)
and finally soaked in milli Q water to allow the mesh
to assume the correct pore size.
The sieves (1.7 mm, 1 mm, 0.5 mm, 0.355 mm,
0.25 mm, 0.212 mm, 0.125 mm, 0.075 mm, 0.053
mm and 0.025 mm) were shaken with a Tyler
ROTAP. Grain size plots and moment statistics were
obtained with the Statistica for Windows software
(StatSoft, 64 Inc., 1997). Based on the grain size
plots and the cumulative weight of sediments in the
ten sieves, it was decided to analyze, for heavy
metals, the grain size fractions (0.355, 0.212, and
0.075 mm) which had the most weight in the sieves.
The finer fractions (0.053 and 0.025 mm) were not
analyzed because only three of the fourteen samples
contained such fine-grained sediments. The three
grain size fractions provided a total of 42 samples for
the analysis of heavy metals. Each sample was
analyzed for the presence of aluminum (Al), bismuth
(Bi), copper (Cu), iron (Fe), manganese (Mn), nickel
(Ni), antimony (Sb), lead (Pb), and zinc (Zn). Table 1
illustrates the distribution of such metals in different
sampling stations and in various selected grain sizes.
Preparation and analysis of the samples
The laboratory preparation of the samples involved
the utilization of the cold acetic acid extraction
protocol established by the Great Lakes Institute for
Environmental Research (GLIER, 1996), University
of Windsor. For each sample, this protocol required:
1) weighing 0.5 g of sediments and placing into a 30
ml pre-washed centrifuge tube; 2) adding 20 ml of
5% Acetic acid (Anlar) into centrifuge tube, and
capping loosely for 10-minutes to allow for gases, if
any, to evolve. Cap tightly thereafter; 3) shaking
each sample for 24 hours at room temperature; 4)
centrifuging each sample at 500 rpm for 10-minutes;
5) rinsing Whatman #4 filter paper two times with
1% HNO3, three times with MQ and three times with
5% Acetic acid. Allow filter paper to drip dry; 6)
filtering contents of the tube, and taking precaution
not to rinse the filter paper; 7) recording weight of
filtrate (Acetic in centrifuge tube); 8) making-up the
solution with the use of MQ to 50 g by weight
measured to the nearest 0.01 g exercising care to
keep pre-weighted bottle very dry during handling to
avoid added error to the solution’s final weight.
Figure 1: Location of the sampling stations along the southern coast of the Caspian Sea
330
Table 1: Distribution of metals in different sampling stations and selected grain sizes
Sample
Sample ID
CS1
CS2
CS3
CS4
CS5
CS6
CS7
CS8
CS9
CS10
CS11
CS12
CS13
CS14
Average
Grain size
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
75
212
355
Al
Bi
Cu
Fe
Mn
Ni
Sb
Zn
138.9
213.3
225.7
155.4
277.7
245.4
249.8
324.1
206.0
122.6
116.7
146.1
190.9
121.8
365.2
182.4
246.3
309.4
70.7
91.4
113.0
72.8
79.7
134.1
57.1
88.1
100.5
51.4
67.1
82.4
73.3
81.9
106.6
53.6
89.3
170.7
121.4
132.1
201.9
106.9
121.4
180.7
1647.2
2050.9
2587.7
12.3
16.7
17.6
8.1
9.9
13.2
8.8
10.1
11.5
7.6
9.2
5.0
7.3
8.7
18.9
11.1
12.0
14.2
5.8
5.7
9.0
5.9
6.0
10.5
7.1
7.3
9.4
4.9
6.4
9.4
7.1
9.4
11.2
6.9
9.4
9.9
6.5
6.6
10.7
14.6
16.3
18.6
114.1
133.8
169.1
1.9
4.7
29.9
5.3
6.4
10.2
1.9
2.7
6.4
1.2
1.3
10.6
0.0
5.8
22.4
1.3
5.0
26.2
1.3
1.7
16.9
0.9
2.8
34.8
1.1
2.7
29.4
0.0
2.6
20.8
0.0
1.2
13.1
0.8
1.3
10.4
5.3
55.3
33.8
2.2
85.0
13.6
23.4
178.3
278.4
1072.6
1801.9
2091.8
628.2
1004.1
1357.0
626.4
894.1
1280.4
349.5
625.2
710.0
771.8
589.2
701.0
1261.7
1031.6
1372.0
493.4
498.7
799.9
413.3
431.8
928.1
516.4
490.3
1041.5
688.2
564.5
860.3
654.0
735.2
1375.7
592.9
766.9
1125.1
496.0
388.6
802.6
1444.5
1742.1
2239.2
10009.1
11564.3
16684.6
222.1
276.7
832.9
111.5
212.1
590.9
171.4
202.5
947.7
431.3
267.0
449.5
238.9
200.7
293.0
231.7
215.9
627.7
134.9
121.8
393.5
99.6
127.9
578.3
153.0
154.5
523.4
215.2
322.5
328.8
371.4
402.8
714.7
416.8
380.4
708.4
104.8
135.5
574.1
268.5
307.3
288.3
3171.2
3327.5
7851.3
4.1
2.7
3.9
0.0
1.2
2.5
1.7
2.3
2.5
1.9
1.7
1.9
0.0
1.6
6.1
2.3
2.4
2.4
2.5
2.7
3.4
1.6
1.4
2.4
1.7
1.6
2.9
1.5
2.0
2.3
1.7
1.6
3.3
1.6
1.7
2.9
1.8
8.6
9.7
3.4
3.6
5.3
25.9
35.1
51.5
7.0
11.7
13.5
4.6
6.7
8.5
4.6
6.0
8.4
0.0
4.3
5.2
0.0
3.6
5.1
7.9
9.1
9.6
2.9
2.9
4.9
0.0
2.7
6.8
3.5
3.3
6.9
4.7
4.3
5.5
4.7
5.5
9.8
3.7
6.2
7.8
3.9
3.4
5.0
10.4
12.0
16.1
57.8
81.7
113.2
3.0
3.1
15.3
2.6
2.4
3.8
2.7
2.1
3.3
2.5
2.1
4.0
4.2
2.0
5.3
3.9
3.4
5.9
3.9
3.7
7.5
3.7
2.3
6.6
3.6
3.0
5.1
2.8
3.2
6.7
4.8
3.6
6.7
4.9
4.3
5.6
10.1
12.5
5.1
15.3
45.2
12.5
67.8
92.9
93.5
Quality control for each batch of analyzed
sample was strictly maintained by placing among the
sample set three method blanks, two samples in
duplicate, one tissue internal reference pool, and two
Certified Reference Materials (Mess-3, LKSD-4).
Metal concentrations in the sediment samples were
determined by Inductively Coupled Plasma Optical
Emission Spectroscopy, IRIS # 701776 (Thermo
Jarrell Ash Corporation). The detection limits (µg/g),
based on the cold acetic protocol, for each of the
metals to be discussed were: A1 10.7, Bi 1.8, Cu 0.7,
Fe 0.5, Mn 0.1, Ni 0.8, Sb 2.2, and Zn 0.2.
331
Table 2: Grain size distribution of sediments in different sampling sites
Sample
COD
CS1
CS2
CS3
CS4
CS5
CS6
CS7
CS8
CS9
CS10
CS11
CS12
CS13
CS14
>1.70
mm
>1.00
mm
>0.500
mm
>0.355
mm
>0.250
mm
>0.212
mm
>0.125
mm
>0.075
mm
>0.053
mm
>0.025
Mm
Total
1.24
7.22
3.00
0.12
0.07
1.80
0.30
1.17
28.16
16.79
0.00
0.03
40.12
71.20
0.30
5.51
2.50
0.08
0.06
0.56
0.22
3.55
0.47
0.06
0.00
0.02
21.31
7.70
0.46
25.47
18.97
0.32
0.10
0.65
8.50
6.45
0.70
0.07
0.85
0.06
24.51
6.50
1.38
17.90
27.65
5.76
2.24
3.87
26.21
5.48
1.25
0.62
5.11
2.65
8.80
3.70
10.35
18.29
21.12
44.96
54.28
23.46
31.63
15.63
11.77
4.41
19.05
19.13
2.49
3.12
4.23
7.47
8.86
18.20
22.17
9.89
13.10
6.38
4.81
1.80
7.78
7.81
1.02
1.28
64.35
14.70
16.65
27.68
20.94
53.68
19.12
52.40
47.83
62.07
62.47
64.05
0.77
3.07
17.42
3.41
1.25
2.86
0.12
6.08
0.92
8.82
4.89
14.14
4.73
6.22
0.33
1.12
0.27
0.03
0.00
0.02
0.01
0.00
0.00
0.11
0.12
0.04
0.02
0.03
0.65
2.29
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.01
0.02
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
CS1
CS2
CS3
CS4
Med. To coarse sand > 0.250mm
CS5
CS6
CS7
CS8
CS9
CS10 CS11 CS12 CS13 CS14
Fine &v.fine sand 0.075 to 0.250mm
coarse to med. Silt <0.075mm
Figure 2: Grain size distribution of sediments in sample stations (by percent)
Grain size distribution
Table 2 and figure 2 shows the grain size distribution
of sediments in sampling sites along the southern
coast of the Caspian sea. In general about 50 percent
of the grain sizes in all samples belonged to grains
greater than 0.212 millimeter and the rest are grains
smaller than 0.212 millimeter in diameter. The
highest percentage of grains in most of the samples
are those having a diameter between 0.125 mm to
0.212 mm and the percentage of grains with less than
0.053 mm are negligible and in most of the samples
are absent. i.e. nearshore sediments contains no or
very low amounts of clay size fractions. The 0.1250.212 mm (36.4%) and 0.250–0.355 mm (20.0%)
sizes are the dominant fractions, accounting for about
56.4 % of the sediments, while silt and clay size
fractions (~63 µm) contribute only 0,0–0.36% of the
332
whole sediment spectrum. The >1.00 mm size
fraction is very high at the sampling site CS-14,
where it account up to 78.90% of the sediment. At
the site CS-11 and CS-12, the dominant size fractions
are 0.125 – 0.250mm.
RESULTS AND DISCUSSION
The distributions of Bi, Al and heavy metals (Fe, Mn,
Cu, Zn, Sb and Ni) within different particle-size
fractions, together with the granulometric values of
Caspian sediments at 14 sampling sites are given in
Table 1. Typical results for some of the stations
studied are presented in Fig. 3. The slops
characterizing metals distributions on various size
sediment fractions have a clearly defined minimum
for the fine fractions of grain size 0.075mm. What is
very surprising in our data is a profound enrichment
of all trace metals’ content in the medium (0.212 mm)
and coarse (0.355 mm) fractions ( Fig. 3 and 4 ).
Thus, the left part of the slope in figure 3 is the result
of natural enrichment in the smallest fractions owing
to the increase of specific sediment surface, while the
middle and right parts of the slope demands a
specific explanation.
Tracem
etal content(ppm
)
Sam pling s tation 1
100.0
Cu
Fe
10.0
Ni
Zn
1.0
75 µm
212 µm
355 µm
Fr action Size
T
rac
em
etalc
o
n
te
n
t(p
p
m
)
Sam pling s tation 7
20.0
15.0
Cu
Fe
10.0
Ni
Zn
5.0
0.0
75 µm
212 µm
355 µm
Fr action Size
Tracem
etal content(ppm
)
Sam pling s tation 11
100.0
Cu
10.0
Fe
Ni
1.0
Zn
0.1
75 µm
212 µm
355 µm
Fr action Size
Tracem
etal content(ppm
)
Ave ra ge for a ll sta tions
1000.0
Cu
100.0
Fe
Ni
10.0
Zn
1.0
75 µm
212 µm
355 µm
Fr action s ize
Figure 3. Grain size effect on trace metals distribution
333
ppm
100000.0
1000.0
10.0
Al
Bi
Cu
Fe
Mn
Ni
Sb
Zn
75
1647.2
114.1
23.4
10009.1
3171.2
25.9
57.8
67.8
212
2050.9
133.8
178.3
11564.3
3327.5
35.1
81.7
92.9
355
2587.7
169.1
278.4
16684.6
7851.3
51.5
113.2
93.5
Metals
Figure 4. Averaged metal concentration in different selected grain sizes
Fe and Mn are the most dominant elements in all size
fractions at all sites followed by Al, Cu, Bi, Sb, Zn,
and Ni (Fig. 4). The higher concentration of Fe has
been observed at sites CS-14 and CS-1. The higher
concentrations of most of the heavy metals are also
observed at sites CS-14 and CS-1. In general the
concentration of all metals increases with increasing
grain size (except at sites CS-4 and CS-5).
A possible reason responsible for anomalously
high concentrations of trace metals content in the
medium and coarse fractions in the study area can be
the formation of large agglomerates (or clusters
larger than 0.212 mm in diameter) from the smaller
particles enriched by contaminants. The formation of
large agglomerates occurs during the generally
accepted drying procedures, all of which are carried
out without prewashing the studied sediments.
Therefore, during any drying procedure, the small
sediment particles will be cemented both by
dissolved organic matter and by sea salts, present in
the marine environment, to form large agglomerates.
In this case, the total amounts of trace metals
retained by each agglomerate particle will be much
larger compared to the amounts which could be
adsorbed only on the outer surface of such
agglomerates. Therefore, the possibility of the
formation of large agglomerates from small
contaminated particles should be seriously
considered when developing standard methods
334
related to the anthropological metal contamination of
sediments.
The increased concentration of metals in the
coarser fractions at the sampling sites may also be
attributed to inputs from the mining and other
anthropogenic sources. Many workers have pointed
out the fact that larger particles stay in a place longer,
often in shallow oxygenated areas (Whitney 1975;
Chao and Theobald 1976; Tessier and others 1982)
and therefore may have more time to develop oxide
coating and therefore absorb more trace metals than
smaller particles. Presence of heavy minerals or
coarse fractions of mine and industrial wastes may
also increase metal concentration in the coarser
fractions (Thorne and Nickless 1981; Moore and
others 1989). The metal data for different size
fractions of the sediment samples collected from
different locations in the study area suggest that the
effects of grain size on the metal distribution in the
sediments are uniform throughout the area. Thus,
control of grain size over metal distribution in
sediments must be considered while dealing with the
heavy metal data of the basin.
The interelemental correlation coefficients for
the different grain-size fractions of the bed sediments
are given in Table 3. Good to fair correlations exist
between Fe-Bi, Fe-Sb, Bi-Sb, Mn-Fe and Bi-Al,
suggesting their similar behavior with grain size.
Table 3 The inter elemental correlation coefficient for different grain size fractions of samples from different
sampling sites
Metals
Al
Bi
Cd
Co
Cu
Fe
Mn
Ni
Sb
Zn
Al
Bi
Cd
Co
Cu
Fe
Mn
Ni
Sb
0.522
-0.441
0.323
-0.109
0.368
0.153
-0.025
0.266
-0.138
0.202
0.235
0.136
0.859
0.411
0.207
0.758
0.232
-0.016
-0.064
0.366
0.420
0.145
0.390
0.301
0.040
0.193
0.281
0.584
0.196
0.083
0.032
-0.277
0.173
0.060
0.636
0.532
0.268
0.951
0.239
0.185
0.494
-0.128
0.312
0.223
0.233
CONCLUSION
The metal data for different size fractions of the
sediment samples collected from different locations
along the southern coast of the Caspian Sea suggest
that the effects of grain size on the metal distribution
in the sediments are uniform throughout the studied
area. With the absence of very fine grain sizes (<63
µm) in sediment samples, gradual increase in metal
concentrations from fine to coarse fractions has been
observed. Very fine sediments are transported to
deeper waters due to rapid sea level change in the
Caspian sea and sediments available at the water
depths of more than 30 meters still tend to show
higher concentration of heavy metals than the
medium or coarse sediment particles (De Mora,
2004).
Anomalously high concentrations of trace metal
content in the medium and coarse sediment fractions
on the seashore direction of the Sea can be then
explained by the followings:
• As sea level change induced mixing in the
shallow near shore waters winnows out the
fine-grain material, pollutants discharged
into this region are not likely to accumulate
in the immediate vicinity and are exported.
Remaining coarser particles that better
document anthropogenic inputs because of
their limited transport and longer residence
time, often in shallow oxygenated areas may
have more time to develop oxide coating
and absorb more trace metals than smaller
particles.
• Formations of large agglomerates, formed
from smaller sediment fraction particles
enriched by various contaminants kept on
their large specific area by adsorption forces,
have been also observed in medium and
coarse sediment fractions. The formed
agglomerates consist of small particles
cemented either by dissolved organic matter
or by sea salts present in the marine
sediment.
•
Presence of heavy minerals or coarse
fractions of lithogenic origin also increase
metal concentrations in the coarser fractions.
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