MERCURY ON FISH -- SOURCES AND CONTAMINATION.

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.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

Mercury distribution in different tissues and trophic levels of fish from a tropical reservoir, Brazil

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. © 2009 Sociedade Brasileira de Ictiologia