Contaminants in food

Heavy metals such as lead, cadmium, mercury and arsenic are chemicals which can be present in the environment from both natural sources and human activity. Human exposure to these metals may be from environmental exposure or contaminated food and water. Accumulation in the body over time can cause harm.

One known source of lead is from lead shot in wild-caught game. Regularly eating lead-shot game can significantly increase exposure to lead. 

Regulatory maximum levels exist for a variety of foods with a known risk of specific heavy metal contamination such as leafy vegetables, fish, meat, fruit products, chocolate, rice and products intended for consumption by babies and young children

Mycotoxins are naturally occurring chemicals produced by different types of moulds (fungi). These moulds can grow on crops and foods such as cereal grains, dried fruits, coffee, nuts, spices and apple juice. 

Environmental conditions affect the growth of moulds and production of these toxins. Warm and/or humid conditions can increase mould growth and mycotoxin production at various points between the field and storage post-harvest. 

Common mycotoxins of concern include:

• Aflatoxins (B1, B2, G1, G2 and M1) 
• Fusarium mycotoxins such as fumonisins B1, B2 and B3
• Tricothecenes such as nivalenol (NIV), deoxynivalenol (DON), T-2 and HT-2 
• Ochratoxin A (OTA)
• Zearalenone
• Patulin
• Ergot alkaloids such as citrinin, sterigmatocystin and Alternaria

Mycotoxins can cause adverse health effects in humans and animals, with aflatoxins being the most harmful type of mycotoxin.

Mycotoxins are naturally occurring and cannot be avoided completely in foods however controls and regulatory maximum levels ensure that exposure from food is as low as reasonably achievable.

Marine biotoxins are naturally occurring chemicals produced by phytoplankton which are consumed by and can accumulate in the edible tissues of live bivalve molluscs such as oysters, mussels and scallops.

Marine biotoxins are regulated in shellfish and there are currently three groups of concern for regulation.

• Paralytic shellfish poisoning (PSP) Toxins
• Amnesic shellfish poisoning (ASP) Toxins
• Lipophilic shellfish toxins (including Diuretic shellfish poisoning toxins)

Monitoring programmes are in place to detect the presence of marine biotoxins in shellfish above regulatory limits and, if detected, affected areas are closed for harvestinguntil levels fall back below unsafe levels. 

Further information on marine biotoxins can be found here.

Persistent organic pollutants are contaminants that can enter the food chain from the environment and are produced due to human activity. 

POPs are a category of chemicals which range from individual compounds to groups of closely related compounds known as congeners which have common properties. These properties include stability and persistence in water, air and soil for many years, toxicity and bioaccumulation in humans and animals.

POPs are under constant review and are added to a list in the Stockholm Convention. The Stockholm Convention is an international agreement designed to eliminate or control occurrence, production and use of harmful chemicals. 

The original list of chemicals contained chemicals including PCBs, Dioxins, DDT, Aldrin and Dieldrin. More recent additions include brominated flame retardants (BFRs), perfluorooctane sulphonate (PFOS), polychlorinated naphthalenes (PCNs) and short-chain chlorinated paraffins (SCCPs).

Alkaloids are naturally occurring toxic compounds which can be found in a variety of plant species. Their purpose is to deter grazing and protect plants from damage from predators. Alkaloids can contaminate food crops in a variety of ways including from seeds or leaves from weeds accidentally harvested within a crop, from contamination of a crop with alkaloid-producing moulds or from production from the crop plant itself.

Low levels of alkaloids can be detected in a variety of crops including cereals, leafy greens such as salads, leaves used to produce teas and occasionally in animal products as transfer from crops used for feed. Common examples of these are tropane alkaloids, pyrrolizidine alkaloids, opium alkaloids and ergot alkaloids. 

Other toxins which are natural constituents of plant products include erucic acid which can be found in some oils, and hydrocyanic acid in apricot kernels.

Maximum levels are set for specific food and alkaloid combinations where known issues exist.

Further information on veterinary medicine residues can be found here.

The main sources of nitrates and nitrites are the naturally present nitrates and nitrites found in vegetables including leafy greens, celery and beetroot. Around 5% of the amount we consume come from foods with added nitrates and nitrites (E249-E252). These are used in foods such as cheeses and processed meats including bacon, ham and cured meats. Their main function is as a food additive which reduces the growth of harmful microorganisms in particular Clostridium botulinum.

All food additives are evaluated for safety including assessment of the risk to human health based on the levels at which an additive is likely to be present in the diet and are required to be used only at the lowest effective levels.  

PFAS are man-made chemicals used for a variety of functions used in non-stick, water- and grease-repellent coatings and firefighting foams. Exposure to these substances can be from a wide variety of sources including food, consumer products and environmental contamination. 

PFAS substances persist for a long time and can gradually accumulate in the environment, and in foods such as animals and plants, including fish, eggs, meats and vegetables. They may also migrate from food processing equipment and packaging materials.

There are four main groups of PFAS that are regulated in GB; perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorononanoic acid (PFNA), and perfluorohexane sulfonic acid (PFHxS).  

Pesticides are chemical or biological substances used to control pests during the growth and storage of crops for food or feed. 

Examples of commonly used pesticides include herbicides to control weed growth, insecticides to protect plants from insect damage, fungicides to control mould growth, nematicides and molluscicides to prevent worm or slug damage, and rodenticides to prevent rodent damage.

Pesticide use is regulated to ensure that levels are safe to use in food and feed production. Maximum Residue Levels (MRLs) are set for a variety of pesticides used in food and feed production and Good Agricultural Practice (GAP) is advised.

In circumstances where a pesticide use for a specific food is not approved and/or there is no import tolerance (import tolerances are an MRL agreed for imported foods even if there is no approved use), a default MRL is set, usually 0.01 mg/kg. Foods which fail to comply with MRLs is not permitted to be placed on the market.

Further links to information on pesticide regulation can be found on the HSE website.

Process contaminants are chemicals produced during the production and/or cooking of food products. 

Acrylamide is a naturally ocurring chemical which is formed when starchy foods are fried, roasted or baked at low moisture levels and temperatures above 120°C. Acrylamide is formed under a chemical reaction called the Maillard Reaction which also produces flavours when food is browned. It is found in food products such as fried potato products (fries, crisps and potato-based bakery products), bakery goods (bread, biscuits, scones, crackers and crisp-breads), baked or fried grain-based cereal products (excluding porridge oats), coffee and roasted coffee substitutes and baby foods such as infant cereals and cereal-based foods.

Food businesses are required to manage acrylamide formation in their products to ensure it is as low as reasonably achievable. Mitigation methods include best practice guidance for individual product types and methods of processing and cooking or baking, and benchmark levels monitored through product testing.

Polycyclic Aromatic Hydrocarbons (PAHs) can be produced during smoking processes such as in smoked salmon.  

Furans can be produced during cooking practices including roasting or heating.