Scientists tested edible seaweeds from five countries and found they contain higher levels of synthetic chemicals called organophosphorus esters compared to regular vegetables. These chemicals are used in plastics and other products, and they build up in seaweed differently than in land plants. People in East Asia who eat a lot of seaweed may be exposed to similar amounts of these chemicals as people who eat many vegetables. While seaweed is nutritious, researchers say we should pay attention to how much of these pollutants we’re consuming when we eat it.

The Quick Take

  • What they studied: Whether edible seaweeds contain harmful synthetic chemicals and how much people might eat through their diet
  • Who participated: Seaweed samples collected from China, Japan, Korea, the USA, and Iceland; the study focused on typical eating patterns of adults in East Asia
  • Key finding: Seaweeds contained 177.5 to 2,017 nanograms of organophosphorus esters per gram of dried seaweed—substantially more than most land vegetables. A specific chemical called AO168 was the most common pollutant found.
  • What it means for you: If you eat seaweed regularly, especially in East Asian countries, you may be exposed to these chemicals at levels similar to eating many vegetables. This doesn’t mean you should avoid seaweed, but it’s worth being aware of, particularly if you consume it frequently.

The Research Details

Researchers collected edible seaweed samples from five different countries and tested them in laboratories to measure how much of specific synthetic chemicals they contained. These chemicals, called organophosphorus esters, are used in manufacturing plastics, flame retardants, and other industrial products. The scientists measured different types of these chemicals and compared the amounts found in seaweed to amounts previously found in land vegetables and seafood.

The researchers also studied how these chemicals accumulate in seaweed versus land plants. They discovered that in seaweed, chemicals that are more water-resistant (hydrophobic) tend to build up more, which is the opposite of what happens in land vegetables. Finally, they calculated how much of these chemicals people in East Asia might consume daily through eating seaweed, based on typical eating habits.

This research is important because seaweed is becoming increasingly popular worldwide as a healthy food, but we don’t know as much about its chemical contamination compared to land vegetables. Understanding where pollutants come from and how they accumulate helps us make informed choices about what we eat. The different accumulation patterns in seaweed versus land plants suggest that seaweed may absorb and hold onto these chemicals in unique ways.

This study tested actual seaweed samples from multiple countries using laboratory analysis, which is a reliable method. However, the study doesn’t specify exactly how many samples were tested or provide detailed information about sampling methods. The research appears to be descriptive rather than experimental, meaning it documents what’s present rather than testing cause-and-effect relationships. The findings are published in a peer-reviewed scientific journal, which means other experts reviewed the work before publication.

What the Results Show

Seaweed samples from all five countries contained organophosphorus esters, with total amounts ranging from 177.5 to 2,017 nanograms per gram of dried seaweed. The most common chemical found was a compound called AO168 oxide, which had never been identified as a major contaminant before. Overall, seaweed contained substantially higher levels of these chemicals compared to many land vegetables that were previously studied.

When researchers looked at how these chemicals accumulate in seaweed, they found an interesting pattern: chemicals that don’t dissolve well in water (hydrophobic chemicals) tend to build up more in seaweed. This is opposite to what happens in land vegetables, where these chemicals don’t accumulate as much. This difference suggests seaweed absorbs and holds onto these pollutants differently than land plants do.

Based on typical eating patterns in East Asia, adults who eat seaweed regularly may consume between 61.24 and 170.6 nanograms of these chemicals per kilogram of body weight per day. This amount is similar to what people consume from eating land vegetables, but higher than what people get from eating seafood.

The study found that different types of organophosphorus esters were present in the seaweed samples, including organophosphite antioxidants and organophosphate esters. The specific chemicals found and their amounts varied somewhat between countries, suggesting different sources of contamination or different environmental conditions. The research also showed that seaweed may actually be a more significant dietary source of these chemicals than seafood, which is surprising since seaweed comes from the ocean.

Previous research has documented organophosphorus esters in various foods and environments, but seaweed hasn’t been thoroughly studied. This research shows that seaweed contains higher levels of these chemicals than many land vegetables that were previously analyzed. The finding that these chemicals accumulate differently in seaweed compared to land plants is new and suggests that seaweed may be a unique pathway for human exposure to these pollutants.

The study doesn’t specify how many seaweed samples were tested or provide detailed information about where exactly the samples came from, which makes it harder to understand how representative the results are. The research is descriptive, meaning it tells us what chemicals are present but doesn’t explain exactly why seaweed contains more of these chemicals or where they come from. The study estimates dietary exposure based on typical eating patterns, but actual exposure varies greatly depending on how much seaweed individual people eat. Additionally, the study doesn’t measure whether these chemical levels actually cause health problems in people who eat seaweed.

The Bottom Line

There is no recommendation to stop eating seaweed based on this research. However, if you eat seaweed regularly (several times per week or more), it may be worth moderating your intake and varying your food sources. This is a precautionary approach based on moderate evidence. People who eat seaweed occasionally (a few times per month) likely have minimal exposure to these chemicals.

This research is most relevant to people in East Asia who eat seaweed regularly as part of their traditional diet, and to people worldwide who have recently started eating seaweed frequently for health reasons. Pregnant women and young children might want to be more cautious since they’re more sensitive to chemical exposures. People who eat seaweed only occasionally don’t need to change their habits based on this research.

If you reduce your seaweed consumption, your exposure to these chemicals would likely decrease relatively quickly since these chemicals don’t stay in your body for very long. However, this research doesn’t provide information about how long it takes to see health benefits from reducing exposure, because it doesn’t establish that current seaweed consumption causes health problems.

Want to Apply This Research?

  • Track seaweed consumption frequency: Record each time you eat seaweed (nori, wakame, kelp, etc.) and note the type and estimated amount. Aim to identify your baseline consumption pattern over 2-4 weeks.
  • If eating seaweed multiple times per week, gradually reduce frequency to 1-2 times per week and diversify your vegetable intake by replacing some seaweed servings with other vegetables. Log this change in the app to monitor your progress.
  • Set a weekly reminder to log seaweed consumption. Create a goal to maintain moderate seaweed intake (1-2 times weekly) and track compliance over months. Note any changes in how you feel, though this research doesn’t establish specific health outcomes to monitor.

This research identifies the presence of synthetic chemicals in seaweed but does not establish that eating seaweed causes health problems. The findings suggest caution rather than avoidance, particularly for regular consumers. If you have concerns about your seaweed consumption or chemical exposure, consult with a healthcare provider or registered dietitian. This information is for educational purposes and should not replace professional medical advice. Pregnant women, nursing mothers, and young children should discuss seaweed consumption with their healthcare provider.