PCBs partition strongly to organic media from water and air, and bioconcentrate and bioaccumulate efficiently in biota.
Most plants are not able to significantly translocate PCBs, so transfer is generally from the air (or water for aquatic plants) to external surfaces, with some transfer to internal leaf tissues, and from the soil (or sediment) to the external surfaces of roots and tubers.
In aquatic systems exposure at low trophic levels is predominantly directly from the water, with efficient bioconcentration taking place. However, strong bioconcentration in prey species leads to bioaccumulation from food becoming more important at higher trophic levels. Air-breathing marine animals are exposed almost entirely through the diet, as air concentrations and air intake are relatively low. Because of the strong tendency to biomag-nify in aquatic systems, and the high lipid content of most marine animals (especially mammals), marine top predators tend to have much higher PCB concentrations than equivalent terrestrial animals. In higher organisms in terrestrial systems exposure is predominantly through the diet. However, many soil invertebrates may absorb PCBs directly from contact with the soil. PCBs bioaccumulate strongly in terrestrial foodchains.
In animals, PCBs are effectively translocated by the blood, and concentrate in lipid-rich tissues. Eggs and milk are rich in lipids, and so the young of many species are often exposed to relatively high doses ofPCBs from their mothers. This is particularly true for many marine mammals, which produce extremely lipid-rich milk for their young.
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