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Journal of Coastal Research
SI 56
797 - 801
ICS2009 (Proceedings)
Portugal
ISSN 0749-0258
Pb isotopic signatures in sediments of a sub-tropical coastal lagoon:
Anthropogenic sources for metal contamination in the Sepetiba Bay
(SE – Brazil)
B. C. A. Cunha†; D. Rocha‡; M. C. Geraldes‡; S. D. Pereira†; and A. C. Almeida ∞
(†)Faculdade de Oceanografia Universidade do Estado do Rio de
Janeiro (UERJ), Rua São Francisco
Xavier 524, 20559-900 Rio de
Janeiro - RJ, Brasil
(‡)Faculdade de Geologia-Universidade (∞) Departamento de Química, Pontifícia Universidade
do Estado do Rio de Janeiro (UERJ), Católica-RJ (PUC - Rio), Rua Marquês de São Vicente
Rua São Francisco Xavier 524, 20559- 225, 22453-900, Rio de Janeiro - RJ, Brasil
900 Rio de Janeiro - RJ, Brasil.
ABSTRACT
CUNHA, B.C.A.; ROCHA, D.; GERALDES, M.C.; PEREIRA, S.D.; ALMEIDA, A.C., 2009. Pb isotopic signatures in
sediments of a sub-tropical coastal lagoon: Anthropogenic sources for metal contamination in the Sepetiba Bay
(SE – Brazil). Journal of Coastal Research, SI 56 (Proceedings of the 10th International Coastal Symposium),
797 – 801. Lisbon, Portugal, ISSN 0749-0258.
The Sepetiba Bay is a coastal lagoon separated from the ocean by beach barrier located 60 km from Rio de
Janeiro city. Situated in the most important economic region in Brazil, the bay has been extensively studied in
relation to the pollution due Zn smelter, domestic sewage and harbor activities. The aim of this study is to
constrain the sediment Pb isotopes signature to define pollution source of metals in the region. The 96 samples
were collected using Van Veen and preparation included dry, sieving, (nitric acid) leaching and mass
spectrometry (ICP-MS). The preliminary isotopic analyses of 37 samples show 206Pb/207Pb ratio variation from
1.188 to 1.341. The Pb isotopes results define groups interpreted as different sources of Pb. The samples from
Guandu river present different Pb compositions (206Pb/207Pb values from 1.188 and 1.190) probably resulting
from Zn-Pb smelter which is transported in the waters to the Sepetiba Bay. The second Pb isotope signature
(206Pb/207Pb values of 1.335 and 1.341) is interpreted as oceanic water source. Both lead are mixed within
Sepetiba bay and when the data is plotted in the 206Pb/204Pb versus 207Pb/204Pb diagram define a linear trend
between two end members. These results when compared to Pb isotopic signatures of gasoline 206Pb/207Pb
values (1.2) and industrial waste (1.16 to 1.35) indicated that the results here presented may be correlated to
these sources. The Pb isotopic signatures of Neoproterozoic lead deposits range from 1.06 to 1.10 and do not
indicate a relation with Sepetiba bay results. Nevertheless the Ingá smelter is a very probably source for metals in
Sepetiba Bay, and the ore used in the industry has Pb isotope signature not yet identified. If this hypothesis is
correct, the Pb isotope signature of Zn ore and industrial sewage are the responsible for the metal pollution in the
area.
ADITIONAL INDEX WORDS: Sepetiba Bay, Pb isotopes, metal pollution
INTRODUCTION
The Sepetiba Bay is a coastal lagoon located 60 km from Rio de
Janeiro city. Situated in the most important economic region in
Brazil (Figure 1), the bay has been extensively studied in relation
to the pollution due Zn smelter, domestic sewage and the harbor
activities. Sepetiba bay is semi-enclosed body of water 450 km2
separated from the ocean by beach barrier (Restinga de
Marambaia). The east part of the inner bay is bordered by
mangroves. The coastline to the north receives polluted flows in
rivers and canals from several towns and industries. The Guandu
River receives drainage basin of the water diverted from the
Paraiba do Sul River and it is the principal source of natural
discharge into Sepetiba bay.
The Lead is a natural rock compound and its introduction into
the environment comprises a risk for the human health. Since the
1920s, automobile exhaust, with Pb additives (alkyl lead), has
exceeded all other sources of anthropogenic Pb emitted into the
environment. Nowadays, more than 95% of lead deposited in the
environment is of anthropogenic origin (Alfonso et al., 2001;
Marcoantonio 2002). Attempts to identify pollution sources have
included the use of elemental values, but total Pb concentrations
alone may be insufficient for separating pollution from natural
background. This is because background Pb concentration is often
highly variable due to natural processes (Niagru, 1990; Helland et
al., 2002). In contrast, Pb isotope abundances are not affected to
any measurable extent by physical or chemical processes in
terrestrial environment. Given the significant isotopic differences
in Pb emissions, researchers have been able to use historical
records of anthropogenic Pb isotope variations to trace the
changing sources of pollutant Pb in continental environment
through time (Hong et al., 1994; Luck and Othman, 2002). Pb
isotopic analysis has been used with great success to trace the
source of elements in recent sediments, to distinguish different
sources, to trace elements from source to burial, and to assess the
effect of remedial actions to reduce atmospheric emissions from a
specific polluter (Veron et al., 1999; Rosman et al., 2000). In
addition, establishing reference sites is a critical factor in
determining the baseline of contaminant background and the
Journal of Coastal Research, Special Issue 56, 2009
797
Pb isotopes in Sepetiba Bay sediments
Figure 1. Location of the Sepetiba Bay and sampled sites.
remediation of impacted landscapes (Niagru, 1989; Monna et al.,
2000).
Pb isotope vertical profiles in recent sediment cores have been
used for various purposes, such as stratigraphic interpretation of
paleoenvironment and recent pollution history (Planchon et al.,
2003; Renberg et al., 2000; Paula and Geraldes, 2006). There has
been of increasing interest in the application of radiogenic isotopic
tracers (Nd, Pb and Sr) in marine deposits to oceanographic
problems, and to the cycling of these elements in seawater
(Hemming and McLennan, 2001; Outridge et al., 2002; Geraldes
et al., 2006). These tracers are largely derived from continental
sources and must ultimately enter the ocean by rivers or in the
form of wind-blown dusts. In estuarine marshes, such a global
atmospheric signal should be recorded, despite local input
(industry, shipping and dense human population), which could
obscure the atmospheric signal. By contrast, local mantle-derived
inputs are evident in hydrothermal Fe-Mn deposits located near
active spreading ridges. River and anthropogenic inputs, and
biological and geochemical cycling may influence the
concentration of metals in estuarine and coastal seawater to a
much greater extent than that occurring in open-ocean water and
deep-sea turbidites. The mechanism for dispersal of these metals,
and their inputs into receiving systems such as sediments, have
been the subject of numerous studies and, in such research, it is
often necessary to attempt to evaluate the impact of local, point
source releases against background levels due to regional or global
contamination (Bollhöfer and Rosman, 2000). The aim of this
study is to constrain the sediment Pb isotopes signature to define
possible pollution sources in the region.
PROCEDURES
The 96 samples were collected using Van Veen in 6 days of
work caaried aut from March to September (2008) and preparation
included drying, sieving, (nitric acid) leaching and mass
spectrometry analisys (ICP-MS). The sampling sites have been
chosen in the all area of Bay (Figure 1) searching 96 samples.
Sample preparations included: (a) dry out and granulometric
separations; (b) weighting and oxidation of organic material; (c)
leaching extraction procedure using nitric acid at 0,1 N. (d) 37
samples were analysed for Pb isotope compositions obtained by
ICP-MS (207Pb/204Pb, 208Pb/204Pb and 206Pb/204Pb ratios).
RESULTS
The preliminary isotopic analyses show 206Pb/207Pb ratio
variation from 1.188 to 1.341. When plotted in the 207Pb/206Pb
versus 208Pb/206Pb diagram, the data define a linear trend
interpreted as a mixture of different sources of Pb (Figure 2 A).
When the Pb isotope data are plotted in the 206Pb/204Pb versus
207
Pb/204Pb diagram (Figure B), three groups of samples may be
identified due different Pb signatures.
The samples SP-11 and SP-12 were collected close to the
Guandu river and may represent the Pb composition of the water
and sediments transported. The 206Pb/207Pb values are 1.188 and
1.191 (respectivelly) and comprise the lower values observed.
Other two samples, represented by SP-22 and SP-23 (collected in
a 10-15m deep water area near the entrance of the bay), yielded
206
Pb/207Pb values of 1.341 and 1.336, respectivelly, and comprise
the higher values obtained. The Pb isotope values indicate
different signatures and may be interpreted as a contamination by
two different pollutant sources and may define possible end
members. The end member A is represented by the samples SP-11
Journal of Coastal Research, Special Issue 56, 2009
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Cunha et al.
and SP-12; the end member B is representd by the samples SP-22
and SP-23. The rest of the samples present intermediary Pb
isotopes values and may be interpreted as mixing of the two end
members.
Table 1. Pb isotopes results obtained from sediments sampled in
Sepetiba Bay
Samples
SP01
SP02
SP03
SP04
SP05
SP06
SP07
SP08
SP09
SP11
SP12
SP13
SP14
SP15
SP16
SP18
SP19
SP22
SP24
SP33
SP37
SP26
SP27
SP28
SP29
SP30
SP31
SP34
SP35
SP38
SP44
SP45
SP47
SP49
SP53
SP58
SP63
Pb206/Pb204
18.447
18.328
18.315
18.332
18.245
18.188
18.312
18.302
18.328
17.963
17.931
18.175
18.285
18.288
18.265
18.188
18.060
18.119
17.860
18.467
18.129
18.501
18.315
18.396
18.212
18.238
18.195
18.192
18.235
18.238
18.285
18.195
18.162
18.169
18.054
18.060
17.724
Pb207/Pb206
1.207
1.199
1.198
1.204
1.211
1.226
1.203
1.205
1.209
1.188
1.191
1.211
1.225
1.287
1.233
1.246
1.324
1.341
1.336
1.277
1.266
1.204
1.197
1.206
1.201
1.205
1.215
1.213
1.223
1.234
1.255
1.244
1.265
1.264
1.290
1.285
1.298
Pb208/Pb206
0.829
0.834
0.835
0.831
0.826
0.816
0.831
0.830
0.827
0.841
0.840
0.826
0.816
0.777
0.811
0.803
0.756
0.746
0.749
0.783
0.790
0.831
0.835
0.829
0.832
0.830
0.823
0.825
0.817
0.810
0.797
0.804
0.791
0.791
0.775
0.778
0.771
The 206Pb/207Pb values presented here can be compared
to the anthropogenic signatures reported in other investigations in
Brazil (Figure 3). Two studies using Pb isotope signatures of
aerosols have been reported: The first study (BOLLHÖFER et al,
1999) reported aerosols Pb signatures from Brazil (9 samples),
Argentina (3 samples) and Chile (9 samples) and show 206Pb/207Pb
values from 1.147 to 1.177. Studies on the Pb isotope composition
Figure 2. 206Pb/204Pb versus 207Pb/204Pb (A) and 208Pb/206Pb versus
207
Pb/206Pb (B) diagram for the Pb isotope data of sediments from
Sepetiba Bay.
of the São Paulo city atmosphere (AYLI, 2001), collected daily
during fourteen months (August, 1999-September, 2000),
indicated 206Pb/207Pb values from 1.142 to 1.273. The values are
related to contribution of gasoline Pb additives and industrial
activities. In addition, investigations on Pb isotopes analysis in
mining waste (galena massive vein hosted in Neoproterozoic
carbonates), and river channel sediments in a transect downstream
from the mine dump, identified the mines as a highly pollutant
(MORAES et al, 2004). Pb isotope studies in sediments are reported
also in Brasilia (DF) and Belém (PA) where 206Pb/207Pb values
range respectively between 1.1526 and 12028 (GIOIA et al., 2003)
and between 1.1622 and 1.2031 (MOURA et al., 2004) and
characterize anthropogenic sources interpreted as sewage and
industrial polluters.
These results when compared to Pb isotopic signatures of
gasoline values (1.2 according to AILY, 2001; GIOIA et al., 2003)
and industrial waste (1.16 to 1.35 according to AILY, 2001; GIOIA
et al., 2003; BOLHOFER AND ROSMAN, 2000; MOURA et al., 2000)
indicated that the results here presented may be correlated to these
sources. The Pb isotopic signatures of Archean Lead deposits
(1.056 – 1.097) reported by DAVID (2006) and investigations on
Pb isotopes analysis in galena massive vein hosted in
Neoproterozoic carbonates (TASSINARI et al., 1990) do not show
similarity with the Sepetiba Bay sediments.
Journal of Coastal Research, Special Issue 56, 2009
799
Pb isotopes in Sepetiba Bay sediments
Figure 3.
206
Pb/207Pb ratios obtained in this study and from the literature.
CONCLUSION
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This work was sponsored by FAPERJ Grant E26/100.662/2007 to M.C.G. and CNPq Grant 554449/2006-2 and
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