Manufactured since the 1940s and widely used in industrial and commercial products, PFAS are commonly referred to as “forever chemicals” because they last a long time in the environment, with some estimated to take over 1,000 years to degrade in nature. Certain PFAS have been linked to reproductive, developmental, and immunological effects in humans and animals, and they have been shown to bioaccumulate (build up) and biomagnify (become increasingly concentrated) in marine food webs.
A key goal of this research is to understand how, or where, salmon are being exposed to PFAS. In other words, is the exposure occurring in open water and coastal areas, or are terrestrial and freshwater inputs, such as river discharges, serving as notable sources of PFAS in salmon?
In September 2025, the field team set out to the mouth of Sashin Creek near Little Port Walter to find the salmon. Instead of using paws, claws, and jaws to capture salmon — a brown bear’s preferred fishing tools — the researchers operated a fishing weir and Fish Accumulation Device (FAD) to sample pink, chum, and Chinook salmon as thousands began their upstream journey. The weir is a dam-like concrete structure first built in the 1930s stretching from one side of the creek to the other. Researchers used hydraulic winches to raise and lower gates that kept Chinook salmon out of the stream while guiding pink and chum salmon into a holding cage. The team then selected a small portion of the pink (2) and chum (4) salmon for sampling before releasing the remaining fish upstream. The researchers captured pink and Chinook salmon using the FAD, a series of nets designed to intercept free-swimming salmon and guide them into a holding pen. In the crystal clear waters of Mist Cove, a short boat ride away from Sashin Creek, the researchers completed their salmon sampling by enticing coho salmon using traditional rod and reel fishing techniques.
Further upstream in Sashin Creek, juvenile rainbow trout live in a closed stream, contained on either side by two waterfalls. Because these fish are exposed to only terrestrial and upstream freshwater sources of PFAS, they are ripe for comparison with the downstream salmon, which we think are exposed to mostly coastal and open waters. The rainbow trout collections were more physically demanding — researchers hiked two miles up steep terrain, following makeshift trails made by wild animals, passing over pink salmon carcasses and fresh wet bear prints and yelling “HEY BEAR” every 30 seconds, to reach Sashin Creek’s headwaters upstream of the salmon collection site. Here, the researchers set minnow traps baited with pink salmon eggs to catch the rainbow trout.
If the types of PFAS detected in the rainbow trout differ from those detected in the salmon, then maybe the source of PFAS exposure in salmon is from marine and coastal waters, or it could be that different diets and trophic positions (where they are in the food chain) drove varying levels of PFAS. However, if there are similarities in the PFAS detected in fish from both locations, then it’s possible that the salmon and rainbow trout share common exposure from freshwater or terrestrial sources, or that PFAS are widespread across the two systems.
The researchers collected 50 fish on this particular trip. In total, the project team has sampled over 100 individuals across six species of varying life stages and origins (wild vs. hatchery), and from both relatively remote (Little Port Walter) and urban (Auke Creek) areas. Water, sediment, and fish feed samples have also been collected to assess other possible sources of exposure. By processing, analyzing and comparing these samples, the team aims to better understand sources, pathways, and implications of PFAS exposure across Alaska’s coastal systems, and provide valuable information on coastal contamination for Pacific Northwest stakeholders to better inform future management.
This work is authorized by the Marine Protection, Research, and Sanctuaries Act (MPRSA) 16 USC § 1431 et seq. and 33 USC §1401 et seq. (1988), and several authorities under the Clean Water Act (CWA) 33 U.S.C. §1251 et seq. (1972).
This Log Book entry was written by Nicholas Castillo.