Final answer:
DDT and PCBs ended up in the ocean through bioaccumulation and biomagnification. These persistent organic pollutants accumulate in organisms and increase in concentration up the food chain, affecting apex predators and remaining in the environment long after their ban.
Step-by-step explanation:
Persistent organic pollutants (POPs), like DDT and PCBs, ended up in the ocean largely through processes like bioaccumulation and biomagnification. These substances, once used for purposes like insect control and industrial applications, were released into the environment where they would accumulate in the tissues of organisms. Due to their chemical stability and fat solubility, they would not only persist in the environment but would also get absorbed by various organisms, starting with small organisms like plankton, and move up the food chain. As larger animals eat the smaller ones, the concentration of these chemicals in their bodies would increase, a process known as biomagnification. This led to higher concentrations of these toxic substances in apex predators. Despite their ban due to environmental and health concerns, these chemicals remain in the environment due to their resistance to breaking down, and continue to be found in remote areas like the Arctic and Antarctic. Consequently, even after their use ceases, the long-lived chemicals can continue to affect wildlife and human health for decades.