Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Biologists have discovered that the beluga whales of Canada's St. Lawrence River have the highest rates of cancer among animals. What is most likely the reason for this high incidence of cancer in these whales?
chemical and pollutant runoff into the ocean
Contamination from industrial waste.