Arsenic can be found in seaweed

30 January, 2023

Seaweed and algae have emerged as an increasingly popular foodstuff. But if we are going to start eating more seaweed, we need better rules about which seaweed we can eat, according to a new report.

– There is a difference between different kinds of seaweed. We would never eat fly agaric although we can eat other mushrooms, says Barbro Kollander at the Swedish Food Agency.

In October last year, the UN released a report saying that food from the sea, including seaweed and algae, will be an increasingly important source of food as we make the transition to a more climate-smart and eco-friendly diet. But gulping down different kinds of seaweed isn’t entirely without risk. Many of them contain far too high amounts of arsenic, heavy metals and iodine. Today we do not know which types of seaweed are safe to eat.

– The problem is that at the moment we aren’t running the same kinds of checks on seaweed that we do on other food and we need to change that, says Barbro Kollander, Senior Chemist at the Swedish Food Agency.

She was involved in writing a report from the food agencies of the Nordic countries which found that it is mainly cadmium, arsenic and iodine that are too high in some seaweed. This also applies to seaweed farmed in the Nordic region.

Major difference between species

The report shows that there is a major difference in content between different species of seaweed and also in different parts of one and the same type of seaweed. The water in which the seaweed grows also affects its content.

Harmful amounts of iodine were found in seaweed species including sugar kelp (Saccharina latissima), oarweed (Laminaria digitata) and tangle (Laminaria hyperborea). Oarweed contained high amounts of inorganic arsenic.

– Eating seaweed is a fairly new thing for us in the Nordic region, says Barbro Kollander.

– We don’t have a tradition of doing so, which means we have no regulatory framework for handling it and no threshold values. Compared with meat production, cereals or vegetables, we know very little about processing and the content of substances harmful to health in seaweed.

Although, so far, cooking with seaweed at home isn’t that common, most of us will have come into contact with seaweed in sushi restaurants for example. That bright green seaweed salad is one example where there’s a risk that the heavy metal content might be too high.

– Basically, not all seaweed is good for us. I tend to compare it with mushrooms. Some you can eat and some you can’t. We’d never think it was a good idea to eat a fly agaric, Kollander points out.

Pregnant and breastfeeding women should be extra cautious about eating products made from seaweed.

Minerals and fibre

Seaweed isn’t just used as an ingredient in its own right; it’s also used to extract alginates as an alternative to gelatine, for example. A lot of research is in progress, including at Chalmers University of Technology in Gothenburg, on extracting proteins from algae. With some species of algae, heavy metals will be carried into the end products and it’s important to choose the right species and to use algae from water with a low burden of substances harmful to health when manufacturing food.

Even if a particular type of seaweed is approved as food in another country, that doesn’t mean it’s OK to eat in the EU.

Japan has an upper limit for the safe intake of iodine of 3,000 microgrammes per day for adults. In Sweden the limit is 600 microgrammes per day.

But what’s so good about seaweed? Barbro Kollander says that seaweed contains fibres, different sorts of minerals and some other vitamins such as vitamin B12.

The report, commissioned by the Nordic Council of Ministers, is intended to serve as underlying documentation in the EU which is currently looking at the safety risks of iodine and heavy metal in seaweed.

Text: Petra Hedbom/TT

Photo: Jessica Gow/TT Arkiv



Text: Petra Hedbom/TT
Photo: Jessica Gow/TT

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