There are three major hazards that may be introduced into the food supply any time during harvesting, processing, transporting, preparing, storing and serving food. These hazards may be microbiological, chemical or physical.

Microbiological hazards

Microbiological hazard occurs when food becomes contaminated by microorganisms found in the air, food, water, soil, animals and the human body. Many microorganisms are helpful and necessary for life itself. However, given the right conditions, some microorganisms may cause a foodborne illness. Microorganisms commonly associated with foodborne illnesses include bacteria, viruses and parasites.

Chemical hazards

Chemical hazards can occur at any point during harvesting, storage, preparation and service. When toxic chemicals used for pest control or for cleaning and sanitizing food contact surfaces and food preparation equipment come into contact with food, the food may be contaminated by those chemicals.

Toxic metals such as copper, brass, cadmium, lead and zinc can be a source of chemical contamination. Zinc, used in galvanized containers (garbage cans) and in gray enamelware containers which may be plated with anatomy or cadmium, can make acidic foods such as orange juice or tomato sauce and pickles poisonous. Pottery dishes with lead glazes should not be used to prepare or serve food.

Intentionally added chemicals help to maintain a food’s freshness or to enhance flavors in foods. Check the food ingredient label for more information about the additives. Excessive use of some additives has been linked (see Fact Sheets on Food Allergies and Food Additives) to cases of lethal allergic reactions
particularly among sensitive individuals, in particular, asthmatics.

Foodservice establishments are prohibited by law from using sulfites to maintain product freshness. However, they are still approved for use in some food processing operations, for example, processing shrimp and manufacturing wine. If they are used, the product must be clearly labeled.

Physical hazards


Physical hazards usually result from accidental contamination and /or poor food handling practices. Examples include, slivers of glass, human hair, nails, false nails, nail polish, pieces of jewelry, metal fragments from worn or chipped utensils and containers, dirt, stones, frilled toothpicks.

Pesticides may leave residues on fruits and vegetables. In general, these residues can be removed by scrubbing the surface and washing with water.

Food irradiation is classified as a food additive and is regulated by the Food and Drug Administration (FDA). Irradiation is a process which destroys pathogenic and spoilage microorganisms without compromising safety, nutrition or quality and significantly lengthens storage life. In general, spices are irradiated as a means of controlling bacterial growth and mold. According to Dr. Donald Thayer of the USDA Agricultural Research Service, irradiation looks promising as a treatment for controlling cylospora in fresh produce like raspberries. Contact your local Cooperative Extension office for the latest information on irradiation.


“Hazard” and “risk” are terms commonly used in scenarios where possible adverse outcomes are expected. Though these two terms are related to each other, they are distinct entities with different meanings.

Hazard is a factor or agent which may lead to undesirable effects, whereas, risk refers to the probability that the effect will occur. The table below compares the estimated risk of certain events that we may encounter within the population.

In the context of food safety, a “hazard” can be classified as a substance or agent present in food that has the ability or the potential to cause an adverse health effect to the consumer. The substance can be a biological, chemical or physical agent. For example, salmonella, a biological agent, may be present in raw eggs. Ingestion of salmonella may result in food poisoning. Therefore, salmonella in food is considered a biological hazard and may also pose a potential risk to the consumer. Mercury, a natural contaminant that may be present in some foods, is regarded as a chemical hazard and could also pose a potential risk to the consumer.

In determining whether there is a “risk” posed to humans from exposure to a specific hazard through food, there must be a consideration of the likelihood of consumption and the nature or severity of the adverse health effect posed by a certain hazard if consumed. While “risk” already implies the existence of a hazard, it has the additional component of the “chance” or “probability” of that happening to the individual or the population as a whole, as well as taking into account the severity and impact of the health effect that may occur as a result of being exposed to the hazard. For example, although salmonella may be present in raw eggs, the risk of getting salmonella food poisoning is minimal when the egg is thoroughly cooked before consumption to eliminate the hazard and thus minimizing the chance of exposure. However, if the eggs are eaten raw, the health risk from salmonella in eggs will be higher as a result of the higher likelihood that the hazard will be present and consumed. Similarly, mercury may be present in food and could pose a potential risk to the consumer. However, as in the cases of most chemical hazards, if the amount of mercury in the food is low, the risk to the consumer will also be low as occasional exposure to low levels of mercury will usually not cause adverse health effects in humans. Also in food safety assessment with respect to chronic toxicity, exposure and health effects of a chemical usually refer to the intake of that chemical over a lifetime. Transient excursion above the safety reference value would have no health consequences provided that the average intake over long period is not exceeded.


Aflatoxin as an Example

Aflatoxin is a food hazard and the concern is on its ability to cause liver cancer when people are exposed to high levels over an extended time. Its level in food is therefore regulated by law to prevent excess exposure. The following hypothetical scenario shows the estimated risk of occurrence of liver cancer due to aflatoxin intake.

According to the average pattern of peanut consumption in Hong Kong and assuming that peanuts contain aflatoxin at a level two times the legal limit, a healthy person who eats peanuts every day of their life would have a risk of cancer due to aflatoxin intake of 1 in 2 300 000 per year. This level of risk is very low and is comparable to the risk of death due to lightening strike.

In general, an exceedance of the level of a food hazard over the regulatory standard does not necessarily cause harm to health. The individual impact should depend on the risk assessment result.




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