A toxin is a poisonous substance produced by living cells or organisms especially a protein, that is capable of causing disease when introduced into the body tissues but is often also capable of inducing neutralizing antibodies or antitoxins.
Toxins can be small molecules, peptides, or proteins that are capable of causing disease on contact with or absorption by body tissues interacting with biological macromolecules such as enzymes or cellular receptors. Toxins vary greatly in their severity, ranging from usually minor and acute (as in a bee sting) to almost immediately deadly (as in botulinum toxin or Botox to you and me).
Any substance poisonous to an organism; often restricted to poisons produced by living organisms. In addition to those from such microorganisms as bacteria, dinoflagellates, and algae, there are toxins in fungi (mycotoxins), higher plants (phytotoxins), and animals (zootoxins, or venoms). The plants include nightshade, poison hemlock, foxglove, mistletoe, and poison ivy. Many plant toxins (e.g., pyrethrins, nicotine, rotenone) apparently protect their producers against certain animals (especially insects) or fungi. Similar defensive secretions in animals may be widely distributed or concentrated in certain tissues, often with some sort of delivery system (e.g., spines, fangs). Animals such as spiders and snakes use venoms to catch prey and often for defense. Many normally edible fishes and shellfishes become poisonous after feeding on toxic plants or algae.
Bacterial exotoxins are proteins of disease-causing bacteria that are usually secreted and have deleterious effects. Several hundred are known. In some extreme cases a single toxin accounts for the principal symptoms of a disease, such as diphtheria, tetanus, and cholera. Bacteria that cause local infections with pus often produce many toxins that affect the tissues around the infection site or are distributed to remote organs by the blood.
Toxins are often distinguished from other chemical agents by their method of production - the word toxin does not specify method of delivery. It simply means it is a biologically produced poison.
Food is packed with natural chemicals that are essential to our health, such
as vitamins and minerals. But some foods contain potentially harmful
substances called natural toxins.
Most natural toxins occur naturally in just a few foods. Other natural toxins
are produced when the food is damaged, or when moulds or other fungi
grow on the food.
These are some of the foods that can contain natural toxins.
Red kidney beans
Dried red kidney beans contain natural toxins called lectins, which can
cause stomach aches and vomiting. These are destroyed if you soak the
dried beans for at least 12 hours and then boil them vigorously for at least
10 minutes in fresh water. Tinned kidney beans have already had this
process applied and so can be used without further treatment.
All potatoes contain natural toxins called glycoalkaloids, usually at low
levels. But higher levels of glycoalkaloids can be found in green parts of
potatoes, sprouted potatoes and potatoes stored in light. Severe
glycoalkaloid poisoning is very rare, but it's important to store potatoes in a
dark, cool and dry place and not to eat green or sprouting parts. If you've
removed the green parts and the potatoes still taste bitter, don't eat them.
And if you come across a green potato crisp, it's probably best not to eat it.
Mouldy or damaged apples may contain a toxin called patulin, particularly
around the bruised or damaged part of the fruit. Don't eat mouldy or
damaged apples and don't use them to make apple sauce or juice.
Toxins formed by algae in the sea and fresh water are called algal toxins.
Shellfish such as mussels, scallops and oysters are more likely to contain
these toxins than other fish.
In the UK, paralytic shellfish poisons (PSP), amnesiac shellfish poisons
(ASP), and the less toxic diarrhetic shellfish poisons (DSP) are the most
common shellfish toxins.
During the period of greatest risk (between April and September) notices
are posted in areas with high PSP, DSP and ASP levels warning people not
to eat shellfish caught locally. Fishing may also be prohibited.
Liver and Vitamin A
Vitamin A is essential in everyone's diet but if you're pregnant and you consume
excessive amounts the developing foetus may be harmed. The Government's
Chief Medical Officer has advised women who are trying to conceive to avoid
taking Vitamin A supplements. As a precautionary measure, these women are
also advised to avoid food rich in vitamin A, such as liver and liver products.
Moulds are usually visible, but toxins produced by moulds and other fungi Ė
mycotoxins Ė are invisible and can penetrate food. So even if you remove mould
from food, it might still contain mycotoxins. The safest option is to throw mouldy
Moulds can grow on most types of food if the conditions are right. They grow
fastest in warm, moist conditions. If bread is kept in a warm environment, mould
will form after only a few days. The best place to store bread is in a bread bin or
cool cupboard. Keeping it in the fridge will help prevent moulds forming, but can
make it go stale more quickly.
Cheeses with an external mould coating, such as Brie and Camembert, or those
with mould running through them, such as Stilton and Danish Blue, are safe to
eat in normal quantities because the moulds have been deliberately introduced.
However, if mould grows on cheese that isnít supposed to be mouldy, you
shouldnít eat it.
Avoiding natural toxins
Usually natural toxins will only be harmful if you consume them in large
quantities over a long period of time. But you can help to reduce the amount
you eat by doing the following things.
- Eat a wide variety of foods.
- Throw away foods after the 'Use by' date.
- Store food properly.
- Donít assume that if something is 'natural' it automatically means itís safe.
- Prepare and cook foods properly.
- Throw away bruised, damaged or discoloured foods.
- Throw away any foods that donít smell or taste fresh, or have
an unusually bitter taste.
Toxoids are toxins that have been exposed to formaldehyde or other chemicals that destroy their toxicities without impairing immunogenicity. When injected into humans, toxoids elicit specific antibodies known as antitoxins that neutralize circulating toxins. Such immunization (vaccination) is very effective for systemic toxinoses, such as diphtheria and tetanus.
During recent years, discussions have started on the risk of bioregulators being used as cemical weapons agents. These types of substances do not belong to the group of toxins but are, nonetheless, grouped with them since their possible use is similar. They are closely related to substances normally found in the body and may be algogenic (causing pain), anaesthetic, or influencing blood pressure. A characteristic of them is that they are active in extremely low doses and frequently have rapid effect.
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