Cooking crabs correctly keeps the claw meat cadmium-free

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There was ten times as much cadmium in the claw meat of crabs that had been cooked with their claws on as in raw claw meat, and levels were even higher if the crabs had been frozen before cooking. Photo: HI (Eivind Senneset)

At several locations in Norway, brown crabs contain high levels of the toxic heavy metal cadmium. By preparing a crab correctly, you can prevent the great majority of the heavy metal from entering the claw meat.

“There is a general problem, which is that cadmium levels in brown crabs are too high, particularly in northern Norway. The good news is that we can avoid exposure to this heavy metal if we prepare the crab correctly”, says Martin Wiech, a research scholar at the Institute of Marine Research (IMR).

Cadmium is transferred during thawing and cooking

Researchers at the IMR have studied the cadmium values in crabs from various parts of Norway, and they have looked at what happens to the cadmium levels when you freeze, thaw and cook the crabs.

Their experiments showed that the vast majority of cadmium is in the brown meat, and more specifically the crab’s digestive gland, which constitutes a large proportion of the innards. The experiments also demonstrated that some of the toxin is transferred to the appreciated white claw meat during thawing and cooking, which explains why one also occasionally finds high cadmium levels in claw meat.

There was ten times as much cadmium in the claw meat of crabs that had been cooked with their claws on as in raw claw meat, and levels were even higher if the crabs had been frozen before cooking. Meanwhile, researchers found less cadmium in the brown meat after thawing and cooking, which confirms that the heavy metal is transferred from the brown meat to the claws.

Cook the claws separately

By separating the claws from the rest of the crab before freezing or cooking, you can prevent the great majority of the cadmium from entering the claws.

“Cadmium levels in raw claw meat are quite low, but our experiments showed that the cadmium leaks from the brown meat to the claw meat if the claws are left on the crab during thawing or cooking”, says Wiech.

It is illegal to tear the claws off live crabs, and it is important to kill the crab before separating the claws from the rest of the body.

“You can kill the crab humanely using an awl, for example, by stabbing it quickly into the hollow under the tail, and then moving the awl around. Then stab the awl into one of the eyes. This method, which destroys the two biggest nerve centres in the crab, is one of the approved ways to kill a crab”, says Wiech.

Cadmium is present in the soil

Cadmium is a toxic heavy metal that accumulates in the bodies of fish, mammals and humans, and consuming excess cadmium can lead to kidney damage, osteoporosis and an increased risk of cancer.

It is naturally present in the soil, and in Norway most of the cadmium that we consume comes from grains, grain products, root vegetables and potatoes, as we eat a lot of these products. There are higher cadmium concentrations in the innards of crabs and other animals, but as we eat these foods less often, for most of us they aren’t an important source of cadmium.

In northern Norway, cadmium values in crabs are higher than in the rest of the country, which was also confirmed by the IMR’s samples. The Norwegian Food Safety Authority advises against eating brown crabs caught north of Saltenfjorden in the county of Nordland, but it is not yet known why crabs there contain more cadmium than elsewhere along the Norwegian coast. Scientists at the IMR are currently trying to find an answer to that particular question.