Thus these creatures must definitely now be classified as hazardous wastes by EPA criteria. The upper layer of water in the oceans plays an important role in this story. In the microlayer, the uppermost surface of the ocean, pollutants are found at concentrations 10 to 100 times greater than the average concentration in ocean water. Plankton are the tiny creatures that form the bottom-most level of all ocean food chains. They carry out photosynthesis, using energy from sunlight to convert carbon dioxide and water into plants, which are then eaten by creatures that are eaten by other creatures, and so forth.
Plankton live in the microlayer because that's where there's most sunlight for photosynthesis.
Therefore they absorb the concentrated pollutants. Then when they are eaten, they pass the pollutants to the next creature, which passes them on to the next creature and so on. Because PCBs are soluble in fat, they are retained in the bodies of fish and mammals and at each step in the food chain, the concentration of PCBs increases. This is simply bad luck. PCBs happen to act like hormones in marine mammals, interfering with their ability to reproduce.