Intensity of parasitic nematodes increases with organochlorine levels in the glaucous gull

1. Organochlorines probably suppress immune functions in birds and mammals, but few field assessments are available. If establishment and/or survival of parasites is limited by host immunity, we would expect increased parasite intensities in animals with high organochlorine burdens, such as the glaucous gull Larus hyperboreus. 2. We collected 40 adult glaucous gulls on Bear Island in the western Barents Sea. Concentrations of nine selected polychlorinated biphenyls (PCB; 28, 52, 99, 101, 118, 138, 153, 170 and 180) and five chlorinated pesticides (hexachlorobenzene, oxychlordane, DDE, DDT and Mirex) were measured in the liver. The abundance of 12 species of intestinal helminths, including one trematode, six cestodes, four nematodes and one acanthocephalan, was determined. 3. After controlling for nutritional condition, no single parasite species was significantly associated with concentrations of PCB or chlorinated pesticides. However, the intensity of all nematodes grouped together was positively correlated with 10 of the 14 organochlorine concentrations measured. The strongest correlations were with p,p' -DDT, Mirex, Sigma 9PCB, and PCB congeners 28, 118, 153, 138, 170 and 180. 4. Although correlative and collected in the absence of immunological data, these data do not refute the hypothesis that organochlorines might affect avian immune function.