Which of the following would most likely contain the highest proportion of PCBs?

Chinook salmon would most likely contain the highest proportion of PCBs due to their position in the food chain and their life cycle. PCBs, or polychlorinated biphenyls, are persistent organic pollutants that accumulate in the fatty tissues of aquatic organisms. The biomagnification process means that as you move up the food chain, the concentration of PCBs increases in organisms that feed on smaller fish or invertebrates.

Chinook salmon are larger fish and are higher up in the aquatic food web. They feed on various smaller fish, which themselves may contain lower levels of PCBs. Consequently, the accumulation of these contaminants through their diet leads to higher concentrations within the tissue of Chinook salmon compared to smaller fish species like sunfish, brook trout, or perch. Furthermore, salmon tend to inhabit waters that may be exposed to industrial discharge or runoff, increasing their risk of PCB accumulation compared to some of the other listed species.

Thus, the characteristics of Chinook salmon, along with their feeding habits and position in the food web, contribute to them having the highest proportion of PCBs among the choices provided.