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The persistent organic pollutants (POPs) are some of the most closely monitored compounds on Earth, due to the combination of their long-life, bioaccumulation and adverse health risks to animals and humans. Global monitoring initiatives have been set up by the UN Environment Programme to provide comparable data for estimating the spread of POPs and to allow better estimates of the POPs present in particular regions. Of the 12 classes of compounds listed in the Stockholm Convention, the polychlorinated biphenyls (PCBs) are one of the most complex. They constitute a group of 209 compounds, depending on the number and position of the chlorine atoms substituted in one or both of the phenyl rings. None of them are natural compounds. Once in the environment, PCBs are absorbed by living organisms and rise up the food chain, accumulating as they go in the fatty tissue in particular. Creatures near the top of the food chain, like birds, polar bears and humans, are especially susceptible due to the increasing concentrations. Toxicity depends on the particular PCB, but several have been designated probable human carcinogens and others present different health risks. In the marine environment, seabirds are regarded as a guide to the degree of PCB pollution, because of their high position in that specific food chain. However, monitoring PCB levels in birds is problematical due to the practical and technical difficulties in collecting samples and the ethical dilemma in testing: for fatty tissues, the birds need to be caught and killed first. Most testing to date has been passive, relying on seabirds that have been found dead, so planning systematic geographical studies over many areas is almost impossible. In order to circumvent these problems, a non-lethal and non-invasive method of sample collection has been formulated by scientists in Japan. They noticed several relatively old literature citations referring to PCB measurement in oil from the preen glands of seabirds. These glands are found at the base of the tail feathers and secrete oil to waterproof the feathers and protect the birds from parasites. The studies examined a limited set of birds, so the broad applicability of the method to seabirds in general had not been tested. Hideshige Takada and colleagues from Hokkaido University, Tokyo University of Agriculture and Technology and the Hokkaido National Fisheries Research Institute extended the study to 30 seabirds covering 10 genera and 13 species. All of the birds had been caught accidentally in drift nets and long-lines in the North Pacific near Japan or in the Bering Sea, or had been killed in traffic accidents. The glands were sampled with a paper wipe and abdominal adipose tissue was removed for comparison. PCBs in the oil were obtained by pressurised liquid extraction and those in the tissue were removed by liquid extraction. All extracts were subjected to extensive chromatographic clean up and analysed by gas chromatography with electron capture detection. The team concentrated on 20 PCB congeners, identified by their IUPAC numbers (8/5, 28, 44, 52, 90/101, 110/77, 118, 128, 132/153, 138/160, 170/190, 180, 187, 206). All preen gland oils were found to contain PCBs, ranging from 9-4384 ng/g lipid, with a geometric mean of 404 ng/g lipid. The corresponding values in adipose tissue were 43-10,307 ng/g. These values were in the same range as other reported values for PCBs in preen gland oil. The oils were richer in the lower-chlorinated PCB congeners than the tissue, probably due to the lower residence time in the oil before secretion, preventing metabolic transformation. The relatively short residence time following absorption means that the values will represent recent exposure to PCBs. The researchers established a weak but significant correlation between the total PCB levels in the preen oil and adipose tissue, which was improved when metabolic losses were taken into account. So, the oil values can be used to estimate the adipose tissue burden within seabirds, within one order of magnitude. This study examined species of auklet, puffin, murrelet, murre, albatross, fulmar, shearwater and petrel, so represents a relatively broad sample. Since the preen gland oil can be sampled non-invasively and non-destructively, simply by wiping the gland, the method will enable strategic studies to be organised on a global basis, targeting particular regions and birds. As the research team say, it could be combined with ecological investigations. In addition, with electronic tagging, it raises the possibility of repeated sampling of the same bird to enable PCB absorption trends to be followed on an individual basis. At the same time, it facilitates studies of the global distribution and transport of PCBs and their effects on the ecology and behaviour of seabirds. Related Links:
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