© 1997 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Consequences of petrochemical ingestion and stress on the immune system of seabirds
Agricultural Experiment Station, University of California Davis, California, 95616, USA
Division of Rheumatology and Clinical Immunology, University of California Davis, California, 95616, USA
Department of Wildlife, Fish and Conservation Biology, University of California Davis, California, 95616, USA
Correspondence to K. T. Briggs: 812 Camino Ramon Road, Danville, Calfiifornia 94562, USA; tel: +5108374264; email: ktbriggs{at}msn.com
The immune system is a target of toxicants and there is increasing awareness of the role of environmental pollutants in altering immune function. Immune suppression may constitute a previously unappreciated source of both acute and chronic impacts on seabirds affected by spilled oil. Thus, it is important to determine (a) if immuno-suppression occurs, (b) its importance compared to other mechanisms of impact, (c) its timing and chronicity relative to oil ingestion and post-spill cleaning efforts, and (d) if something can, and should be, done to mitigate its effects. The published evidence concerning immune suppression among oiled seabirds is incomplete and much of it is indirect. Among oiled birds, leukocyte numbers (especially lymphocytes) are depressed in the circulation and the major lymphoid organs (spleen and bursa of Fabricius). At the same time, bone marrow hypercellularity, with an emphasis on erythropoiesis, suggests an adaptive shift from white cell to red cell production in response to haemolytic anaemia. Secondary fungal and bacterial infections, common among seabirds in rehabilitation centres, emphasize the immunosuppressive qualities of petrochemicals. Furthermore, inflammation of the gastrointestinal tract following oil ingestion leads to malabsorption of nutrients (which is immunosuppressive), damage to mucosal immune defences, and impairment of responses to certain antigens, such as those of foods. Unfortunately, direct challenge by viral or bacterial pathogens has been incorporated into very few relevant, laboratory studies: compared with experimental controls, domestic birds fed petroleum distillates and/or oil-emulsifying agents suffer greater mortality, and have depressed ability to kill or phagocytize bacterial pathogens. Cell-mediated immune mechanisms are more sensitive to the toxic effects of petrochemical ingestion than are mechanisms related to antibody production. Petrochemical ingestion produces abnormal concentrations or accelerated metabolism of adrenal corticosteroids. The same is true for birds subjected to handling stress, such as occurs during experimentation with wild birds, and during cleaning of oil-soaked birds. Corticosteroid hormones affect the immune system in many ways, including changes in numbers, and depression of function among lymphocytes. Results of the few recent studies of birds released from cleaning facilities are consistent with the notion of chronic, toxic, or immune system problems. These birds suffer higher than expected mortality rates, disappear from expected breeding and dispersal areas, and generally fail to breed for one or more years. Better long-term success might be obtained with improved assessment of immune function during captivity, and with the use of non-specific potentiators of immune function.
Keywords: immune system, petroleum ingestion, seabirds, stress effects