Concentrations of organic (OrgHg) and inorganic mercury (InorgHg) were assessed in different fish tissues (liver, muscle, kidney, gut and gonads) and trophic levels collected in an impacted tropical reservoir in southeastern Brazil. Organic mercury concentrations in muscle were remarkably higher in the carnivorous species Hoplias malabaricus and Oligosarcus hepsetus. The ratios of OrgHg in relation to total mercury (%OrgHg) in muscle also varied according to the species trophic level: 93% for carnivores, 84% for omnivores, 73% for algivores/planktivores and 58% for detritivores. The %OrgHg in the gut tissue of carnivores (78%) was much higher than that found in omnivores (30%), possibly reflecting a process of trophic biomagnification in the reservoir. On the other hand, the InorgHg concentrations in muscle decreased with the trophic level increase, suggesting that this form of mercury did not biomagnify through the food web. Gonads contained the least total mercury, and approximately all of this mercury was represented by the organic form (83 to 98%). The kidney and the liver of all fish species contained less than 50% OrgHg. We suggest that the low %OrgHg in the liver is related to different capacities or strategies of OrgHg detoxification by the fish.Concentrações de mercúrio orgânico (OrgHg) e inorgânico (InorgHg) foram avaliadas em diferentes tecidos e níveis tróficos de peixes (fígado, músculo, rim, trato digestivo e gônadas) coletados em um reservatório tropical impactado, no sudeste do Brasil. Concentrações de OrgHg no músculo foram notavelmente maiores em carnívoros (Hoplias malabaricus e Oligosarcus hepsetus).As porcentagens de OrgHg em relação ao mercúrio total (%OrgHg) no músculo também variaram de acordo com o nível trófico das espécies: 93% para os carnívoros, 84% para os onívoros, 73% para os algívoros/planctívoros e 58% para os peixes detritívoros. Além disso, a %OrgHg encontrada no trato digestivo dos peixes carnívoros (78%) foi substancialmente superior a encontrada nos onívoros (30%), possivelmente refletindo um processo de biomagnificação trófica no reservatório. Por outro lado, as concentrações de InorgHg no músculo diminuíram com o aumento do nível trófico, sugerindo que esta forma do mercúrio não biomagnificou ao longo da cadeia alimentar. As gônadas apresentaram as menores concentrações de mercúrio total e grande parte deste estava na forma orgânica (83 a 98%). Por outro lado, rins e fígado de todas as espécies de peixes apresentaram menos que 50% de OrgHg. Sugere-se que a baixa %OrgHg no fígado possa estar relacionada às diferentes capacidades ou estratégias de destoxificação do OrgHg nesses peixes.
Hydroelectric reservoirs can stratify, producing favorable conditions for mercury methylation in the hypolimnion. The methylmercury (MeHg) can be exported downstream, increasing its bioavailability below the dam. Our objective was to assess the mercury levels in plankton, suspended particulate matter (SPM) and fish collected upstream (UP) and downstream (DW) from the Reservatório de Samuel dam, an Amazonian reservoir that stratifies during half of the year. Mercury concentrations in both SPM and plankton were similar between the two sites, which could indicate there are no conditions favoring methylation at the moment of sampling (absence of stratification). Almost all mercury found in the muscle of fishes was in organic form, and differences of mercury levels between sites were dependent on the fishes trophic level. Herbivores showed similar mean organic mercury levels (UP = 117 lg g -1 ; DW = 120 lg g -1 ; n = 12), whereas omnivores (UP = 142 lg g -1 ; DW = 534 lg g -1 ; n = 27) and carnivores (UP = 545 lg g -1 ; DW = 1,366 lg g -1 ; n = 69) showed significantly higher values below the dam. The absence of a reservoir effect in herbivores is expected, since they feed on grassy vegetation, near the riverbanks, which is not much influenced by mercury in aquatic systems. On the other hand, the higher mercury levels below the dam observed for omnivores and carnivores suggest a possible influence of the reservoir since they feed on items that could be contaminated by MeHg exported from upstream. The results highlight the necessity of assessing areas downstream of reservoirs.
Human occupation of the Amazon region has recently increased, bringing deforestation for agriculture and open-cast mining, activities that cause environmental degradation and pollution. Families of new settlers in mining areas might have a diet less dependent on abundant fish and their children might also be impacted by exposures to mining environments. Therefore, there is compounded interest in assessing young children's nutritional status and neurobehavioral development with regard to family fish consumption. Anthropometric (z-scores, WHO standards) and neurologic [Gesell developmental scores (GDS)] development in 688 preschool children (1-59 months of age) was studied. Overall, the prevalence of malnutrition [i.e., moderate stunting (≤2 H/A-Z), underweight (≤2 W/A-Z), and wasting (≤2 W/H-Z) were respectively 0.3% (n = 2), 1.6% (n = 11), and 2.5% (n = 17). Children's mean hair Hg (HHg) concentration was 2.56 μg/g (SD = 1.67); only 14% of children had HHg concentrations lower than 1 μg/g and 1.7% had ≥5 μg/g. The biomarker of fish consumption was weakly but positively correlated with GDS (Spearman r = 0.080; p = 0.035). In the bivariate model, attained W/H-Z scores were not significantly correlated with GDS. A moderate level of GDS deficits (70-84%) was seen in 20% of children. There was significant correlation between family fish consumption and children's hair Hg (HHg) (Spearman r = 0.1756; p < 0.0001) but no significant correlation between children's HHg and W/H-Z scores. However, the multivariate model showed that breastfeeding, a fish consumption biomarker (HHg), maternal education, and child's age were statistically significant associated with specific domains (language and personal-social) of the Gesell scale. In this mining environment, family fish-eating did not affect children's linear growth, but it showed a positive influence (along with maternal variables) on neurodevelopment. Health hazards attendant on a high prevalence of moderate neurodevelopment delays coexisting with exposure to multiple neurotoxic substances merits further investigation in poor environmental settings of tin-mining areas.
RESUMO O mercúrio ocorre naturalmente no meio ambiente, entretanto, devido aos diversos usos que se faz do metal, suas concentrações vêm aumentando no meio e consequentemente na biota. Este metal pode ocorrer como mercúrio metálico ou como diferentes espécies químicas orgânicas ou inorgânicas, sendo a espécie química deste metal importante para a compreensão da sua toxicologia. A forma do Hg mais tóxica é o metilmercúrio, e as condições e sítios propícios para a metilação do metal vem sendo estudados. Além da concentração e forma do metal no meio, para o entendimento das concentrações na biota também é importante a avaliação de fatores como idade, tamanho, hábito alimentar, sexo entre outros. Os fatores físico-químicos do ambiente também devem ser considerados por influenciar na metilação do Hg e na absorção deste metal pela biota. O estudo com peixes é importante quando se trata de ecossistema aquático porque estes organismos apresentam diferentes hábitos alimentares e de vida e ocupam diferentes nichos. Além disto, quando se trata de contaminação humana, peixes são o alimento mais contaminado por mercúrio que os homens consomem. Estudos sobre peixes cultivados em piscicultura vêm demonstrando que estes são menos contaminados do que os provenientes de ambientes naturais. No entanto, a ração fornecida a esses peixes pode representar uma importante fonte de contaminação e, portanto, deve ter um rígido controle. Palavras-chave: Mercúrio, peixe, aqüicultura, contaminação, ecossistema aquático. ABSTRACT MERCURY ON FISH-SOURCES AND CONTAMINATION. Mercury occurs naturally in the environment, however, due to the diverse array of its use, the concentrations have been increase in the environment and, consequently, in the biota. This metal can occur as metallic mercury or as different organic or inorganic chemical species, being these chemical classifications important criteria to the understanding of its toxicology. The most toxic mercury species is the methylmercury, and suitable conditions and sites for methylation have been studied. Besides the environmental concentrations and the chemical species, to understand the biota concentrations a wide range of factors are important to be assessed, as age, size, food habit, sex and others. The physic-chemic environmental factors must be considered because of their effects on the Hg methylation and biota absorption. Fish study is important if to deal with aquatic ecosystem because this organism presents different food and life habits and is engaged in different niches. Moreover, when deal with human contaminations, there are the most mercury contaminated food consumed. Studies on farmed fishes have showed these fishes less contaminated than those proceeding from natural environments. However, the supplied ration to those fishes can represent an important contamination source and, because of that, should have a strict control.
Recebido em 4/2/10; aceito em 7/10/10; publicado na web em 26/1/11 BIOCONCENTRATION AND BIOMAGNIFICATION OF METHYLMERCURY IN GUANABARA BAY, RIO DE JANEIRO.Methylmercury was determined in water and aquatic biota from Guanabara Bay. Trophic transfer of methylmercury was observed between trophic levels from prey (microplankton, mesoplankton and fish with different feeding habits) to top predator (pelagicdemersal fish). Top predator fish presented the highest methylmercury concentrations (320.3 ± 150.7 µg kg -1 dry wt.), whereas microplankton presented the lowest (8.9 ± 3.3 µg kg -1 dry wt.). The successive amplification of methylmercury concentrations and its bioconcentration factor with increasing trophic levels from base to top indicate that biomagnification may be occurring along the food web. Results suggest the importance of feeding habits and trophic level in the bioaccumulation of methylmercury by aquatic biota.Keywords: biotransference of methylmercury; water and organisms; trophic levels. INTRODUÇÃOExiste uma grande preocupação com relação ao aumento da poluição ambiental resultante do incremento do emprego intensivo e extensivo de produtos químicos, da liberação de substâncias potencialmente tóxicas, dos lançamentos de efluentes industriais e urbanos, bem como de seus efeitos para os ecossistemas e, consequentemente, para o homem. 1 Com o aumento das atividades industriais, agrícolas e mineradoras, bem como o crescimento populacional observados no último século, uma série de contaminantes (matéria orgânica, poluentes orgânicos e um grande número de compostos metálicos) vem sendo liberada para o meio ambiente, principalmente para a atmosfera e os ecossistemas aquáticos. 2 Os contaminantes de compostos metálicos presentes nos efluentes das atividades antrópicas apresentam pouca solubilidade na água resultando, então, em baixas concentrações, mesmo em locais próximos às suas emissões pontuais, via efluente. Entretanto, em ambientes estuarinos, os contaminantes metálicos estão preferencialmente associados ao material particulado em suspensão, que lhes serve de veículo para áreas mais distantes das suas fontes. 3 Dentre os diferentes metais que despertam interesse ambiental, presentes nos efluentes industriais e agrícolas e que, também, em diversas regiões apresentam concentrações naturais relativamente elevadas, encontra-se o mercúrio (Hg). A exposição ambiental ao Hg via cadeia alimentar, principalmente para consumidores de nível trófico superior, incluindo-se o homem, é significativamente maior, uma vez que este metal apresenta alta toxicidade e capacidade de sofrer biomagnificação ao longo das cadeias tróficas. 4 Este metal na sua forma orgânica mais tóxica, metilmercúrio (MeHg), é bioacumulado em até um milhão de vezes ao longo da cadeia trófica aquática, desde a sua base (microorganismos e plâncton) até os organismos de topo (peixes predadores e mamíferos) através de adsorção na superfície corporal e, principalmente, pela ingestão de alimento (peixes, crustáceos e cefalópodes). 5 O metilmercúrio é um age...
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