I didn’t know so search for it

Understanding Mercury Bioaccumulation in Dolphins

Mercury, a heavy metal, enters marine ecosystems through various sources, including industrial discharge, atmospheric deposition, and natural geological processes. Because dolphins are apex predators, they accumulate mercury through the food chain. Smaller fish ingest mercury, and when dolphins consume those fish, the mercury becomes concentrated in their tissues. This process, known as bioaccumulation, results in higher concentrations of mercury in top predators like dolphins compared to organisms lower in the food web.

https://iere.org/how-much-mercury-was-found-in-the-dolphin-meat-they-tested/