Industrial chemical carcinogens, such as PCBs, have been concentrating up the food chain for years and building up in animal fat. Many were banned in 1979 and fortunately have since been in decline in terms of daily intake levels. But one dietary source still remains a threat: fish and fish oil (see also here, here, here, here). Eggs may also be highly contaminated. Some PBCs act as xenoestrogens; they can have estrogenic effects and may adversely affect male sperm counts and may even be responsible for early onset puberty.
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