Chemical Food Contaminants

Food Contaminants

Food contamination refers to the presence in food of harmful chemicals and microorganisms which can cause consumer illness where chemical food contamination is mostly attached with toxicity or carcinogenic reactions while microbes are well known for fatal and nonfatal diseases.  The impact of chemical contaminants on consumer health and well-being is often apparent only after many years of processing prolonged exposure at low levels (e.g., cancer). Chemical contaminants present in foods are often unaffected by thermal processing (unlike most microbiological agents). Chemical contaminants can be classified according to the source of contamination and the mechanism by which they enter the food product. There are number of chemical food contaminants identified and tested and regulated for the wellbeing of human race. These chemical come under following categories:

Dioxins

Polychlorinated biphenyls (PCBs)

Food allergens

Heavy metals

Melamine

Mycotoxins

Pesticides

Radiation contamination

Veterinary drug residues

Dioxins

Dioxins are a class of chemical contaminants and it is also called as persistent organic pollutants (POPs), meaning they take a long time to break down once they are in the environment. Dioxin is a general name for a large group of chemical compounds with similar structure. These compounds are made up of carbon, oxygen, hydrogen and chlorine atoms. The number of the chlorine atoms and their positions in the dioxin molecule are what determines the toxicity of different dioxins. The most toxic dioxin has four chlorine atoms in positions 2, 3, 7 and 8. This dioxin ( 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin) is often referred to as TCDD or “dioxin”. TCDD is the most studied and the most toxic of the dioxins.

Dioxins are formed during combustion processes such as waste incineration, forest fires, and backyard trash burning, as well as during some industrial processes such as paper pulp bleaching and herbicide manufacturing. Dioxins are highly toxic and can cause cancer, reproductive and developmental problems, damage to the immune system, and can interfere with hormones. The most toxic chemical in the class is 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD). Dioxins are found throughout the world in the environment and they accumulate in the food chain, mainly in the fatty tissue of animals and more than 90% of human exposure is through food, mainly meat and dairy products, fish and shellfish. The highest environmental concentrations of dioxin are usually found in soil and sediment, with much lower levels found in air and water.

Dioxins, Furans, PCBs

Dioxins, furans, and polychlorinated biphenyls (PCBs) (All contain phenyl rings of carbon atoms) are a class of similar chlorinated aromatic organic compounds, where Dioxins have two phenyl rings connected by two oxygen atoms. On contrary, Furans have one or two phenyl rings connected to a furan ring and PCBs have two phenyl rings attached at one point. One or more chlorine atoms can attach to any available carbon atom, allowing for 100 - 200 forms of each. Dioxins and dioxin-like furans have no known commercial or natural use. They are produced primarily during the incineration or burning of waste; the bleaching processes used in pulp and paper mills; and the chemical syntheses of trichlorophenoxyacetic acid, hexachlorophene, vinyl chloride, trichlorophenol, and pentachlorophenol. PCBs were once synthesized for use as heat-exchanger, transformer, and hydraulic fluids, and also used as additives to paints, oils, window caulking, and floor tiles. Production of PCBs peaked in the early 1970s and was banned in the United States after 1979.

Exposure

Human exposure to PCDDs, PCDFs, and PCBs may occur through background (environmental) exposure, and accidental and occupational contamination. Over 90 percent of human background exposure is estimated to occur through the diet, with food from animal origin being the predominant source. PCDD and PCDF contamination of food is primarily caused by deposition of emissions from various sources (e.g. waste incineration, production of chemicals) on farmland and water bodies followed by bioaccumulation up terrestrial and aquatic food chains. Other sources may include contaminated feed for cattle, chicken and farmed fish, improper application of sewage sludge, flooding of pastures, waste effluents and certain types of food processing. If the dioxin-like PCBs (non-ortho and mono-ortho PCBs) are also considered, the daily TEQ intake can be a factor of 2-3 higher. Special consumption habits, particularly one low in animal fat or consumption of highly contaminated food stuffs may lead to lower or higher TEQ intake values, respectively. Compared to adults, the daily intake of PCDDs/PCDFs and PCBs for breast fed babies is still 1-2 orders of magnitude higher on a per body weight basis. The latest WHO field study showed differences between the PCDD/PCDF and PCB contamination of breast milk, with higher mean levels in industrialized areas (10-35 pg I-TEQ/g milk fat) and lower mean levels in developing countries (< 10 pg I-TEQ/g milk fat).

High exposure may also be caused by food items accidentally contaminated. Known examples are the contamination of edible oil, such as the Yusho (Japan) and YuCheng (Taiwan) food poisoning. For a group of Yusho patients, average intake by ingestion of the Kanemi rice oil contaminated with PCBs, PCDFs and polychlorinated quarterphenyls (PCQs) was estimated at 154000 pg I-TEQ/kg bw/day, which is five orders of magnitude higher than the reported average background intake in several countries.

Mechanism of Action

A broad variety of data primarily on TCDD but also on other members of the class of dioxin-like compounds has shown the importance of the Ah (dioxin) receptor in mediating the biological effects of dioxin where data have been collected in many experimental models in multiple species including humans. The precise chain of molecular events by which the ligand-activated receptor elicits these effects is not yet fully understood. However, alterations in key biochemical and cellular functions are expected to form the basis for dioxin toxicity.

Effects of Dioxins on Human Health

Short-term exposure of humans to high levels of dioxins may result in skin lesions, such as chloracne and patchy darkening of the skin, and altered liver function. Long-term exposure is linked to impairment of the immune system, the developing nervous system, the endocrine system and reproductive functions. Chronic exposure of animals to dioxins has resulted in several types of cancer. The developing fetus is most sensitive to dioxin exposure. Newborn, with rapidly developing organ systems, may also be more vulnerable to certain effects. Some people or groups of people may be exposed to higher levels of dioxins because of their diet (e.g., high consumers of fish in certain parts of the world) or their occupation (e.g., workers in the pulp and paper industry, in incineration plants and at hazardous waste sites).

Prevention and Control of Dioxin Exposure

Proper incineration of contaminated material is the best available method of preventing and controlling exposure to dioxins. It can also destroy PCB-based waste oils. The incineration process requires high temperatures, over 850°C. For the destruction of large amounts of contaminated material, even higher temperatures - 1000°C or more - are required. Trimming fat from meat and consuming low fat dairy products may decrease the exposure to dioxin compounds. Also, a balanced diet (including adequate amounts of fruits, vegetables and cereals) will help to avoid excessive exposure from a single source. This is a long-term strategy to reduce body burdens and is probably most relevant for girls and young women to reduce exposure of the developing fetus and when breastfeeding infants later on in life. However, the possibility for consumers to reduce their own exposure is somewhat limited.

Reference:  

http://www.who.int/mediacentre/factsheets/fs225/en/

http://www.who.int/ipcs/publications/en/exe-sum-final.pdf

http://unsolvedmysteries.oregonstate.edu/flow_02

http://www.greenfacts.org/en/dioxins/l-2/dioxins-1.htm