Final answer:
DDT, EPN, and PCBs are Persistent Organic Pollutants (POPs) known for being durable in the environment, bioaccumulating, and toxic, leading to ecological impacts like the thinning of bird eggshells.
Step-by-step explanation:
The substances DDT, EPN, and PCBs all have in common that they are considered Persistent Organic Pollutants (POPs). These chemicals share the distinctive characters of being long-lasting in the environment, bioaccumulating in the food chain, and being toxic to wildlife and potentially humans. An example highlighting their impact can be observed in biomagnification, a process where these substances become more concentrated at each successive level of the food chain. This has been especially harmful to predatory birds like eagles, leading to the thinning of eggshells and decreased reproduction rates. After the banning of DDT and PCBs in many parts of the world, some of the affected bird populations have shown recovery.