Some seaweeds, like the one shown here, are a source of essential nutrients but may also expose consumers to unsafe levels of heavy metals. Credit: Adapted from ACS Food Science & Technology 2024, DOI: 10.1021/acsfoodscitech.3c00476
Key points:
- Researchers measured the beneficial nutrients and toxic elements of 6 types of seawood in Hawaii.
- Four of the six of at least were excellent sources of at least one essential mineral.
- However, two farmed species contained elevated lead levels, which are above those recommended for safe eating in Taiwan.
Seaweed is a popular food around the world, but it has a downside: it might also expose consumers to heavy metals that accumulate in the fronds before harvest.
Given seaweed’s importance in Hawaii, researchers at the University of Hawai‘i at Ma̅noa, decided to analyze key nutrients and metals in seaweed species grown around the island. For the study, published in ACS Food Science & Technology, researchers obtained six types of seaweed that were either cultivated or collected in the wild. They measured the beneficial nutrients and toxic elements in each species and used statistics to differentiate between samples. They found that:
- Four of the six tested seaweeds were excellent sources of at least one essential mineral—with greater than 20% of the recommended daily value per serving of either iron, manganese, or both calcium and magnesium.
- The amounts of protein, fat, carbohydrates and fiber varied significantly across the tested species, and generally aligned with previous nutritional assessments for three of the seaweeds.
- Two wild species that are not commonly consumed, S. aquifolium and S. echinocarpum, had the highest levels of arsenic-containing compounds—far exceeding safe consumption limits established by other countries.
- Two farmed species, H. formosa and G. parvispora, contained elevated lead levels, which are above those recommended for safe eating in Taiwan.
Overall, the team found that Hawaiian seaweeds provide many essential minerals and nutrients, but may also expose consumers to unsafe levels of heavy metals, depending on factors such as seaweed type and growing conditions.
Previously published studies suggested that boiling or rinsing other seaweed species, which weren’t included in this work, could remove some harmful substances. But these techniques may also strip away beneficial nutrients.
Now, the researchers are collaborating with seaweed growers to study the impact of growing location and common cooking practices on levels of heavy metals and nutrients in Hawaiian seaweeds. Their findings could inform future regulations and ensure nutritious and safe seaweed food products.