DISTRIBUTION OF Cr, Pb, Cu, Cd AND Zn IN SEDIMENTS OF THE

Transkrypt

Proceedings of ECOpole
Vol. 2, No. 2
2008
Mariusz MACHERZYNSKI1, Witold RECZYŃSKI2 Andrew PARKER3
Jerzy GÓRECKI1 and Janusz GOŁAŚ1
DISTRIBUTION OF Cr, Pb, Cu, Cd AND Zn
IN SEDIMENTS OF THE DOBCZYCE DAM RESERVOIR
(SOUTHERN POLAND)
ROZKŁAD ZAWARTOŚCI Cr, Pb, Cu, Cd i Zn W SEDYMENTACH
ZAPOROWEGO ZBIORNIKA DOBCZYCKIEGO
USYTUOWANEGO W POŁUDNIOWEJ POLSCE
Summary: Sediments play a fundamental role in the behaviour of contaminants in aquatic systems. Various
processes in sediments, eg adsorption-desorption, oxidation-reduction, ion exchange or biological activities, can
cause accumulation or release of metals and anions from the bottom of reservoirs, and have been recently studied
in Polish waters [1-3]. Sediment samples from layer A: (1÷6 cm depth in direct contact with bottom water); layer
B: (7÷12 cm depth moderate contact); and layer C: (12+ cm depth, in theory an inactive layer) were collected in
September 2007 from six sites representing different types of hydrological conditions along the Dobczyce
Reservoir (Fig.1). Water depths at the sampling points varied from 3.5 to 21 m. We have focused on studying the
distribution and accumulation of several heavy metals (Cr, Pb, Cd, Cu and Zn) in the sediments. The surface,
bottom and pore water (extracted from sediments by centrifugation) samples were also collected. Possible
relationships between the heavy-metal distribution in sediments and the sediment characteristics (mineralogy,
organic matter) as well as the Fe, Mn and Ca content of sediments, have been studied. The O2 concentrations in
water samples were also measured. The heavy metals in sediments ranged from 19.0 to 226.3 mg/kg of dry mass
(ppm). The results show considerable variations in heavy-metal concentrations between the 6 stations, but not in
the individual layers (A, B, C). These variations are related to the mineralogy and chemical composition of the
sediments and their pore waters.
Keywords: sediment, heavy metals, distribution, accumulation, immobilization
The Dobczyce Reservoir (127 Mm3) is situated 30 km south of Krakow and supplies
about 60 % of the drinking water to the more than 1 million inhabitants. It consists of three
main parts: the Myślenice Basin (P1-P3), Wolnica Bay (P5) and the Dobczyce Basin (P6),
representing the three different types of hydrological conditions in the Dobczyce Reservoir.
In this study the distribution of several metals (total Cu, Zn, Cr, Pb and Cd) in sediments
and partition of Cu and Zn between sediments and pore (inerstitial) water, was determined.
In order to define the weakly-bound portion of Cu and Zn in equilibrium with sediments,
pore water samples were also examined. If the equilibrium is disturbed in certain
conditions, weakly-bound polluting phases can be readily released into water [4, 5]. The
concentration and distribution of the three elements Ca, Mn and Fe, known to play a role in
ion exchange within suspensions and sediments, have been monitored in the pore water and
sediment samples, in order to find possible correlations between Cu, Zn, Cr, Pb and Cd and
these elements. Accompanying analyses of physical and chemical properties of water and
sediment samples are also presented.
1
Department of Environmental Chemistry, 2 Department of Analytical Chemistry, AGH University of Science and
Technology, al. A. Mickiewicza 30, 30-059 Kraków, email: [email protected]
3
University of Reading, RG6 6AB Reading, School of Human and Environmental Sciences, United Kingdom
282
Mariusz Macherzynski, Witold Reczyński, Andrew Parker, Jerzy Górecki and Janusz Gołaś
Fig. 1. Dobczyce Reservoir: stations and sample nomenclature
Materials and methods
Samples were taken on 3rd and 4th September, 2007, during moderate thermal and
distinct oxygen stratifications. Samples were placed in polypropylene boxes (sediments)
and high-density polyethylene bottles and vials (waters). They were kept in portable
freezers until transported to our laboratories and stored in refrigerators. The pore water
samples (PW) were extracted from fresh sediments (about 450 g) by centrifugation
(4000 rpm, 300 to 900 s).
All chemicals used were of analytical grade. Solutions were prepared from double-distilled,
deionized water. Water and pore water samples for metal analyses were immediately
acidified with HNO3 to obtain 0.2% solutions. Finally, all liquid samples were filtered using
nitrocellulose membranes (450 nm). Sediment samples (PS) were carefully mixed, dried in
air (40°C), carefully crumbled, sieved at 2 mm and wet-digested (two repetitions for each
sample) with the use of the microwave system MultiWave 3000 - Anton Paar. The
analytical chemistry equipment, procedures and statistical approach are described elsewhere [6]. The mineralogy of the sediments (both whole-sample and clay fraction) was
determined by X-ray diffraction analysis (XRD). In the case of whole-sample analysis the
sediments were ground in an agate mortar. The ground samples were side-loaded to obtain
random powder mounts. The clay fraction (less than 2 µm) was separated by sedimentation
after ultrasonic disaggregation, and analysed using the methods of Weir et al [7]. This
method is semi-quantitative, with a possible relative error ± 10%. The concentration of
metals in sediments is expressed as ppm (mg per 1 kg of a dry mass). The concentration of
metals and anions in pore water samples was measured in µg/dm3, and recalculated to ppb
(µg per 1 kg of dry mass), when the content of pore water in sediment was
determined: Table 1.
Distribution of Cr, Pb, Cu, Cd and Zn in sediment samples from the Dobczyce dam reservoir …
283
Table 1
Contents of pore water and organic matter in sediments. Temperature and O2 concentration in waters
SAMPLE
PS1A
PS1B
PS1C
PS2A
PS2B
PS2C
PS3A
PS3B
PS3C
PS4A
PS4B
PS4C
PS5A
PS5B
PS5C
PS6A
PS6B
PS6C
mass of pore
water / kg of
dry sediment
[kg]
0.70
0.35
0.43
0.77
0.64
0.71
1.60
1.14
0.71
1.56
1.24
1.25
1.58
1.30
0.76
2.09
1.55
1.29
% of pore water
in sediment
% of org.
matter in
sediment
41.0
26.1
30.1
43.4
39.0
41.5
61.6
53.2
41.5
61.0
55.4
55.6
61.3
56.5
43.1
67.6
60.8
56.4
6.2
4.7
5.2
6.2
6.2
6.7
7.7
8.0
5.0
8.5
7.8
7.8
8.3
6.8
5.4
9.2
8.3
8.4
surface/
bottom water
temp. [°C]
surface/
bottom water
oxygen
[mg /dm3]
19.5 / 18.8
6.94 / 6.99
19.6 / 19.2
7.08 / 5.31
19.7 / 18.2
7.76 / 0.66
20.3 / 12.0
8.69 / 0.63
20.3 / 19.8
8.60 / 7.32
20.6 / 11.6
8.91 / 1.40
Results and discussion
XRD analyses
The whole-sample analyses reveal that every sediment consists of quartz (36÷66% internal percentage of X-ray crystalline phases in ground bulk sample), mica (16÷39%),
kaolinite/chlorite (6÷24%) and albite (2÷16%). Microcline at P1 (1÷4%) and P5 (5÷10%)
and calcite at P1, P2 and P4 (2÷4%) were also identified. The clay analyses show
a predominance of illite and expandable clays (smectite and illite-smectite). In total it is
85÷90% (internal percentage of clay minerals in clay-size fraction). The minor clays in this
fraction are chlorite (5÷14%) and kaolinite (0÷5%). The content of clays and grain-size of
sediments are two of the major factors influencing the quantity of heavy metals in
sediments from the Dobczyce Reservoir [6].
Distribution of total, Cr, Pb, Cd, Cu and Zn in sediment samples
The concentrations of total Cr, Pb, Cd, Cu and Zn in sediment samples are presented in
Figures 2a and 2b. The average for each metal is 104.7, 44.2, 0.085, 37.5 and 147.3 ppm,
respectively. The results show considerable variations of each heavy metal concentration at
the 6 stations, but not in the individual layers (A, B, C). As a rule the mean concentration of
each metal rises from PS1 to PS4, then reduces in P6 to the level of about P3 (Fig. 3). The
concentrations in P5 are always lower than in P4 (roughly at the level of P2). The source of
heavy metals in this point is not the Raba River, but the Wolnica stream. These results,
except for P6, are very well correlated (r = 0.896 to 0.987, n = 15) with the organic matter
content. The content of organic matter and clay/silt fraction is the highest at P6 (the
284
Dobczyce Basin) [6], but the Myślenice Basin seems to be an efficient “heavy metal trap”
during normal weather conditions.
250
200
Cr
Cu
200
co ncentration [pp m ]
con cen tration [p p m ]
Pb
150
b
a
Cd*1000
100
50
Zn
150
100
50
0
6C
6A
6B
PS
PS
5B
5C
PS
PS
4C
4B
5A
PS
PS
PS
3C
4A
PS
PS
3B
PS
3A
PS
2C
2B
sampling points
PS
PS
1C
1B
2A
PS
PS
PS
PS
PS
1A
1B
1C
PS
2A
PS
2B
PS
2C
PS
3A
PS
3B
PS
3C
PS
4A
PS
4B
PS
4C
PS
5A
PS
5B
PS
5C
PS
6A
PS
6B
PS
6C
PS
PS
PS
1A
0
sampling points
Fig. 2. Concentrations of Cr, Pb, Cd (c*1000) - (a) and Cu, Zn - (b) in sediments. Standard deviation bars, n = 4
Pb
250,0
Cr
Cd*1000
Cu
concentration [ppm]
200,0
Zn
150,0
100,0
50,0
0,0
P1
P2
P3
P4
P5
P6
sampling points
Fig. 3. The mean concentrations of Cr, Pb, Cd (c*1000), Cu and Zn in sediments in each sampling point
The same trends for Pb (concentration range 17.8÷24.1 ppm) and Cr (32.3÷70.0 ppm)
were observed in the summer of 2006 [6], but the mean concentrations were about 50%
lower. It is important to point out that only the stations PS2, PS5 and PS6 were examined in
[6], but the comparison made only in these three points still shows much higher - almost
50% - concentrations of Pb in our samples. Moreover, in the summer of 2005, lower levels
of Pb (6.8÷58.1 ppm) were determined in the sediment samples, collected at the 17 stations
from the Dobczyce Reservoir [8]. However, it was noted in [9] that Pb was found in
sediments at a level of 16.1÷50.3 ppm in 1994 and 4.1÷30.8 ppm in 1998. The
concentration of Pb is highly negatively correlated with the concentration of Ca in sediment
samples (r = –0.835, n = 18), which corresponds to (r = –0.964, n = 9) in [6], and might
suggest competition between these divalent metals for available sorption sites within the
285
sediment. The concentration of Pb is very well correlated with the concentration of Fe in
sediment samples (r = 0.817, n = 18), which was not observed in the summer of 2006.
Chromium is a contaminant mainly due to the tanning industry further up the Raba
River. Again, a comparison of the results with data from years 2006 [6] and 2005 [8] shows
the considerable (more than 100%) increase of Cr content in sediments in the years
2005-2007. The concentration of Cr in sediments is very well correlated with Fe (r = 0.951,
n = 18), which corresponds to (r = 0.853, n = 9) in [6]. Also, a distinct correlation of Cr
with the total Mn concentration in sediments (r = 0.732, n = 18) was observed. It is
important to note that mean and maximal concentrations of Pb, Cr in sediments tend to
increase in the years 2005-2007. Cadmium is present in sediment samples at the levels of
0.056÷0.114 ppm, when in 2005 [8] it was in the range 0.11 to 0.96 ppm. It was noted in
[9] that Cd was found in sediments at a level of 0.5÷1.2 ppm in 1994 and 0.3÷1.7 ppm in
1998. Distinct correlations between Cd and concentrations of Ca, Fe and Mn in sediments
have not been found.
Table 2
Concentrations of Ca, Fe and Mn in sediments. Relative standard deviation, n = 4
SAMPLE
PS1A
PS1B
PS1C
PS2A
PS2B
PS2C
PS3A
PS3B
PS3C
6.99
5.97
4.41
2.61
2.99
2.63
0.59
0.63
0.81
7.8
3.4
0.4
2.0
0.6
0.7
1.7
2.9
0.1
19.56
19.43
18.68
29.12
30.38
28.46
34.93
35.23
31.08
2.1
2.1
2.2
4.5
0.6
2.9
0.8
1
1.5
0.45
0.40
0.52
0.73
0.70
0.77
1.37
1.04
0.85
RSD % n=4
2.7
3.5
3.5
4.6
1.2
4.3
0.9
2.6
0.9
SAMPLE
PS4A
PS4B
PS4C
PS5A
PS5B
PS5C
PS6A
PS6B
PS6C
0.95
1.12
0.88
0.31
0.34
0.19
0.42
0.52
0.63
22.4
10.9
1.4
2.0
3.0
13.9
10.6
15.9
1.0
37.88
50.27
35.46
23.07
26.06
22.72
34.85
37.42
32.75
0.8
1.5
0.9
14
2.3
10.1
9.9
0.1
0.6
1.64
1.81
0.98
0.48
0.53
0.45
2.47
1.60
1.09
2.7
5.2
1.9
17.3
1.7
8.4
9.0
19.9
0.2
CCa
[mg/g d.m.]
RSD % n=4
CFe
[mg/g d.m.]
RSD % n=4
CMn
[mg/g d.m.]
CCa
[mg/g d.m.]
RSD % n=4
CFe
[mg/g d.m.]
RSD % n=4
CMn
[mg/g d.m.]
RSD % n=4
286
Concentrations of Cu vary between 19.0 and 61.7 ppm and were measured at a level of
16÷45 ppm in 2005[8], 35.7÷58.0 ppm in 1994 and 5.5(6.5) ÷45.4 ppm in 1998 [9, 10]. The
concentration of Cu is negatively well correlated with the concentration of Ca in sediment
samples (r = –0.742, n = 18) and very well correlated with the concentration of Fe
(r = 0.939, n = 18) and Mn (r = 0.771, n = 18). Concentrations of Zn vary between 82.2 and
226.3 ppm and was measured at a level of 49÷148 ppm in 2005 [8], 206÷454 ppm in 1994
and 129÷476 ppm in 1998 [9]. The concentration of Zn is highly negatively correlated with
the concentration of Ca in sediment samples (r = –0.740, n = 18) and very well correlated
with the concentration of Fe (r = 0.884, n = 18).
Comparison of results for Pb, Cu and Zn with data from years 2005, 1994 and 1998
suggests that heavy flood-like events or sudden drawdowns and freshets in the Dobczyce
Reservoir cause relocation of sediments, simultaneous leaching of heavy metals, and
considerable annual and site-dependent variability of their concentrations.
The total Ca, Fe and Mn concentration in sediment samples in mg/g of dry mass is
presented in Table 2. These elements take part in ion exchange, crystallisation and
precipitation within the sediments or compete with other cations. The concentration of Ca
in sediments tends to be independent of depth in each core and is highest at the PS1 (coarse
silt sediment). The concentration of Ca in the sediment from PS5C is much lower. This was
also observed in [11], where the whole 90 cm sediment core from the Wolnica Bay was
examined with the use of a PIXE method. The Ca concentrations observed are in
accordance with the results from year 2005 [12], but are 4-6 times lower than in summer
2006 [6]. A possible explanation is a different sampling time - the warm end of June 2006
and the first part of September 2007, when a distinct oxygen stratification was already
observed at P3, P4 and P6 (Table 1). Precipitation of phosphorus with calcite and its
deposition onto sediments can cause its removal from a shallow eutrophic lake. For
example, in the Lake Constance, it has been estimated that 35% of the seasonal total P loss
from the water column is caused by P co-precipitation with calcite [13]. Increased oxygen
consumption through microbial activity can cause the depletion of O2, and reducing
conditions. Under these conditions the insoluble forms of Ca2+ and PO 34− (eg CaHPO4·H2O,
Ca4H(PO4)3·2.5H2O and Ca3(PO4)2) can be released from sediment particles to the sediment
pore water and then transferred to the water column. The fate of phosphates may be
different. They can either form an insoluble complex of Fe3(PO4)2, or accompanying S2–
anions can produce SPO 34− soluble anions [14], but at the same time Ca2+ cations can be
easily transferred to the water column through molecular diffusion or via mass transfer.
Table 3
Equilibrium ratios (K) between the concentration of metal in sediment and its pore water
SAMPLE
P1A
P1B
P1C
P2A
P2B
P2C
P3A
P3B
P3C
KCu
2807
8194
6772
825
3088
2245
6381
7524
8467
KZn
3038
5166
4993
2788
7425
6348
3339
5065
3038
SAMPLE
P4A
P4B
P4C
P5A
P5B
P5C
P6A
P6B
P6C
KCu
6956
8705
42584
1577
3947
1492
3164
4437
3631
KZn
4173
5352
6353
2125
3976
4324
2269
2940
3083
287
In the case of Fe, the concentrations of this element in sediments are in accordance
with data obtained in the summer of 2006 [6], but in the case of data from [12], the
concentrations were similar only at the shallow points (P1, P2, P5). The Mn concentrations
are similar to data from 2005 [12], except for the deepest P6. In [9], the concentrations of
Fe in sediments were 7.7÷26.2 ppm in 1994 and 0.9÷35.9 ppm in 1998. In the case of Mn,
the concentrations were 0.3÷1.6 ppm in 1994 and 0.3÷3.3 ppm in 1998.
Equilibrium ratio (K) between the concentrations of Cu and Zn in sediment and pore water
samples
Sediment - pore water equilibrium coefficients (K), calculated as the ratio between the
concentration of each metal in a sediment and its pore water, are presented in Table 3. The
K value indicates the accumulation and possible immobilization of each metal as well as its
affinity to the active compounds within sediments. Copper and Zn are relatively efficiently
fixed in the analysed sediments (mean KCu ≈ 6800 and KZn ≈ 4400) in comparison with the
mean KPb ≈ 400, KAs ≈ 900 and KCr ≈ 9000 [6]. The strong affinity of Cu towards sediments
explains its low concentrations in pore water samples at all the six stations - mean value
11 ppb (µg/kg of dry mass), compared with the results from [15], where the mean
concentration of Cu in pore waters was 80 ppb, and the calculated KCu did not exceed 500
[12]. The KZn was not determined before.
Conclusions
1.
2.
3.
4.
The concentrations of total Cr, Pb, Cd, Zn and Cu in the 18 sediment samples at the
6 sampling points (P1-P6) of the Dobczyce Reservoir do not exceed the acceptable
limits for heavy metal content in drawn out sediments [16]. However, in 9 samples,
the concentration of Cr exceeds 100 ppm and these samples are classified in the Class
III (relocation to the advisable place in water or limited degree land disposal) of the
“Criteria for evaluation of water sediments pollution” [17]. Pb, Cd, Zn and Cu are at
the levels to classify the sediments in the Class I (not polluted) or Class II (slightly
polluted).
The results show considerable variations of each heavy metal concentration at the
6 stations, but not in the individual layers (A, B, C) of each sediment. The mean
concentration of each metal rises from PS1 to PS4, and lowers in P6 - the most
distant point from the Raba River estuary. The concentrations in P5 are always lower
than in P4 and are related to the different geo- and biochemical conditions in Wolnica
Bay. It is important to note that during the last 3 years, there was no heavy flood
event at the Dobczyce Reservoir and the mean and maximum concentrations of Pb,
Cr are higher than observed in the last years. However, Cd shows a different
tendency.
The concentrations of each heavy metal in stations P1 to P5 are very well correlated
with the organic matter content of the sediment. In several cases, significant
correlations between the concentrations of Pb, Cr, Cu and Zn and the content of Ca,
Fe and Mn (less distinct) in sediment have been found.
The concentrations of total Cu and Zn in pore water samples are very low and do not
even exceed the acceptable values for drinking water [18]. The sediment - pore water
288
equilibrium coefficients (K = csediment/cpore water), indicating the bioaccumulation and
chemical fixation of the metal to the sediment, have been determined.
Acknowledgements
This work was supported in part by the Kosciuszko Foundation Inc. - An American
Center for Polish Culture since 1925, and by the Polish Ministry of Science and Higher
Education under grant no. 3 T09D 094 29.
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289
ROZKŁAD ZAWARTOŚCI Cr, Pb, Cu, Cd i Zn W SEDYMENTACH
ZAPOROWEGO ZBIORNIKA DOBCZYCKIEGO
USYTUOWANEGO W POŁUDNIOWEJ POLSCE
Streszczenie: Sedyment ma zasadniczy wpływ na rozmieszczenie i przemieszczanie się szkodliwych składników
w systemach wodnych. Procesy, takie jak: adsorpcja-desorpcja, utlenianie-redukcja, wymiana jonowa, aktywność
biologiczna, mogą spowodować akumulację lub uwalnianie metali i anionów z osadów dennych zbiorników
wodnych i są ostatnio przedmiotem badań równieŜ w Polsce [1-3]. Próbki sedymentów - warstwa A: 1÷6 cm
(bezpośredni kontakt z wodą przydenną), B: 7÷12 cm (umiarkowany kontakt) oraz C: 12+ cm (teoretycznie
nieaktywna warstwa sedymentu) zostały pobrane we wrześniu 2007 roku z 6 punktów reprezentujących odmienne
warunki hydrogeologiczne Zbiornika Dobczyckiego. Głębokość w tych punktach wahała się w granicach od
3,5 do 21 m. Głównym celem eksperymentu było określenie rozkładu i akumulacji kilku metali cięŜkich (Cr, Pb,
Cd, Cu i Zn) w tych sedymentach. Przy okazji zostały pobrane próbki wody wierzchniej i przydennej oraz
otrzymano próbki wody porowej poprzez odwirowanie sedymentów. W analizie wyników omówiono
prawdopodobne zaleŜności pomiędzy rozkładem metali cięŜkich w sedymentach a właściwościami tych
sedymentów (skład mineralogiczny, zawartość materii organicznej), a takŜe zawartością Fe, Mn i Ca w tych
próbkach. Dodatkowo zmierzono zawartości tlenu w próbkach wodnych. Zawartości metali cięŜkich w badanych
próbkach znajdują się w przedziale od 19,0 do 226,3 mg/kg suchej masy (ppm). Wyniki te wskazują na znaczące
róŜnice stęŜeń poszczególnych metali w róŜnych 6 punktach pobrania próbek, ale nie w przekrojach poprzecznych
(A, B, C) kaŜdego badanego rdzenia sedymentu. Zaobserwowane róŜnice są związane z właściwościami
mineralogicznymi i składem chemicznym sedymentów i ich wód porowych.
Słowa kluczowe: sedyment, metale cięŜkie, rozkład zawartości, akumulacja, immobilizacja

DISTRIBUTION OF Cr, Pb, Cu, Cd AND Zn IN SEDIMENTS OF THE

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