Harbor Porpoises Ingest So Much Poison Their Milk Is Toxic to Their Calves

Harbor porpoises ingest so much poison their milk is toxic, researchers have warned.

Polychlorinated biphenyls (PCBs) are a group of 209 artificial chemicals that were once widely used in the production of electrical equipment, paints and surface coatings.

According to the National Oceanic and Atmospheric Administration (NOAA), 1.5 billion pounds of PCBs were produced between the 1920s and their ban in 1979 (in the U.S.) and the 1980s (in Europe). While they are now illegal, the toxins persist in the environment, where they continue to harm animals' health.

And now, calves have a more potent mix of PCBs in their bodies than their mothers do, a "tragic irony" given the harmful effect of the chemicals on brain development.

This is because mothers unwittingly detox themselves of the PCBs during feeding, say researchers writing in the journal Science of the Total Environment—a process they call "pollutant offloading."

"PCBs appear to be particularly persistent in relation to other legacy toxins," Rosie Williams, Lead Author and PhD Researcher at ZSL and Brunel University in London, told Newsweek. "Despite being banned [in Europe] the 1980s, they continue to be an ongoing problem."

"The latest U.N. Environmental Program assessment estimated that 14 million tonnes of PCB contaminated equipment and material still needs to be destroyed."

These chemicals enter the water—and the marine food chain—from the land in runoff, the wind or the seabed. Tooth whales like the bottlenose dolphin, the orca and the harbor porpoise have some of the highest doses of PCBs because of their high position on the food chain—generally speaking, the higher up you go, the longer the substances have to accumulate.

Now, research reveals that some of the most persistent of these chemicals remain in the mother's body and are absorbed in the mother's milk, so that they are passed onto infants through lactation.

"It's a tragic irony that juvenile porpoises are being exposed to a toxic cocktail of chemicals during feeding—when all they're supposed to be getting are the vital nutrients they need for the crucial developmental stage of their life," Williams said in a statement.

Typically, PCBs have been measured as a group rather than separate chemicals but, says Williams, it is not possible to fully understand how they affect wildlife if we do not understand the type and the quantities that animals are ingesting. This is because each PCB has a different level of toxicity that depends on its chemical structure.

In the paper, Williams and colleagues analyzed concentrations of chemicals in found in blubber, using a data set, including 696 harbor porpoises stranded in the U.K. between 1992 and 2015. The results show that the types of PCBs present in the blubber vary according to factors such as age, sex and location.

While adult females had higher proportions of highly chlorinated types, it was the youngsters who had higher proportions of the less chlorinated types. These chemicals can damage neurological development and suppress the immune and reproductive system, researchers say. Lightly chlorinated PCBs have also be linked to tumor growth.

According to the study's authors, the most likely explanation for these differences between mothers and calves is the process of maternal offloading—with mothers unintentionally transferring some of the most harmful toxins to their young due to differences in lipid solubility levels between chemicals.

It is "reasonable" to say the young in the study had been exposed to "toxic concentrations" of PCBs, write the study's authors.

In contrast, male adults had some of the highest levels of PCBs as they continued to accumulate more over a lifetime. Unlike females, they could not offload or detoxify through reproduction.

The good news is that since bans came into force, levels of PCBs in the environment have been on the decline. "PCBs continue to be eliminated and we expect this decrease to continue," Williams says. She hopes the study will help identify and eliminate sources of chemical contamination to help protect marine animals.

However, PCBS are not the only problem facing harbor porpoises. There are plenty of other harmful chemicals that are being transferred onto youngsters through their mother's milk.

This "dangerous cocktail of chemicals" includes mercury, flame retardants and chlorinated pesticides, which can react with one another to increase overall toxicity, Williams warns.