Chemical Contamination of Food

Jessica Clifton

by Jessica Clifton

20th May 2020

The chemical contamination of food is almost inevitable because of various environmental and food processing factors. Food can also be chemically contaminated during handling, storage, and transport.

Most cases of food contamination are very negligible and unnoticeable in terms of parts per million. For instance, a pizza delivered to your house can be contaminated by very small concentrations of ash from the firewood.

Chemical contamination is not necessarily dangerous or harmful to health if the chemical contaminant is nontoxic or at very low concentration. In fact, some food ingredients like preservatives are technically more harmful to health than many of the so-called chemical contaminants from the environment.

Regulations to prevent contamination

Strict protocols are required by law to prevent harmful chemical contamination of food. Specific regulations cover the following:

  • Harvesting (e.g. fruits and vegetables)
  • Processing
  • Handling
  • Storage
  • Transporting

Specific regulations may vary from country to country or from region to region. Regulations set the required protocols and also the limits of acceptability of specific contaminants. For example, the European Council regulations on hygiene procedures for food handling can be summarised into three points:

  1. Contaminated food with unacceptable levels of contaminants and which pose dangers to human health are prohibited from being sold on the market.
  2. Contaminant levels should be kept at very low levels based on food handling protocols.
  3. Contaminant levels shall be kept as low as can reasonably be achieved following recommended good working practices. Food business operators are responsible for implementing safety measures.
Food manufacturers are strictly regulated and have to meet stringent standards

Food manufacturers are strictly regulated and have to meet stringent standards

What is chemical contamination?

Generally speaking, chemical contamination refers to the unintentional and unwanted addition or presence of certain chemical substances in places where these chemicals don’t belong. This could include the workplace, home, natural environment, and food.

Chemical contamination also covers chemicals that may be normally present but are too high in concentration and have potentially serious health hazards. They may either cause acute poisoning or chronic diseases. Some toxic chemicals can cause organ damage and may even lead to cancer.

Chemical contaminants in food range from non-harmful, like unintended edible ingredients, to toxic substances. These contaminants may come from the source of the food. For instance, fresh vegetables may contain trace amounts of fertilisers and insecticides. Hence, it is crucial that we thoroughly wash vegetables before cooking or eating them raw.

In some instances, chemical contaminants may already be in food before they are processed. For instance, meat products may contain synthetic vitamin metabolites and hormone supplements.

Unlike biological pathogens like bacteria, many chemical contaminants in food cannot be easily neutralised by just cooking the food. This is particularly true for heavy metals like lead. However, there are safety thresholds. Here is a list of the safety limits of some common contaminants in food.

Heavy metals:

  • Lead – 1.5mg/kg
  • Cadmium – 1.0mg/kg
  • Mercury – 0.5mg/kg

Polycyclic aromatic hydrocarbons:

  • Benzo(a)pyrene – 5.0µg/kg
  • Sum of benzo(a)pyrene, benz(a)anthracene, benzo(b)fluoranthene and chrysene – 30.0µg/kg

Dioxin and dioxin-like PCBs:

  • Sum of dioxins – 3.5pg/g wet weight
  • Sum of dioxin and dioxin-like PCBs – 6.5pg/g wet weight
  • Sum of PCB28, PCB52, PCB101, PCB138, PCB153 and PCB180 – 75ng/g wet weight

How does chemical contamination of food occur?

The contamination of food may occur in several ways at different stages such as during:

  • Farming 
  • Processing 
  • Manufacturing 
  • Packaging 
  • Storing 
  • Transporting 
  • Cooking 

In many cases it is unavoidable, but contamination can be significantly minimised down to non-harmful levels and these precautionary measures must start from the source of the food. All types of food are ultimately derived from the following:

  • Agriculture
  • Aquaculture 
  • Fishing industry
  • Horticulture

Various types of contaminants may get into the food sources because of the cultivation and raising methods. Fertilisers and pesticides, for instance, are commonly used in farming for vegetables, fruits, and grains. Trace amounts of these chemicals may remain in food when these agricultural products are harvested.

Examples of chemical contamination of food

The chemical contamination of food may vary in terms of the type of contaminant and the concentration of the contaminant. The toxicity of chemical contaminations is also dependent on the type and concentration. Chemical contaminants can be classified into the following: 

  • Industrial chemicals – During the food processing and storing stages, some of the raw food ingredients or the final product itself may become contaminated with industrial chemicals. Contaminants may include sanitizers and detergents. At home, food may also be contaminated if you use unclean containers or containers that were used for chemicals.
  • Agricultural chemicals – Fruits and vegetables are considered healthy, but their risk of biological and chemical contamination is relatively high. They are typically exposed to herbicides, pesticides, and fertilisers. Even after cleaning after harvest, certain amounts of these agricultural chemicals may still be present on the surface. Some amount may be absorbed.
Fruits and vegetables are considered as healthy food but the risk of biological and chemical contamination is relatively high

Fruits and vegetables are considered healthy, but their risk of biological and chemical contamination is relatively high

  • Toxic metals – Food can be contaminated by heavy or toxic metals from the environment, from containers, and from cooking utensils. Some of these items are manufactured using non-food grade materials. For instance, some acidic food can react with galvanised metal containers.
  • Preservatives – Sulphites and nitrates are some examples of food preservatives that are commonly added to processed meat to extend the shelf life. Some preservatives also improve the taste of food. However, too many preservatives can be harmful to health.
  • Naturally occurring toxins – Some food contaminants are naturally occurring toxins such as those from pufferfish and shellfish. Organisms produce them as a means of protecting themselves from predators, which include humans. Fresh seafood products are particularly at risk of being contaminated by naturally-occurring toxins. 

What are some ways to keep chemicals from contaminating food?

Although chemical contamination of food is impossible to totally eliminate, there are several ways to minimise the contamination down to the safe levels. Potential sources of contaminations are everywhere – from the soil where agricultural products are cultivated to the food containers and cooking utensils.

The best that we can do is to minimise the amount of contamination and prevent toxic levels. Generally, standard protocols and regulations must be followed. Here are some tips that you can use:

  • Always label food containers and chemical containers
  • Be careful in handling the chemicals that you use in your work
  • Wear the necessary protective gear at work, especially when handling toxic chemicals like pesticides
  • Follow the instructions indicated by the chemical manufacturers such as contact time and temperature
  • Avoid using metal food storage containers for acidic food or beverages


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