environmental contaminants. dioxins and pcbs what are dioxins and pcbs? colourless, odourless...
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Post on 23-Dec-2015
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- Environmental Contaminants
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- Dioxins and PCBs What are Dioxins and PCBs? colourless, odourless organic compounds Dioxins are colourless, odourless organic compounds containing carbon, hydrogen, oxygen and chlorine. many different dioxins There are many different dioxins, of which 17 are known to be toxic to humans. The most toxic known dioxin is 2,3,7,8-tetra-chloro-di-benzo-p-dioxin (2,3,7,8-TCDD) Significant concentrations of this compound can be measured in parts per trillion (PPT).
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- Dioxins are ubiquitous environmental contaminants, having been found in: Soil Surface water Sediment Plants Animal tissue half-lives ranging from months to years. They are highly persistent in the environment with half-lives ranging from months to years. low water solubility They have low water solubility, meaning that they remain in soil and sediments that serve as environmental reservoirs from which the dioxins may be released over many years.
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- chlorinated aromatic hydrocarbons PCBs (poly-chlorinated biphenyls) are chlorinated aromatic hydrocarbons produced by the direct chlorination of biphenyls. There are about 209 related PCBs, known as congeners of PCBs, of which 20 reportedly have toxicological effects. Some of the PCBs have toxicological properties similar to those of dioxins and are therefore often referred to as dioxin- like PCBs. persistent in soil and sediments. Like dioxins, PCBs are widespread environmental contaminants and are very persistent in soil and sediments. sediments in sewage receiving streams It has been suggested that highly contaminated bottom sediments in sewage and receiving streams may represent a reservoir for the continued release of PCBs into the environment.
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- Occurrence in Foods Grazing animals growing vegetables Grazing animals and growing vegetables may be exposed directly, or indirectly, to these contaminants in the soil. Leafy vegetables pasture Leafy vegetables and pasture can also become contaminated through airborne transport of dioxins and PCBs. surface waters and sediments bioaccumulated Dioxins in surface waters and sediments are accumulated by aquatic organisms and bioaccumulated through the food chain. concentration of dioxins in fish The concentration of dioxins in fish may be hundreds to thousands of times higher than the concentrations found in surrounding water and sediments.
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- dioxins are not very soluble in water Because dioxins are not very soluble in water, they tend to accumulate in the fatty tissues of animals and fish. the longer the lifespan of the animal, the longer the time it has to accumulate dioxins and PCBs. Theoretically, the longer the lifespan of the animal, the longer the time it has to accumulate dioxins and PCBs. Foods that are high in animal fat, such as milk, meat, fish, eggs contribute about 80% of the overall human exposure Foods that are high in animal fat, such as milk, meat, fish, eggs and related products are the main source of dioxins and PCBs and contribute about 80% of the overall human exposure, although almost all foods will contain these contaminants at some (generally very low) level owing to their ubiquitous nature.
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- The main contributors to the average daily human intake of dioxins and PCBs have been found to be: milk and dairy products milk and dairy products, contributing between 16 and 39%; meat and meat products meat and meat products, contributing between 6 and 32% fish and fish products fish and fish products, contributing between 11 and 63%. Other foods Other foods, mainly vegetables and cereals, contributed 6 26% Human milk Human milk can contain elevated levels of dioxins, some of which can pass to the infant during lactation.
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- Effects on Health accumulate dioxins in fatty tissue Humans accumulate dioxins in fatty tissue mostly by eating dioxin-contaminated foods. carcinogens Dioxins and PCBs have a broad range of toxic and biochemical effects, and some are classified as human carcinogens. damage to the immune and reproductive systems neuro-behavioural effects In animal testing, dioxins have been implicated in causing damage to the immune and reproductive systems, developmental effects and neuro-behavioural effects. The most commonly observed adverse health effect in humans following acute over-exposure to dioxins and PCBs is the skin disease chloracne, a particularly severe and prolonged acne-like skin disorder.
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- Sources man-made contaminants Dioxins are often man-made contaminants and are formed as unwanted byproducts of industrial chemical processes, such as the manufacture of paints, steel, pesticides and other synthetic chemicals, wood pulp and paper bleaching, and also in emissions from vehicle exhausts and incineration. volcanic eruptions forest fires Dioxins are also produced naturally during volcanic eruptions and forest fires. Most industrial releases of dioxins are strictly controlled under pollution prevention and control regulations. Currently, the major environmental source of dioxins is incineration.
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- Stability in Foods highly stable Dioxins and PCBs are highly stable with reportedly long half- lives. accumulate in fatliver slowly metabolised In animals, they accumulate in fat and in the liver and are only very slowly metabolised by oxidation or reductive dechlorination and conjugation. persist in animal tissues They are therefore likely to persist in animal tissues, especially fatty tissue, for long periods. are not generally affected significantly by food processing They are not generally affected significantly by food processing such as heat treatments, or fermentation.
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- Control Options It is generally agreed that the best means for preventing dioxins and PCBs from entering the food chain is to control their release into the environment. prohibited the use of most PCBs The EU has prohibited the use of most PCBs from 1978 and for certain applications from 1986.
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- Product Use While studies suggest that there is no cause for alarm from potential health issues concerning dioxins in the diet, may help to minimise any potential exposure of consumers to dioxins in food: choosing leaner cuts of meat removing the skin from chicken trimming the fat off meat drinking reduced- or low-fat milk washing of fruit and vegetables to remove any airborne dioxin-contaminated dust particles
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- Legislation New EU regulations on contaminant levels in foods have recently been introduced. These new regulations will require tougher safety controls in food-manufacturing plants. The regulations aim to ensure a harmonised approach to the enforcement of permitted contaminant levels across the EU. Regulation (EC) 1881/2006 sets maximum levels for certain contaminants, including dioxins and dioxin-like PCBs in foods.
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- Heavy Metals What are Heavy Metals? high-density metallic element that is toxic or poisonous The term heavy metal refers to any relatively high-density metallic element that is toxic or poisonous even at low concentrations. natural components of the earths crust Heavy metals are natural components of the earths crust and cannot be destroyed. Although there are many elements that are classified as heavy metals, the ones of most concern, with respect to their biotoxic effects and presence in food, are: arsenic Cadmium Lead mercury
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- Occurrence in Foods 1- Arsenic fish and other seafood The major source of arsenic in the diet is from fish and other seafood, although the daily intake is estimated to be less than 0.35 mg. marine environment sea fish have arsenic levels about 10 times higher than freshwater fish The marine environment has a great impact on arsenic levels as sea fish have arsenic levels about 10 times higher than freshwater fish. children have the lowest intake. Children have a lower intake of arsenic than adults, and young children have the lowest intake.
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- 2-Cadmium None of the most commonly consumed foods None of the most commonly consumed foods were found to be high in cadmium. Cerealsfruitvegetables Cereals, fruit and vegetables are the main source of cadmium in the diet, making up about 66% of the mean cadmium intake. The other sources (Less important) include: meat Fish Liver Kidney molluscs young children have the lowest intake Children have a lower intake of cadmium than adults, and young children have the lowest intake.
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- 3-Lead None of the most commonly consumed foods None of the most commonly consumed foods were found to be high in lead, although some Member States reported high lead levels in meat and fish. Children have a lower lead intake than adults Children have a lower lead intake than adults.
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- 4-Mercury fishfruit vegetables The main source of mercury in the diet is fish, followed by fruit and vegetables. In fish and shellfish, mercury is present in the form of methylmercury, while in most other food groups it is present in its inorganic form. action of micro-organisms in marine and freshwater sediments Methylmercury is formed from inorganic mercury by the action of micro-organisms in marine and freshwater sediments. Predatory species of fish contain higher levels of mercury Predatory species of fish at the top of the food chain, such as tuna, generally contain higher levels of mercury, but their contributi
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