Chemical Hazards & Control Measures


It is interesting that chemical hazards have had more bad press in South Africa than microbiological hazards. We should all be able to recall the Sudan red issues we had several years ago, not to mention the melamine scandal which continues to plague the food industry. There have also been product recalls due to cleaning chemical contamination in soft drinks. The use of hormones in the dairy industry sparked public outrage when milk was shown to be contaminated.

Given the publicity it is imperative that there are suitable control measures in place for chemical hazards. Some chemicals are extremely poisonous and if ingested may result in severe vomiting within a few minutes and in some case fatalities. Some chemicals may cause cancer or other serious chronic disease (Sprenger, 2009).

Chemical hazards may originate from a number of sources.

Poisonous plants and fish

They may be present in the raw materials such as naturally occurring toxins which are present in red kidney beans, toadstools and certain fishes. There is a regulation prohibiting the use of comfrey in South Africa for this reason. Beans require proper cooking to ensure the destruction of the toxic substance.

Scombrotoxic fish poisoning is caused by toxins which accumulate in the body of some fish, mainly the Scombridae family. This can happen if the fish are not stored below 4 degrees – hence the need to ensure the cold chain is maintained from catch to processing. 65% of all outbreaks of food poisoning related to fish in the UK can be traced back to this chemical.

Scombrotoxic poisoning results from the conversion of histidine to histamine, and 50ppm is enough to make you sick, even though at these levels the fish does not appear spoiled. Once the toxins are present they cannot be destroyed by heat - even in the canning process. Outbreaks have involved raw and canned tuna, smoked, canned and soused mackerel, canned sardines, pilchards, herring, anchovies and salmon.

Fish may also be the source of ciguatoxin entering the food chain. This toxin accumulates in the head, liver, gonads and roe of carnivorous fish such as reef cod, grouper, red bass and moray eel.

We are familiar with “red tide”. Red tide is a high concentration of Karenia brevis, a microscopic marine algae that occurs naturally but normally in lower concentrations. In high concentrations, its toxin paralyzes the central nervous system of fish so they cannot breathe. Dense concentrations appear as discolored water, often reddish in color. It is a natural phenomenon, but the exact cause or combination of factors that result in a red tide outbreak are unknown. Red tide is also potentially harmful to human health as humans can become seriously ill from eating oysters and other shellfish contaminated with red tide toxin. This is known as paralytic shellfish poisoning and diarrhetic shellfish poisoning.

Poisons introduced on the farm

Examples of chemical hazards that can be introduced at the farm include pesticides, herbicides, fungicides and fertilizers. These are mainly associated with plants, vegetables and cereals. Antibiotics used on animals can land up in the meat or milk if the withdrawal periods are not ensured. Animal feeds can be contaminated. In 1999, there was a major recall of Belgian animal products due to high levels of dioxin. This was thought to have originated from contaminated animal fat used in the animal feedstuffs.

There is a requirement to test water to ensure this is not contaminated with heavy metals as copper and lead can cause illness. Mercury compounds can pollute water that may be used for food production - hence the regulations relating to heavy metal levels in foods.

Chemicals could also be introduced via the trucks used, if these were previously used for transporting paint, industrial chemicals etc. Hence the need to check the previous loads and to ensure that dedicated tankers are used. The Codex guideline for the transportation of bulk foods as referenced in Regulation 918 of the Health Act is very useful in setting up the correct control systems.

Poisons introduced in processing

Unsafe additives such as raw materials contaminated with Sudan red or agricultural produce as discussed above can result in products being contaminated. Nitrates and nitrites are added to ham and bacon to inhibit the growth of Cl. Botulinum and Cl. Perfringens and to produce the red colour. However these chemicals can cause cancer and as such their level are controlled by law. Packaging can introduce unsafe chemicals such as antimony.  South Africa supplied tinned pineapples to Florida where hundreds of students became ill allegedly due to poorly lacquered cans.

Metals such as copper, zinc and cadmium can used found in equipment and these should not be used in direct contract with foods.

Even fumes from petrol and diesel forklifts have been found to contaminate food.

Controls for chemical hazards

Accidental contamination can be prevented by safe and secure storage of chemicals either on farm or even in the processing environment.
Chemicals should always be stored separately from food.
Food should never be stored in old chemical containers and vice versa.
Chemicals must be used in accordance with the suppliers’ specifications.
Cleaning chemicals must be diluted as the supplier indicates to ensure there is no residue.
Chemical containers should always be suitably labeled.
Food should be protected or stored away when cleaning and pest control activities take place.
Only food grade packaging should be used with a written specification and guarantee from the supplier that chemical leaching will not occur.
Electric forklifts should be used if there is possible contamination by fumes.
Staff should be trained on the correct and safe use of cleaning chemicals.
IF food additives are used, staff must be trained and supervised to ensure their safe use.
Testing should confirm the correct additions have taken place.
Maintenance activities must ensure food grade lubricants are used if there is the possibility of direct food contact.

Food should only be purchased from reputable suppliers in accordance with agreed specifications. Suppliers must guarantee in writing that fish has not been obtained from polluted waters or pesticides residues are in line with maximum legal limits, etc. This cannot be overemphasized as this route is the most common entry point for chemical hazards.


For more detail on mycotoxins please consult the article on the website by Rika Kemp.

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