Marine associated avifauna (seabirds) are exposed to wide ranges of environmental contaminants due to spending a large portion of their time in the aquatic environment. Vectors of exposure to metal pollution include external contact, by inhalation, and most generally by ingestion of food and incidental seawater. Seabirds are often considered marine ecosystem bioindicators due to their high trophic level, long lives, and wide geographic ranges. All seabirds are not equally vulnerable to contaminants due to their generalist diets accompanied with varying abilities to excrete, metabolize, or sequester xenobiotics (foreign chemical substances). We examined the concentration of metals in the kidney, liver, breast muscle, and feathers of seven species of adult seabirds commonly found in South Florida: brown pelican Pelecanus occidentalis (n=15), northern gannet Morus bassanus (n=15), double-crested cormorant Phalacrocorax auritus (n=15), royal tern Thalasseus maximus (n=18), osprey Pandion haliaetus (n=15), herring gull Larus argentatus (n=8), and laughing gull Leucophaeus atricilla (n=16). Specimens were collected from four wildlife rehabilitation centers after the bird has died due to trauma or illness; specimens were frozen at death at the respective centers and dissected in the lab. Total mercury analysis used a Direct Mercury analyzer (DMA-80).
Mercury is a highly toxic nonessential heavy metal that is emitted into the atmosphere by both natural and anthropogenic sources. Total mercury concentrations are thought to be equivalent to methylated mercury in tissues of organisms. Preliminary results were highly variable between species, individuals, and tissue types. Total mercury in the breast muscle, kidney, liver, and feathers ranged from 0.559 to 9.57 µg/g (dry wt), 2.06 to 12.16 µg/g (dry wt), 2.18 to 42.67 µg/g (dry wt), and 1.57 to 11.93 µg/g (dry wt), respectively. In the liver and kidney, values of methylmercury between 20 and 30 µg/g (wet wt) are associated with morbidity and mortality effects in terrestrial bird species. In feathers, total mercury concentrations of 5 µg/g (dry wt) are similarly associated with sublethal systemic and reproductive problems. Royal terns had the highest total mercury in three tissues whereas both gull species had the lowest values in all tissues. Additionally, cormorants and royal tern feathers had total mercury levels above the 5 µg/g threshold. Further assessment will help confirm whether seabird species in South Florida face a significant threat from metal pollution. Variability in metal concentrations between species and tissue types will be discussed in conjunction with concurrent stable isotope analyses in the context of trophic relationships.