Subchronic effects of methylmercury on plasma and organ biochemistries in great egret nestlings

Abstract

In recent years, high concentrations of mercury have been found in wading birds in Florida, USA. Great egret (Ardea alba) chicks (2 weeks old) were dosed orally daily with the equivalent of 0, 0.5, or 5 microg/g Hg as methylmercury chloride in the diet for up to 12 weeks. Weakness of the legs or paralysis occurred in all high-dosed birds. Geometric mean blood Hg concentrations were 0.17, 10.3, and 78.5 microg/g (wet wt), respectively. Mercury concentrations for organs (microg/g wet wt), including brain (0.22, 3.4, and 35, respectively), liver (0.34, 15.1, 138, respectively), and kidney (0.28, 8.1, and 120, respectively), increased in a dose-dependent manner. Total glutathione (GSH) peroxidase activity was significantly lower in the plasma, brain, liver, and kidney of the high-dosed group. Plasma aspartate aminotransferase activity increased with mercury treatment, whereas lactate dehydrogenase activity decreased. Four other plasma chemistries were decreased significantly in the high-dosed group and included uric acid, total protein, albumin, and inorganic phosphorus. Lipid peroxidation increased in liver (low and high dose) and brain (high dose). Tissue changes in concentrations of reduced thiols included decreased total thiols and protein-bound thiols in liver, decreased protein-bound thiols in kidney, and increased GSH in kidney and brain. Activities of GSH S-transferase and oxidized glutathione reductase increased in liver. In kidney, GSH S-transferase and glucose-6-phosphate dehydrogenase activities increased with mercury dose. These findings, including apparent compensatory changes, are compared to other Hg studies where oxidative stress was reported in egrets, herons, and diving ducks in the field and mallards in the laboratory.

Oxidative stress response of Forster's terns (Sterna forsteri) and Caspian terns (Hydroprogne caspia) to mercury and selenium bioaccumulation in liver, kidney, and brain

“…Increased hepatic GSSG:GSH ratio was related to Hg in mallards, greater scaup, and double-crested cormorants. However, in two studies where birds were dosed with MeHg at various concentrations, hepatic GSH was not affected in common loons and increased only slightly in great egrets (Ardea alba) [34,35]. Pied flycatcher (Ficedula hypoleuca) nestlings exposed to lower Hg than the present study, in combination with other metals at contaminated field sites exhibited increased hepatic GSH [36].…”

“…Increased hepatic lipid peroxidation as TBARS related to Hg exposure has been reported in young black-crowned nightherons, young and adult double-crested cormorants, and great egret nestlings [11,34]. Other evidence of hepatotoxicity linked to Hg in birds includes increased activities of plasma enzymes in young snowy egrets and double-crested cormorants where elevated alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (AP), and lactic dehydrogenase (LDH) activities appeared to reflect hepatocellular disruption, as supported by histopathological findings that included increased vacuolar changes in hepatocytes as well as correlations of increased liver inflammation with blood and tissue Hg concentrations in snowy egrets [13].…”

Toxicity Reference Values and Tissue Residue Criteria for Protecting Avian Wildlife Exposed to Methylmercury in China

“…Adverse effects, related to immune function, were observed in individuals fed the lesser dose, whereas individuals fed the greater dose exhibited adverse effects on tissues related to immune and nerve functions (Spalding et al 2000b ) . In a study of the biochemical effects of MeHg (Hoffman et al 2005 ) , only activities of the enzyme aspartate aminotransferase (AST) in blood plasma, and thiobarbituric acid-reactive substances (TBARS) in liver of individuals fed the lesser dose were signi fi cantly greater than those of the control group. However, there were signi fi cant changes in activities of glutathione peroxidase (GSH-Px), aspartate aminotransferase (AST), lactate dehydrogenase, and in the concentrations of uric acid, total protein, and inorganic phosphorus in tissues of individuals fed the greater dose.…”

Blood oxidative stress and antioxidant defense profile of White Stork Ciconia ciconia chicks reflect the degree of environmental pollution

“…The mechanisms producing the harmful effects of oxidative stress are complex with different biomolecular mechanisms associated with ecotoxicological and ecological aspects (Koivula & Eeva 2010). Components of the antioxidant defense system have the widest scope and greatest potential for use as subcellular biomarkers of the contamination of birds with metals from the environment (Berglund et al 2007(Berglund et al , 2011Hoffman 2002;Hoffman et al 2005Hoffman et al , 2009Hoffman et al , 2011Kamiński et al 2009a;Kurhalyuk et al 2006a, b;Kenow et al 2008;Koivula et al 2011;Martinez-Haro et al 2011;Mateo et al 2003;Mateo & Hoffman 2001).…”

“…Antioxidants and their oxidation products are important indicators of oxidative stress induced by toxic chemicals from environment (Berglund et al 2007(Berglund et al , 2011Hoffman 2002;Hoffman et al 2005Hoffman et al , 2009Hoffman et al , 2011Kamiń-ski et al 2009a, b;Kurhalyuk et al 2006a, b;Kenow et al 2008;Koivula et al 2011;Martinez-Haro et al 2011;Mateo et al 2003;Mateo & Hoffman 2001).…”