Researchers at Woods Hole Oceanographic Institution (WHOI) unveiled a hazardous cocktail of pesticides when analysing the brain matter of 12 marine mammals; eleven cetaceans and one gray seal stranded near Cape Cod, Massachusetts.

This is the most extensive study of pollutants in marine mammals’ brains and it confirms suspicions of marine mammals being the carrier of a vast array of different chemicals that have found their way into marine ecosystems.

Lead author Eric Montie analyzed the cerebrospinal fluid and the gray matter of the cerebellum in the twelve animals and found them to contain a long row of different man-made chemicals, including a group of especially widespread substances labelled “the dirty dozen” by environmentalists. Many countries banned the “the dirty dozen” as early as the 1970s due to their adverse effect on human health, but they are unfortunately still present in our environment.

Montie didn’t just test for the presence of certain chemicals; he also measured their concentration and found one instance where it was surprisingly high.

“The biggest wakeup was that we found parts per million concentrations of hydroxylated PCBs in the cerebrospinal fluid of a gray seal”, says Montie. “That is so worrisome for me. You rarely find parts per million levels of anything in the brain.”

PCBs are neurotoxicants known to disrupt the thyroid hormone system. Other examples chemicals found in the tested mammals are DDT (diklorodifenyltriklorethane), which can cause cancer and disturb reproduction, and PBDEs (polybrominated diphenyl ethers); a type of flame retardants known to impair the development of motor activity and cognition.

Co-author Chris Reddy, a senior scientist in the WHOI Marine Chemistry and Geochemistry Department, describes the new study as “groundbreaking because Eric measures a variety of different chemicals in animal tissues that had not been previously explored. It gives us greater insight into how these chemicals may behave in marine mammals.”

The results of this study was published online April 17 in Environmental Pollution.