HEAVY METALS ON FLUVIAL SEDIMENTS
FROM A TOBACCO PLANTATION IN THE SOUTH OF BRAZIL
Torres, JPM1*; Lima, RG2,
Etges, V2; Turci, SR3; Ferreira, MA2, Hermes,
N2 and Malm, O1.
1Laboratorio de Radioisótopos Eduardo Penna Franca,
Instituto de Biofísica Carlos Chagas Filho, UFRJ, Rio de Janeiro, Brazil (jptorres@biof.ufrj.br
or jpmtorres@uol.com.br).
2Curso de Mestrado em Desenvolvimento Regional,
UNISC, Rio Grande do Sul, Brazil
3COMPREV, INCA, Rio de Janeiro, Brazil.
Abstract
Tobacco is one of the main exportation products of the south of Brazil.
Its production relies on several agrochemicals. These products (e.g.
phosphorous fertilizers and ditiocarbamate fungicides) are know to have
considerable amounts of metals like Zn, Cd and Mn in their composition. Another
product have also copper in its composition.
To proceed a first approach
to the environmental quality of a watershed were tobacco is being cultivated
for more than 30 years, fluvial sediments were collected at 9 locations in the
Rio Pardinho basin, near the town of Santa Cruz do Sul, RS. After total
digestion of the samples, the final extracts were ressuspended in HCl 0,1 N and
analyzed by means of FASS (Varian 1475). Enrichment factors using Fe as a
conservative element was used to express the obtained results. In most of the
samples, the heavy metal levels were low. Only cadmium showed a small
enrichment in one of the analyzed sediments.
Introduction
Beside
dozens of organic substances, several products now in use in agriculture,
especially fertilizers, algaecides and fungicides, contain heavy metals like
Zn, Cd, Mn and Cu in its constitution. In tropical areas, the environmental
fate of these compounds after agrochemical application is only sparsely understood.
In
order to understand the effects of intensive cultivation of tobacco (that use
each year large amounts of such products), the ecosystem health of a small
river in the South Brazil is being investigated by a multidisciplinary group
(IDRC, 1999). In Brazil, especially in the south, the agricultural development
is based in small to medium size properties that resembles quite well the old
18’s situation in Europe. In fact, a great contingent of population of these
areas consist nowadays of descendents of Germans and Italians that immigrated
to Brazil in the last years of 1800.
Study area
Figure 1 – Study area in the south part of Brazil (adapted from Lobo and Costa, 1997).
The Pardinho River (ca. 50 Km long) is a tributary of the Pardo. They
belong to the Jacuí River watershed, the largest freshwater basin of Rio Grande
do Sul State (Figure 1). The weather in this region may be very cold especially
in strong winters. Probably due to a high precipitation index, in the past most
of this riverbanks were covered with tropical forests that once were part of
the Atlantic forest that covered most part of the Brazilian coast. Although the
German colonization of these upper part of the area is rather recent (150
years), older Portuguese settlements (e.g. Rio Pardo) where established in the
middle of the 17th. Century (Etges, 1991).
The riverheads, located at Sinimbu and
Boqueirão do Leão municipalities (Figure 1) are a mix of river rapids and
plateaus with more or less limited floodplains, that may be covered during the
raining season. Traditional tobacco cultivation usually using animal traction
is wide spread along the course of the River and spare bottles of different
pesticides are commonly found in the riverbanks.
Material and methods
Bottom sediments from 7 locations along the Pardinho
River were collected using a polyethylene scoop, and stored in plastic bags
that were stored in iceboxes during their transport to the Radioisotopes
Laboratory in Rio de Janeiro. The sediments were sieved in 200 mesh sieves and
the fraction smaller than 74 mm (clay + silt + fine sand)
were analyzed for their total content of heavy metals (Cd, Cu, Cr, Fe, Mn, Ni
and Zn) after digestion in Teflonâ bombs with strong acids
(HF, NNO3 and HClO4), the final extracts were
ressuspended in HCl 0,1 N and the metal determination were done by conventional
flame AAS (Varian 1475). Reagent blanks and certified reference materials were
analyzed in each batch of 10 samples (All samples were analyzed in triplicates)
(Fiszman et al, 1984).
Results and discussion
The results, expressed as mg/kg (ppm) of dry sediment are presented in table 1.
Table
1- Total heavy metal contents (ppm) of the sediments of the Pardinho River
watershed.
|
|
Cd |
Cu |
Cr |
Fe |
Mn |
Ni |
Zn |
|
Sinimbu 1 |
0.55 |
68.8 |
106.0 |
73996 |
1393 |
69.0 |
70.0 |
|
Sinimbu 2 |
1.05 |
56.8 |
88.5 |
71871 |
1083 |
54.8 |
75.0 |
|
Rio Pardinho |
0.60 |
57.8 |
101.8 |
69121 |
1015 |
53.5 |
78.3 |
|
Santa Cruz do Sul 1 |
0.45 |
42.0 |
158.3 |
79183 |
1132 |
76.0 |
64.3 |
|
Santa Cruz do Sul 2 |
0.48 |
42.3 |
38.5 |
47558 |
925 |
25.3 |
61.8 |
|
Santa Cruz do Sul 3 |
0.35 |
40.3 |
73.3 |
57996 |
1157 |
41.0 |
58.8 |
|
Rio Pardo |
0.15 |
8.8 |
12.0 |
10656 |
191 |
7.8 |
16.3 |
|
Mean crust** |
0.20 |
55.0 |
100.0 |
56300 |
950 |
75.0 |
70.0 |
|
Average shale** |
0.30 |
33.0 |
90.0 |
41000 |
770 |
52.0 |
95.0 |
|
Background RPS* |
0.01 |
36 |
53.0 |
62388 |
1235 |
29.0 |
104.0 |
* Paraiba do Sul riverheads
(Malm et al, 1986).
** Forstner and
Wittman,1981.
All of the observed results
are within the same order of magnitude of the mean crust value or the average
shale, thus they cannot be considered polluted. However, when the results are
expressed by enrichment factor using Fe as a conservative element, the results
for cadmium found near the town of Sinimbu showed some enrichment (> 4). The
net concentration, around 1 ppm, tough not very high, are similar the one that
can be found in other rivers and in shallow bays near industrialized areas of
Brazil (Lacerda et al, 1982; Torres, 1992). This concentration, observed near
the riverheads of a non-industrialized area (present study) may be reflecting
anthropogenic inputs of these toxic metal that is present as impurities of
different fertilizers.
The
same pattern of a mild cadmium contamination was observed in other areas in
where the same kind of fertilizers are used (De Boo, 1990).
References
1.
IDRC-Canada,
1999. Project Grant No. 50386. Tobacco growing and ecosystem effects.
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Etges,
VE. 1991. Sujeição e resistência: os camponeses gauchos e a indústria do fumo.
Edunisc. Rio Grande do Sul, Brasil.
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Lobo
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