Download Chemicals in Our Bodies and Our Environment: Vitamins, Food

Chapter 10
Chemicals in Our Bodies and Our Environment:
Vitamins, Food Additives, Pesticides, and More
Review Questions
1. Vitamins are noncaloric nutrients that are essential for normal body function.
2. Vitamins enable the body to absorb and digest materials, build compounds required
by the body, and preserve existing cellular components.
3. Vitamins can be either fat-soluble or water-soluble.
4. Fat-soluble vitamins have the potential to be toxic because excess amounts are stored
in fatty tissue and are not excreted in the urine.
5. Vitamin A: Vitamin A is required for the production of a substance essential for
vision and is also required for growth in children.
Vitamin B: The family of B vitamins acts as coenzymes, are involved in the
production of energy, the synthesis of DNA and RNA, and the processing of proteins.
Vitamin C: This vitamin is required for the proper formation of collagen, an
important structural protein. Vitamin C is also involved in immune system response
and is an antioxidant.
Vitamin D: This vitamin is converted to a hormone that regulates the uptake of
calcium from the intestine, thereby controlling calcium levels in bone tissue.
Vitamin E: Vitamin E is an antioxidant
Vitamin K: This vitamin is needed for the synthesis of proteins that are essential for
blood clotting.
6. Coenzymes are substances that are required for normal enzyme function and are not
able to be made by the human body.
7. Antioxidants are compounds that prevent oxidative damage caused by the presence of
free radicals.
8. Free radicals are highly reactive, unstable molecules that sometimes result from
biochemical processes involving oxygen.
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9. Free radicals are formed in the human body during some biochemical processes that
involve oxygen. Other factors that increase free radical formation in the body include
pollution, tobacco, radioactivity, sunlight, and some medical conditions.
10. Since free radicals promote oxidation, oxidative stress is the accumulated damage
due to free radical activity in the body.
11. Phytochemicals are chemicals that occur in plants in small quantities and have
antioxidant activity. Phytochemicals are common in highly colored fruits and
vegetables.
12. Carrots are a dietary source of vitamin A. Vitamin A is required for the synthesis of
a substance that allows our eyes to detect light, especially at night.
13. Synthetic versions of vitamin E include butylated hydroxyanisole (BHA), butylated
hydroxytoluene (BHT) and propyl gallate. These compounds are used in packaged
foods that are susceptible to oxidation.
14. The tiny concentrations of metal ions that are present in food originate from the
machinery used to harvest and process the food and from metals in the soil. Metal
ion contaminants typically result from the machinery used to harvest and process the
food.
15. Sequesterrants are substances that form strong chemical bonds to metal ions, thereby
preventing the metal ions from catalyzing the oxidation of food products. Citric acid
and EDTA (ethylenediaminetetraacetic acid) are examples of common
sequesterrants.
16. The role of food preservatives is to prevent microorganisms, such as bacteria, fungi,
and molds, from multiplying and releasing toxic substances that spoil food products.
17. Osmosis is defined as the tendency for water to travel through a semi-permeable
membrane from a less concentrated solution to a more concentrated solution.
18. Weak acids are frequently used as preservatives because many of them are toxic to
microorganisms, but are non-toxic to humans.
19. Some common weak acids used as preservatives include benzoic acid (sodium
benzoate), propionic acid (sodium propionate), sorbic acid (sodium sorbate), acetic
acid, and citric acid.
20. Two inorganic salts that are used as preservatives include sodium bisulfite
(NaHSO3) and sodium nitrite (NaNO2).
21. Two health concerns associated with the use of nitrates in food relate to its ability to
bind to iron in our blood, preventing it from carrying oxygen, and the potential
conversion of nitrate in the body to potential carcinogens known as nitrosamines.
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22. Additives, other than preservatives, that may be found in processed food include
sweeteners, emulsifiers, coloring agents (beta-carotene and other food colors),
bleaching agents, thickening agents (carrageenan, xanthan gum and proplyene glycol
alginate), and flavor enhancers (MSG or monosodium glutamate).
23. A pesticide is a compound or substance that kills and/or controls the population of an
undesirable organism. An insecticide is a pesticide that kills insects. Examples of
insecticides include DDT and malathion. Herbicides are pesticides that kill plants,
such as weeds. 2,4 – D is an example of a herbicide. Fungicides are pesticides that
control the growth of fungus. Powdered sulfur is an example of a fungicide.
24. Pesticides work by blocking vital metabolic processes essential for life in the target
organism. Because of their mechanism of action, several are also toxic to humans.
25. The pesticide DDT has an effect on the reproductive abilities of birds, fish and
humans. DDT contaminates water, is concentrated in the fatty tissue of fish, and
ultimately gets into the food chain.
26. The food chain is defined as a sequence of species, each of which feeds upon the
preceding one. A food web incorporates interlocking food chains. Bioaccumulation
is the process by which compounds become collected over time in certain biological
systems. Bioconcentration is the process by which compounds diffuse from an
unfavorable environment to a more favorable one, and, as a result, become more
concentrated in the more favorable environment. Biomagnification is the process by
which a chemical increases its concentration along a food chain.
27. Humans are at the “top” of the food chain because we are able to feed on all of the
species preceding us in the chain.
28. Organophosphates and carbamates function as nerve poisons. Both compounds
inhibit enzymes in the central nervous system.
29. Organophosphates and carbamates are acutely toxic to humans because they are
known to have an immediate effect on health. In humans, acute exposure through
inhalation, consumption, and even skin absorption poses an immediate health risk.
30. There are many natural insecticides, including nicotine, the pyrethrins (from the
chrysanthemum), rotenone (from the roots of certain bean plants), pheromones, and
juvenile hormones.
31. Agent Orange is composed of the herbicides 2,4-dichlorophenoxy acetic acid (2,4D), 2,4,5-trichlorophenoxy acetic acid (2,4,5-T), and 2,3,7,8-tetrachlorodiebnzo-pdioxin (2,3,7,8-TCDD).
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32. Agent Orange was used by the United States as a defoliant of military targets in the
Vietnam War. Although controversial, the exposure to Agent Orange is believed to
produce numerous chronic health problems.
33. Glyphosate, a commonly used herbicide that kills almost all plants, is structurally
similar to organophosphate insecticide except that one of the four oxygen atoms
surrounding the phosphorus is replaced by the amino acid glycine.
34. PCBs are polychlorinated biphenyls. PCB are chemically inert liquids, difficult to
burn, have a low vapor pressure, are good electrical insulators, and are inexpensive
to produce. As a result, they were used extensively as a coolant fluid in power
transformers and capacitors. They were also used as plasticizers and in carbon-less
copy paper, de-inking solvents, and waterproofing agents.
35. Commercial processes that produce dioxin and furan byproducts include the
bleaching of paper pulp, the incineration of garbage, and the recycling of metals.
36. Anthropogenic sources of dioxin include incinerators, paper mills, and pulp mills.
37. Dioxins, furans, and PCBs accumulate in the food chain because they are
hydrophobic and have a tendency to dissolve in fatty matter.
38. Fish and meats represent the primary sources of dioxin for humans.
39. The toxicity equivalency, or TEQ, scale is a measure of the concentration of various
organochlorines in terms of the amount of 2,3,7,8-TCDD that would produce the
same toxic effect. In this scale, 2,3,7,8-TCDD is arbitrarily given a score of 1.0.
40. Chloracne is a common reaction or biological response in humans resulting from the
exposure to several types of organochlorine compounds.
41. Environmental estrogens are environmental chemicals that either mimic or block the
action of estrogen or accelerate the breakdown of the natural hormone. Thus, they
interfere with the biochemistry of natural estrogen. Environmental estrogens are a
health problem because they have been linked to infertility and an increased risk of
reproductive organ cancer.
42. Several chemicals can act as environmental estrogens, including DDT, PCBs,
dioxins, bisphenol-A, nonylphenyl, and phthalate esters.
43. DES is diethylstilbestrol, a synthetic estrogen taken by women to prevent
miscarriages.
44. Adverse health effects resulting from the use of DES were seen in the offspring of
women who took DES. Many female offspring are sterile, while a smaller
percentage has developed a rare form of vaginal cancer. Male offspring have an
increased incidence of abnormalities in their sexual organs, and may experience
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decreased average sperm counts. Additionally, these males may have an increased
risk of developing testicular cancer.
45. Bisphenol-A is used as a raw material for polycarbonate plastics and epoxy resins.
Nonylphenol results from the breakdown of materials used in detergents,
spermicides, and some plastics. Phthalates are commonly used as plasticizers.
46. Phytoestrogens are plant-based estrogen mimics commonly found in soy products,
broccoli, wheat, apples, and cherries.
Understanding Concepts
47. Vitamins are often called “trace” or “micro” nutrients because they are needed only
in very small amounts. While we typically require gram quantities of proteins,
carbohydrates, fats, and some minerals on a daily basis, only milligram, or in some
cases microgram, quantities of vitamins are required each day.
48.
HO
O
O
HO
HO
OH
Vitamin C
H3C
CH3
CH3
CH3
OH
CH3
Vitamin A
Vitamin C is water-soluble because it has several hydroxyl (-OH) groups that can
hydrogen bond to water. Vitamin A, which contains only one hydroxyl group, has
limited water-solubility. Due to its extensive non-polar hydrocarbon structure,
however, vitamin A is highly soluble in fatty tissue.
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49. Fat-soluble vitamins are carried by fat-transporting proteins in the blood. Watersoluble vitamins are absorbed directly into, and travel freely in, the bloodstream.
50. The concentrations of fat-soluble vitamins in foods are generally not altered by
cooking them in water. The concentrations of water-soluble vitamins in foods,
however, decrease when they are cooked in water.
51. It is easier to develop a vitamin C deficiency than a vitamin A deficiency because,
unlike vitamin C, vitamin A is fat-soluble and can be stored in fat tissue for use by
the body for a period of several weeks.
52. There are several mechanisms whereby antioxidants prevent damage by free
radicals. Some antioxidants prevent the destruction of cell membranes in regions
containing C=C bonds, regions particularly sensitive to free radicals. Other
antioxidants either react with O2 molecules and prevent them from reacting with free
radicals or they act to prevent the production of free radicals.
53. Free radicals damage biological tissue by either disrupting cell membranes affecting
the transport of substances into and out of the cell or they destroy proteins and DNA,
thereby altering the operation of cellular processes.
54. A cholesterol derivative in skin is converted into a precursor of vitamin D by the
ultraviolet radiation from sunlight. This precursor is subsequently converted by the
body into the regulatory hormone.
55. Vitamin D controls the uptake of calcium and phosphorus through the intestinal wall
into the bloodstream. Both of these elements are needed for proper bone formation
and maintenance.
56. A disease called rickets, resulting from vitamin D deficiency, was common in
children living in climates with little sunshine. The addition of vitamin D to milk, a
common food for children, prevents rickets and ensures proper calcium uptake and
bone formation.
57. There are various mechanisms by which foods can spoil. The decomposition of
unsaturated fatty acids by oxygen produces rancid foods. Additionally,
microorganisms, such as bacteria, molds, and fungi, can multiply in foods and
secrete toxic substances that spoil food.
58. Foods become rancid through the decomposition of unsaturated fatty acids by their
reaction with oxygen to produce carboxylic acids, aldehydes, and ketones that are
often foul-tasting and foul-smelling.
59. Vitamin E is a natural antioxidant found in all vegetable oils that acts to prevent the
oxidation of the double bonds of its fatty acid components.
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60. Dehydration is an effective food preservation technique because it prevents the
growth of microorganisms such as bacteria, molds, and fungi that secrete chemicals
that spoil foods. These microbes require water to grow and thrive.
61. Propionates are preservatives that are effective against bacteria, molds, and fungi.
Sorbates are effective against only molds and fungi, but not bacteria.
62. When nitrites are added to meat, the nitrite ion binds to the iron in the blood and
muscle tissue creating a reddish or pink color.
63. The use of pesticides is a concern because of its potential impact on human health.
Approximately one-half of the foods eaten in the United States are contaminated
with measurable levels of at least one pesticide. Because of the potential impact on
humans, especially infants and children, that could result from eating foods
contaminated with these chemicals, pesticide sale and use is regulated.
64. Businesses that consider insecticides important to their economic well being include
farmers, citrus growers, governments and municipalities interested in controlling
insect-borne diseases, and companies producing household insecticides for the
control of roaches, termites, ants, and other pests.
65. DDT stays in the environment for considerable periods of time. It persistence is
related to its low vapor pressure, slow rate of evaporation, low reactivity to light,
microorganisms, or other chemicals, and to its very low solubility in water.
Additionally, because of its low water solubility and its high solubility in
hydrocarbon-rich media, DDT accumulates in the fats of fish and animals where it
can reach highly toxic levels.
66. Fat-soluble substances are more likely to bioaccumulate than water-soluble
substances because these materials selectively diffuse from water that is consumed
and accumulate in fatty tissue, becoming more concentrated over time.
67. A substance is bioaccumulated by a combination of the processes of
bioconcentration and biomagnification. Bioconcentration results when chemicals
that are more soluble in hydrocarbon-rich media diffuse from an aqueous
environment into a non-polar one, such as fatty tissue. Through the process of
bioconcentration, fat-soluble compounds become more concentrated over time.
Biomagnification occurs when the concentration of a chemical increases as one
moves up the food chain. When an organism is consumed by one higher on the food
chain, all of the fat-soluble chemicals are retained by the higher organism. Thus,
when humans eat fish, meats, and dairy products, the fatty components of these
foods and their retained chemicals are carried up the food chain, increasing their
concentration along the way.
68. A food chain is a sequence of species, each of which feeds upon a pre-ceding one in
the chain. A food web consists of interlocking food chains.
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69. DDT and other organochlorines have been shown to affect the reproductive abilities
of fish, birds, and animals. Organophosphate and carbamate compounds inhibit
enzymes in the nervous system, and thus function as nerve toxins.
70. Malathion is more toxic to insects than to humans because insects metabolize it by a
different mechanism. Since the metabolic pathways of rats are more similar to
humans than to insects, malathion is probably low in toxicity to rats.
71. Organophosphates and carbamates are not as environmentally persistent as are the
organochlorine compounds. Additionally, they do not exhibit the bioaccumulation
problems of organochlorine compounds like DDT. Unfortunately, unlike
organochlorine compounds, organophosphates and carbamates exhibit increased
levels of acute toxicity in humans and animals.
72. In general, while they are generally unstable, natural pesticides are not necessarily
any less toxic than are synthetic ones.
73. PCBs have become an environmental issue because of their once widespread use,
their persistence in the environment, and their bioaccumulation in living systems.
PCBs have been shown to have a potentially adverse impact on human health,
especially in reference to growth and development.
74. PCBs are found in all parts of the world because of their persistence in the
environment. PCBs are resistant to breakdown by chemical and biological agents
and are relatively insoluble in water. The small amounts of PCBs present in surface
waters are constantly being volatilized and deposited on land or in water after
traveling in the air for several days.
75. The health effects of PCBs are controversial. The most common reaction to an acute
exposure to PCBs is chloracne. The effects of chronic exposure and/or
bioaccumulated PCBs are less well defined. The consumption of large amounts of
fish with a high PCB content is believed to be detrimental to human and animal
reproduction. PCBs are also believed to affect cognitive development in children.
76. Environmental estrogens are able to affect hormonal activity because they either
bind to the estrogen receptor to either mimic or block the action of the hormone
itself or they accelerate the breakdown of the natural hormone.
77. Evidence obtained from alligator populations in Florida, birds in the Great Lakes
area, families whose mothers consumed the synthetic estrogen DES, and studies
using laboratory animals indicates that environmental estrogens can cause
reproductive problems, embryo mortality and deformities, reproductive system
abnormalities, and cancer.
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Synthesizing Ideas
78. In the absence of sunlight, vitamin D production would cease. The ultraviolet
components of sunlight are required to convert a cholesterol derivative found in skin
to vitamin D. Factors that limit sun exposure include excessive cloud cover and the
need to stay indoors during extended periods of winter.
79. Vitamin E acts as an antioxidant, a substance that prevents the oxidative damage
caused by free radicals. Symptoms of vitamin E deficiency include scaly skin,
sterility, and the decay of muscle tissue.
80. EDTA, ethylenediaminetetraacetic acid, is sometimes used as an antidote to heavy
metal poisoning because it chelates, or binds to, metals.
81. The antibiotic properties associated with honey are likely due to the presence of
naturally occurring weak organic acids that are toxic to microorganisms.
82. Adding pure sugar cane to an open wound will draw water from the surrounding
tissues through the process of osmosis. This local “dehydration” will inhibit the
growth of microbes since microorganisms require water for both survival and
population growth.
83. Benzoic acid (acidic conditions):
O
C
OH
Benzoate anion (basic conditions):
O
C
O-
Benzoic acid is an effective preservative while benzoate is not because only the
molecular (non-ionic) form of the acid is toxic to the microbe. Benzoate is used as a
preservative in foods because the anion reverts back to the molecular acid in the
acidic environment of the food product.
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84. While certain weak organic acids are toxic to many microorganisms, they are not
particularly toxic to humans. Because many of these acids and their salts occur
naturally in some foods and are readily metabolized in your body, there is little
health concern associated with their use. The use of inorganic salts as preservatives,
however, can represent a health risk to certain individuals. Some individuals are
allergic to sulfur-containing substances such as sulfites. Also, nitrates can be
converted to potentially carcinogenic nitrosamines.
85. Sulfites are used to protect wine and other grape products. The active weak acid is
the bisulfite ion formed from either sulfur dioxide gas or sulfite salts dissolved in
water. Thus, sulfites are ideal preservatives for aqueous solutions. Nitrites are used
to preserve cooked and cured meats. The active weak inorganic acid is the nitrite ion
that binds iron in blood and muscle tissue. Since the conversion of this anion to an
active acid is not required in the food product, this preservative is ideal for solid
foods like ham, bacon, and hot dogs.
86. DDT’s persistence is related to its low vapor pressure, slow rate of evaporation, low
reactivity to light, microorganisms, or other chemicals, and to its very low solubility
in water. Its persistence made it an ideal insecticide. One spraying often afforded
protection from insects for weeks to years. Unfortunately, because of its low water
solubility and its high solubility in hydrocarbon-rich media, DDT accumulates in the
fats of fish and animals and where it can reach highly toxic levels.
87. DDT is hydrophobic and is not readily secreted into the urine. Rather, DDT
accumulates in the fatty tissue of animals and fish where it can reach toxic
concentrations.
88. Insecticides that are persistent because of their hydrophobic character tend to
bioaccumulate in biological systems because of bioconcentration and
biomagnification. Thus, the concentration of persistent insecticides increases as one
goes up the food chain. Non-persistent insecticides are rapidly degraded by chemical
and biological agents in the environment into non-toxic water-soluble compounds.
These compounds tend not to accumulate in food chains.
89. a) Chocolate contains a methylxanthine known as theobromine that acts as a
stimulant. The structure of theobromine is given below.
O
CH3
C
HN
C
C
C
N
CH
O
N
CH3
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N
Because dogs and other animals metabolize theobromine more slowly than humans,
small amounts of theobromine in dogs cause the release of epinephrine which can
result in cardiac arrhythmias and even death.
b) The difference in the toxicity of arsenic in humans and owls results from the
different biochemical processes that occur in each. Thus, the uncoupling of
metabolic processes, such as oxidative phosphorylation, that occurs in humans must
not occur in owls.
90. Non-specific insecticides can migrate from the areas to which they were applied into
the rest of the environment. Insecticides can evaporate, travel in the air and
eventually be deposited on land or in water distant from their original site of
application and have an adverse effect on the new ecosystem.
91. PCBs and their by-products persist in the environment well after their production
ceased in 1977 because of their stability, their extensive usage, and the careless way
in which they were disposed. PCBs still remain in use in many electrical
transformers around the world. Old transformers that have been discarded were
simply dumped in landfills where their PCB contents leaked out and are leaching
into the ground. Once released into the environment, PCBs can exist for many years
since they are resistant to chemical and biological degradation, and are hydrocarbonsoluble allowing them to bioaccumulate in living systems.
92. a) Individuals eating a diet consisting of meats, fish, poultry, dairy products, and
eggs would be exposed to hydrophobic chemicals such as DDT, PCB, and dioxin.
b) Individuals consuming a vegan diet would be exposed to chemicals such as
organophosphate and carbamate pesticides, and phenoxy and glyphosate herbicides.
c) Individuals eating a vegetarian diet consisting of fresh fruits, vegetables, dairy
products, and eggs would be exposed to both hydrophobic chemicals in dairy
products and eggs, and common insecticides and herbicides.
93. Hydrophobic materials are much less soluble in salt water than they are in
freshwater. Since their concentration is higher in freshwater, the concentration of
these substances in the fatty tissue of freshwater fish should also be higher.
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