Final answer:
Biological magnification causes extremely high levels of toxic chemicals in fish-eating birds. Substances such as PCBs and heavy metals bioaccumulate in fish species at different trophic levels in aquatic ecosystems. Birds that eat these fish can accumulate PCBs at least one order of magnitude higher than those found in the lake fish.
Step-by-step explanation:
Biological magnification causes extremely high levels of toxic chemicals in fish-eating birds. Biological magnification, also known as biomagnification, is the increasing concentration of persistent, toxic substances in organisms at each trophic level. In aquatic ecosystems, substances such as polychlorinated biphenyls (PCBs) and heavy metals like mercury, lead, and cadmium, bioaccumulate in fish species at different trophic levels. As birds that eat these fish consume higher levels of these toxic substances, they can accumulate PCBs at least one order of magnitude higher than those found in the lake fish.