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Contaminants

With a history of over fifty years of contributing to animal feed, fishmeal and fish oil are very well known ingredients which are manufactured from raw materials that are sourced from the natural environment. Being natural resources sourced from across the world, these resources can sometimes be exposed to naturally occurring contaminants of various types that might be in the soil, water, or air. Human activity is the main source of this contamination, which has a tendency to end up in the seas.

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Regulatory frameworks exist at multiple levels at both national and international levels (eg: EFSA for food intended for direct human consumption, and CODEX alimentarius for feed for food producing animals).  Importantly, these regulations keep developing based on the state of the science as our understanding of threats grows and our ability to measure them improves. For some contaminants, the body of science is growing but is still in its relative infancy. The continuation of support for high quality scientific research to underpin national government policy decisions and any future regulation or management in this area is essential. A range of potential contaminants have been reported as present or at risk in marine ingredients, some of these include:

Perfluoroalkyl and polyfluoroalkyl substances (PFAS)

PFAS are a group of chemicals that are found in a variety of everyday products like packaging, cookware, clothes, and refrigerants. In January 2023, the European Commission introduced maximum levels (MLs) for PFAS in a range of food types (eggs, fish, milk, and meat products). No MLs presently exist for feeds or any feed ingredients, though this is a likely follow on. Analysis of fishmeal samples for different types of PFAS show that this contamination is highly variable both geographically and which types are present in any given sample. The current scientific understanding and technical methodologies needed to test for PFAS at the very low concentrations found in food are a very recent development. In 2022, the Norwegian Marine Research Institute released its technical report on contaminants in farmed Salmon, rainbow trout, cod and arctic char with values averaging 0 μg/kg. (https://www.hi.no/en/hi/nettrapporter/rapport-fra-havforskningen-en-2021-40).

Dioxins

Dioxins and dioxin-like compounds (DLC) are by-products of many industrial as well as some natural processes such as forest fires. Dioxin is a generic term given to two chlorinated structures namely polychlorinated dibenzo-para dioxins (PCDD) and polychlorinated dibenzo furans (PCDF). DLC include dioxin-like polychlorinated biphenyls (DL-PCBs) that have the same toxic mechanism as PCDD/Fs. There are many different types of these compounds, with 75 PCDD, 135 PCDF and 130 PCB “congeners” known about that differ depending upon the number and position of the chlorines in their structure. Because dioxins are very stable, they have a very high tendency towards bioaccumulation and biomagnification in various aquatic organisms. The most important direct source for dioxins to the aquatic and marine environment is through deposition of airborne particle-bound dioxins. EU Regulations implemented in September 2012 stipulated measures to monitor and control dioxins in fats and oils. Fish oils containing higher levels of dioxins are treated with activated carbon, or other methods, to reduce the dioxin content before they can be used for feed or food purposes.

  • Berntssen MH, Lundbye AK, Torstensen BE (2005) Reducing the levels of dioxins and dioxin‐like PCBs in farmed Atlantic salmon by substitution of fish oil with vegetable oil in the feed. Aquacult. Nutr. 11: 219-231.
  • Berntssen MHG, Julshamn K, Lundebye AK (2010a) Chemical contaminants in aquafeed and Atlantic salmon (Salmo salar) following the use of traditional versus alternative feed ingredients. Chemosphere 78: 637–646.
  • Berntssen MHG, Olsvik PA, Torstensen BE, Julshamn K, Midtun T, Goksøyr A, et al. (2010b) Reducing persistent organic pollutants while maintaining long chain omega-3 fatty acid in farmed Atlantic salmon using decontaminated fish oils for an entire production cycle. Chemosphere 81: 242–252.
  • Berntssen MHG, Maage A, Julshamn K, Oeye BE, Lundebye AK, (2011) Carry-over of dietary organochlorine pesticides, PCDD/Fs, PCBs, and brominated flame retardants to Atlantic salmon (Salmo salar L.) fillets. Chemosphere 83: 95−103.
  • Glencross BD, Baily J, Berntssen, MHG, Hardy R, MacKenzie S, & Tocher DR, (2020). Risk assessment of the use of alternative animal and plant raw material resources in aquaculture feeds. Reviews in Aquaculture, 12(2), 703-758.

Microplastics

Microplastics (and nanoplastics) are a global challenge and affect the whole seafood supply chain. At this stage, we know that plastics and microplastics are ingested by marine life. What we don’t know is the level of risk attached to the ingestion for the consumer of seafood products that may contain plastics or microplastics. This area is another that is hampered by a lack of standardised analytical methodology. Work has progressed showing that like other contaminants, the levels of microplastics in fishmeal is highly variable both geographically and the types that are present in any given sample. Studies on the origins of this contamination in fishmeal are yet to be published.

  • [https://doi.org/10.1016/j.aquaculture.2020.736316].

Arsenic

Arsenic (As) compounds are considered a toxic heavy metal and are often found in an organic form in fish, where they can be present as both lipid soluble and water-soluble compounds. The most common organic form of arsenic (arsenobetaine) is considered to be non-toxic. However, the inorganic compounds are highly poisonous and have been widely used as insecticides. When consumed by humans, arsenic leads to brain damage, compromises the immune system and is also a carcinogen. Analysis of samples of fishmeals have shown total arsenic arsenic levels in the range of 3.4–8.3 mg/kg. However, a more recent study, has found that inorganic arsenic comprises only a small (<2%) fraction of the total arsenic content. However, only a small percentage of the inorganic arsenic is converted into any of the organic forms. Organic arsenic readily accumulates in the muscle of fish, whereas the toxic inorganic form tends to taccumulates mostly in the viscera.

  • Amlund H, Berntssen MHG (2004). Arsenobetaine in Atlantic salmon (Salmo salar L.): influence of seawater adaptation. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology 138: 507-514.
  • Amlund H, Francesconi KA, Bethune C, Lundebye AK, Berntssen MHG (2006) Accumulation and elimination of dietary arsenobetaine in two species of fish, Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.). Environmental Toxicology and Chemistry 25: 1787-1794.
  • Glencross BD, Baily J, Berntssen MHG, Hardy R, MacKenzie S, Tocher DR, (2020). Risk assessment of the use of alternative animal and plant raw material resources in aquaculture feeds. Reviews in Aquaculture, 12(2), 703-758.

Cadmium

Cadmium (Cd) is a natural element and makes up about 0.1 mg/kg of the Earth's crust and can be found throughout our environment and food.  Although cadmium is considered a toxic heavy metal for terrestrial organisms, it exhibits a nutrient type distribution in the ocean with internal cycling of cadmium in the ocean influenced by biological activity. Surveys of cadmium concentrations in marine organisms have shown that some species accumulate higher levels of cadmium than others, with the heavy metal typically being more concentrated in the viscera (gut) than the meat of those animals.

  • Berntssen MHG, Lundebye AK, Hamre K (2000) Tissue lipid peroxidative responses in Atlantic salmon (Salmo salar L.) parr fed high levels of dietary copper and cadmium. Fish Physiology and Biochemistry 23: 35-48.
  • Berntssen MHG, Aspholm OO, Hylland K, Bonga SEW, Lundebye AK (2001) Tissue metallothionein, apoptosis and cell proliferation responses in Atlantic salmon (Salmo salar L.) parr fed elevated dietary cadmium. Comp. Biochem. Physiol. C-Toxicol. Pharmacol. 128: 299-310.
  • Berntssen MHG, Waagbo R, Toften H, Lundebye AK (2003) Effects of dietary cadmium on calcium homeostasis, Ca mobilization and bone deformities in Atlantic salmon (Salmo salar L.) parr. Aquacult. Nutr. 9: 175-183.
  • Glencross BD, Baily J, Berntssen MHG, Hardy R, MacKenzie S, Tocher DR, (2020). Risk assessment of the use of alternative animal and plant raw material resources in aquaculture feeds. Reviews in Aquaculture, 12(2), 703-758.

Lead

Lead (Pb), another well-known heavy metal, occurs in the environment both naturally and, to an increasing extent, from anthropogenic activities such as mining and smelting, battery manufacturing and the use of leaded petrol (gasoline). Lead contamination of food arises mainly from the environment or during food processing. Although lead exists in both organic and inorganic forms, only inorganic lead has been detected in food.

  • Glencross BD, Baily J, Berntssen MHG, Hardy R, MacKenzie S, Tocher DR, (2020). Risk assessment of the use of alternative animal and plant raw material resources in aquaculture feeds. Reviews in Aquaculture, 12(2), 703-758.

Mercury

Mercury (Hg) and most of its compounds are renowned for being extremely toxic.  Mercury can be biomethylated to form organic compounds such as methylmercury, which is most toxic form. Methylmercury (meHg) is often formed in aquatic systems, and as such it tends to be accumulated from bacteria through to fish via aquatic food chains. Notably, species of fish that are in a high trophic position in the food chain, such as sharks and scrombrids (mackerels and tunas), tend to contain higher concentrations of methylmercury than other species, as it continues to accumulate in each animal upon consumption, a process referred to as biomagnification. Due to this biomagnification process, fish and other aquatic species are considered as one of the main sources of meHg exposure in the human diet. Attention has been given to the sources of fish meals used in a survey of Norwegian salmon feeds, Berntssen et al. (2010a) found that meHg was the dominant form present, comprising more than 80% of the mercury content.

  • Berntssen MHG, Hylland K, Julshamn K, Lundebye AK, Waagbo R (2004) Maximum limits of organic and inorganic mercury in fish feed. Aquacult. Nutr. 10: 83-97.
  • Amlund H, Lundebye AK, Berntssen MHG (2007) Accumulation and elimination of methylmercury in Atlantic cod (Gadus morhua L.) following dietary exposure. Aquatic Toxicology 83: 323-330.
  • Berntssen MHG, Julshamn K, Lundebye AK (2010a) Chemical contaminants in aquafeed and Atlantic salmon (Salmo salar) following the use of traditional versus alternative feed ingredients. Chemosphere 78: 637–646.
  • Glencross BD, Baily J, Berntssen MHG, Hardy R, MacKenzie S, Tocher DR, (2020). Risk assessment of the use of alternative animal and plant raw material resources in aquaculture feeds. Reviews in Aquaculture, 12(2), 703-758.​​​​​​​

Mineral oil hydrocarbons (MOH)

Mineral oil hydrocarbons (MOH) comprise a wide range of chemical compounds obtained mainly from petroleum distillation and refining. MOH are mostly used for lubricants (gears, valves etc) in production, heat transfer fluids, and hydraulic fluids. They are largely found as potential environmental contaminants, either already present in the biomass, coming from engine emissions, spills, or use of contaminated additives. There two groups of mineral oil hydrocarbons, mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH), both of petrochemical and synthetic origin and both having differing effects on human health. EFSA experts provisionally concluded that mineral oil saturated hydrocarbons (MOSH) do not pose a health concern. EFSA also confirmed that some substances in the group known as mineral oil aromatic hydrocarbons (MOAH) are a possible health concern.

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