Mercury in Feathers and Blood of Gulls from the Southern Baltic Coast, Poland.

Gulls were assessed as sentinels of contamination in the coastal zone of the Southern Baltic, research material being obtained from dead birds collected on Polish beaches and near fishing ports in 2009-2012. In feathers and blood of four gull species: herring gull (), common gull (), black-headed gull (s), and great black-backed gull (), concentration of total mercury (Hg) was assayed, taking into account the type of feathers, sex, and age. Stable isotopes (δN, δC) were used as tracers of trophic position in the food web. In the study, feathers and blood were compared as non-invasive indicators of alimentary exposure introducing mercury into the system. In order to do that, the correlations between mercury concentrations in the blood, feathers, and the birds' internal tissues were examined. The strongest relations were observed in the liver for each species  = 0.94,  = 0.001;  = 0.89,  = 0.001;  = 0.53,  = 0.001;  = 0.78,  = 0.001. While no correlation was found with feathers, only developing feathers of juvenile herring gulls were found to be a good indicator immediate of exposure through food ( = 0.71,  = 0.001;  = 0.73,  = 0.001;  = 0.89,  = 0.001;  = 0.86,  = 0.001;  = 0.83,  = 0.001). Additionally, based on studies of herring gull primary feathers, decrease of mercury concentration in the diet of birds over the last two decades is also discussed.