Foreign substances

Those substances are normally termed foreign which do not naturally occur in foods, but rather contaminate them through outside influence. It is mostly man who is – directly or indirectly – responsible for foreign substances in food.

We divide foreign substances into various groups:

Residues: These are substances that are purposely used for certain effects in the production or storage of foods (or raw products) and that are still left over partially in the end product. Examples of such substances are fertilizers, nitrates and pathogenes (like salmonella etc) pesticide sprays or veterinary medicines (like hormones, antibiotics).

Environmental contaminants: These are substances that inadvertently come into contact with the foods (or raw products) and partially permeate them. Such substances are emitted by industry, traffic, etc. and released into the water, air and soil and can contaminate the foods. Examples are heavy metals or organochlorine compounds.

Food additives: In this group are the substances that are intentionally added to foods and that are supposed to remain there during processing and preparation, such as artificial/chemical preservatives, thickeners, colourings or flavourings. (Since this web site deals mainly with unprocessed products, additives will not be discussed further here.)

Foreign substances do not necessarily have to be harmful for human beings. Whether or not they do indeed represent a danger depends on the individual substances and above all on the amounts present in food.

Pesticides (plant-protective agents)

In the cultivation of plants pesticides and fertilizers, among other things, are used as needed.

Herbicides make up the largest share of pesticides. These are used to combat weeds. In addition there are fungicides (substances against fungal diseases of the plants) and substances against destructive animals such as insects, slugs or worms. All pesticides must be officially authorized.

In principle, all of these substances should be used \"as much as necessary, as little as possible.\" Legislators stipulate exact maximum levels of these substances that are allowed to be present in a food when it is harvested or consumed.

If these maximum allowance levels for residues are not exceeded, there is no fear of danger to our health. Residues in foods are monitored by official food surveillance. In approximately half of the fruits and vegetables tested no residues are found. The maximum allowance levels are exceeded in an average of 2–3% of the random samples. This is much more frequent with fruits and vegetables from abroad than with domestic products.

Heavy metals

Foods are inadvertently contaminated with heavy metals from the environment, above all lead, cadmium and mercury.

The contamination of foods with lead has been continuously diminishing for years. This welcome development is due above all to the introduction of lead-free fuel and to the reduction of lead emissions in industry.

In contrast, the pollution of foods with cadmium has remained unchanged for years. Heavily polluted are above all innards, crustaceans and molluscs (shellfish). Among plant foods, celeriac and spinach show a high cadmium content.

Mercury is found in plant foods – with the exception of some wild mushrooms – in only very small concentrations.

On the whole, the maximum allowance levels for heavy metals are only rarely and only minimally exceeded. Based on current knowledge, a health danger from heavy metals in plant foods is not generally detectable.

Organochlorine compounds

To the organochlorine compounds belong such compounds as polychlorinated biphenyl (PCB), perchlorethylene (PER), and pesticides such as lindane, DDT or dioxin. For these substances, however, there are now numerous prohibitions or restrictions on use. Their contents in foods are accordingly continuously declining. In plant foods above all, contamination with organochlorine compounds is almost insignificant.

Nitrate, nitrite, nitrosamines

The nitrates are generally classified as foreign substances. More can be found about them in the chapter Harmful substances.

Tips for reducing the content of foreign and harmful substances in fruits and vegetables

• Always wash fruits and vegetables thoroughly in order to remove superficial residues, dirt and blemishes.
• The nitrate content of leafy vegetables can be greatly reduced if stalks, stems, large ribs and the outer leaves are removed.
• Pour away the water in which nitrate-rich vegetables have been cooked.
• Choose domestic products if possible; buy fruits and vegetables when they are naturally in season and whenever possible products from outdoor cultivation.
• Protect them while being stored including heat, oxidation and insects.
• Pour away water after soaking legumes.