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Food Safety And The Science Of Toxicology


Plants and other organisms were collected for food and medicinal purposes through the ages. Early humans probably learned through experience about the harmful properties of poisonous plants, insects and animals (venom). Domestication of food plants led to reduced levels of natural toxins and allergens. Poisons were used in killing, for example, in arrows or used maliciously to poison people. However, plants were also used as cures against poisoning. Treatment followed on a rational base only when toxicology became a science and when mechanisms of toxicity were understood.


Various kinds of poisons exist. Natural toxins occur as part of the composition of the food plants or animals. They often provide a natural defense mechanism in plants such as the poison gossypol in cotton plants. Other examples are toxins in certain mushrooms, toxic glycoalkaloids in potatoes, psoralens in celery and parsley, and, safrol in nutmeg and cinnamon.

Natural toxic contaminants occur in nature and could be heavy metals such as cadmium, and mercury. However, food could also become contaminated by exposure to organisms during agricultural practices or during improper storage of agricultural products. For example, the fungal toxin, aflatoxin, can develop under certain environmental conditions. This toxin contaminates crops and enters the food chain, thereby posing a risk to humans who consume contaminated foods.

Pesticides are synthetic or semi-synthetic chemicals. They are called toxic substances rather than toxins.


Toxicology is the study of the adverse effects of natural toxins and toxic substances on the human or animal body. Very basically, it is the science of poisons.

A toxicologist is qualified in the science and study of toxins/toxic substances. Specialities include clinical toxicology (specialises in the diagnosis and treatment of toxic symptoms), industrial toxicology (specialises in poison in an occupational situation), regulatory toxicology (specialises in regulatory requirements for the toxicological assessment of new chemicals, which could be human or veterinary medicines, and pesticides) and environmental toxicology (specialises in the toxic effects on the environment).

One of the most prominent pioneers of the science of toxicology was Paracelsus (1493-1541). He was born in Switzerland and became famous as a lecturer in medicine at the University of Basel and as the town physician. He is often quoted for the famous words "What is there that is not poison? All things are poison and nothing (is) without poison. Solely the dose determines that a thing is not a poison".

All chemicals can be toxic at a certain dose. In modern toxicology, the term "threshold" refers to the dose or concentration of a substance. This concept can be illustrated by the example of a substance called strychnine. In small amounts, strychnine is a tonic but in large doses it is poisonous. Another example is water - certain amounts are essential to life whereas large amounts cause death by drowning.

Internationally standardised toxicological assessments can be conducted to determine the toxicity of chemicals. Pesticides that are used on food crops and food additives used in the preparation of food are subject to tests to determine their acute, subchronic and chronic toxicity. Additional tests are conducted to determine potential allergenicity, teratogenicity, endocrine disruption and carcinogenicity. These characteristics collectively describe the inherent toxicity or the hazard of that substance. From the results of all these test the concentration (dose) at which no adverse effects on laboratory animals is observed is called the No Adverse Effect Level (NOAEL). As an additional measure a safety factor of 100 or 1000 is applied to the NOAEL to come to an Acceptable Daily Intake (ADI) level.

Pesticides are applied to protect crops against insects, weeds and pathogen infections. Statutory limits for pesticides, called Maximum Residue Limits (MRLs), are set for the residues on food crops. The MRL depends on a country's agricultural practices, climate and the environment. A withdrawal period, during which no further pesticide is applied, is determined to reach an acceptable MRL for a specific crop.

What Is The Situation In South Africa?

The risk of toxicity due to exposure to pesticides is very small provided that pesticides are used according to registration requirements. As a safety measure the sum of all the MRLs of a specific pesticide used on various crop plants must not exceed the ADI for that pesticide. In South Africa the calculated value for all regulated pesticides is less than 100% of the ADI.

To prevent or reduce exposure to natural toxins and contaminants, various preventative agricultural and storage practices are possible. The introduction of Hazard Analysis Critical Control Points (HACCP) in food safety management is important. Tolerance levels are often prescribed by legislation as the limit above which such a natural toxin or contaminant shall not be present in food.

Food Additives

The ADI of food additives is determined by the Codex Alimentarius Commission, an international body under the joint auspices of the Food and Agriculture Organisation (FAO) and the World Health Organisation (WHO). The level of exposure and the limits in food are very stringent and agreed on internationally by consensus at meetings of member countries of the Codex Alimentarius Commission.

What Other Ways Are There To Determine Risk To Foods?

There are other ways of determining risks associated with food, such as epidemiology, which involves observing and studying the health patterns of groups of people. Another method of determining risk of food is by mathematical modeling.


Many life-threatening toxic chemical substances and natural toxin have been identified and governments and international bodies carefully scrutinize new ones. Legislation is stringent to ensure the safety of food. Traditional methods and knowledge about naturally occurring toxins must be communicated to ensure that these toxins do not become problematic.

Prepared for FACS by WRi (2017)

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