Final answer:
The extremely high levels of toxic chemicals in fish-eating birds are caused by the biomagnification of substances like polychlorinated biphenyls (PCBs) and heavy metals. PCB concentrations increase as you move up the food chain, and birds that eat these fish can have PCB levels much higher than the fish. Heavy metals, like mercury, lead, and cadmium, also accumulate in fish, which when consumed by birds, result in high levels of toxic chemicals.
Step-by-step explanation:
The extremely high levels of toxic chemicals in fish-eating birds are primarily caused by the biomagnification of certain substances. One such substance is polychlorinated biphenyls (PCBs), which were used as coolant liquids in the past. PCB concentrations increase as you move up the trophic levels of the food chain, resulting in birds that eat these fish having PCB levels that are much higher than those found in the lake fish.
Another factor is the accumulation of heavy metals like mercury, lead, and cadmium. These metals are typically produced as by-products of industrial activities. As they enter the aquatic ecosystems, they get biomagnified and accumulate in the tissues of predatory fish species. When fish-eating birds consume these contaminated fish, they are exposed to high levels of these toxic metals.
Therefore, consuming fish that have accumulated high levels of PCBs and heavy metals is the main cause of the extremely high levels of toxic chemicals in fish-eating birds.