The antioxidant ethoxyquin (EQ) is one of a number of legally permitted additives that are added to the fish-meal used in fish feed in order to prevent it from becoming rancid. A small percentage of the additive is incorporated in the flesh of the fish. A person who regularly consumes 300 g salmon a day could be ingesting as much as 15% of the acceptable daily intake (ADI) of EQ.
Ethoxyquin in feed
Ethoxyquin is required to be added to fish-meal in order to prevent it from exploding during sea transport and storage. The European Union has set an combined upper limit for ethoxyquin and other antioxidants (BHA and BHT) of 150 mg per kg of feed. Data obtained from fish-feed and feed-ingredient monitoring programmes have not revealed any instances of this limit being exceeded in Norwegian feed.
Transfer from feed to fish
The direct addition of ethoxyquin to food for human consumption is not permitted within the European Union, but it may be used as a plant pesticide and as an animal feed additive. Feeding trials on fish have shown that some EQ is carried over from the feed to the flesh of the fish. In order to maintain a satisfactory level of public health, threshold values known as maximum residue limits (MRL) have been set. Several different MRLs exist for ethoxyquin, depending on which type of food is involved. The limits also differ from one country to another. The USA has adopted an MRL of 0 mg/kg for milk, 0.5 mg/kg for meat and eggs, 3 mg/kg for chicken liver and 5 mg/kg for fat. In Japan there is an MRL of 1 mg/kg for fish, while the European Union has not set an MRL for EQ in animal foodstuffs.
The highest concentration of EQ found by NIFES in salmon fillets was 0.2 mg/kg, while the average value in any individual year between 2005 and 2009 ranged from 0.02 to 0.04 mg/kg. MRLs can be established both for substances such as EQ and for their metabolites, if these are found in sufficiently high concentrations in foodstuffs.
In salmon, EQ is metabolised primarily to ethoxyquin dimer (EQDM), and the highest combined concentration of EQ and EQDM found by NIFES in salmon fillet was 2.5 mg/kg. In comparison, the MRL for the sum of EQ and various metabolites in pears is 3 mg/kg. NIFES has investigated the toxicity of EQDM and its effects on fish health and food safety. No negative effects on growth or signs of discomfort were observed in rats that were given feed to which 2500 times more synthetic EQDM than the acceptable daily intake had been added, which suggests that rats can tolerate relatively high doses of EQDM.
Is it safe to eat fish that have been given ethoxyquin in their feed?
In order to ensure that consumption of additives will not put our health at risk, the health authorities have established maximum acceptable daily intake levels of additives used in food, as they have for pesticides. ADIs are defined as the amount of a substance that may be consumed by a person on a daily basis throughout their life without damage to their health. The level is set on the basis of the toxicity of the substance involved. The World Health Organization and its independent expert committee (Joint FAO/WHO Meeting on Pesticide Residues, JMPR) has set a daily ADI in plants of 0.005 mg/kg body weight for the sum of EQ and three of its metabolites.
Analyses of EQ in fillets from a number of farmed species (cod, salmon, halibut and trout) have shown that EQ can contribute between 4 and 15% of the ADI on daily consumption of a 300 g portion of fish (the metabolites that are found in plants and are included in the JMPR’s ADI do not occur in fish). To date, no ADI has been established for the combined concentration of EQ and EQDM).
Is ethoxyquin toxic?
Everything is toxic if it is consumed in sufficiently large amounts, which is to say that the amount of a given substance that we consume is what determines whether or not it can damage our health. Large amounts of EQ can damage the liver and kidneys in rats. However, the amount of EQ that we consume by eating fish is negligible, and farmed fish is therefore regarded as being safe to eat. The European Food Safety Authority is currently re-evaluating permitted feed additives such as EQ. Better knowledge of the toxicity and health effects of feed additives will be a key element of the decisions that it makes.