Researchers at the University of BC, say the toxic chemical 4NP was found in 46 of orca samples. The Department of Fisheries and Oceans provided UBC with samples from the necropsies that were done on orcas who were found dead along the coast. 

Researchers stated that 4NP can leak into the ocean by industrial run-off, waste water and treatment plants. The chemical is then consume by organisms that the orcas eat! 

https://vancouversun.com/news/local-news/ubc-study-whales-toxic-chemicals