“We know that brown crabs can contain high levels of cadmium, particularly in northern Norway. How the crab is prepared also affects how much of the heavy metal ends up in the end product. We wanted to look at how much cadmium the crab products sold in shops actually contain”, explains Sylvia Frantzen, a researcher at the Institute of Marine Research (IMR).
Scientists took samples of whole, cooked brown crabs, crab claws, stuffed crab shells, tinned crab pâté and tinned crab meat from shops in the Bergen area and in Svolvær. Our analyses found high levels of the heavy metal cadmium in several of the products.
Cadmium is a toxic heavy metal that accumulates in the bodies of fish, mammals and humans, and consuming excessive amounts of cadmium can lead to kidney damage, osteoporosis and an increased risk of cancer.
Scientists found the highest levels of the heavy metal in the brown meat of the whole, cooked crabs, which contained much higher values than the other products. Earlier research revealed that the heavy metal is mainly in the digestive gland, which makes up a large proportion of the brown meat.
A maximum level has been set for the amount of cadmium permitted in the claw meat of crabs, which is 0.5 mg of cadmium per kg, but there is no such limit for the brown meat. Nevertheless, the Norwegian Food Safety Authority advises women of childbearing age and children against eating it. The brown meat of the whole, cooked crabs analysed in this study contained cadmium levels as high as 2.7 mg per kg.
The researchers also found high levels of cadmium in mixed crab meat products such as tinned crab pâté and stuffed crab, with all of the samples of these products containing more cadmium than is allowed in claw meat. The products with the highest cadmium levels had more than three times the permitted level for claw meat. The highest value found in stuffed crab was 1.4 mg per kg, while it was even higher in crab pâté, which had up to 1.8 mg per kg.
Mixed crab meat products contains a mixture of white claw meat and brown meat from the shell. This explains their high cadmium levels: when you mix the brown meat that is high in cadmium with white meat, the end product inevitably also has high levels of cadmium.
“Most of the cadmium is in the brown meat, so if you use this product you also get the heavy metal”, says Frantzen.
There is not much cadmium in the white claw meat of raw crabs, but recent research has shown that the heavy metal is transferred from the brown meat to the claws if the crab is frozen and thawed, or if it is cooked with the claws on.
The crab claws that were sold loose had the lowest cadmium levels, but with big differences between the various batches of claws. This may suggest that the claws came from crabs caught in different areas. The Norwegian Food Safety Authority has warned against eating crab from areas north of Saltenfjorden in the county of Nordland, as cadmium levels are particularly high in the crabs caught there.
“When you buy loose crab claws in a shop, you don’t know where they were caught, or whether or not they were cooked on the crab. All of the samples that we took from loose crab claws showed low cadmium levels, which suggests that those particular claws had been cooked separately from the rest of the crab”, says Frantzen.
The claw meat of the whole, cooked crabs contained more cadmium than the loose claws, which indicates that some of the cadmium may have entered the claw meat during cooking. Nevertheless, only one of these samples exceeded the permitted level of cadmium.