Download Dioxins and PCBs

Environmental Contaminants
 Dioxins and PCBs
 What are Dioxins and PCBs?
 Dioxins
are colourless, odourless organic compounds
containing carbon, hydrogen, oxygen and chlorine.
 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).
 Dioxins are ubiquitous environmental contaminants, having
been found in:
 Soil
 Surface water
 Sediment
 Plants
 Animal tissue
 They are highly persistent in the environment with half-lives
ranging from months to years.
 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.
 PCBs (poly-chlorinated biphenyls) are chlorinated aromatic
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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 ‘‘dioxinlike PCBs’’.
Like dioxins, PCBs are widespread environmental
contaminants and are very persistent in soil and sediments.
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.
 Occurrence in Foods
 Grazing animals and growing vegetables may be exposed
directly, or indirectly, to these contaminants in the soil.
 Leafy vegetables and pasture can also become contaminated
through airborne transport of dioxins and PCBs.
 Dioxins in surface waters and sediments are accumulated by
aquatic organisms and bioaccumulated through the food chain.
 The concentration of dioxins in fish may be hundreds to
thousands of times higher than the concentrations found in
surrounding water and sediments.
 Because dioxins are not very soluble in water, they tend to
accumulate in the fatty tissues of animals and fish.
 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
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.
 The main contributors to the average daily human intake
of dioxins and PCBs have been found to be:
 milk and dairy products, contributing between 16 and 39%;
 meat and meat products, contributing between 6 and 32%
 fish and fish products, contributing between 11 and 63%.
 Other foods, mainly vegetables and cereals, contributed 6–
26%
 Human milk can contain elevated levels of dioxins, some of
which can pass to the infant during lactation.
 Effects on Health
 Humans accumulate dioxins in fatty tissue mostly by eating
dioxin-contaminated foods.
 Dioxins and PCBs have a broad range of toxic and
biochemical effects, and some are classified as human
carcinogens.
 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.
 Sources
 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.
 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.
 Stability in Foods
 Dioxins and PCBs are highly stable with reportedly long half-
lives.
 In animals, they accumulate in fat and in the liver and are only
very slowly metabolised by oxidation or reductive
dechlorination and conjugation.
 They are therefore likely to persist in animal tissues, especially
fatty tissue, for long periods.
 They are not generally affected significantly by food
processing such as heat treatments, or fermentation.
 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.
 The EU has prohibited the use of most PCBs from 1978 and
for certain applications from 1986.
 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
 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.
 Heavy Metals
 What are Heavy Metals?
 The term ‘‘heavy metal’’ refers to any relatively high-density
metallic element that is toxic or poisonous even at low
concentrations.
 Heavy metals are natural components of the earth’s 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
 Occurrence in Foods
 1- Arsenic
 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.
 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 a lower intake of arsenic than adults, and young
children have the lowest intake.
 2-Cadmium
 None of the most commonly consumed foods were found to be
high in cadmium.
 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
 Children have a lower intake of cadmium than adults, and
young children have the lowest intake.
 3-Lead
 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.
 4-Mercury
 The main source of mercury in the diet is fish, followed by fruit
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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.
Methylmercury is formed from inorganic mercury by the action of
micro-organisms in marine and freshwater sediments.
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.
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.
 Effects on Health
 1-Arsenic
 Additionally, inorganic As3+ salts are more toxic than As5+
salts (Organic arsenic ).
 Illnesses associated with excessive inorganic arsenic intake
include:
 skin
 lung
 heart conditions
 gastrointestinal diseases
 possible carcinogenic effects.
 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.
 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.
 2-Cadmium
 Human intake of cadmium occurs mostly through food or
through smoking.
 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
 3-Lead
 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.
 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
 Stability in Foods
 Heavy metals are stable elements and persist for long periods
in the environment.
 There is no evidence to suggest that levels of heavy metals in
foods are changed significantly by processing.
 For example, methylmercury can be found in canned fish that
has undergone a severe thermal process.
 Control Options
 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.
 Examples include vegetables and produce grown in soils
contaminated naturally, or by industrial activity, and large
predatory fish.
 It is also important to ensure that heavy-metal contamination
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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 for heavymetal 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.
It is also important to ensure that all processing water is
sourced from potable supplies that are not contaminated with
heavy metals.
 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.
 The perchlorate anion consists of a chlorine atom
surrounded by four oxygen atoms
 perchlorate anion is a very strong oxidising agent.
 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
 Effects on Health
 Exposure to high doses of perchlorate has been found to
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interfere with iodine uptake into the thyroid gland.
Perchlorate appears to remove an iodine ion from a protein
that transports the iodine to the thyroid, leading to iodine
deficiency.
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.
Pregnant women and their unborn children are therefore at the
greatest risk of iodine deficiency.
 Sources
 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.
 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.
 Stability in Foods
 Perchlorate is very soluble in water, stable under most
environmental conditions and very mobile in most media.
 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.
 Control Options
 Control is currently centred on reducing contamination of soil
and water with perchlorate.
 Biological remediation appears to have the most promise for
dealing with contaminated sites.
 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 also offer promise for
treating perchlorate-contaminated water.
 Legislation
 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.
 Reference: Lawley R., Curtis L. and Davis J. The food
safety hazard guidebook. RSC Publishing.