Download Chemistry In Your Life

Chapter 10
Chemicals in Our Bodies and
Our Environment
Good Effects, Bad Effects
Copyright W. H. Freeman and Company ·
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Chemistry Applied
•Vitamins
•Food Additives
•Pesticides
•Dioxin and PCB’s
•Synthetic hormones in the
environment
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Vitamins
• Vitamins are essential, noncaloric nutrients.
• Vitamins are needed in very small amounts.
• Our bodies cannot synthesize vitamins; they are obtained
entirely from our diet or from vitamin supplements.
• A healthy diet containing fresh vegetables, fruits, whole
grains and complete protein sources provides the
recommended daily amount of vitamins and minerals.
• Vitamins are divided into two classes: water soluble and
fat soluble.
• A vitamin’s class determines how it is absorbed into the
bloodstream and transported, whether it can be stored in
the body, and how easily it is lost from the body.
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Vitamins
1. Vitamin C and members of the
vitamin B family are water soluble.
• Water soluble vitamins are absorbed directly into the
bloodstream where they travel freely.
• They are not stored in the tissues to any great amount
so are not toxic. Excess amounts are secreted in the
urine.
• Water soluble vitamins are diminished in foods cooked in
water.
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Vitamins
• Vitamin C is water soluble because it contains many
hydroxyl groups.
• Vitamin C is required for the production of collagen, an
important connective tissue.
• A deficiency of vitamin C results in the disease, scurvy,
characterized by skin lesions and tooth loss.
• Vitamin C is found in fresh fruits and vegetables,
especially citrus fruits.
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Vitamins
• A deficiency of vitamin C leads to the disease scurvy,
characterized by skin lesions and tooth loss.
• Vitamin C is an antioxidant and is also involved in the
body’s immune response against infection.
• Many people ingest large amounts of vitamin C to try to
ward off colds. Its effectiveness is inconclusive and
people are advised to refrain from taking massive doses
of vitamin C.
• The other water soluble vitamins are all members of the B
family.
• The B vitamins all act as coenzymes, molecules that
cannot be synthesized by the body but are required for
the activity of certain enzymes.
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Vitamins
Copyright W. H. Freeman and Company ·
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Vitamins
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Vitamins
2. Vitamins A, D, E, and K are fat
soluble.
• The fat soluble vitamins are carried by fat-transporting
proteins in the blood.
• Fat soluble vitamins can accumulate in fatty tissue, so levels
of fat soluble vitamins can build up to toxic doses if megadoses are taken.
• Fat soluble vitamins may be missing from the diet for weeks
since reserves are generally stored in the fatty tissues.
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Vitamins
• Vitamin E is an antioxidant.
• It is present in eggs, vegetable oil, nuts, and other fatty
plant based foods.
• A deficiency of vitamin E leads to scaly skin, sterility and
decay of muscle tissue.
• When O2 is used by the body, small amounts of highly
reactive molecules called free radicals are formed.
• Free radicals damage living cells by disrupting cell
membranes. They are also damaging to proteins and
DNA.
• Vitamin E and other antioxidants prevent this damage
from happening.
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Vitamins
• Vitamin A is present in mild, eggs, and liver and in the
form of beta-carotene, found in vegetable sources. Betacarotene is converted to vitamin A once inside the body.
• Vitamin A is involved in vision and is required for proper
growth in children.
• Lack of vitamin A leads to night blindness.
• Vitamin D can be made in the body by the action of UV
light on the skin. It is routinely added to milk as a
vitamin supplement.
• Vitamin D is involved in the uptake of calcium through the
intestinal wall.
• Vitamin D deficiency leads to a disease called rickets.
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Vitamins
• Vitamin K is required to make the proteins involved in
blood clotting. A routine injection of vitamin K is given to
newborn infants.
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Vitamins
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Vitamins
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Food Additives
3. Antioxidants prevent foods from
becoming rancid.
• When food spoils, it is often the result of the oxidation of
unsaturated fatty acids.
• Antioxidants added to the food prevent this process from
occurring by interfering with one of the first steps in the
process.
• Vegetable oils come with their own antioxidant, vitamin
E.
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Food Additives
• Several vitamin E mimics have been
synthesized and are used in
packaged food products susceptible
to oxidation.
• These include BHA (butylated
hydroxyanisole), BHT (butylated
hydroxytoluene), and Propyl
Gallate.
• Small numbers of metal ions in food
catalyze the oxidation reactions in
food. Sequestrants are often added
to foods to bind these metal ions in
order to reduce their reactivity.
• Citric acid and EDTA
(ethylenediaminetetraacetic acid)
are typical sequestrants.
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Food Additives
4. Dehydration and certain chemicals
act as food preservatives.
• The simplest way to preserve foods is to dehydrate them.
Microbes cannot grow in the absence of water.
• Adding common table salt acts to dehydrate foods
because it draws water to itself and thus out of the food.
Concentrated sugar solutions work in the same way.
• The principle involved is called osmosis, the movement of
water across a membrane from a dilute solution to a more
concentrated solution.
• Freeze drying is a second way to dehydrate foods. All
water is removed by placing frozen foods in a vacuum.
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Food Additives
• Organic acids – Many food preservatives are toxic to
microorganisms, but not toxic to humans.
• Benzoic acid, in the form of sodium benzoate, is a
commonly added preservative.
• Propionic acid (calcium or sodium propionate) is added to
baked goods, cheeses, and other no-liquid products.
• Sorbic acid (calcium, sodium, or potassium sorbate) is
added to the same foods, but is only useful against molds
and fungi, not bacteria.
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Food Additives
• Sulfites – Sodium bisulfite, NaHSO3, kills bacteria and is
used to protect wine and other grape products.
• Some people are allergic to sulfites so foods and
beverages containing them must include a warning label.
• Bisulfites can be produced by reacting sulfur dioxide or a
sulfite with water.
SO2(g) + H2O(l)  H2SO3  H+ + HSO3SO3- + H2O  HSO3- + OH-
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Food Additives
• Nitrites – Sodium nitrite is used to preserve cooked and
cured meats such as ham, bacon, hot dogs, sausages, and
luncheon meats.
• Nitrites prevent the growth of the bacteria which causes
botulism and causes the meats to assume a pink or
reddish color which is more appealing than their natural
brown or gray color.
• Nitrites occur naturally in the body and react with
hemoglobin preventing it from carrying oxygen. About 12% of our hemoglobin is tied up in this way.
• Enzymes keep the level of nitrites low in most people, but
in some people, this enzyme is defective and nitrite
poisoning can occur.
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Food Additives
• A major concern is whether or not nitrites can be
converted into carcinogenic nitrosamines in the body.
This issue is still controversial.
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Food Additives
5. Some additives are used to enhance the
appearance, texture, and flavor of food.
• Another category of food additives includes colors and bleaching
agents. Currently used coloring additives in the US are:
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Food Additives
• Thickening agents and texture modifies are also added to
foods.
• These include carrageenan, a carbohydrate extracted from
Irish moss; xanthan gum; locust bean gum; propylene
glycol alginate and various cellulose derivatives.
• Flavor enhancers such as MSG or monosodium glutamate,
disodium guanylate, and disodium inosinate are added to
allow manufacturers to use inferior-quality ingredients but
still produce a pleasing taste.
• MSG can cause headaches in some people
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Pesticides: An Introduction
6. Pesticides kill undesirable organisms
but are also toxic to humans.
• A pesticide is a substance that kills or otherwise controls
an organism that humans find undesirable.
• Pesticides function by blocking a vital metabolic process in
the organism for which they are toxic.
• Pesticides are generally toxic to organisms, including
humans, other than the target organism.
• The most important forms of pesticides are
•Insecticides – DDT, matlathion – kill insects
•Herbicides – 2,4-D – kills plants, especially weeds.
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Pesticides: An Introduction
•About one billion kilograms of pesticides are used annually
in North America.
•Almost half of this is used in agriculture. Pesticides (along
with inorganic fertilizers) allow the production of large
amounts of food on relatively small amount of land.
•The greatest agricultural use of insecticides occurs in the
growing of cotton, and of herbicides in the growing of corn
and soybeans.
•Fungicides are used to protect seed during storage, and to
kill fungi on plants before the penetrate the leaves or stem.
•About half the foods eaten in the US contain measurable
amounts of at least one pesticide. For this reason many
pesticides have been banned or their use restricted.
•Living plants themselves sometimes produce natural
pesticides which are no less toxic to humans than synthetic
ones.
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Pesticides: An Introduction
•Pesticides often migrate from where they are applied to the rest
of the environment and often show up in our water supplies.
•Some common persistent pesticides are:
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Pesticides: An Introduction
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Pesticides: An Introduction
7. DDT is an infamous insecticide
whose effects are still with us.
• In the 1940’s through the 1960’s DDT was commonly used
as an insecticide against
•mosquitoes which can carry malaria and yellow fever
•body lice which can transmit typhus
•fleas which can carry the plague.
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Pesticides: An Introduction
7. DDT is an infamous insecticide
whose effects are still with us.
•DDT was part of the WW2 malaria reduction program that
saved the lives of more than 5 million people worldwide.
•In 1962, Rachel Carson wrote “Silent Spring” in which the
role of DDT in decreasing the populations of many birds was
documented.
•DDT has been banned in developed countries since the early
1970,s due to its persistence in the environment and its
negative effect on the reproduction of insect eating birds.
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Pesticides: An Introduction
8. Organochlorine molecules accumulate
in living matter.
• Organochlorine compounds tend to accumulate in fish in
concentrations millions of time greater than in the water in
which them swim
• Bioconcentration of these materials occur because they a
fish’s blood is directly exposed to organochlorine
compounds dissolved in the water in which they swim.
• After accumulating in the fatty tissues of small fish, the
organochlorines become biomagnified when larger fish eat
smaller fish.
• The organochlorine concentrations are typically highest at
the top of the food chain.
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Pesticides: An Introduction
• DDT biomagnification in the food chain:
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Pesticides: An Introduction
9. Organophosphate and carbamate
insecticides do not bioaccumulate but are
toxic.
• Organophosphate compounds consist
of a central phosphorous atom forming
five bonds to:
•A doubly bonded oxygen or sulfur
(P=O or P=S)
•Two singly methoxy (-OCH3) or
ethoxy (-OC2H5) groups, (-OR)
•A longer, more complicated R group
attached through an oxygen or sulfur
atom (-OR or –SR)
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Pesticides: An Introduction
• Carbamate insecticides contain a
central carbonyl group rather than a
phosphorous atom.
• Both organophosphate and carbamate insecticides function
by reacting with and inhibiting enzymes in the central
nervous systems of the insects targeted.
• These insecticides are non-persistent in the environment and
decompose within days are weeks. They are seldom found
in the food chain.
• Organophosphate and carbamate insecticides are much more
toxic to humans than are organochlorines. Exposure during
application can result in immediate health problems.
Copyright W. H. Freeman and Company ·
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Pesticides: An Introduction
• Common organophosphate pesticides include:
•Malathion (low toxicity to mammals)
•Diazinon (toxic to birds)
•Parathion (very toxic to humans, birds, and other nontargeted organisms. It has been banned in some
developed countries.
•Dichlorvos (A volatile insecticide used in flea collars and
some aerosol insecticides)
•Common carbamate pesticides include:
•Carbaryl (low toxicity to mammals, toxic to honeybees)
•Aldicarb (very toxic to humans)
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Pesticides: An Introduction
10. Some insecticides are natural products
or substances derived from them.
• Many plants synthesize
their own natural
insecticides: nicotine,
rotenone, pheromones,
and juvenile hormones.
• Another group of natural
pesticides are the
pyrethrins which paralyze
insects, but generally do
not kill them.
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Pesticides: An Introduction
• Rotenone is derived from the roots of certain bean
plants and is used as a crop insecticide. It is also used
to kill fish.
• Both pyrethrins and rotenone are destroyed by
sunlight. Synthetic pyrethrins which are more stable
have been developed.
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Herbicides, PCB’s, Dioxins, and Furans
11. Phenoxy herbicides are used to kill
broad-leaf weeds and brush.
• Phenoxy herbicides are based on a benzene ring connected
by an ether oxygen to a short chain carboxylic acid. Two
or three chlorine atoms replace ring hydrogens in
commercial herbicides.
• The two herbicides based on this system are 2,4-D (2,4dichlorophenoxyacetic acid) and 2,4,5-T (trichlorophenoxy
acetic acid).
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Herbicides, PCB’s, Dioxins, and Furans
• 2,4-D is used to kill broad-leaf weeds in lawns, golf
courses, etc. while 2,4,5-T is used for clearing brush from
roadsides and power line corridors.
• Farmers who mix and use large quantities of 2,4-D have
an increased incidence of no-Hodgkin’s lymphoma.
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Herbicides, PCB’s, Dioxins, and Furans
12. Dioxin is a highly toxic by-product of
2,4,5-T production.
• A trace contaminant,
dioxin, is produced
during the manufacture
of 2,4,5-T.
• During the Vietnam War, large amounts of Agent Orange
(a mixture of 2,4-D and 2,4,5-T) was used as a defoliant.
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Herbicides, PCB’s, Dioxins, and Furans
• Civilians and soldiers who were exposed believe the their
chronic health problems resulted from the dioxin in this
substance. This is still a controversial issue.
• The manufacture and use of 2,4,5-T were phased out in
North America in the mid 1980’s.
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Herbicides, PCB’s, Dioxins, and Furans
13. Glyphosate is a herbicide that kills
almost all plants.
• The most widely used herbicide is glyphosate. It is the
herbicide in Roundup and is rather nontoxic. It kills almost
all plants.
• Recently, genetically engineered soybeans have been
produced that are resistant to Roundup. This is
controversial because of possible allergenic problems from
soybean derived foods, and the possibility of resistance
moving naturally from soybeans to other plants.
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Herbicides, PCB’s, Dioxins, and Furans
14. PCBs are multiuse organochlorine
compounds.
• Polychlorinated biphenyls, or PCB’s, were a major
environmental concern in the 1970’s and 80’s.
• They are a major environmental contaminant due to
careless dispose practices. They persist for a very long
time in the environment.
• PDB’s are implicated in problems with human growth and
development.
• Examples of PCB’s are:
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Herbicides, PCB’s, Dioxins, and Furans
• PCB’s find application in coolant fluids in power
transformers, plasticizers, carbonless copy paper, de-inking
solvent used to recycle newspaper, heat-transfer fluids, and
waterproofing agents.
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Herbicides, PCB’s, Dioxins, and Furans
15. PCBs released into the environment
will be recycled for years.
• PCB’s are widespread and persistent environment
contaminants.
• US Production of PCB’s was halted in 1977, however old
supplies still remain in use in many electrical transformers.
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Herbicides, PCB’s, Dioxins, and Furans
• Biomagnification of PCB’s in the food chain:
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Herbicides, PCB’s, Dioxins, and Furans
16. PCBs are contaminated by furans.
• Strong heating of PCBs in the presence of oxygen can
produce small amounts of dibenzofurans:
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Herbicides, PCB’s, Dioxins, and Furans
17. There are many environmental sources
of dioxins and furans.
• Many industrial processes produce PCDFs and PCDDs as
by-products. Contributors include bleaching of paper
pulp, incineration of garbage, and recycling of metals.
• Most pulp and paper mills have switched from Cl2 to
chlorine dioxide, ClO2, which produces much smaller
levels of furan and dioxin.
• Incineration is now the largest source of dioxins in the
environment.
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Herbicides, PCB’s, Dioxins, and Furans
18. We are exposed to dioxins, furans,
and PCBs mainly via our diet.
• More than 90% of human exposure to dioxins is through
the food we eat.
• Meat, fish, and dairy products contribute the most.
• The combined concentrations of organochlorines is reported
as the equivalent amount of 2,3,7,8 TCDD, that by itself,
would produce the same toxic effect.
• The TEQ scale is used for reporting this toxicity. A value of
1.0 on this scale is defined as the toxicity of pure 2,3,7,8
TCDD.
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Herbicides, PCB’s, Dioxins, and Furans
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Herbicides, PCB’s, Dioxins, and Furans
19. The health effects of PCBs, furans,
and dioxins are still controversial.
• Conclusions about the extent to which PCBs, furans, and
dioxins cause toxic reactions in humans are still tentative
and controversial.
• Most PCBs are not acutely toxic to humans. Heavy
exposure of workers in electrical capacitor plants has not
resulted in a higher overall death rate, however.
• Of greater concern is the toxic effect on human and animal
reproduction. Children born to women who consume large
amount of contaminated fish suffered some growth
retardation and lower results on memory tests.
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Herbicides, PCB’s, Dioxins, and Furans
• In 2000, the EPA issued a draft concluding that 2,3,7,8TCDD is a human carcinogen, and that other dioxin are as
well.
• It has been calculated that 1000 of the 1,000,000 new
cancer cases each year may arise from intake of dioxins,
furans, and PCB’s
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Environmental Estrogens
20. Certain synthetic organic chemicals
interfere with natural estrogen.
• Certain environmental chemicals, even ones with little
chemical resemblance to estrogen itself, can bind to the
estrogen receptor and either mimic or block the action of
estrogen itself.
• The compounds are called environmental estrogens and
include the organochloride insecticides as well as some
PCB’s and dioxins, and a variety of common industrial
organic compounds the contain oxygen.
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Environmental Estrogens
• Several non-organochlorine environmental estrogens are of
concern. These include bisphenol-A, Nonylphenol, and
phthalate esters.
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Environmental Estrogens
21. What is the evidence that
environmental estrogens can affect
health?
• The most famous case of environmental hormone-like
chemical contamination was a massive DDT spill in Lake
Apopka, Florida in 1980 where alligator reproduction was
severely affected.
• Embryo mortality and deformities of birds in the Great Lake
area have been traced to pollutants such as PCBs and
dioxins.
• Women who took the synthetic estrogen DES
(diethylstilbesterol) between 1948 and 1971 to prevent
miscarriage bore daughters, many of whom were sterile
and other who developed a rare form of vaginal cancer.
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Environmental Estrogens
• Girls prenatally exposed to high levels of DDE reach
puberty a full year before those with low exposure.
• Some scientists discount these effects, however, citing the
much greater amounts of naturally occurring plant based
estrogen mimics called phytoestrogens, consumed in the
average diet.
• Common plant sources of estrogen mimics are all soy
products, broccoli, wheat, apples and cherries.
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Tying Concepts Together: Tiny
concentrations of chemicals in our
bodies
• Vitamins in small amounts are necessary for good health,
however an overdose can prove fatal.
• Organochlorine compounds are unlikely to improve your
health but also may not damage everyone. Some
scientists believe that if a chemical is below a certain
threshold value, it will have no noticeable effect. The
environmental estrogens in our bodies may lie below their
threshold for biological action.
• It has been found that the average level of dioxins in
humans is several times lower that the minimum dose
required to cause reproductive problems in rats.
Widespread problems in humans are not expected.
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Summarizing the Main Ideas
• Vitamins are essential in small amounts for good health.
• Water soluble vitamins consist of C and the B group.
• Fat soluble vitamins are A, D, E, and K.
• Vitamin E is an important antioxidant
• Synthetic antioxidants, similar to E, are often added to
foods.
• Sequestrants, such as citric acid and EDTA salts, are added
to foods to reduce metal ion concentrations, which catalyze
oxidation reactions in food.
• Dehydration preserves foods.
• Sulfites and nitrites are used to prevent microbial growth in
food, however these ions may cause human health
problems.
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Summarizing the Main Ideas
• The main categories of pesticides are insecticides and
herbicides.
• Many organochlorine compounds undergo bioaccumulation
in the environment and consequently are present in high
concentrations at the top of the food chain.
• Organophosphate and carbamate insecticides do not
bioaccumulate but some of them are acutely toxic.
• Massive amounts of herbicides are used annually to kill
weeds. Phenoxy herbicides, like 2,4-D, are used on lawns.
The herbicide 2,4,5-T is invariably contaminated with
2,3,7,8-TCDD, a high toxic compound in the dioxin class.
• PCBs are persistent organochlorine compounds which were
improperly disposed of in the past and are common
pollutants in the environment.
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Summarizing the Main Ideas
• Most of the toxicity in PCB samples arises from furans which
are produced when PCB’s are heated.
• Human exposure to PCBs, furans, and dioxins is expressed
as the TEQ value.
• Human health effects from these compounds are not
precisely known and are controversial.
• The most serious health effects occur the children born to
women exposed to the chemicals.
• Environmental estrogens are synthetic compounds that
interfere with natural hormones in the body.
• Evidence that environmental estrogens may affect humans
is based mainly on studies of wildlife.
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