Potential risks of natural mercury levels to wild predator fish in an Amazon reservoir

Abstract

Mercury (Hg) is a toxic metal that bioaccumulates in aquatic organisms and along food chain. Many studies have reported the problem of mercury exposure in aquatic systems from Amazon basin, but very few have focused on the potential risks to wild fish. The present study reports the bioaccumulation of mercury and alterations in target organs of the predator fish Hoplias malabaricus (traíra) from Samuel reservoir, Amazon basin, Northern Brazil. About 18% of fish had mercury levels in muscle exceeding the safe limit for ingestion through food, established by WHO (0.5 μg Hg g(-1)). Fish were separated in two groups according to mercury bioaccumulation in liver (<0.2 μg Hg g(-1)-group I and >0.2 μg Hg g(-1)-group II) for biomarker comparisons. Catalase activity and number of macrophage centers were statistically higher in group II, confirming the potential of Hg to interfere with redox balance and to recruit defense cells to the liver. Conversely, erythrocyte nuclear alterations were less frequent in group II, indicating a more rigorous selection of erythrocytes or hormesis pattern of response. Glutathione S-transferase activity, lipid peroxidation, and histopathological analyses were not statistically different in the liver and gills of both groups. Comparison of lipid peroxidation levels of these fish with others captured in Southern Brazil during another study and the high incidence of morphological alterations in the liver and gills suggest that the bioaccumulation of mercury during continuous exposure is posing potential risks to the species.

Lack of Information Hides the Impact of Human Activities in Estuarine Fish From Southern of Brazil

“…According to Lease et al, (2003) the thin lamellar epithelium in gills is adapted for gas and ions exchange, and the alterations as described in the current study may affect the physiological role of gills corroborating the discussion above (Lease et al, 2003). The hyperplasia of secondary lamellae is an increase in cell number followed by lamellae fusion due to long-term exposure to chemicals (Bernet et al, 1999, Poleksic et al, 1994Brito et al, 2012;Silva et al, 2012). This kind of lesion is the most important obstruction for gas diffusion and impairment for osmorregulation (Pacheco et al, 2002).…”

“…Additionally the observed severity of lesions in gills revealed the chronic exposure to pollutants in both studied sites, leading to potential physiological disturbs to the species. These findings were recently described by our group to other species of Brazilian tropical species naturally exposed to pollutants (Brito et al, 2012;Oliveira Ribeiro et al, 2005;Osório et al, 2014;Rabitto et al, 2011;Silva et al, 2012). According to the authors the histopathological findings investigated in tissues as gills are among the most efficient to evaluate the acute or chronic exposure and fish health.…”

“…Necrosis represents a permanent damage in liver and is related with organ failure after long-term of exposure, and have been described as of high ecological importance (Bussolaro et al, 2012;Miranda et al, 2008;Osório et al, 2014;Rabitto et al, 2005). In addition, necrosis is a validated endpoint of effect due to multiple pollutants exposure of fish (Oliveira Ribeiro et al, 2002;Rabitto et al, 2011;Silva et al, 2012).…”

Ultrastructural effects on gill tissues induced in red tilapia Oreochromis sp. by a waterborne lead exposure

“…Gills are sensitive subjects for identifying under the effect of heavy metals on it by various histopathological alterations including hypertrophy and hyperplasia of epithelial cells, lamellar fusion, hyper secretion of mucous, and lamellar aneurysm (da Silva et al, 2012, dos Santos et al, 2012, Pereira et al, 2013).…”

The mobilization of hazardous elements after a tropical storm event in a polluted estuary

“…The Tubarão estuary (Santa Catarina, Brazil) is 120 km long, with a water flow that increases toward the estuary and a drainage area of 4728 km 2 , it receives contributions from seven principal freshwater inputs: the Bonito, Rocinha, Orotoria, Capivaras, Braco do Norte, Palmeiras, and Capivari rivers (Silva et al, 2012;Prefeitura de Lauro Muller, 2014).…”