Very high levels of undesirable substances in halibut weighing over 100 kg, but low levels in smaller halibut

Foto: Eivind Senneset

Large halibut weighing over 100 kg contain very high levels of undesirable substances, according to a new survey. Halibut weighing less than 40 kg, however, which accounted for more than 80 per cent of the analysed fish, contained low levels of undesirable substances like mercury and organic contaminants. For 85 per cent of the halibut analysed, the levels of undesirable substances were below the EU maximum level in all parts of the fillet.

Several smaller surveys conducted a few years ago indicated that the levels of undesirable substances, especially organic contaminants, could be very high in Atlantic halibut. On assignment for the Norwegian Food Safety Authority, NIFES therefore initiated a comprehensive survey of important undesirable substances in Atlantic halibut from Norwegian waters. Between September 2013 and March 2016, a total of 392 halibut were collected along the entire Norwegian coast and in the open sea from the Barents Sea in the north to Skagerrak in the south, focusing on areas important for commercial fishing of this species. The halibut were analysed for metals such as arsenic, cadmium, mercury and lead, and organic contaminants such as dioxin, dioxin-like PCBs and non-dioxin-like PCBs. The results of the survey are now available in a new report.

High levels in large halibut, less in smaller ones

The halibut that were analysed in this study differed greatly in size. The smallest fish weighed 0.7 kg, while the biggest weighed 225 kg, and the average weight was 24 kg. Most of the fish collected belonged to the weight class that are caught the most, i.e. fish weighing up to 40 kg. The scientists found a link between weight and the amount of undesirable substances.

‘The bigger the fish, the higher the levels of contaminants,’ says NIFES scientist Bente Nilsen, one of the scientists behind the report.

The scientists analysed samples from two different parts of the fillet. They analysed one sample from the relatively lean part (B-cut), which is the major part of the fillet people normally eat, and one sample from the more oily belly part of the halibut muscle (I-cut). The level of organic contaminants was about three times higher in the oily part than in the lean part. Less than two per cent of the halibut contained concentrations of organic contaminants in the B-cut that exceeded the EU maximum level for these substances in fish fillet for human consumption. In the more oily belly part, however, 15 per cent of the analysed fish contained levels of dioxins and dioxin-like PCBs that exceeded the maximum level.

The concentration of organic contaminants increased gradually with the size of the fish, in both the B-cut and the I-cut. While less than one per cent of the halibut weighing less than 40 kg contained concentrations of organic contaminants in the B-cut that exceeded the maximum limit, 60 per cent of the fish weighing more than 120 kg contained concentrations in the leaner part of the fillet that exceeded the maximum limit.

‘Our results show that, in fish above 100 kg, there is a high risk that the levels of organic contaminants exceed the maximum level,’ says Nilsen.

As regards halibut weighing between 11 and 40 kg, which is the category most caught and sold, the situation is very different.

‘In smaller fish, the risk of exceeding the maximum level is low,’ says the NIFES scientist.

Also when it comes to mercury in halibut, there is great variation between individual fish. Two per cent of the halibut contained levels of mercury exceeding the EU and Norwegian maximum level, and the levels increased gradually with the size of the fish. While no fish weighing less than 39 kg exceeded the maximum level, about one-fifth of the halibut weighing between 60 and 225 kg contained mercury above the maximum level.

High levels in halibut from Sklinnabanken

The levels of mercury and organic contaminants in Atlantic halibut also varied between different geographical areas, and the highest levels were found in an area off the coast of Nordland county, near Sklinnabanken fishing ground in the Norwegian Sea.

‘Our findings indicate that a diet with much halibut from this area near Sklinnabanken can lead to an unwanted high intake of mercury, dioxins and dioxin-like PCBs,’ says Nilsen.

The levels of cadmium and lead in the halibut were very low, only just above the quantification limit.

To summarise, 85 per cent of the halibut analysed in this survey contained levels of both metals and organic contaminants below the maximum level in all parts of the fillet. Only halibut weighing more than 100 kg contained levels that far exceeded these limits. With the exception of halibut from Sklinnabanken, it is safe to eat halibut weighing less than 100 kg.

Based on this survey, the Norwegian Food Safety Authority has asked the Directorate of Fisheries to ban all fishing of halibut of more than two metres in length (approx. 100 kg) and to ban all fishing of halibut from an area near Sklinnabanken.

 

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