Healthy living Safe food: a look at undesirable substances

Substances that are harmful to health can enter food in various ways. A distinction is made between residues and contaminants.

Residues are the remains or breakdown products of substances that are deliberately used during food production and remain in or on food. These breakdown products can be formed through plant or animal metabolism or as a result of exposure to sunlight.

Even when pesticides are used appropriately, residues can still be found in food. However, if the applicable regulations are observed, these present no risk to health. Animal-derived products may sometimes contain residues of veterinary medicines.

Contaminants refer to substances that find their way into food by accident. Contaminants may be the unwanted by-products of food production. They may be formed during the production or processing of foods of animal and plant origin. However, they can also get into the food from other sources, such as the environment. These include microorganisms that cause foodborne infections. This is known as microbial contamination.

Contaminants also include various chemical substances. These include dioxins, furan, polycyclic aromatic hydrocarbons (PAHs) and acrylamide. In addition, food can sometimes absorb harmful substances from its packaging, for example phthalate plasticizers or per- and polyfluoroalkyl substances (PFAS).

Pesticide residues

Pesticides are used to protect cereals, fruit and vegetables against pathogens and pests. These agents are important not only for plant growth, but also during the storage and transport of food. When the food is sold, it may still have pesticide residues on or in it.

Fruit and vegetables in particular can contain pesticide residues. In rare cases, animal-derived foods also have these residues. This occurs if the animals have eaten feed that has been treated with pesticides.

Residues of veterinary medicines

All animal-derived foods may contain residues of veterinary medicines. This includes dairy products, eggs, meat, sausages and fish.

One group of veterinary medicines used in livestock farming is antibiotics. These are used to treat bacterial infections.

If a farm animal is treated with veterinary medicines, a certain withdrawal period is mandatory. Only after this withdrawal period has ended can the animal be used for food production.

Heavy metals and arsenic

Heavy metals are naturally present in the earth’s crust and can get into food in various ways. This is not automatically a matter of concern, as some heavy metals absorbed through food are classed as essential. These essential trace elements include zinc, iron, manganese and copper.

However, there are also heavy metals that are harmful to health, such as mercury and cadmium.

Heavy metals and arsenic are contained in certain foods and can be harmful to health:

• Cadmium: this heavy metal can be found in vegetables, edible mushrooms and animal offal. Cadmium can cause damage to the kidneys and bones, for example.
• Mercury: inorganic mercury can be found in fruit, vegetables and edible mushrooms, for example. Organic mercury is mainly ingested through consumption of fish and mussels. Organic mercury compounds in particular are harmful to humans. Mercury can cause damage to the kidneys and nerves, for example. Organic mercury in particular can affect the development of the nervous system in an unborn baby if ingested by the mother during pregnancy.
• Arsenic: this semi-metal is a common contaminant in food. It can be found, for example, in rice and rice products, fish, mussels and shrimps. Ingesting arsenic can lead to the development of cancer and nervous system disorders.

Dioxins and polychlorinated biphenyls (PCBs)

Dioxins and polychlorinated biphenyls (PCBs) are found everywhere in the environment and take a very long time to break down. Dioxins are released during combustion processes. They can be created during industrial production but also as a result of house and forest fires. They adhere to dust particles and are distributed in the environment with them.

In the past, PCBs were used in electrical components, as hydraulic fluid and as plasticizers. Their use has been banned in Germany since 1989. However, PCBs can still be produced by combustion and can be released from older building materials.

As dioxins and PCBs are found everywhere in the environment, livestock also absorb them in their feed, to which dust or soil particles stick. These persistent chemical compounds accumulate in the fatty tissue of animals. People absorb dioxins and PCBs by eating animal-derived foods such as meat, fish, eggs and milk as well as products made with these.

Acrylamide and furan

Acrylamide and furan are substances that can be created when heating food. They are regarded as undesirable by-products of food production and processing.

Acrylamide is a by-product of the browning reaction. It is created when food is fried, baked or roasted, i.e. when the temperature is high and humidity is low. Acrylamide formation starts at temperatures from 120°C and increases rapidly at 170°C to 180°C. Certain amino acids found in coffee, cereals and potatoes increase the risk of acrylamide formation.

Examples of foods that frequently contain acrylamide include:

• French fries and potato chips
• Bread
• Breakfast cereals
• Cookies and waffles
• Crispbread and crackers
• Coffee

Furan is a volatile compound that may be present in food that has been roasted or exposed to high temperatures in sealed containers. Particularly high levels can be found in the following foods:

• Coffee and cocoa
• Roasted nuts
• Toast
• Convenience foods and canned foods
• Baby food

Adults primarily absorb furan by drinking coffee. Breakfast cereals are among the main sources of exposure for children and adolescents. Babies and young children are most likely to absorb furan by eating baby food (ready-made food).

Polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons are found, for example, in food that has been smoked or contains smoke flavorings.

Food that can contain PAHs includes fish and meat products, soups, sauces and snacks. The PAH content of smoked food is usually higher than that of products containing smoke flavorings.

PAHs are also created when meat is cooked over an open fire and fat drips onto the embers and burns. The PAHs are carried onto the food by the resulting smoke.

Per- and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances are highly stable chemicals that can build up in the human body and the environment. As they are resistant to fat, water and dirt, they are used in many areas to coat materials, for example for non-stick frying pans, water-resistant clothing or coated food packaging. People are primarily exposed to PFAS through food, but they can also be exposed through the air they breathe.

The Federal Institute for Risk Assessment (BfR) answers the most frequently asked questions about PFAS.

Phthalate plasticizers

Phthalates are used as plasticizers for plastics. They can be found in cables, hoses and food packaging, among other items. If food comes into contact with materials that contain phthalates, the phthalates can be transferred to the food. This can occur during processing, for example, if oil is fed through hoses that contain phthalates or if food packaging contains phthalates.

The Federal Institute for Risk Assessment (BfR) answers the most frequently asked questions about phthalate plasticizers.

Further information about food packaging (in German) can be found in the brochure about plastic food packaging (“Lebensmittelverpackungen aus Kunststoff”), available from consumer advice centers.

Pesticides residues and veterinary medicine residues

The amount of pesticide residues absorbed from food is usually so low that it does not pose a health risk. The health risk associated with residues of veterinary medicines in animal-derived products is also low. This is because a withdrawal period has to be observed after veterinary medicines are administered and no food can be produced from the animal that was treated until after this period has ended. The official food control administration uses controls to ensure that withdrawal periods and legally stipulated maximum quantities are met.

Despite this, the use of antibiotics in livestock production carries the risk that antibiotic-resistant bacteria will develop or increase in number in the animals. These bacteria can be ingested through food and, under certain circumstances, cause infections if they are not killed by cooking, baking or roasting.

Dioxins and polychlorinated biphenyls (PCBs)

It is believed that some dioxins and PCBs increase the risk of cancer. Animal testing has also shown dioxins and PCBs to cause disorders and changes affecting the immune system and reproductive organs, especially in male rats. Animal testing also detected damage to the liver and thyroid gland caused by dioxins and PCBs.

In people, inflammatory skin changes (chloracne) as well as indications of liver damage or changes to the fat metabolism have been recorded in connection with the intake of very high amounts of dioxins or PCBs. However, these were triggered by accidents or deliberate poisoning, i.e. through extremely high amounts, and not through the normal intake of small amounts via food. In Germany, the levels of environmental pollution but also contamination of food and humans by dioxins have significantly reduced since the end of the 1980s.

Furan and acrylamide

The damaging effects of furan have been confirmed during animal testing, with higher doses leading to cancer. Animal testing also demonstrated that furan can damage the liver if absorbed over an extended period. Such effects have not yet been observed in humans.

Acrylamide has also been studied using animal testing. A higher dose in food increases the risk of genetic changes and tumors. The effect of acrylamide on humans is still unclear.

Polycyclic aromatic hydrocarbons (PAHs)

Some PAHs found in smoke and smoke flavorings are suspected of damaging the human genome and causing cancer. To date, this has been demonstrated in studies involving cells and animals. Some PAHs have been classed as “carcinogenic in humans”.

The amounts of such substances can be kept low through controlled production conditions. There are also maximum limits that have to be observed for PAHs in food, including smoked fish and meat products.

Per- and polyfluoroalkyl substances (PFAS)

Elevated concentrations of certain PFASs in the blood can reduce antibody production following vaccination. Elevated concentrations in the blood are also thought to cause increased cholesterol levels. High PFAS levels in the blood during pregnancy can cause a baby to have a low birth weight.

To prevent PFAS from causing health damage, restrictions already apply to some substances in this group. For example, the production of perfluorooctanoic acid (PFOA) and its precursors has been prohibited in the European Union since July 2020. Consumer products are also subject to strict maximum levels of PFOA and its precursors. Maximum levels of PFAS are also stipulated for certain foods.

Phthalate plasticizers

There are many different phthalates with different detrimental effects on health. Certain phthalates are classed as reproductive toxicants. In animals, some phthalates can impair the development of the male reproductive organs and affect the onset of puberty and the hormone system. Animal testing has shown other phthalates to damage the liver, thyroid gland and pituitary gland.

To prevent such damage to humans, maximum levels have been established for all phthalates. Some phthalates are completely prohibited in food packaging. As a result, the amount of phthalates absorbed from food packaging is usually so low that it does not pose any health risk.

To protect consumers, maximum levels have been established for most contaminants in food. Producers must guarantee the safety of the food they produce. The official food control administration also checks that all maximum levels are observed.

Further information about the basic principles of food safety can be found in the “Understanding food safety” brochure published by the Federal Ministry of Agriculture, Food and Regional Identity.

Consumers can also protect themselves by taking note of a few things when buying and preparing food. In addition to good food hygiene, the following measures are important:

Wash and peel food

Washing or peeling fruit and vegetables before use partially removes residues and contaminants. Cold water usually suffices; there is no need to use washing-up liquid, warm water or special cleaning agents.

In the case of rough surfaces, a vegetable brush can also help. Rubbing fruit and vegetables dry after washing them also removes residues. In the case of lettuce, the outer leaves can be discarded.

Replace chargrilling with browning

Roasting, searing, baking and frying food can produce acrylamide and furan. The more intensely food is heated, the more acrylamide or furan is produced.

Fewer harmful substances are produced when food is cooked at temperatures below 180°C. In the case of ready-made products, it can help to follow the cooking recommendations on the packaging. When barbecuing, it is also healthier to cook food at a lower temperature rather than chargrill it.

Enjoy in moderation

As livestock and wild animal offal can contain not only heavy metals but also dioxins, PCBs and PFAS, it is better not to consume them too often. Pregnant women, women who are breastfeeding or planning a pregnancy, and children should particularly avoid wild boar offal as a precaution.

Wild mushrooms can contain particularly high amounts of cadmium and mercury. However, eating these occasionally does not present any health risks. People who eat wild mushrooms regularly should consume no more than 200 to 250 grams per week.

If smoke flavorings have been added to a food, this must be indicated on the ingredients list. Smoked foods must also be clearly labeled. Consumers can take care to only eat such products in moderation.

Maintain a broad and varied diet

People who eat a broad and varied diet reduce the risk of consuming large amounts of the harmful substances that may occur in individual foods. A varied diet also helps people consume as many different nutrients as possible.