Polonium 210 Po , uranium ( 234 U , 238 U ) and plutonium ( 238 Pu , 239 + 240 Pu ) bioaccumulation in marine birds

The aim of this work was the determination of Po, U, U, Pu and Pu concentration in marine birds which permanently or temporally live in the southern Baltic Sea coast. We chose 11 species of seabirds: three species permanently residing at southern Baltic Sea, four species of wintering birds and three species of migrating birds. The results show that analyzed radionuclides are non-uniformly distributed in the marine birds. The highest activities of Po were observed in feathers, muscles and liver. The highest uranium content was found in liver, rest of viscera and feathers, while plutonium in the digestion organs and feathers. Omnivore seabirds accumulated more polonium, plutonium than species that feed on fish, while herbivore seabirds accumulated more uranium than carnivore.


Introduction
The estimation of the size of contamination caused by alpha radioactive elements in the natural environment and their effects on living organisms is one of the most important issues of the radiochemical and radiological protection.Among alpha radioactive elements present in the environment, polonium plays an important role because 210 Po belongs to the most radiotoxic nuclides to human beings.The most important natural source of 210 Po in the environment is uranium decay series starting from 238 U. Polonium is strongly accumulated in the marine biota and for this reason it is an important source of radiation dose in the body of marine animals (Skwarzec, 1995).The intensive studies on the occurrence and distribution of 210 Po in the ecosystem of the southern Baltic help to recognize mechanisms and circulation of polonium in the environment.Uranium occurs naturally in the Earth's crust and occurs in much higher concentrations, along with thorium and rare earth element in the area where monazite sand prevails (Skwarzec, 1995).The average concentration of uranium in the Earth's crust is 410 -4 %.The isotope 238 U is the parent nuclide of the radioactive decay uranium-radium series.Uranium is relatively highly toxic to human, both chemically and radiologically (its progeny are highly radioactive).Various components of uranium can penetrate the blood from alveolus pockets in the lungs or through the gastrointestinal tract.The presence of uranium in the body can cause damage to the kidney, leading to nephritis (Tutu et al., 2005).Most of uranium in the environment is located in terrigenic materials (Skwarzec et al., 2006).Natural uranium concentration in rivers varies linearly with salinity (Skwarzec, 1995).Man-made plutonium is widespread all over the world, takes part in geochemical circulation and accumulates in the food chain.The main source of plutonium in Poland and the Baltic Sea, before the Chernobyl accident, was global fallout from nuclear weapons testing.Other sources of plutonium, e.g.releases from the spent fuel facilities at Sellafield (UK) and Cap de la Hague (France), are less important (Skwarzec, 1995;Strumińska-Parulska and Skwarzec, 2010).Plutonium can be accumulated in the marine biota and for this reason it is an important source of radiation dose in the body of marine animals (Skwarzec,1995).The total 239+240 Pu amount in the Baltic Sea was estimated at 15.2-24.2TBq and over 90% is deposited in sediments, about 0.2 TBq exists in water and only a few GBq is accumulated in biota (Salo et al., 1986) (Tomiałojć and Stawarczyk, 2003).Most of them are double-environment animals.That is why they are an important part of the ecosystems.Seabirds are a very important element of the trophic chain of marine ecosystem.Particularly the birds' feathers are often used as a bioindicator of metal contamination of marine and air environment (Burger and Gochfeld, 1997).Knowledge on the polonium, uranium and plutonium distribution in birds is very poor.From over 9000 species of birds in the world, 438 species have been registered in Poland, of which 230 birds live in the Polish area of the Baltic Sea (Tomiałojć and Stawarczyk, 2003).The aim of this work was determination of 210 Po, 234 U, 238 U, 238 Pu and 239+240 Pu concentration in marine birds from the southern Baltic Sea coast as well as recognition of their accumulation in different organs and tissues analyzed birds.Moreover, the studies can help to recognize the radionuclides sources in marine birds as well as their connection with their diet and living habits.

Material and Methods
Among bird species registered in the Polish area of the southern Baltic Sea, there are three main groups: sea birds which permanently reside, principally in Gdansk Bay and Puck Bay, wintering birds and migratory birds.

Po
The results of 210 Po concentration in tissues and organs of marine birds from the southern Baltic Sea are shown in Tab. 1.The data show that 210 Po is non-uniformly distributed in tissues and organs of the seabirds.The highest 210 Po concentrations were mostly in liver and ranged from 0.16 Bq kg -1 ww in tufted duck to 18.90 Bq kg -1 ww in long-tailed duck.The high 210 Po concentrations were also observed in feathers and ranged from 0.47 Bq kg -1 ww in tufted duck to 5.70 Bq kg -1 ww in great cormorant.Among the analyzed species of sea birds, the highest 210 Po concentration in whole organism was measured in long-tailed duck at 3.54 Bq kg -1 ww (Tab.1).
The 210 Po concentration in tissues and organs of this bird was much higher than in the rest of the analyzed species of sea birds.The analysis of diet and feeding habit showed that it is a very important aspect of 210 Po accumulation in tissues and organs of sea birds from the southern Baltic Sea.The 210 Po concentration was higher in omnivore marine birds as as long-tailed duck, velvet scoter, black guillemot and eurasian coot feeding on crustaceans, mollusks, fish, plants and algae.The 210 Po concentration was lower in tissues and organs of predatory fish-feeding seabirds as great cormorant and common guillemot or herbivore birds as tufted duck.The results of our studies show that the 210 Po concentration was higher in wintering sea birds such as long-tailed duck, black guillemot and velvet scoter.The differences in accumulation of trace elements in birds are also connected with diet and place of residence (Skwarzec and Fabisiak, 2007).

U and 238 U
The results of 234 U and 238 U concentration as well as total uranium concentration in organs and tissues of analyzed marine birds were presented in Table 1.The obtained results indicated that uranium is non-uniformly distributed in tissues and organs of analyzed marine birds.The highest values of 234 U and 238 U were measured in rest of viscera: from 46.6 and 48.3 mBq kg -1 ww in razorbill to 919 and 921 mBq kg -1 ww in tufted duck and in feathers as well: from 68.7 and 76.7 mBq kg -1 ww in eurasian coot to 341 and 294 mBq kg -1 ww in great cormorant.Further studies showed the maximum uranium concentrations were found in herbivorous as eurasian coot and tufted duck while lower were estimated for predatory as razorbill and great cormorant.(Tab.1).Food is a very important source of uranium in marine birds.The uranium concentration was higher for visitant birds in region of the Gulf of Gdańsk in period from October to April (tufted duck and eurasian coot).On account of birds moulting, we observed higher uranium concentration for species, which permanently live on the land (great cormorant, common eider, eurasian coot).
The obtained results are in agreement to values reported for marine organisms in southern Baltic Sea (Skwarzec, 1995).Bioaccumulation of uranium by marine birds is slight, because his radionuclide is quickly removed from organism.

34004-p.2 ICHMET 2012
Tab.1 Polonium 210 Po, uranium 234 U and 238 U and plutonium 238 Pu and 239+240 Pu concentrations in organs and tissues of analyzed seabirds (Skwarzec and Fabisiak, 2007;Boryło et al., 2010;Strumińska-Parulska et al.,  These birds had also the highest 239+240 Pu concentrations in feathers, viscera and skeleton.Permanently residing in the southern Baltic Sea seabirds were characterized by the highest plutonium concentrations in liver (great cormorant, tufted duck).Detailed diet analysis and organs of 239+240 Pu accumulation allowed for statement that both inhalation and food play a significant role in its supply.Bird which eat fish (great cormorant, common guillemot) are characterized by much lower 239+240 Pu concentrations in analyzed organs and tissues similarly as their food -fish (Skwarzec, 1995).239+240 Pu concentrations in feathers, skeleton and viscera were lower within only fish-eating birds (great cormorant, common guillemot) in comparison to birds which feed with bivalves, crustaceans or phytobenthos (eurasian coot, razorbill, black guillemot, red-throated diver).These results confirm previous research that fish-eating birds are characterized by lower concentrations of radionuclides in comparison to omnivores (higher concentrations) or plant-and larvaeeating birds (the highest concentrations).
All results of 238 Pu and 239+240 Pu plutonium concentrations are presented in Table1.The obtained results indicated that the plutonium is non-uniformly distributed in organs and tissues of analyzed seabirds.