Heavy metals in tributaries of Pampulha Reservoir, Minas Gerais

Abstract

A great amount of heavy metals enter Pampulha Reservoir via it's main tributaries (Sarandi and Ressaca). Although no water quality classification has been carried out for these tributaries, the reservoir is expected to be in class 2 of the CONAMA-86 system. As part of a monitoring scheme of the Pampulha Watershed, heavy metals (Zn, Pb, Cd, Ni, Cu, Cr, Mn and Fe) were investigated in the water at a control site (considered free from direct human influence) and at potential sites of toxicity and contamination during August (dry season) and November (wet season) of 1998. The results for the first sampling period showed relatively high concentrations of zinc (0.22 mg.L-1) in the upper portion of the reservoir. The highest values of nickel and chromium (0.19 and 0.89 mg.L-1, respectively) were found in the initial portion of the Sarandi Stream, while the highest concentrations of lead (0.05 mg.L-1), cadmium (0.014 mg.L-1), manganese (0.43 mg.L-1) and iron (15.25 mg.L-1) were detected in the Ressaca Stream by the landfill dump of Belo Horizonte. A relatively high concentration of cadmium was also detected at the confluence of the two streams. During the second sampling period, there was an increase in the concentrations of zinc at all sampling sites except the control, with values varying from 0.71 mg.L-1 (the Sarandi Stream) to 2.50 mg.L-1 (the Ressaca Stream). Lead, cadmium, nickel and chromium concentrations were also higher in the Ressaca Stream, but not detected at the other sampling sites. Copper values were higher than in the first period: 0.10 mg.L-1 at the control up to 0.38 mg.L-1 at the confluence of the streams. Similar results were found for manganese and iron, with values reaching up to 19.30 and 125 mg.L-1, respectively. Moreover, all values recorded in the second sampling period were much higher than recommended for class 2 waters. These results emphasize the need for such monitoring in relation to better water quality management of this reservoir.

Full text

Braz. J. Biol., 61(3): 363-370
HEAVY METALS IN TRIBUTARIES OF PAMPULHA 363
HEAVY METALS IN TRIBUTARIES OF PAMPULHA
RESERVOIR, MINAS GERAIS
RIETZLER, A. C.,1 FONSECA, A. L.2 and LOPES, G. P.3
1Departamento de Biologia Geral, ICB, UFMG, Belo Horizonte, MG
2 EFEI, Instituto de Engenharia Mecânica de Itajubá, MG
3Centro de Recursos Hídricos e Ecologia Aplicada, EESC, USP, São Carlos, SP
Correspondence to: Arnola C. Rietzler, Departamento de Biologia Geral, Universidade Federal de
Minas Gerais, Av. Antônio Carlos, 6627, CEP 31270-901, Belo Horizonte, MG, Brazil,
e-mail: rietzler@mono.icb.ufmg.br
Received April 18, 2000 – Accepted August 25, 2001 – Distributed August 31, 2001
(With 2 figures)
ABSTRACT
A great amount of heavy metals enter Pampulha Reservoir via it’s main tributaries (Sarandi and
Ressaca). Although no water quality classification has been carried out for these tributaries, the reservoir
is expected to be in class 2 of the CONAMA-86 system. As part of a monitoring scheme of the Pampulha
Watershed, heavy metals (Zn, Pb, Cd, Ni, Cu, Cr, Mn and Fe) were investigated in the water at a control
site (considered free from direct human influence) and at potential sites of toxicity and contamination during
August (dry season) and November (wet season) of 1998. The results for the first sampling period showed
relatively high concentrations of zinc (0.22 mg.L–1) in the upper portion of the reservoir. The highest values
of nickel and chromium (0.19 and 0.89 mg.L–1, respectively) were found in the initial portion of the Sarandi
Stream, while the highest concentrations of lead (0.05 mg.L–1), cadmium (0.014 mg.L–1), manganese (0.43
mg.L–1) and iron (15.25 mg.L–1) were detected in the Ressaca Stream by the landfill dump of Belo Horizonte.
A relatively high concentration of cadmium was also detected at the confluence of the two streams. During
the second sampling period, there was an increase in the concentrations of zinc at all sampling sites except
the control, with values varying from 0.71 mg.L–1 (the Sarandi Stream) to 2.50 mg.L–1 (the Ressaca Stream).
Lead, cadmium, nickel and chromium concentrations were also higher in the Ressaca Stream, but not detected
at the other sampling sites. Copper values were higher than in the first period: 0.10 mg.L–1 at the control
up to 0.38 mg.L–1 at the confluence of the streams. Similar results were found for manganese and iron, with
values reaching up to 19.30 and 125 mg.L–1, respectively. Moreover, all values recorded in the second sampling
period were much higher than recommended for class 2 waters. These results emphasize the need for such
monitoring in relation to better water quality management of this reservoir.
Key words: heavy metals, monitoring, Pampulha Watershed, water quality.
RESUMO
Metais pesados em tributários da represa da Pampulha, Minas Gerais
Os efluentes lançados nos principais tributários da represa da Pampulha (Sarandi e Ressaca) estão em
grande parte representados por metais pesados. Embora não haja enquadramento para a qualidade da água
destes tributários, por apresentarem trechos canalizados, os limites recomendados para o reservatório o classificam
como classe 2. Dentre os aspectos ecotoxicológicos considerados no monitoramento da Bacia da Pampulha,
foram investigados teores de metais pesados (Zn, Pb, Cd, Ni, Cu, Cr, Fe e Mn) na água, em locais com potencial
de toxicidade e contaminação, durante agosto (estação seca) e novembro/98 (estação chuvosa). Os primeiros
resultados mostraram concentrações relativamente elevadas de zinco (0,22 mg.L–1) na porção inicial do re-
servatório. No início do Córrego Sarandi, foram encontrados os maiores teores de níquel e cromo (0,19 e 0,89
mg.L–1, respectivamente), enquanto as maiores concentrações de chumbo (0,05 mg.L–1), cádmio (0,014
mg. L–1), manganês (0,43 mg.L–1) e ferro (15,25 mg.L–1) foram encontradas no Córrego Ressaca, onde está situado
o aterro sanitário de Belo Horizonte. Uma concentração relativamente elevada de cádmio também foi verificada

Braz. J. Biol., 61(3): 363-370
364 RIETZLER, A. C., FONSECA, A. L. and LOPES, G. P.
na junção dos córregos Sarandi e Ressaca. No segundo período de análises, verificou-se um aumento
nas concentrações de zinco em todos os pontos de amostragem, exceto no controle, com valores entre
0,71 (Córrego Sarandi) e 2,50 mg.L–1 (Córrego Ressaca). Chumbo, cádmio, níquel e cromo apresentaram-
se em maiores concentrações no Córrego Ressaca, não tendo sido detectados nos demais pontos de
amostragem. Os valores de cobre foram mais elevados que os obtidos em agosto/98, entre 0,10 (controle)
e 0,38 mg.L–1 (junção). O mesmo foi verificado em relação ao manganês e ao ferro, cujos valores chegaram
a 19,3 e 125,0 mg.L–1, respectivamente. Além disso, todos os valores de metais detectados no segundo
período de amostragem estiveram muito acima dos valores recomendados para águas classe 2. Os resultados
mostram a necessidade de continuidade do monitoramento desses metais, devido ao interesse na melhoria
da qualidade da água do reservatório.
Palavras-chave: metais pesados, monitoramento, Bacia da Pampulha, qualidade da água.
INTRODUCTION
Heavy metals may enter aquatic ecosystems
through natural processes such as soil leaching,
rock erosion, and volcanic activity. In addition,
numerous sources, at times difficult to identify,
originate from industrial activity, as well as from
domestic effluents, and sludge from treatment plants
(Jackson, 1992).
The Pampulha watershed is of importance for
the city of Belo Horizonte, representing a large green
area suitable for leisure activities. Surface area is
97 km2. Within this watershed, the reservoir of
Pampulha was constructed in 1938, and recons-
tructed in 1957; this waterbody has a surface area
of approximately 2.4 km2 and a maximum depth of
16 metres (Pinto-Coelho, 1997). Initially a tourist
attraction and recreational area, it was also used
as a source of water for various parts of the city
until the last decade, at which time, problems with
the quality of the water became evident (Pinto-
Coelho, 1992; Giani, 1994). At present, the main
tributaries which comprise the watershed (namely
the Sarandi and Ressaca streams) receive effluents
from industries of the area, domestic effluents, solid
wastes, wastes from flood run-off, and liquid
wastes from land-fill dumps. These wastes include
considerable quantities of heavy metals, which
directly affect the water quality and aquatic biota
of the reservoir (Champs, 1992; Pinto-Coelho &
Greco, 1998).
Barbosa et al. (1998) carried out a mass
balance analysis of the reservoir for nitrogen and
phosphorus, considering estimations of the quan-
tities of these elements entering, leaving and being
retained within the water body. A high level of
eutrophication was recorded, with greatest loads
of N and P being supplied by the Sarandi and
Ressaca streams.
Pinto-Coelho (1997) has monitored the
reservoir since 1984, with particular emphasis on
limnological aspects, generating a database on the
water quality deterioration over the last 15 years.
According to the latter author, this deterioration
has led to the disappearance of some zooplankton
taxa, including Scolodiaptomus corderoi and Bos-
mina sp. which were abundant in the last decade,
but not recorded since 1994.
In view of these environmental problems, the
Municipal Prefectures of Belo Horizonte and Conta-
gem, in conjunction with Copasa (the Sanitation
Company of Minas Gerais) and Feam (State Foun-
dation of the Environment), elaborated programmes
of sanitation and recuperation for the water-shed.
Included in these measures were the removal and
treatment of industrial and domestic effluents, and
prevention of the addition of untreated effluents
to the tributaries of the reservoir.
In this context, as part of a project on moni-
toring the quality of the water and sediments of the
watershed, with the aim of providing information
on ecotoxicological aspects for management and
recuperation planning of the reservoir, the present
study was carried out to determine the concen-
trations of the metals zinc, lead, cadmium, nickel,
copper, chromium, iron, and manganese at various
locations in the watershed. Of particular interest was
how such concentrations would compare to the limits
established for class 2 waters of the CONAMA-86
system; the Sarandi and Ressaca streams have been
considered to belong to this class.
MATERIAL AND METHODS
The location of the sampling points are shown
in Fig. 1. Water samples were collected in August
(dry season) and November (wet season) of 1998.

Braz. J. Biol., 61(3): 363-370
HEAVY METALS IN TRIBUTARIES OF PAMPULHA 365
RESULTS
Zinc concentrations varied between 0.00048
and 0.22 mg.L–1 in the dry season, and 0.71 and 2.50
mg.L–1 in the wet season (Fig. 2a). Considering the
limit established by CONAMA-86 for Class 2
waters, the concentrations found during the wet
season exceed the permissible limit for all sampling
points, especially in the Ressaca Stream, where the
value was 13.8 times greater than this limit (Table 1).
The values obtained for lead and cadmium are
shown in Figs. 2b and c, respectively. For both
metals, values varied from below the limit of analy-
tical detection (0.002 and 0.0006 mg.L–1, respectively),
to above the permissible limits.
The Ressaca Stream showed values above
the permissible during both dry and wet seasons,
being 0.05 to 0.82 mg.L–1 for lead, and 0.014 and
0.18 mg.L–1 for cadmium. During the wet season,
values were extremely high, surpassing the limit by
a magnitude of 27.5 times for lead and 180 times for
cadmium (Table 1).
Fig. 1 — Location of sampling points in the Pampulha Watershed.
19º54'S
Sampling sites
1
2
3
4
5
2 km
– Control
– Sarandi
– Ressaca
– Confluence
– Reservoir
– Industries
3
Landfill
dump of
Belo Horizonte
Ressaca
Stream
Sarandi
Stream
1
5
4
Pampulha Reservoir
19º52'S
44º02'WGr 44º00'WGr
2
N
Lead, zinc, nickel, cadmium, copper, iron,
manganese and chromium concentrations were
determined following the methodology described
in APHA (1995), with concentrated nitric acid di-
gestion. Water samples of one litre in volume were
taken at each sampling point, with 5 ml of HNO3
being added to each. Digestion was carried out in
a fume cupboard to give a final volume of 20-30 ml.
These samples were stored for subsequent
analysis using atomic absorption spectrometry.

Braz. J. Biol., 61(3): 363-370
366 RIETZLER, A. C., FONSECA, A. L. and LOPES, G. P.
Fig. 2 — Heavy metal concentrations in the water samples collected in August (dry season) and November (wet season)
of 1998, in the Pampulha Watershed.
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
mg.L
–1
mg.L
–1
mg.L
–1
mg.L
–1
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
20
16
12
8
4
0
Manganese
Dry season Wet season
g
Dry season Wet season
h
160
120
80
40
0
Iron
Dry season Wet season
e0.4
0.3
0.2
0.1
0
Copper fChromium
1
0.8
0.6
0.4
0.2
0
d
ND ND ND ND ND
Dry season Wet season
Nickel
0.5
0.4
0.3
0.2
0.1
0
ND ND
ND ND ND NDND
Dry season Wet season
c0.2
0.16
0.12
0.08
0.04
0
Cadmium
b
ND ND ND ND ND ND ND
Dry season Wet season
Lead
1
0.8
0.6
0.4
0.2
0
a
CL
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
Control
Sarandi
Ressaca
Confluence
Reservoir
CL
CL CL
CL
CL
CL
CL
Dry season Wet season
Zinc
3
2.4
1.8
1.2
0.6
0
CL indicates concentration limits for class 2 waters and ND indicates values below the limits of detection by spectrophotometry,
such limits (in mg.L ) being 0.002 (Pb); 0.0006 (Cd); 0.008 (Ni); and 0.005 (Cr).
–
1
Dry season Wet season
ND ND ND ND ND
mg.L
–1
mg.L
–1
mg.L
–1
mg.L
–1

Braz. J. Biol., 61(3): 363-370
HEAVY METALS IN TRIBUTARIES OF PAMPULHA 367
Nickel concentrations varied between 0.0082
and 0.40 mg.L–1, considering both sampling pe-
riods. Fig. 2d shows that, during the dry season, the
highest values were found in the Sarandi and Res-
saca streams, while during the wet season, the highest
values were found in the Ressaca Stream (Table 1),
surpassing during both seasons, the legal limit.
Highest copper concentrations were found
during the second sampling period, varying between
0.00048 and 0.012 mg.L–1 in the dry season, and 0.10
and 0.38 mg.L–1 in the wet (Fig. 2e). During the wet
season, such values were greater than that per-
mitted for class 2 waters, at all sampling locations
(Table 1).
TABLE 1
Number of occasions that the concentration limit for class 2 waters were surpassed, at the five
sampling points in Pampulha Watershed.
Metal Sampling points Dry season Wet season
Control –4.4
Sarandi –3.9
Zinc Ressaca –13.8
Confluence Sarandi/Ressaca –7.5
Reservoir 1.2 5.7
Control ––
Sarandi ––
Lead Ressaca 0.7 27.5
Confluence Sarandi/Ressaca ––
Reservoir ––
Control ––
Sarandi ––
Cadmium Ressaca 14.0 180.0
Confluence Sarandi/Ressaca ––
Reservoir ––
Control ––
Sarandi 7.6 –
Nickel Ressaca 4.0 16.0
Confluence Sarandi/Ressaca ––
Reservoir ––
Control –5.0
Sarandi –5.5
Copper Ressaca –12.0
Confluence Sarandi/Ressaca –19.0
Reservoir –70
Control ––
Sarandi 17.8 –
Chromium Ressaca –4.0
Confluence Sarandi/Ressaca ––
Reservoir ––
Control –25.7
Sarandi 3.2 3.3
Manganese Ressaca 4.3 193.0
Confluence Sarandi/Ressaca 1.8 65.0
Reservoir 2.3 6.8
Control –625.0
Sarandi 48.5 8.5
Iron Ressaca 76.2 425.0
Confluence Sarandi/Ressaca 18.2 225.0
Reservoir 17.5 15.7

Braz. J. Biol., 61(3): 363-370
368 RIETZLER, A. C., FONSECA, A. L. and LOPES, G. P.
Chromium concentrations varied between
0.0078 and 0.8 9 mg.L–1 in the dry season, and from
below the detectable limit (0.005 mg.L–1) to 0.20
mg.L–1 in the wet season (Fig. 2f). Highest values
were obtained in the Sarandi Stream during the dry
season, and the Ressaca Stream during the wet
(Table 1), surpassing the permitted level by mag-
nitudes of 17.8 and 4, respectively.
Manganese concentrations varied between
0.0024 and 0.43 mg.L–1 during the dry season, and
0.33 and 19.3 mg.L–1 during the wet (Fig. 2g). Highest
concentrations were recorded during the wet sea-
son, principally in the Ressaca Stream, and at the
confluence of the Sarandi and Ressaca (Table 1),
surpassing the permissible limit by magnitudes of
193 and 65, respectively.
For iron, highest values were found during the
wet season at all sampling points, with the exception
of within the reservoir (Fig. 2h). Such values varied
from below the detection limit to 15.2 mg.L–1 in the
dry season, and from 3.15 to 125 mg.L–1 in the wet.
The permissible limit was surpassed at all sampling
locations in both seasons, with the exception of the
Control location during the dry season (Table 1).
DISCUSSION
Among the environmental impacts of human
activities are included changes in the biogeochemical
cycling of trace metals, which enter the environment
from liquid and solid effluents, and via the atmos-
phere, accumulating in depositing areas. Several of
these metals may be considered as essential elements
for living organisms, such as Zn, Co and Cu, only
becoming toxic at elevated environmental concen-
trations. Others, such as Pb, Hg and Cd, are not
used by organisms, although being chemically related
to the essential metals, and are toxic at very low
concentrations (Odum, 1985; Freedman, 1995).
The bioavailability of heavy metals in aquatic
ecosystems is related to a wide variety of physical
and chemical factors, such as the chemical form
of the metal, the pH of the water, the presence of
calcium and magnesium ions (expressed as water
hardness), nutrient concentrations and the quantity
and nature of material in suspension (Pain, 1995;
Ripley et al., 1996). In general, such metals are less
toxic in hard waters, as the toxicity is diminished by
the formation of complexes with carbonate ions, and
by competition with calcium ions (Wren et al., 1995).
Investigations on the toxicity of lead to
aquatic organisms, carried out by the Environmental
Protection Agency of the USA (USEPA, 1985), in-
dicated an LC50 of 0.6 mg.L–1 of Pb for Daphnia
magna in water with a hardness of 54 mg.L–1 of
CaCO3 increasing to 1.9 mg.L–1 in water with a hard-
ness of 152 mg.L–1 of CaCO3. A similar pattern was
found for the fish Pimephales promelas, Salmo
gairdneri, and Lepomis macrochirus (Pain, op.
cit.). Similarly, Demayo et al. (1982) found that the
toxicity for Daphnia magna of cadmium was bet-
ween 0.034 and 0.060 mg.L–1 in moderately hard
waters, and less in harder waters. The elevated
concentrations of lead and cadmium found in the
present study during the wet season at location 3
(the Sarandi Stream) (0.82 mg.L–1 for lead, and 0.18
mg.L–1 for cadmium), in combination with the
moderate water hardness (90 mg.L–l CaCO3), would
suggest a toxic effect for cladocerans if exposed
to such waters.
Zinc is often encountered in the environment
bound with sulphur, its bioaccumulation depending
on the trophic level (Eysink et al., 1988). In an
examination of heavy metal concentrations in
zooplanktonic organisms and the macrophyte Eich-
hornia crassipes within Pampulha Reservoir, Pinto-
Coelho & Greco (1998), found that zinc was the
metal with highest concentrations in the biomass
(on average approximately 177 mg.L–1 for the
zooplankton and 69 mg.L–1 for E. crassipes), such
values being far greater than those found in the
water. According to the authors, the position of
the zooplankton in the second and third trophic
levels permitted bioaccumulation of this element
in their biomass.
The zinc concentrations found in the present
study confirm the accumulative potential of this
element for the aquatic biota, especially the values
recorded during the wet season, when the limit
permitted for class 2 waters (0.05 mg.L–1) was sur-
passed at all sampling locations (Table 1). The
sampling location chosen as the control also had
a concentration 1.2 times greater than the permis-
sible level during the dry season, bringing into
question whether this location can really be con-
sidered as a control.
Although copper is essential for chlorophyll
synthesis, toxic concentrations occur in the environ-
ment as a result of mining, smelting, acid preci-
pitation, and the use of this element in the form of

Braz. J. Biol., 61(3): 363-370
HEAVY METALS IN TRIBUTARIES OF PAMPULHA 369
oxide or sulphate as a pesticide, algicide, and
fungicide (Laurén & McDonald, 1986). According
to Boldrini & Pereira (1987), copper concentrations
between 0.005 and 0.015 mg.L–1 do not cause
deleterious effects on various aquatic organisms.
However, the concentrations recorded in the
present study, during the wet season, were all
greater than the above quoted values.
The elevated concentrations of nickel found
in the Sarandi and Ressaca streams during the dry
season, and in the Ressaca Stream during the wet
season, could also be causing negative effects on
the biota.
Hexavalent chromium is highly mobile in
aquatic environments, and is toxic for many orga-
nisms. On the other hand, Cr III is much less toxic,
and is indeed essential in human and animal
nutrition. This form tends to be associated with
solid material, and is relatively immobile in the
environment. The most important reducers found
in natural systems are organic compounds and
divalent iron. Iron acts as a redox catalyst,
transforming Cr VI to Cr III in environments rich in
organic matter (Burge & Hug, 1998). According to
the latter authors, Fe II is an important agent in the
remediation of areas contaminated with Cr VI. In
contrast, manganese hydroxides (III e IV), present
in such areas, can act as reoxidizers, forming Cr VI.
The concentrations of iron found in the pre-
sent study were far superior to those of manganese,
during both sampling periods, at all sampling loca-
tions, except at the control location during the dry
season. Considering the high concentrations of
both Fe and Mn naturally found in this watershed,
analysis of the species present of Mn, Fe and Cr,
especially in the Sarandi and Ressaca streams, could
help in designing remediation measures for the wa-
tershed.
River sediments are potential sources of con-
tamination, including heavy metals, for aquatic
ecosystems. During the last decade, much of the
research on metal pollution in water has concen-
trated on controlling mechanisms for the mobility
and bioavailability of different metal species, with
regard to different size classes of particles, as in
general, metal concentrations in sediments increase
with decreases in particle size (Murray et al., 1999).
The majority of transported and sedimented ma-
terial in the tributaries of the Pampulha Watershed
consist of sand, reaching 73% at the confluence
of the Sarandi and Ressaca streams (Rietzler et al.,
in prep.). Within the reservoir, clay is predominant
(68%).
Considering the above information, and the
affinity of heavy metals for small particles, one
might expect very low values of all metals at lo-
cation 5 (the reservoir), which in fact was not the
case. These results emphasize the necessity for an
increased degree of examination of the species of
metal present, which, together with knowledge of
the sediment particle size classes, should permit a
greater understanding of the processes influencing
metal concentrations in the sediments.
The sampling points considered critical for
metal analysis were the Sarandi and Ressaca
streams. Within the industrial complex of Contagem,
point 2 (Sarandi) receives a great part of the
effluents from iron and steel industries (chromium,
nickel, and copper residues), civil conctruction
(cement), solvents and paints (oxides of nickel and
chromium, used as pigments). According to Feam,
10 of the 30 industries located in this industrial
complex, as well as one other nearby, can be
considered as principally responsible for the
emission of pollutants to this watershed. The high
concentrations of metals at point 3 (Ressaca Stream)
may be related to the polluting action of liquid
wastes from land-fill dumps. The elevated
concentrations recorded during the wet season
might be related to point sources of industrial
effluents, the land-fill dump of the city, and rain
drainage.
The results of the present study emphasize
the necessity for continued monitoring of heavy
metals in this watershed, as part of the efforts to
improve the water quality of the reservoir.
Acknowledgments — The authors are grateful to: the
Department of Hydraulics and Sanitation of the São Carlos
School of Engineering, University of São Paulo, for the
use of the atomic absorption spectrophotometer; Júlio Cesar
Trofino, technician of the Sanitation Laboratory of the
latter department, for the heavy metal analysis; biologist
Luíz Antônio Rocha, for invaluable assistance in the field;
and Kennedy Roche (UFMS), for linguistic assistance.

Braz. J. Biol., 61(3): 363-370
370 RIETZLER, A. C., FONSECA, A. L. and LOPES, G. P.
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