Orca whales were discovered with a toilet paper chemical in their livers and skeletal muscles. It's just the 'tip of the iceberg' for one of the most contaminated marine mammals in the world.

• Scientists found Southern Resident and Bigg's orcas with 4-nonylphenol in their livers and skeletal muscles.
• 4NP is associated with the production of toilet paper.

Orca whales are some of the most contaminated marine mammals in the world.

The species are full of chemicals — from "highly toxic and carcinogenic" PCBs to the infamous insecticide DDT.

Now, a group of scientists has discovered another chemical of concern — and it's associated with toilet paper.

Scientists at the University of British Columbia, British Columbia Ministry of Agriculture and Food, and Fisheries and Oceans Canada, found a chemical known as 4-nonylphenol — along with dozens of other chemicals — in the liver and skeletal tissue of 12 dead Southern Resident and Bigg's orcas.

The chemical 4NP belongs to a group of chemicals known as alkylphenols, which UBC researcher Juan José Alava described to Insider as "very toxic."

Although Alava, and other researchers who spoke to Insider, noted it is too early to decisively conclude how orcas are affected by 4NP, their discovery raises some alarm.

The amount of 4NP found in the killer whales, which tended to be higher in the blood-rich liver tissues, reached exceptionally higher in one calf.

"These contaminants basically can affect reproduction, development, and we know, based on the weight of evidence, affect cognitive function and also the nervous system," Alava said. "So we are here talking about contamination that is harmful to the environment and harmful to this species of killer whales."

Alava said that the exact source of 4NP affecting whales is unknown, the chemical can be found primarily in sewage sludge and wastewater treatment plants. It is also used in detergents and cosmetic products.

In addition to 4NP, over half of the contaminants discovered in the orcas belonged to a category of chemicals known as PFAS — commonly referred to as forever chemicals because of their difficulty breaking down in the environment. PFAS can be found in drinking water, fish, and in trace amounts in human blood, and can heighten the risk for diseases like cancer and liver disease in humans.

The study authors noted that it was the first time 7:3-fluorotelomer carboxylic acid, a type of PFA, was found in an orca from the Pacific Northwest. Alava noted that 7:3 FTCA has not been found in British Columbia before, and could indicate that the pollutant is moving its way through the food systems.

'They're just being killed by 1,000 cuts'

Although Biggs and Southern Residents are both threatened by the possibility of extinction, Southern Residents, whose numbers are failing to grow, have scientists especially concerned.

In addition to habitat loss, climate change, and entanglement in fishing gear, Southern Resident orcas struggle with their food supply.

Overfishing means that there is not enough food. And contaminants in the environment mean that when there is food, it could very well be full of chemicals. Because orcas eat so much, they usually have a higher concentration of chemicals in comparison to their smaller marine counterparts.

Southern Residents rely on Chinook salmon to supplement their diet. The discovery of chemicals in their system means that Chinook salmon also have contaminants in their system — a warning for people who also consume the salmon.

But more than that, a lack of a good food supply is affecting the reproduction of orcas, Deborah Giles, a scientist and research director at the nonprofit Wild Orca, told Insider.

Giles' own research found that 69% of pregnancies held by Southern Resident Orcas were unsuccessful, with 33% failing late into the pregnancy or immediately after birth.

"And those females that are losing their calves are nutritionally deprived which of course works to increase the impacts of chemicals," Giles said.

Chemicals are also being transferred between mothers and fetuses. The UBC study, which looked at a Southern Resident known as J32, found that all the chemicals found in her were transferred to her fetus. J32 died in 2014 while trying to give birth to her fetus, Giles noted.

"They're just being really truly killed by 1000 cuts," Giles said.

'This is just the tip of the iceberg'

"Too few" orcas had been screened to determine the scope of 4NP contamination in killer whales, study authors noted, but even getting this amount of data on orcas — which are usually studied after they are dead — is an impressive task.

Alava told Insider that because of limited access to orca whale organs, he doesn't believe him or the team he worked with will be able to do a necropsy study like this again any time soon.

The lack of data means there are still many unanswered questions: Why are some species less affected by certain chemicals than others? How much of a role do these chemicals play in the endangerment of this species? How many chemicals will researchers continue to find? And which of the dozens of detrimental chemicals found in the environment should scientists and regulators focus on when trying to save the species?

Irvin Schultz, a manager at NOAA's Environmental Chemistry Program, who spoke with Insider about the research, also said that because these particular chemicals have not been screened before, more needs to be done to determine their true impact on the species.

"It's definitely more than trace levels," Schultz said. "So it is something that gets your attention, and maybe it's definitely something to continue to measure and keep track of."

Schultz, whose lab focuses on measuring other contaminants — like polyaromatic hydrocarbons that occur naturally after burning fossil fuels — says it's also important to keep in mind that killer whales are being exposed to so many more contaminants.

"The real value for this study is providing some data for compounds that haven't been monitored or measured as frequently," Schultz said.

And scientists like Giles are continuing to pay attention to what other unknown chemicals killer whales may be holding in their bodies.

"My guess is that the more we look, the more we're going to find with regard to chemicals, manmade chemicals that are finding their way through the food web and into our apex predators like whales," Giles said. "And I think that's the terrifying part for me is that I do believe that this is just the tip of the iceberg with regard to what we will find."