Food contamination refers to the presence of harmful chemicals and microorganisms in food, which can cause consumer illness. This article addresses the chemical contamination of foods, as opposed to microbiological contamination, which can be found under foodborne illness. The impact of chemical contaminants on consumer health and well-being is often apparent only after many years of processing and prolonged exposure at low levels (e.g., cancer). Unlike food-borne pathogens, chemical contaminants present in foods are often unaffected by thermal processing. Chemical contaminants can be classified according to the source of contamination and the mechanism by which they enter the food product. Agrochemicals Agrochemicals are chemicals used in agricultural practices and animal husbandry with the intent to increase crop yields. Such agents include pesticides (e.g., insecticides, herbicides, rodenticides), plant growth regulators, veterinary drugs (e.g., nitrofuran, fluoroquinolones, malachite green, chloramphenicol), and bovine somatotropin (rBST). Environmental contaminants Environmental contaminants are chemicals that are present in the environment in which the food is grown, harvested, transported, stored, packaged, processed, and consumed. The physical contact of the food with its environment results in its contamination. Possible sources of contamination and contaminants common to that vector include: Air: radionuclides (caesium-137, strontium-90), polycyclic aromatic hydrocarbons (PAH) Water: arsenic, mercury Soil: cadmium, nitrates, perchlorates Packaging materials: antimony, tin, lead, perfluorooctanoic acid (PFOA), semicarbazide, benzophenone, isopropylthioxanthone (ITX), bisphenol A Processing/cooking equipment: copper or other metal chips, lubricants, cleaning and sanitizing agents Naturally occurring toxins: mycotoxins, phytohemagglutinin, pyrrolizidine alkaloids, grayanotoxin, scombrotoxin (histamine), ciguatera, shellfish toxins (see shellfish poisoning), tetrodotoxin, among many others. Pesticides and carcinogens There are many cases of banned pesticides or carcinogens found in foods. Greenpeace exposed in 2006 that 25% of surveyed supermarkets in China stocked agricultural products contaminated with banned pesticides. Over 70% of tomatoes that tested were found to have the banned pesticide Lindane, and almost 40% of the samples had a mix of three or more types of pesticides. Tangerine, strawberry, and Kyofung grape samples were also found contaminated by banned pesticides, including the highly toxic methamidophos. Greenpeace says there exists no comprehensive monitoring on fruit produce in the Hong Kong as of 2006. In India, soft drinks were found contaminated with high levels of pesticides and insecticides, including lindane, DDT, malathion and chlorpyrifos. Formaldehyde, a carcinogen, was frequently found in the common Vietnamese dish, Pho, resulting in the 2007 Vietnam food scare. "Health agencies have known that Vietnamese soy sauce, the country's second most