Effects and mechanisms of PCB ecotoxicity in food chains: algae double right arrow fish double right arrow seal double right arrow polar bear

Wildlife populations are adversely affected in polluted environments. Never theless, a cause-and-effect relationship between excessive exposure to chlo rinated hydrocarbons and induction of pathologic disorders in animals, is d ifficult to demonstrate without verification from experiments following the rationale of Koch's postulates. Deleterious effects of chlorinated chemica ls such as DDT on songbird reproduction, as demonstrated by the clutch size of eggs in a nest, however, is an example, where exposure and causation ar e apparent. With amelioration of DDT pollution, clutch size increases, and the cause-and-effect relationship is established. Similar examples of expos ure to DDT and PCBs inducing reproductive disorders and endocrine disruptio n among marine mammals have been documented in industrialized nations of no rthern Europe and in the upper latitudes of the Northern Hemisphere. Popula tion declines in ringed, grey and harbor seals are apparently due to a rapi d decrease in their rates of reproduction(1). These latter observations are best interpreted in light of experiments conducted by Reijnders(2). Reijnd ers exposed harbor seals to relatively high dietary levels of PCBs and indu ced PCB-blood-lipids among seals to an average of 25 mg/kg compared to 10 m g/kg among controls. The treated seals had a significantly reduced reproduc tive rate. A relationship between increased PCB-blood-levels in vivo and th e decrease in reproductive rates in this experiment is highly instructive f or interpreting the decline of fertility in seal populations in polluted Ba ltic Sea waters. These linked observations are dependent upon demonstration of pathologic mechanisms associated with occlusion and stenosis of the ute rine lumen among affected females in seal populations. PCB congeners apparently disrupt endocrine-system-functions leading to, or associated with, increases in endometriosis, fetal abortion, glomerulonephr opathies and osteoporosis. This observation is further highlighted by Reijn ders experiment, which closely replicated the range of PCB concentrations f ound in seal populations living in a variety of PCB polluted waters. Various PCB congeners differentially accumulate in brain, liver and adipose tissues in young and old seals. Further research of PCB toxic effects on o rgan systems of these animals and other species is thus indicated. This report, then, examines the process of PCB bioaccumulation within the m arine food chain from fish to seals, whales, other marine mammals and to po lar bears. Environmental toxic pollutants affect animals within the food ch ain in different ways but ultimately they affect humans as well.