Blood organochlorines, immune function and health of free-ranging northern fur seal pups (Callorhinus ursinus)

Abstract

This study examined organochlorine (OC) contaminant levels in blood and milk along with immune function and health of northern fur seals ( Callorhinus ursinus) from St. George Island, Alaska. This portion of the Pribilof Islands breeding stock has undergone a long-term decline between 4 and 6% per year for unknown reasons. To examine the possible role of neonatal OC exposure on health, two cohorts of pups (69 total) and 33 matched periparturient dams were captured for blood and milk sample collection. From the second cohort of 49 neonates, 43 were re-sampled 29 to 51 days later. OCs were extracted from whole blood and milk to identify 15 polychlorinated biphenyl (PCB) congeners and 4 metabolites of dichloro-diphenyl-trichloroethane by high performance liquid chromatography. Peripheral blood lymphocytes were isolated and cryopreserved for in vitro lymphoproliferative immunoassays. These cellular function assays, along with complete blood cell counts, growth rates and survival through the early developmental period, were used as indicators of health status. Humoral immune function was assessed by in vivo antibody responses to tetanus vaccination. Mean blood levels of PCBs were higher in neonate samples than in pups one to two months old. Seven of the eight congeners detected in blood were higher (lipid weight) in neonate blood than in dam blood or milk. First-born neonates were exposed to higher levels of OCs from ingested milk and had higher blood levels of OCs than neonates of older, multiparous dams. Higher OC exposure in neonates was correlated to higher blood OC levels and poorer lymphoproliferative responses as well as lowered serum. retinol and thyroxine. Higher proportions of pups born to old dams developed tetanus antibodies compared to the pups of young dams. Higher OC exposure and poor immune responses in first-born pups may indicate a higher risk of secondary morbidity and mortality than for pups born to multiparous dams but an affect on growth rate or survival to midway through the nursing period was not detected. Evidence of substantial OC contaminant exposure at a critical period of development for the immune system must be considered as a potential contributing factor to reduced post-weaning survival.