Throughout any animal"s lifetime, exposure to pollutants changes from place to place and from time to time. Exposure impacts different species to varying degrees too. Orcas tend to live for longer than porpoises, for example, so they have more time to accumulate chemical pollutants in their bodies. They also feed at a higher level within the food chain, so they are eating bigger fish and other marine mammals which themselves contain contaminants. Deaville explains that POPs are stored within the blubber. When an animal"s nutritional state deteriorates, either seasonally or as a result of illness perhaps, those toxic contaminants are released into the blood as the fat layer thins. Toxic chemicals are also passed on to calves via breast milk and so a mother can unwittingly offload toxic pollution onto a firstborn calf, sometimes resulting in death.