RESUMO
Mercury and more specifically methylmercury have been reported as hazardous environmental pollutants able to accumulate along the aquatic food chain with severe risk for animal and human health. Adult male zebrafish (Danio rerio) were distributed in two groups: a control group (fed with uncontaminated food) and a MeHg-contaminated group (fed with food containing 13.5µgHgg(-1) (dry wt)). Five fish per condition were removed after 7, 21 and 63 days. Bioaccumulation of mercury was determined and muscle samples from control and exposed groups were fixed for histological and ultrastructural studies. In contaminated muscles were observed a decrease of the inter-bundle surface, mitochondria with variable shapes, sizes and cristae disorganization, also decreasing the surface area and inter-bundle surfaces. Indeed, damage in the endoplasmic reticulum cisternae was observed. For statistical evaluation the damages in mitochondria was quantified by image. According to the current results, methylmercury affects the structure of fibre cells of D. rerio after trophic and low dose exposure.
RESUMO
Within a multidisciplinary research programme set up in French Guiana (Amazonian basin), twelve fish species from six food regimes were collected from the upper part of the Maroni River in order to analyze mercury (Hg) distribution in six organs (gills, liver, kidneys, skeletal muscle, stomach, and intestine) and to look for a relationship between Hg organotropism and food regimes. As many studies have shown, mercury biomagnification leads to extremely marked differences in muscle accumulation levels: the average ratio between extreme concentrations measured in piscivorous and herbivorous species was almost 500. A first principal component analysis on primary Hg concentration variables showed that biomagnification had a marked effect, masking differences between Hg distribution in the organs according to fish species and their food regimes. In order to avoid this, we determined ratios between Hg concentrations measured in the different organs and in the skeletal muscle, considered as the reference tissue for biomagnification effects. A new principal component analysis using these normalized values, in conjunction with a Ward's hierarchical clustering method, revealed that there is a link between Hg organotropism and the food regimes, with comparatively high [Hg]gills/[Hg]muscle ratios for the herbivorous species; high [Hg]intestine-liver-kidneys/[Hg]muscle ratios for the benthivorous and periphytophagous species, and, in contrast, ratios of less than 1 in the different organs for the piscivorous and omnivorous species. Our determinations of methylmercury (MMHg) percentages in the food consumed by the fish (aquatic macrophytes, terrestrial material from the river banks, biofilms, benthic invertebrates, fish muscle tissues), according to the different food regimes (herbivorous, periphytophagous, benthivorous, omnivorous, carnivorous, piscivorous), showed that this criterion can account for the differences in Hg distribution in the fish organs. For instance, the periphytophagous and benthivorous fish species ingest biofilms and small benthic invertebrates with quite low MMHg burdens (18% and 35 to 52% of Hgtotal, respectively). The highest [Hg]organs/[Hg]muscle ratios were observed for the liver and kidneys, the two principal target organs for inorganic Hg in fish. On the other hand, the piscivorous species ingest a large amount of fish of varying size, with high MMHg percentages in their muscle tissue (nearly 80%); Hg organotropism is characterized by high MMHg concentrations in the skeletal muscle and comparatively low [Hg]organs/[Hg]muscle ratios.