What is Arsenic in Seaweed?
Seaweed naturally absorbs trace elements from its marine environment, including the metalloid arsenic. The key distinction for dietary safety lies in the type of arsenic present: organic or inorganic. Organic arsenic compounds, such as arsenosugars, are largely considered non-toxic and are the predominant form in most commercially available seaweeds. In contrast, inorganic arsenic, a known human carcinogen, is the form that poses a health risk. While all seaweeds contain some amount of arsenic, the levels and proportion of the dangerous inorganic form vary significantly by species.
Which Seaweed Has Arsenic? The Species to Watch
While a variety of seaweeds contain arsenic, one species stands out for its high levels of the inorganic form: hijiki (Hizikia fusiforme or Sargassum fusiforme). Several food safety agencies, including those in the UK, Canada, and Australia, have issued warnings against its consumption due to its elevated inorganic arsenic content. For example, one Australian survey found hijiki seaweed with inorganic arsenic levels 23 to 48 times higher than other tested varieties like nori. Consuming even small amounts of hijiki can lead to an intake of inorganic arsenic exceeding recommended daily limits.
Other Brown Seaweeds
Some brown seaweed species, including other members of the Sargassum genus, have also been found to have higher levels of inorganic arsenic. A study focusing on species from the coasts of China found that several brown seaweeds posed considerable carcinogenic risks, with inorganic arsenic levels far exceeding limits set for infant food additives. This is why consumers should be aware of the specific type of seaweed they are eating, especially when it is from the brown algae family.
Lower-Risk Seaweeds for Your Nutrition Diet
For those who want to include seaweed in their diet without the high risk associated with hijiki, several varieties are generally considered safer due to their lower inorganic arsenic content. In these species, the majority of the arsenic is in the less harmful organic form.
- Nori: Used to wrap sushi, nori typically has low levels of inorganic arsenic. A study found negligible inorganic arsenic concentrations in nori samples.
- Wakame: Often found in miso soup and seaweed salads, wakame contains primarily arsenosugars, the safer organic form.
- Kombu: A type of kelp used to make dashi broth, kombu also contains predominantly organic arsenic. However, it can be very high in iodine, so moderate consumption is still recommended.
- Dulse: A reddish seaweed sold as dried flakes or leaves, dulse has been reported to have low levels of inorganic arsenic.
How to Reduce Arsenic Exposure from Seaweed
For those still concerned about arsenic, especially in brown seaweeds, certain preparation methods can help reduce levels.
- Soaking: Studies have shown that soaking hijiki in water for a period of time, especially with a bit of salt, can significantly reduce its total arsenic content. The water used for soaking should always be discarded.
- Boiling and Steaming: Cooking methods like boiling and steaming can also lead to a loss of arsenic, which can dissolve into the cooking water. As with soaking, it is important to discard the cooking water to minimize intake.
- Balanced Intake: Health authorities recommend consuming hijiki only in moderation or avoiding it altogether. A balanced diet with a variety of foods will naturally limit your exposure to any single food contaminant.
Comparison of Common Edible Seaweeds and Arsenic Levels
| Seaweed Type | Brown/Red/Green | Primary Arsenic Form | Inorganic Arsenic Risk Level | Common Uses |
|---|---|---|---|---|
| Hijiki (Hizikia fusiforme) | Brown | Mostly inorganic | High; consumption discouraged by several agencies | Salads, stews (less common in modern cuisine) |
| Nori (Pyropia) | Red | Mostly organic (Arsenosugars) | Low; generally safe in moderation | Sushi rolls, snacks |
| Wakame (Undaria pinnatifida) | Brown | Mostly organic (Arsenosugars) | Low; generally safe in moderation | Miso soup, salads |
| Kombu (Laminaria) | Brown | Mostly organic (Arsenosugars) | Low; generally safe in moderation (high iodine requires moderation) | Dashi broth, cooking |
| Dulse (Palmaria palmata) | Red | Mostly organic | Low; generally safe in moderation | Seasoning, bacon-like strips |
Conclusion: Making Informed Choices
As with all dietary choices, moderation and knowledge are key to ensuring a healthy nutrition diet. While seaweed offers numerous nutritional benefits, including minerals and dietary fiber, the risk posed by inorganic arsenic in some varieties, particularly hijiki, cannot be ignored. By understanding which seaweed has arsenic at higher levels and opting for safer varieties, you can enjoy the health benefits of sea vegetables with minimal risk. Always check the labels of seaweed products and be mindful of your overall consumption, especially if you eat seaweed regularly. You can find more information from reputable sources like the FDA on environmental contaminants in food.
Note: Specific arsenic levels can vary based on the sourcing location and environmental conditions of the seaweed. For the most up-to-date health information, consult resources from national food safety agencies.
Food and Drug Administration (FDA) Information on Arsenic in Food
