Organic solvents are currently used to remove persistent organic pollutants (POPs) from fishmeal. However, a new doctoral thesis points to the fact that vegetable oil can do the job just as efficiently, but in a more environmentally-friendly manner.
Fishmeal and fish oils are among the main sources of POPs in animal feed and food. Fish caught in certain areas of the sea contain high levels of POPs. These POPs break down very slowly and, as such, remain in the food chain. The water is removed when fishmeal and oil are produced from fish, resulting in a higher concentration of POPs in the end products.
As POPs are fat-soluble, it is necessary to separate the fat to decontaminate the fishmeal. Today the chemical hexane is used to achieve this, but the doctoral research demonstrates that vegetable oil can do the job just as efficiently.
“Soybean oil proved to be an equally efficient cleaning agent as solvents and it is also more environmentally friendly. Fish oil can also be used to decontaminate fish meal,” says Nofima Senior Scientist Åge Oterhals.
In his doctoral project Oterhals has studied processes that may be used to remove dioxins, polychlorinated biphenyls (PCB) and brominated flame retardants from both fishmeal and fish oil. This knowledge is in considerable demand from both the industry and the authorities. The method of using vegetable oil in the cleaning process is ready for industrial use.
“Decontamination with fish or soybean oil may be implemented at existing fishmeal factories and is anticipated to require lower investments. If you decontaminate with solvents such as hexane, you require separate plants with comprehensive safety equipment.” says Oterhals.
He also studied two processes to decontaminate fish oil from POPs. The oil may be decontaminated by adding “activated carbon”, which adsorbs the POPs, and then removing the carbon. POPs may also be removed using molecular distillation, a process in which the POPs evaporate and are separated from the bulk oil.
The results showed that activated carbon efficiently removes dioxins from fish oil and to a lesser degree removes PCB. However, it does not remove brominated flame retardants.
“In many cases you will succeed using activated carbon, but this is reliant on the relationship between the dioxin and PCB level in the raw material and whether the aim is to reduce other POPs,” explains Oterhals.
Molecular distillation proved to be more or less equally efficient for all these POPs and consequently the best method for removing POPs from fish oil. But nutrients such as vitamins and cholesterol disappeared along with the POPs. However, it is possible to preserve at least 80 percent of the nutrients in cleaned oil using this method.
“In Norway decontamination by molecular distillation is utilised on fish oil used in food and health food products. When the fish oil is used as an ingredient in fish feed, other experiments show that cleaned oil does not produce negative effects. To the contrary, Nofima has carried out experiments which indicate that this has a favourable effect on the salmon,” said Oterhals.
The EU has set maximum limits for the amount of POPs permitted in fishmeal and fish oil. A large proportion of the Norwegian industry’s raw materials originate from the Norwegian Sea and Barents Sea, where the content of POPs is low. Consequently, cleaning of fishmeal and fish oil is so far unnecessary, but must be taken into account if it becomes relevant to use raw materials from other areas. In Denmark, the industry receives a lot of raw materials from the Baltic Sea and the North Sea. The content of POPs in these areas is higher and consequently a portion of the fishmeal and fish oil must go through a decontamination process.
European Union regulations for levels of POPs are likely to change from 1st January 2012. The proposed new levels, if adopted, will lead to tighter restrictions.
Norway has had lower maximum limits for fish oils used in food and health food products than the EU, so stricter requirements from the EU will be of little consequence for Norwegian fish oil producers. The Norwegian maximum limits are also in accordance with the voluntary maximum limits adopted by the refining industry.