Part I: Seaweeds—Detoxifiers or Toxic Risk?
Seaweeds have long been valued for their ability to cleanse and create movement in the body, particularly in the digestive tract—and in recent years, they’ve gained popularity as a “natural detox” food and supplement. From Traditional Chinese Medicine, where seaweeds are used to disperse stagnation and clear toxins, to the enduring practice of seaweed bathing in Ireland, seaweeds have been used across cultures to support elimination, healing, and internal cleansing.
But what gives seaweeds this potential? What molecular tools allow seaweeds to bind—or compete with—metals and minerals in their environment, and possibly in your body when you ingest them?
Seaweeds are known as detoxifiers, not just for humans, but also in environmental applications—which is why there is concern among seaweed-consuming folks and some regulatory agencies about contaminants in seaweed. Contaminants are pervasive, though often dilute, in our ocean ecosystems, and many seaweeds have powerful mechanisms through which they can accumulate and concentrate some of these toxins, sometimes several times the concentration found in seawater.
However, the ways seaweeds interact with toxins—whether in the water or in our guts—is complex and not fully understood. We know that seaweed uptake of contaminants such as heavy metals in their ocean environment is highly variable by species and season. Depending on the form of a heavy metal and the conditions in which the seaweed is growing, it may not absorb contaminants immediately—or at all—even if they are present in the water for weeks. While concern about heavy metal contamination in seaweeds is well-founded, it’s important to remember these key points: just because a contaminant is present in the water does not mean the seaweed will absorb it—and just because a contaminant is present in the seaweed does not mean it is bioavailable to the human body.
Though seaweeds themselves may contain toxic heavy metals, some of the same compounds that allow them to bind heavy metals in the ocean may also help sequester toxins in the digestive tract and support their safe elimination from the body. But what’s actually happening in the growing seaweed’s environment—and in your digestive tract when you eat it—is not a black-and-white story, but a nuanced, ongoing exploration. Through this article series, I hope to begin unraveling this story. To date, I haven’t found any study that fully addresses all the intricacies involved—and because human trials involving contaminants are often ethically or financially unfeasible, much of what we do know comes from in vitro models or animal studies. In addition, most research focuses on isolated seaweed compounds, with relatively few studies examining whole-form seaweeds.
This article series will dive into the complex science behind seaweeds and chelation. Over the course of these articles, we’ll explore:
seaweeds’ relationship to heavy metals, minerals, and radioactive elements in their environments;
how seaweed phytochemicals bind to or interact with these elements in the human digestive tract;
bioavailability—an informed look, based on available in vitro and animal studies, at how whole seaweeds and the elements they contain may be transformed or eliminated through digestion;
how different preparation methods affect the bioavailability of toxins and may enhance seaweeds’ detox capabilities;
how antioxidant compounds in seaweeds may mitigate oxidative stress caused by metal contaminants;
the dynamics of seaweed–contaminant interactions in ocean environments—when and why uptake occurs, how it happens, and what it means for seaweed food safety.
The focus of this article series is mainly on seaweeds’ interactions with heavy metals, radioactive isotopes, and minerals, which are chemically similar. Other environmental contaminants, like PCBs, are also a concern, though they behave quite differently. This topic may be discussed in a future article.
Selected References
Besada, V., Andrade, J. M., Schultze, F., and González, J. J. 2009. “Heavy Metals in Edible Seaweeds Commercialised for Human Consumption.” Journal of Marine Systems 75(1–2): 305–313. https://doi.org/10.1016/j.jmarsys.2008.10.010
Circuncisão, A. R., Catarino, M. D., Cardoso, S. M., and Silva, A. M. S. 2018. “Minerals from Macroalgae Origin: Health Benefits and Risks for Consumers.” Marine Drugs 16(11): 400. https://doi.org/10.3390/md16110400
Davis, T. A., Volesky, B., and Mucci, A. 2003. “A Review of the Biochemistry of Heavy Metal Biosorption by Brown Algae.” Water Research 37(18): 4311–4330. https://doi.org/10.1016/S0043-1354(03)00293-8
García-Sartal, C., Barciela-Alonso, M. C., and Bermejo-Barrera, P. 2013. “Study of Cooking on the Bioavailability of As, Co, Cr, Cu, Fe, Ni, Se and Zn from Edible Seaweed.” Microchemical Journal 108: 92–99. https://doi.org/10.1016/j.microc.2012.10.003
Holdt, S. L., and Kraan, S. 2011. “Bioactive Compounds in Seaweed: Functional Food Applications and Legislation.” Journal of Applied Phycology 23(3): 543–597. https://doi.org/10.1007/s10811-010-9632-5
Huang, L., Lee, J.-Y., Park, Y.-K., and Lee, J. 2025. “Heavy Metals in Seaweed: Implications for Health Benefits, Risks, and Safety Regulations.” Journal of Agriculture and Food Research 21: 101830. https://doi.org/10.1016/j.jafr.2025.101830
Mac Monagail, M., Cornish, L., Morrison, L., Araújo, R., and Critchley, A. T. 2017. “Sustainable Harvesting of Wild Seaweed Resources.” European Journal of Phycology 52(4): 371–390. https://doi.org/10.1080/09670262.2017.1365273
Shanmugam, S., Shakila, R. J., Shalini, R., Aanand, S., Jayakumar, N., Arisekar, U., and Manikandan, B. 2024. “Bioaccessibility of Toxic Heavy Metals/Metalloids in Edible Seaweeds: Exposure and Health Risk Assessment.” Food Research International 182: 114135. https://doi.org/10.1016/j.foodres.2024.114135