title: 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.
authors.affiliation: US Geological Survey, Patuxent Wildlife Research Center, Beltsville Laboratory, BARC-E, Maryland 20705, USA. david_hoffman@usgs.gov
authors.forename: David J
authors.initials: DJ
authors.lastname: Hoffman
authors.forename: Marilyn G
authors.initials: MG
authors.lastname: Spalding
authors.forename: Peter C
authors.initials: PC
authors.lastname: Frederick
mesh_terms: D000821:Animal Feed; D000818:Animals; D001219:Aspartate Aminotransferases / Q000097:blood; D001717:Birds; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000378:metabolism; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D015227:Lipid Peroxidation; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008767:Methylmercury Compounds / Q000097:blood / Q000633:toxicity*; D018384:Oxidative Stress / Q000187:drug effects*; D010758:Phosphorus / Q000378:metabolism; D012709:Serum Albumin / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D008767:Methylmercury Compounds; D012709:Serum Albumin; D013438:Sulfhydryl Compounds; D014874:Water Pollutants, Chemical; D010758:Phosphorus; D005979:Glutathione Peroxidase; D001219:Aspartate Aminotransferases; C004925:methylmercuric chloride