Chemical hazards can occur at any point in both the external and internal food chain. When toxic chemicals used for pest control or substances used for cleaning and sanitising food contact surfaces and food preparation equipment come into contact with food, then food may be contaminated by those chemicals.

Mercury, copper, cadmium, lead and zinc are just some of the toxic metals that can give rise to chemical contamination of foodstuffs. Zinc used in galvanized containers and in enamelware containers can make acidic foods such as citrus fruits, rhubarb, tomatoes and pickles harmful to eat, as the metal leaches into the food and may subsequently make the end consumer ill.

There is a requirement to control chemical hazards at each and every step in the production process, for example during, storage, preparation and service. A common form of chemical contamination can arise from poor and uncontrolled cleaning practices carried out in kitchens. Chemicals, if diluted to a stronger mix than the manufacturer specifies then they can leave residues behind that can taint food.