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The aim of present study was to evaluate the Hg concentration in twospecies 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 Hgcontamination to adjacent aquatic environment. Methods: Soil, suspended particulatematter and fish samples were sampled in a paddy field in South Brazil. A cold vaporsystem, coupled with a GBC 932 atomic absorption spectrophotometer was used for totalHg determinations in samples. Results: The paddy soil shows Hg concentration 2-foldhigher (mean 31 ng g-1) in comparison to background areas (not cultivated). Suspendedparticle matter Hg concentration in paddy channels (mean 232.5 ± 44.2 ng g–1) are 1.5times higher than the regional background. The analyzed fish specimens Astyanax sp inpaddy showed Hg concentration 4-fold higher and significant different to backgroundarea. 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 andMan whitney test hypothesis to Hg concentration in fish tissue from paddy suggests thatAstyanax sp. can be a good biomonitor of Hg contamination, whereas Corydoras paleatusis a potential biomonitor. However, more studies with Corydoras are necessary in orderto aggregate consistency to this hypothesisO objetivo do presente estudo foi avaliar a concentração deHg em duas espécies de peixes (Astyanax sp e Corydoras paleatus) e seu uso potencialcomo biomonitor, a fim de saber se o uso de pesticidas e fertilizantes na lavoura podelevar a contaminação por Hg ao ambiente aquático adjacente. Métodos: Solo, materialparticulado em suspensão e amostras de peixes foram coletadas em um campo dearroz no sul do Brasil. Um sistema de vapor frio acoplado a um espectrofotômetro deabsorção 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 maiselevada (média de 31 ng g–1), em comparação com a área controle (não cultivado). Aconcentração de Hg no material particulado em suspensão dos canais de irrigação doarroz (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 concentraçãode Hg 4 vezes maior e, significativamente diferentes da área controle. A concentraçãomédia de Hg em peixes foi: 51,7 ± 19,5 ng g–1 em Astyanax sp e 156,8 ± 44,0 ng g–1 emCorydoras paleatus. Conclusões: Considerando a regressão linear e o teste de hipótese de 192 Kütter, V.T. et al. Acta Limnologica BrasiliensiaSince 1908, the rice production is cultivatedin paddies in the Southern Brazil (Beskow, 1986).Nowadays, Brazil is the ninth largest rice producerin the world (Wong, 2004). The Rio Grande doSul State produces 68% of the national production(CONAB, 2013). This region is part of the PampaBiome that covers about 63% of Rio Grande do SulState (IBAMA, 2004).The Pampa has a great biodiversity includingendemic species, some of them endangered orat risk of extinction (Marques  et  al., 2002).Notwithstanding the considerable number ofendangered species, this region has received littleattention in terms of environmental research(Bencke, 2010).The paddy has a considerable impact on aquaticanimals, since many species that inhabit nearestareas, swamps and lagoons, move to them after theflood. Furthermore, this environment has greatecological significance because it represents animportant feeding, resting and breeding area forbirds, including migratory species that comes fromNorth and South America’s (Dias & Burger, 2005).Studies with fish demonstrated that this animalgroup is a good indicator of environmental health(Van der Oost et al, 2003; Raimundo et al., 2011).In this group, the main Hg incorporation intissue occurs through feeding (Kidd et al., 1995;Snodgrass et al., 2000). The MeHg is absorbed bythe gut and accumulated in tissues, where it can bebiomagnified because of the long half-life of thiscompound (Lacerda & Malm, 2008). Therefore, aspredator fish are in the top of the food web, theyhave the highest concentrations of this metal inrelation to species which are at the bottom.Mirlean  et  al. (2005), who investigated Hglevels in lakes near the paddy region in the SouthernBrazil, found that the main source of Hg in this areais the atmospheric deposition. In this same study,the authors have proposed the use of Astyanax sp asa bioindicator of Hg contamination in studied area,once these species have shown a good correlationwith Hg levels in the environment.The genus Astyanax has been appointed byseveral authors as an excellent biomonitor of aquaticecosystems, responses of countless biomarkers,such as histopathological assays (Prado et al., 2011;1. IntroductionMercury (Hg) is considered a highly toxic metaland has been used in the composition of pesticidesutilized in rice fields (Smart & Hill, 1968). In Brazil,the use of pesticides containing Hg was banned inthe 70’s. Although the input of anthropogenic Hghad been stopped at these sites after the banishment,its effects persist in the environment and biota.Studies on paddies in Japan have reported aninsignificant reduction of Hg soil contaminationover eight years of study (Nakagawa & Yumita,1998). Furthermore, more recent studies in paddiesreported 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 2.2to 4.4 ng g-1 in rice grains. Actually the large use offertilizers in the rice production can intensify themethylation process in paddy fields due to bacteriagrowth stimulation.Amongst the three Hg forms, the organicform MeHg is the most toxic to humans even inlow concentrations (Zahir et al., 2005). AlthoughHg presents low concentration in water, it can bepotentially biomagnified, reaching very higherconcentrations in predatory fish, which can resultin an increased risk of developing health problemswhen consumed by humans (NRC, 2000).According to the report of the Committee onthe Toxicological Effects of Methylmercury in theUnited States, the major source of human exposureto MeHg is the consumption of contaminatedfish (NRC, 2000). Innumerous studies have beendemonstrated that more than 80% of the totalHg 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 theprocess of Hg conversion into MeHg by anaerobicmicroorganisms (Rothenberg & Feng, 2012).Moreover, some studies have demonstrated that thisprocess can also occur in the intestine of some fishspecies 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, enquantoCorydoras paleatus é um biomonitor potencial. No entanto, mais estudos com Corydorassão necessárias, a fim de agregar consistência a este estud

Mercury bioaccumulation in fishes of a paddy field in Southern of Brazil