Abstract:
The aim of present study was to evaluate the Hg concentration in two
species of fish (Astyanax sp and Corydoras paleatus) and its potential use as a biomonitor,
in order to know if the use of pesticides and fertilizers in paddy can enhance the Hg
contamination to adjacent aquatic environment. Methods: Soil, suspended particulate
matter and fish samples were sampled in a paddy field in South Brazil.
A cold vapor
system, coupled with a GBC 932 atomic absorption spectrophotometer was used for total
Hg determinations in samples. Results: The paddy soil shows Hg concentration 2-fold
higher (mean 31 ng g-1) in comparison to background areas (not cultivated). Suspended
particle matter Hg concentration in paddy channels (mean 232.5 ± 44.2 ng g–1) are 1.5
times higher than the regional background. The analyzed fish specimens Astyanax sp in
paddy showed Hg concentration 4-fold higher and significant different to background
area. The mean Hg concentration in fish was: 51.7 ± 19.5 ng g–1 in Astyanax sp and 156.8
± 44.0 ng g–1 in Corydoras paleatus. Conclusions: Considering the linear regression and
Man whitney test hypothesis to Hg concentration in fish tissue from paddy suggests that
Astyanax sp. can be a good biomonitor of Hg contamination, whereas Corydoras paleatus
is a potential biomonitor. However, more studies with Corydoras are necessary in order
to aggregate consistency to this hypothesis
O objetivo do presente estudo foi avaliar a concentração de
Hg em duas espécies de peixes (Astyanax sp e Corydoras paleatus) e seu uso potencial
como biomonitor, a fim de saber se o uso de pesticidas e fertilizantes na lavoura pode
levar a contaminação por Hg ao ambiente aquático adjacente. Métodos: Solo, material
particulado em suspensão e amostras de peixes foram coletadas em um campo de
arroz no sul do Brasil. Um sistema de vapor frio acoplado a um espectrofotômetro de
absorção atômica (GBC 932) foi usado para as determinações de Hg total nas amostras.
Resultados: O solo da lavoura de arroz apresentou concentração de Hg 2 vezes mais
elevada (média de 31 ng g–1), em comparação com a área controle (não cultivado). A
concentração de Hg no material particulado em suspensão dos canais de irrigação do
arroz (média de 232,5 ± 44,2 ng g–1) é 1,5 vezes mais elevada do que na área controle.
Os espécimes de peixes Astyanax sp analisados na área de cultivo mostraram concentração
de Hg 4 vezes maior e, significativamente diferentes da área controle. A concentração
média de Hg em peixes foi: 51,7 ± 19,5 ng g–1 em Astyanax sp e 156,8 ± 44,0 ng g–1 em
Corydoras paleatus. Conclusões: Considerando a regressão linear e o teste de hipótese de
192 Kütter, V.T. et al. Acta Limnologica Brasiliensia
Since 1908, the rice production is cultivated
in paddies in the Southern Brazil (Beskow, 1986).
Nowadays, Brazil is the ninth largest rice producer
in the world (Wong, 2004). The Rio Grande do
Sul State produces 68% of the national production
(CONAB, 2013). This region is part of the Pampa
Biome that covers about 63% of Rio Grande do Sul
State (IBAMA, 2004).
The Pampa has a great biodiversity including
endemic species, some of them endangered or
at risk of extinction (Marques et al., 2002).
Notwithstanding the considerable number of
endangered species, this region has received little
attention in terms of environmental research
(Bencke, 2010).
The paddy has a considerable impact on aquatic
animals, since many species that inhabit nearest
areas, swamps and lagoons, move to them after the
flood. Furthermore, this environment has great
ecological significance because it represents an
important feeding, resting and breeding area for
birds, including migratory species that comes from
North and South America’s (Dias & Burger, 2005).
Studies with fish demonstrated that this animal
group is a good indicator of environmental health
(Van der Oost et al, 2003; Raimundo et al., 2011).
In this group, the main Hg incorporation in
tissue occurs through feeding (Kidd et al., 1995;
Snodgrass et al., 2000). The MeHg is absorbed by
the gut and accumulated in tissues, where it can be
biomagnified because of the long half-life of this
compound (Lacerda & Malm, 2008). Therefore, as
predator fish are in the top of the food web, they
have the highest concentrations of this metal in
relation to species which are at the bottom.
Mirlean et al. (2005), who investigated Hg
levels in lakes near the paddy region in the Southern
Brazil, found that the main source of Hg in this area
is the atmospheric deposition. In this same study,
the authors have proposed the use of Astyanax sp as
a bioindicator of Hg contamination in studied area,
once these species have shown a good correlation
with Hg levels in the environment.
The genus Astyanax has been appointed by
several authors as an excellent biomonitor of aquatic
ecosystems, responses of countless biomarkers,
such as histopathological assays (Prado et al., 2011;
1. Introduction
Mercury (Hg) is considered a highly toxic metal
and has been used in the composition of pesticides
utilized in rice fields (Smart & Hill, 1968). In Brazil,
the use of pesticides containing Hg was banned in
the 70’s. Although the input of anthropogenic Hg
had been stopped at these sites after the banishment,
its effects persist in the environment and biota.
Studies on paddies in Japan have reported an
insignificant reduction of Hg soil contamination
over eight years of study (Nakagawa & Yumita,
1998). Furthermore, more recent studies in paddies
reported high concentration of methylmercury
(MeHg) in rice grains (Zhang et al., 2010a,b;
Zhao et al., 2010; Zhu et al., 2011; Peng et al.,
2012; Rothenberg et al., 2012; Li et al., 2013).
In Brazil, the study developed by Silva et al.
(2010) found Hg concentrations ranging from 2.2
to 4.4 ng g-1 in rice grains. Actually the large use of
fertilizers in the rice production can intensify the
methylation process in paddy fields due to bacteria
growth stimulation.
Amongst the three Hg forms, the organic
form MeHg is the most toxic to humans even in
low concentrations (Zahir et al., 2005). Although
Hg presents low concentration in water, it can be
potentially biomagnified, reaching very higher
concentrations in predatory fish, which can result
in an increased risk of developing health problems
when consumed by humans (NRC, 2000).
According to the report of the Committee on
the Toxicological Effects of Methylmercury in the
United States, the major source of human exposure
to MeHg is the consumption of contaminated
fish (NRC, 2000). Innumerous studies have been
demonstrated that more than 80% of the total
Hg present in fish tissue is in the form of MeHg
(Silva et al., 2011; Kannan et al., 1998).
The characteristics of paddy are favorable to the
process of Hg conversion into MeHg by anaerobic
microorganisms (Rothenberg & Feng, 2012).
Moreover, some studies have demonstrated that this
process can also occur in the intestine of some fish
species when they are fed with inorganic mercury
(Rudd et al., 1980; Leaner & Mason, 2002).
de Man Whitney para a concentração de Hg em tecidos de peixes da lavoura de arroz,
sugere que Astyanax sp. pode ser uma bom biomonitor de contaminação Hg, enquanto
Corydoras paleatus é um biomonitor potencial. No entanto, mais estudos com Corydoras
são necessárias, a fim de agregar consistência a este estudo
