by John Thompson, Western Washington University
Seaweeds are consumed by many people living on or near the Salish Sea – from Indigenous peoples revitalizing the ancient foodways of their cultures to those simply seeking a readily available and highly nutritious protein source – but little is known about whether contaminants in the Sea’s waters could create health concerns for the people who eat it.
A new study just published by researchers at Western Washington University in the scientific journal PLoS One reports concentrations of up to 162 chemical contaminants in three species of edible seaweeds (bullwhip kelp, bladderwrack, and spiral bladderwrack) at 43 sites throughout the Salish Sea, both in United States and Canadian waters.
The researchers — Principal Investigator and WWU Fairhaven College Research Associate Jennifer Hahn, WWU Professor and Chair of the Department of Environmental Sciences Ruth Sofield, and WWU Marine Scientist Kathy Van Alstyne — found that most contaminants occurred at levels too low to be a concern for human health. However, a few toxic chemicals – arsenic, cadmium, mercury, PCBs, lead, and benzo[a]pyrene – were found in high enough concentrations that the study’s authors recommend that people consume less than the typical amount of 5 grams of dried seaweed per person per day when the seaweeds are harvested at specific higher-risk sites; 5 grams of dried seaweed is the equivalent of about one-and-a-half cups of freshly collected seaweed.
Of the 162 contaminants found in the samples, the one that worried the researchers the most were polychlorinated biphenyls, or PCBs. Banned for use in the U.S. since 1971, PCBs are extremely long-lasting compounds that were formerly used in electrical transformers and as a flame retardant. PCBs have been shown to be cancer-causing agents that “bioaccumulate” in the organisms that ingest them; the larger and more longer-lived the organism, the more PCBs it is able to store in its tissues which may cause harm to the organism. Once that organism – whether it is a fish, a seaweed, or shellfish — is eaten by humans, the PCBs then begin bioaccumulating in its new host. High exposure to PCBs can cause cancer, birth defects, developmental delays, and liver changes.
Of the 43 sampling sites, some of the most heavily contaminated seaweeds were found near highly industrialized sites such as Victoria Harbor in B.C. and Waterman Point near Bremerton and Smith Cove near the Seattle Cruise Terminal.
The study was initially motivated by tribal members asking whether the seaweeds they were harvesting were safe to eat, said Hahn, the lead author of the paper and a recent graduate of WWU’s Department of Environmental Studies’ master’s-degree program. Hahn also did the majority of the sampling, often via her kayak or a small boat. WWU students helped process the samples and prepare them to be tested.
“These are traditional foods for many of the Coast Salish peoples,” said Hahn. “But given the highly industrialized nature of many parts of the Salish Sea, they correctly had concerns about pollutant levels in the foods that they had traditionally harvested for so long. That’s what got me started down this rabbit hole, knocking on doors and building relationships to put together a project that took more than six years to complete, and ended up with me sampling from Campbell River, B.C., all the way south to Olympia.”
Hahn, who has taught wild food harvesting and cooking workshops to local tribes and First Nations for more than a decade, said some of the sample sites were not easy to reach even by kayak, which given Hahn’s career as a wilderness guide who has solo kayaked from the Salish Sea to Alaska, is saying something.
“Some of those sample sites were pretty tough,” she said. “Between the currents and the weather, there were for sure times when I just couldn’t get out that day.”
Sofield said the study fills a niche in the vital understanding of an increasingly important local food source.
“This study was quite an effort – there aren’t many studies that do cross-border sampling like this, and there is little understanding of seaweed contamination in the Salish Sea,” she said.
The studies’ co-authors include researchers from WWU’s Shannon Point Marine Center and Department of Environmental Sciences, the SeaDoc Society, the Washington State Department of Fish and Wildlife, the Washington State Department of Health, the NOAA Northwest Fisheries Science Center, and the University of California Davis Health and Food Safety Laboratory System. Funding for the study was provided by Western’s Border Policy Research Institute and the SeaDoc Society, a program of the Karen C. Drayer Wildlife Health Center, School of Veterinary Medicine, University of California at Davis.
The studies’ authors caution that while contaminant concentrations can be high enough to have human health risks, these risks need to balanced with the nutritional benefits from consuming seaweeds, which are low in fat and can be high in fiber, minerals, and antioxidants.
“What we don’t want to get lost is how good seaweed is for you. It’s extraordinarily nutritious, and many folks are calling it ‘the new kale.’” Hahn said. “But at the same time we need to be able to show anyone looking to harvest seaweed where they can do it most safely, and how much of it they should eat.”
Reference (open access)
Hahn JL, Van Alstyne KL, Gaydos JK, Wallis LK, West JE, Hollenhorst SJ, et al. (2022) Chemical contaminant levels in edible seaweeds of the Salish Sea and implications for their consumption. PLoS ONE 17(9): e0269269. https://doi.org/10.1371/journal.pone.0269269