Fishes of the Gulf of Maine

Metal levels in feathers of 12 species of seabirds from Midway Atoll in the northern Pacific Ocean

Anthropogenic input of mercury (Hg) into the environment has elevated risk to fish and wildlife, particularly in northeastern North America. Investigations into the transfer and fate of Hg have focused on inhabitants of freshwater aquatic ecosystems, as these are the habitats at greatest risk for methylmercury (MeHg) biomagnification. Deviating from such an approach, we documented MeHg availability in a terrestrial montane ecosystem using a suite of insectivorous passerines. Intensive and extensive sampling of Bicknell’s thrush (Catharus bicknelli) indicated significant heterogeneity in MeHg availability across 21 mountaintops in northeastern North America. Southern parts of the breeding range tended to be at greater risk than northern parts. Mean blood Hg concentrations for Bicknell’s thrush at 21 distinct breeding sites ranged from 0.08 to 0.38 ug/g (ww) and at seven Greater Antillean wintering sites ranged from 0.03 to 0.42 ug/g (ww). Overall concentrations were significantly greater in wintering than in breeding areas. Mercury exposure profiles for four passerine species on Mt. Mansfield, Vermont indicated greatest MeHg uptake in Bicknell’s thrush and yellow-rumped warbler (Dendroica coronata) and lowest in blackpoll warbler (Dendroica striata) and white-throated sparrow (Zonotrichia albicollis). The MeHg and total Hg ratio in blood in these four species was nearly 1:1. There was no correlation between blood and feather Hg concentrations in breeding Bicknell’s thrush, in part because of apparent retention of winter Hg body burdens, within-season variation of MeHg availability, and confounding factors such as influences from age. Adult thrushes had significantly higher concentrations of feather Hg than did young-of-the-year. Although individual patterns of inter-year feather Hg concentrations were disordered, some individuals exhibited bioaccumulation of MeHg. Female blood Hg concentrations were significantly lower than males’, in part because females have additional depurating mechanisms through eggs. Older male Bicknell’s thrushes that breed in New England are therefore likely at greatest risk. Mechanisms for Hg methylation in montane areas without standing water are not yet fully understood. However, recent studies indicate that MeHg is present in forest tree leaves and leaf detritus; saturated soils and other moist microhabitats may also contribute to MeHg availability. Our finding of a correlation between regional litterfall Hg flux patterns and Bicknell’s thrush blood Hg concentrations demonstrates on-site availability of MeHg. Further investigations into MeHg availability in montane environments are recommended to assess risk to insectivorous passerines, particularly the Bicknell’s thrush.

Mercury concentrations in Bicknell's thrush and other insectivorous passerines in Montane forests of northeastern North America.

Liver, muscle, kidney, and feather samples from nine species of seabirds were analyzed for total and organic (methyl) mercury (MM). Total mercury (TM) levels in liver showed great intra- and inter-species variations, with the concentrations varied from 306 μg/g (dry weight) in black-footed albatross (Diomedea nigripes) to 4.9 μg/g in arctic tern (Sterna paradisaea), while MM levels were less relatively variable. The order of MM concentrations in tissues of all the seabirds except oldsquaw (Clangula hyemalis) was as follows: liver > kidney > muscle. The mean percentage of MM in total was 35%, 36%, and 66% in liver, kidney, and muscle, respectively, for all the species. Statistically significant negative correlations were found between the proportion of MM to TM and concentrations of TM in the liver and muscle of black-footed albatross and in the liver of laysan albatross. Furthermore, the percentage of MM decreased with an increase in TM concentrations in the liver, muscle, and kidney of all the species. Black-footed albatross had the highest concentration and burden of mercury in the liver, wherein more than 70% of the TM occurred as inorganic mercury. On the other hand, the mercury burdens in feathers were less than 10% of the body burdens, indicating that excretion of mercury by moulting is negligible. The results suggest that some seabirds are capable of demethylating MM in the tissues (mainly in liver), and store mercury as an immobilizable inorganic form in the liver. It is noteworthy that the species with a high degree of demethylation capacity and slow moulting pattern showed low mercury burdens in feathers.

Mercury levels and its chemical form in tissues and organs of seabirds

Food chain differences affect heavy metals in bird eggs in Barnegat Bay, New Jersey.

We analyzed mercury levels in shrimp (Palaemonetes sp.), Blue Crabs (Callinectes sp.), fish (Tarpon Megalops atlantica and Tilapia Tilapia mossambica), lizards (Ameiva exsul), Cattle Egret (Bubulcus ibis) and Moorhen (Gallinula chloropus) in three estuaries in Puerto Rico in 1988. There were no quantifiable concentrations greater than the method detection limit of mercury in shrimp, crabs and lizards from any site. Mercury levels were also below detection limits in Tilapia, except for specimens collected at Frontera Creek, allegedly contaminated with mercury. However, mercury levels ranged from 92–238 μg/kg (wet weight) in Tarpon, a predaceous fish that feeds on smaller fish. Few of the birds had detectable levels of mercury. Our results indicate relatively low concentrations of mercury in biota collected in all of the three estuaries at most trophic levels, although 10 of 12 Tarpon fillet samples from Frontera had detectable mercury compared to 3 of 12 fillet samples for the other two lagoons.

D. Gochfeld

Papers

Mercury bioaccumulation in organisms from three Puerto Rican estuaries.