Sea otters living along the coastline of Canada’s British Columbia province carry residues of “forever chemicals” in their bodies, according to a new study,  and those living near dense human populations or shipping lanes are the most heavily impacted. The research was published in the journal Environmental Toxicology and Chemistry, authored principally by scientists at the University of British Columbia (UBC).

While most health research on exposure to long-lived, human-made chemicals — per- and polyfluoroalkyl substances, better known as PFAS — have been human studies, scientists are growing increasingly aware that wildlife are also at risk. It’s now well-established that in humans, PFAS can cause cancer or liver damage, lower immunity, impair fertility and trigger other health problems.

This study on sea otters (Enhydra lutris) analyzed tissue samples from 11 animals that had recently died. All carried PFAS in their livers.

Forever chemicals were developed and first manufactured in the mid-20th century by 3M and Dupont. They make products stain, water and heat resistant — and can take hundreds or thousands of years to break down. They’re now ubiquitous worldwide, found in everything from human blood and drinking water to soils used to grow food and the marine environment.

Sea otters, which live in coastal waters across the North Pacific Ocean, are endangered and their populations are decreasing, according to the IUCN, the global wildlife conservation authority.

Numerous threats, from habitat loss to a warming ocean and pollution, could erase progress that has brought the species back from local extinction. Oil spills could pose even bigger concerns for the species than PFAS, said Peter Ross, a senior scientist at the British Columbia-based nonprofit Raincoast Conservation Foundation who wasn’t involved in the study.

In British Columbia, sea otters were extirpated by 1929 after centuries-long demand for their fur. They fared only slightly better in the U.S. state of California, where the population dropped to about 50. With concerted reintroduction from 1969-1972 and ongoing conservation efforts, they made a dramatic comeback along Canada’s coast. As of 2017, there were roughly 8,000 sea otters in British Columbian waters.

But now, scientists are quantifying an additional threat to their recovery and long-term survival. PFAS exposure weakens immunity and threatens sea otters’ health in numerous ways, limiting their ability to withstand other challenges.

When adult southern sea otters (E. l. nereis) living along the California coast began dying off from infectious diseases, researchers found that polluted water compromised immunity in adults, and that those with high concentrations of PFAS had a greater chance of contracting deadly diseases, according to findings published in the journal Chemosphere.

Ross told Mongabay that the findings are “no surprise, but troubling nonetheless.” He added that this should “remind people that we’ve known that this class of … chemicals are a health risk to some species, including humans, and we’ve been really, really slow to work through the regulatory frameworks that we have in place.”

PFAS accumulate in marine mammals

PFAS are a class of manufactured chemicals used in industrial and household products that are found in firefighting foams, food packaging, nonstick pans, fabrics, cosmetics and electronics. They’re now produced and used all over the world.

PFAS enter the sea mostly as wastewater and runoff. Species considered highly susceptible to contamination include sea otters and other predatory marine mammals with relatively long lifespans, in part because the chemicals can accumulate in high concentrations in animals that sit higher up on the food chain.

Sea otters are mainly exposed by eating contaminated prey. Scientists also suspect that these chemicals may transfer to unborn otters by crossing the placenta or may pass to babies in mother’s milk.

The new study notes that “[t]here is growing concern about the toxic effects of PFAS on marine life and the future negative impacts they will have on marine ecosystems as they continue to bioaccumulate and biomagnify in marine food webs.”

Canadian sea otters are not the only marine species affected by these chemicals. A 2022 study by several of the same researchers found PFAS in killer whales (Orcinus orca) in British Columbian waters. Older studies confirmed that sea otters in the U.S. states of California, Washington and Alaska, and across the Pacific in Russia, were contaminated with PFAS.

Studying PFAS in sea otters

This was the first study looking at PFAS in British Columbia’s sea otters, the northern subspecies (E. l. kenyoni), and finding research subjects was challenging. Samples can only ethically be taken from otters that have died, and they must be found, uneaten, shortly after death. The team was able to take liver tissue from 11 otters, as well as muscle samples from five of them. They tested these specimens for 40 types of PFAS.

The lab analysis identified eight different PFAS chemicals in the animals’ livers. Only one muscle sample tested positive, and just for a single type: perfluorooctanesulfonamide (PFOSA).

That finding wasn’t surprising. Because of the way PFAS bind to liver proteins, the chemicals readily accumulate in liver tissue. Researchers found that three types of forever chemicals comprised more than 80% of PFAS in the otters’ livers: (PFOSA), perfluorononanoic acid (PFNA) and perfluorooctane sulfonate (PFOS), which is globally one of the most pervasive and widely studied types of PFAS.

Concentrations were relatively low, according to Dana Price, the study’s lead author, who is a master’s degree student at UBC’s Institute for the Oceans and Fisheries. Levels were far lower than those found in British Columbia’s killer whales. One possible reason posited by the study authors was that sea otters have very fast metabolisms, which help them eliminate some contaminants: They eat roughly a quarter of their body weight in food every day.

The contaminant level was also significantly lower than that found in previous studies of sea otters in California — less than one-tenth the amount, likely because of higher levels of PFAS along that state’s more developed, heavily populated coastline. Another factor may be the timing of the studies. The California research was conducted decades ago, and Price told Mongabay that pollution may be lower now in some regions because of new regulations for certain types of PFAS.

Under the Canadian Environmental Protection Act, PFOS and PFOSA were listed as toxic substances in 2006, reducing their manufacture and use; later, in 2012, certain other types of PFAS were added to that list.

The government is again taking action. In March 2025, the Canadian government’s “State of PFAS Report” recommended that most PFAS be designated as “toxic substances” and proposed tighter rules on its use, import and manufacture.

Parties to the Stockholm Convention on Persistent Organic Pollutants, an international environmental agreement, have also regulated PFOS and some PFAS. Unlike Canada, the U.S. is not a ratified party to the agreement. However, the U.S. Environmental Protection Agency negotiated with 3M, a leading PFAS manufacturer, to voluntarily phase out the use of PFOS, PFOSA and other related chemicals in the early 2000s.

Impairing health

Even at low levels, there can be negative health effects from exposure to PFAS. Yet it’s hard to gauge the true consequences without further research, given that these chemicals don’t exist in isolation, but interact with other contaminants, Price said.

Unlike whales, sea otters stay close to home. Since they usually have a range of no more than 50 square kilometers (19 square miles), they provide a better indicator of pollution in the area where they live.

The researchers categorized the 11 otters they tested into two groups: those living farther north, above Vancouver Island — an area relatively unpopulated by people — and a southern group found to the south or west, living near dense human populations and shipping lanes. Unsurprisingly, the northern group that lived in a more pristine location carried far lower PFAS concentrations than those living in more developed areas.

Both Price and Ross noted that it’s unclear whether living sea otters contain similar levels of PFAS or if testing dead animals may have biased the results. They added that the study size was small, so more research is needed to confirm the findings.

Potential regulation

Across the world, headlines regularly report PFAS pollution, and scientists, doctors, public health experts and conservationists have advocated regulating these chemicals.

Ross said he “wholeheartedly” supports the Canadian government’s steps toward adopting tighter rules for PFAS. In his estimation, Canada tends to fall somewhere between the European Union, which has stricter rules for chemical contaminants such as PFAS, and the U.S., which takes more of a “free market” approach.

Cassie Barker, senior program manager at Environmental Defence, a Toronto-based advocacy group, told Mongabay in an email that sea otters had made a “joyful recovery” in British Columbia’s waters but “PFAS will continue to contaminate their homes, and potentially harm their health unless Canada bans these ‘forever chemicals’ from products.”

“We urge Canada to follow through on its promise to protect species and people by declaring PFAS toxic and expediting necessary regulations to get these chemicals out of products,” she said.

Banner image: Sea otters, which live in coastal waters across the North Pacific Ocean, are endangered and their populations decreasing. Image by Mike Baird via Wikimedia Commons (CC BY 2.0).

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Citations:

Price, D., Trites, A. W., Raverty, S., Cottrell, P., Cottrell, B., Zysk, I., & Alava, J. J. (2025). Concentrations of per- and polyfluoroalkyl substances in Canadian sea otters (Enhydra lutris) are higher near urban centers. Environmental Toxicology and Chemistry. doi:10.1093/etojnl/vgaf226

Lee, K., Alava, J. J., Cottrell, P., Cottrell, L., Grace, R., Zysk, I., & Raverty, S. (2022). Emerging contaminants and new POPs (PFAS and HBCDD) in endangered Southern Resident and Bigg’s (Transient) killer whales (Orcinus orca): In utero maternal transfer and pollution management implications. Environmental Science & Technology, 57(1), 360-374. doi:10.1021/acs.est.2c04126

Kannan, K., Agusa, T., Perrotta, E., Thomas, N. J., & Tanabe, S. (2006). Comparison of trace element concentrations in livers of diseased, emaciated and non-diseased southern sea otters from the California coast. Chemosphere, 65(11), 2160-2167. doi:10.1016/j.chemosphere.2006.06.003

Hart, K., Gill, V. A., & Kannan, K. (2008). Temporal trends (1992–2007) of perfluorinated chemicals in northern sea otters (Enhydra lutris kenyoni) from south-central Alaska. Archives of Environmental Contamination and Toxicology, 56(3), 607-614. doi:10.1007/s00244-008-9242-2

Andrews, D. Q., Stoiber, T., Temkin, A. M., & Naidenko, O. V. (2025). Discussion. Has the human population become a sentinel for the adverse effects of PFAS contamination on wildlife health and endangered species? Science of The Total Environment, 901. doi:

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