Study assesses risk of toxic metal and iodine intake from macroalgae and halophytes in Portugal
These marine plants are currently considered functional foods, offering a valuable source of essential nutrients and bioactive compounds.
A team of researchers from the Faculty of Sciences and Technology of the University of Coimbra (FCTUC), in collaboration with the University of Aveiro, analysed levels of toxic metals and iodine in macroalgae and halophytes — plants naturally adapted to saline environments — collected across Portugal.
These marine plants are recognised as functional foods due to their nutritional and bioactive properties. However, their increasing popularity and limited research have raised questions about potential health risks.
The study found that arsenic and iodine are the two main elements that may limit the safe consumption of macroalgae, particularly brown algae, which are the most widely consumed. Halophytes, by contrast, could be a safer alternative when grown in uncontaminated areas.
Arsenic is classified as a Group I carcinogen by the World Health Organization’s International Agency for Research on Cancer (IARC), and high iodine intake may affect thyroid function. Monitoring these elements is already underway in several European countries, following a 2018 recommendation from the European Food Safety Authority (EFSA) to ensure food safety and support the sustainable development of the sector.
“Our goal was to determine whether cadmium, lead, mercury, arsenic and iodine levels in these ‘marine greens’ exceed known safety limits,” explains Elsa Teresa Rodrigues, a researcher at the Centre for Functional Ecology (CFE) and the Department of Life Sciences at FCTUC. “We also evaluated the potential contribution of different species and sampling sites to marine farming and the blue economy in Portugal, since contamination levels vary depending on where the plants grow.”
The results show that estuarine areas are unsuitable for marine agriculture, while Portugal’s rocky coastline offers safer conditions.
The researchers argue that marine farming should only be allowed in areas with proven environmental quality and that food products must meet high safety standards, offer fair market value, bring both economic and environmental benefits, including the reuse of by-products in other industries.
They also urge the European Commission to set maximum limits for arsenic and iodine in edible seaweed and call for strict national monitoring. Meanwhile, they advise consumers to limit their intake of brown algae, given their high levels of arsenic and iodine, which may pose health risks.
The scientific article “Risks of exceeding health-based guidance values for toxic metals and metalloids through seaweed and halophyte consumption” is available here.
(Nota de imprensa elaborada por Sara Machado, FCTUC)