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 contribution to total
mercury intake is small as consumption levels are low. Fruit,
mushrooms and vegetables are other sources of mercury. they also
have a lower bodyweight and so, potentially, a relatively larger
intake/kg bodyweight Although children have a low total intake of
mercury than adults, they also have a lower bodyweight and so,
potentially, a relatively larger intake/kg bodyweight.
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Effects on Health 1-Arsenic inorganic As 3+ salts are more
toxic than As 5+ salts (Organic arsenic ). Additionally, inorganic
As 3+ salts are more toxic than As 5+ salts (Organic arsenic ).
Illnesses associated with excessive inorganic arsenic intake
include: skin lung heart conditions gastrointestinal diseases
possible carcinogenic effects.
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nerve injury stomach problems Organic arsenic does not cause
cancer, nor is it thought to damage DNA, but exposure to high doses
may cause nerve injury and stomach problems. majority of arsenic in
seafood is present in the organic However, the majority of arsenic
in seafood is present in the organic, less toxic form, and during
digestion of such compounds, the arsenic is not released, or is
released only very slowly. This explains why very few cases of
arsenic poisoning are associated with seafood consumption, despite
the high levels observed.
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2-Cadmium food smoking Human intake of cadmium occurs mostly
through food or through smoking. kidney damage In humans, long-term
exposure may lead to kidney damage, as cadmium tends to accumulate
in the kidneys. Other adverse health effects include: Diarrhoea
Stomach pains Bone defects Immune-system damage possible damage to
DNA and carcinogenic effects
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3-Lead foodwaterair Lead enters the human body via food, water
and air. Its adverse effects include: disruption of haemoglobin
synthesis kidney damage increased blood pressure Miscarriage
nervous-system disruption reduced fertility learning disabilities
and behavioural problems in children.
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4-Mercury It is highly toxic and can cause: disruption of the
nervous system Brain damage damage to DNA and chromosomes allergic
reactions adverse reproductive effects
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Stability in Foods stable elements persist for long periods in
the environment. Heavy metals are stable elements and persist for
long periods in the environment. no evidence to suggest that levels
of heavy metals in foods are changed significantly by processing
There is no evidence to suggest that levels of heavy metals in
foods are changed significantly by processing. methylmercury can be
found in canned fish that has undergone a severe thermal process.
For example, methylmercury can be found in canned fish that has
undergone a severe thermal process.
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Control Options avoiding those food commodities that are likely
to have been exposed to large concentrations Control of heavy metal
levels in foods relies largely on avoiding those food commodities
that are likely to have been exposed to large concentrations of
metal contaminants in the primary production environment.
vegetables and produce grown in soils contaminatedlarge predatory
fish. Examples include vegetables and produce grown in soils
contaminated naturally, or by industrial activity, and large
predatory fish.
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It is also important to ensure that heavy-metal contamination
cannot arise from the use of inappropriate food processing
equipment. Manufacturers must ensure that all equipment is
constructed from food grade materials that meet the required
standards. Regulations in many countries set maximum levels
Regulations in many countries set maximum levels for heavy- metal
contaminants in certain foodstuffs. It is the responsibility of
manufacturers to ensure that these limits are observed, and that
ingredients are sourced from reputable suppliers. all processing
water is sourced from potable supplies that are not contaminated
with heavy metals. It is also important to ensure that all
processing water is sourced from potable supplies that are not
contaminated with heavy metals.
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Perchlorate What is Perchlorate? Perchlorate is: a chemical
that occurs naturally and is also manufactured. very soluble in
water stable under most environmental conditions very mobile in
most media has been recognised in the United States as an emerging
contaminant, mainly associated with industrial activity and space
exploration. Owing to this, there has been increasing interest in
the levels of perchlorate in soil, groundwater, drinking water,
irrigation water and food.
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perchlorate anion The perchlorate anion consists of a chlorine
atom surrounded by four oxygen atoms perchlorate anion very strong
oxidising agent perchlorate anion is a very strong oxidising
agent.
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Occurrence in Foods During 2004, the US FDA (Food and Drug
Administration) conducted an initial survey investigating the
perchlorate levels in a variety of products, including: Milk (more
important) bottled water (more important) lettuce tomatoes carrots
spinach melons
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Effects on Health interfere with iodine uptake into the thyroid
gland Exposure to high doses of perchlorate has been found to
interfere with iodine uptake into the thyroid gland. emove an
iodine ion from a protein that transports the iodine to the thyroid
Perchlorate appears to remove an iodine ion from a protein that
transports the iodine to the thyroid, leading to iodine deficiency.
disrupts thyroid development and function This, in turn, disrupts
thyroid development and function, and may lead to a reduction in
thyroid production. The thyroid plays an essential role in
regulating metabolism, and in the developing foetus and in infants,
thyroid hormones are essential for normal growth and development of
the nervous system. greatest risk of iodine deficiency Pregnant
women and their unborn children are therefore at the greatest risk
of iodine deficiency.
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Sources water and soil near military installations and around
the industrial plants The highest levels of perchlorate
contamination are found in water and soil near military
installations and around the industrial plants where the chemical
is manufactured. enter plants when they are irrigated with
perchlorate- containing water Perchlorate is thought to enter
plants when they are irrigated with perchlorate- containing water,
or when they are cultivated in soil containing natural perchlorate
or perchlorate-containing fertilisers or water.
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Stability in Foods soluble in watertable under most
environmental conditions very mobile in most media Perchlorate is
very soluble in water, stable under most environmental conditions
and very mobile in most media. it tends to accumulate in foods that
have a high water content Because of its high water solubility and
stability, it tends to accumulate in foods that have a high water
content, such as cucumbers, melons and tomatoes, when they are
grown in soils contaminated with perchlorate or irrigated with
perchlorate-contaminated water.
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Control Options Control is currently centred on reducing
contamination of soil and water with perchlorate. Biological
remediation Biological remediation appears to have the most promise
for dealing with contaminated sites. Some bacteria possess
perchlorate reductase enzymes Some bacteria possess perchlorate
reductase enzymes, which could possibly be used to treat
contaminated water, although, currently, systems involving the use
of these micro-organisms have not been commercialised and are not
used by US water authorities. Commercial anion-exchange systems
Commercial anion-exchange systems also offer promise for treating
perchlorate-contaminated water.
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Legislation drinking water babies The US Environmental
Protection Agency has recommended a safe level for perchlorate in
drinking water of 24.5 mg/litre, but suggests that a safe level for
babies should be 4.0 mg/litre.
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Reference: Lawley R., Curtis L. and Davis J. The food safety
hazard guidebook. RSC Publishing.