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Transcript
Environmental Health and Toxicology
Chapter 8
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Outline:
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Environmental Health Hazards
 Global Disease Burden
 Emergent and Infectious Diseases
 Antibiotics and Pesticide Resistance
 Toxicology
Distribution and Fate of Toxins
Minimizing Toxic Effects
Measuring Toxicity
Risk Assessment
Public Policy
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ENVIRONMENTAL HEALTH HAZARDS
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Health - A state of complete physical, mental,
and social well-being.
Disease - An abnormal change in the body’s
condition that impairs important physical or
psychological functions-.
 Diet and nutrition, infectious agents, toxic
chemicals, physical factors, and
psychological stress all play roles in
morbidity (illness) and mortality (death).
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Global Disease Burden
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Health agencies calculate disability-adjusted
life years (DALYs) as a measure of disease
burden.
 Chronic diseases now account for nearly
60% of the 56.5 million total deaths
worldwide each year.
- Progress in eliminating communicable
diseases such as smallpox, polio, and
malaria, is allowing people to live longer.
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Disability-Adjusted Life Year
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WHO reports communicable diseases are
responsible for nearly half of all 1.2 billion
DALY’s lost each year.
 About 90% of all DALY losses occur in
developing world where one-tenth of all
health care dollars are spent.
- Malnutrition exacerbates many diseases.
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Emergent Diseases and Infectious Diseases
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An emergent disease is one not previously
known or that has been absent for at least 20
years.
 An important factor in the spread of many
diseases is speed and frequency of
modern travel.
 Malaria is one of the most prevalent
remaining infectious diseases.
- SARS and Avian Flu
- HIV/AIDS has the largest death toll from
an emergent disease.
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Ecological Diseases
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Domestic animals and wildlife also
experience sudden and widespread
epidemics.
 Distemper Virus (Seals)
 Chronic Wasting Disease (Deer and Elk)
- Transmissible Spongiform
Encephalopathies
 Black-Band Disease (Coral)
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Infectious Disease Outbreaks
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Antibiotic and Pesticide Resistance
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Protozoan parasite that causes malaria is
now resistant to most antibiotics, while the
mosquitoes that transmit it have developed
resistance to many insecticides.
 Short life spans.
- Speeds up natural selection and
evolution.
 Human tendency to overuse pesticides
and antibiotics.
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Antibiotic and Pesticide Resistance
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Antibiotic Use
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At least half of the 100 million antibiotic
doses prescribed in the U.S every year are
unnecessary or are the wrong drug.
Many people do not finish full-course.
More than half of all antibiotics manufactured
in the U.S. are routinely fed to farm animals
to stimulate weight gain.
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Toxicology
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Dangerous chemicals are divided into two
broad categories:
 Hazardous - Dangerous
- Flammable, explosive, irritant, sensitizer,
acid, caustic.
 Toxic - Poisonous
- Can be general or very specific. Often
harmful even in dilute concentrations.
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Toxicology Cont’d
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Allergens - Substances that activate the
immune system.
 Antigens - Allergens that are recognized as
foreign by white blood cells and stimulate
the production of specific antibodies.
- Other allergens act indirectly by binding
to other materials so they become
antigenic.
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Toxicology Cont’d
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Sick Building Syndrome
 Headaches, allergies, and chronic fatigue
caused by poorly ventilated indoor air
contaminated by molds, carbon monoxide,
nitrogen oxides, and other toxic chemicals.
- Worker absenteeism and reduced
productivity.
 EPA estimates $60 billion annual loss.
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Toxicology Cont’d
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Neurotoxins - Special class of metabolic
poisons that specifically attack nerve cells.
 Different types act in different ways.
- Heavy Metals kill nerve cells.
- Anesthetics and Chlorinated
Hydrocarbons disrupt nerve cell
membranes.
- Organophosphates and Carbamates
inhibit signal transmission between nerve
cells.
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Toxicology Cont’d
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Mutagens - Agents that damage or alter
genetic material.
 Radiation
Teratogens - Specifically cause abnormalities
during embryonic growth and development.
 Alcohol - Fetal Alcohol Syndrome
Carcinogens - Substances that cause cancer.
 Cigarette smoke
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Endocrine Hormone Disrupters
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Chemicals that disrupt normal endocrine
hormone functions.
 Hormones are chemicals released in blood
by glands to regulate development and
function of tissues and organs elsewhere
in the body.
- Environmental Estrogens and
Androgens
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Diet
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Strong correlation between cardiovascular
disease and the amount of salt and fat in an
individual’s diet.
 Highly-processed foods, fat, and smokecured, high-nitrate meats appear to be
associated with cancer.
 Nearly 2/3 of all Americans are considered
overweight.
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DISTRIBUTION AND FATE OF TOXINS
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Solubility - Chemicals are divided into two
major groups:
- Dissolve more readily in water.
- Dissolve more readily in oil.
 Water-soluble compounds move rapidly
through the environment, and have ready
access to most human cells.
 Oil-soluble molecules generally need a
carrier to move through the environment.
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Bioaccumulation and Biomagnification
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Cells have special mechanisms for
Bioaccumulation - Selective absorption and
storage.
 Dilute toxins in the environment can build
to dangerous levels inside cells and
tissues.
Biomagnification - Toxic burden of a large
number of organisms at a lower trophic level
is accumulated and concentrated by a
predator at a higher trophic level.
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Biomagnification
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DDT
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DDT is a synthetic chemical compound once used widely in the United States and throughout
the world as a pesticide (a chemical substance used to kill weeds, insects, rodents, or other
pests). It is probably best known for its dual nature: although remarkably effective in destroying
certain living things that are harmful to plants and animals, it can also be extremely dangerous
to humans and the environment.
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The abbreviation DDT stands for dichlorodiphenyltrichloroethane. DDT was first produced in the
laboratory in 1873. For more than half a century, it was little more than a laboratory curiosity—a
complicated synthetic (produced by scientists) compound with no apparent use.
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Then, in 1939, Swiss chemist Paul Hermann Müller (1899–1965) discovered that DDT was
highly poisonous to insects. The discovery was very important because of its potential for use in
killing insects that cause disease and eat agricultural crops. For his work, Müller was awarded
the Nobel Prize in medicine in 1948.
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DDT's environmental problems arise because of two important properties: persistence and lipidsolubility. The term persistence refers to the fact that DDT does not break down very easily.
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Once the pesticide has been used in an area, it is likely to remain there for many years. In
addition, DDT does not dissolve in water, although it does dissolve in fatty or oily liquids. (The
term lipid-solubility is used because fats and oils are members of the organic family known as
lipids.)
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Since DDT is not soluble in water, it is not washed away by the rain, adding to its persistence in
the environment. But since DDT is lipid-soluble, it tends to concentrate in the body fat of
animals.
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Before the dangers of DDT were known, crops and people alike were
sprayed with the chemical to protect against bothersome insects.
DDT is used today in such African nations as Zimbabwe and Ethiopia to control
mosquitoes and the tsetse fly. These two insects cause serious diseases, such as
malaria and sleeping sickness. DDT saves lives when used on the tsetse fly in Lake
Kariba in Zimbabwe. But once sprayed on the lake, DDT does not disappear very
quickly. Instead, it is taken up by plants and animals that live in the lake. Studies
have shown that the concentration of DDT in the lake itself is only 0.002 parts per
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billion. But algae in the lake have a concentration of 2.5 parts per million.
Clutch of mallard eggs contaminated by DDT. The accumulation of
DDT in many birds causes reproductive difficulties. Eggs have thinner
shells that break easily, and some eggs may not hatch at all
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DDT & The American Bald Eagle
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The bald eagle (Haliaeetus leucocephalus) is currently listed as a
federally threatened species in Washington. In July 1999, the U.S. Fish
and Wildlife Service published a proposal to delist the bald eagle under
the Endangered Species Act.
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At the time the species was listed, environmental contaminants were
cited as the primary reason for its decline. Beginning in the 1940's,
dichloro diphenyl trichloroethane (DDT) and other organochlorine
pesticides became widely used as insecticides.
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In the late 1960's and early 1970's, it was determined that
dichlorophenyl-dichloroethylene (DDE), the principal breakdown product
of DDT, accumulated in the fatty tissues of adult female bald eagles and
resulted in thin shells and reproductive failure (Wiemeyer et al. 1972,
1984; Grier 1982).
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Due to the bioaccumulative and persistent nature of DDT and the
adverse reproductive effects elicited by DDT, particularly on birds, its
use was banned in the United States in 1972.
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Agent Orange
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During the Vietnam War, US military forces sprayed nearly 19 million gallons of herbicide on
about 3.6 million acres of land in Vietnam and Laos to remove forest cover, destroy crops, and
clear vegetation from the perimeters of US bases. This effort, known as Operation Ranch Hand,
lasted from 1962 to 1971.
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Various herbicidal (plant-killing) formulations were used, but most were mixtures of 2 herbicides
known as phenoxy herbicides because of their chemical structures:
2,4-dichlorophenoxyacetic acid (2,4-D)
2,4,5-trichlorophenoxyacetic acid (2,4,5-T)
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Each formulation was shipped in a chemical drum marked with an identifying colored stripe. The
most widely used mixture contained equal parts 2,4-D and 2,4,5-T. Because this herbicide
came in drums with orange stripes, it was called Agent Orange. Today, Agent Orange is used to
refer generally to all the phenoxy herbicides sprayed at the time.
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The 2,4,5-T was contaminated with small amounts of dioxins, which were created
unintentionally during the manufacturing process.
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Dioxins are a family of biologically active compounds formed during the manufacturing of paper
and some other industrial processes. Because they can remain in the environment for years,
they form part of a group of chemicals known as "persistent organic pollutants."
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The particular dioxin present in Agent Orange, 2,3,7,8-tetrachlorodibenzo-p-dioxin, or TCDD, is
unusually toxic.
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Persistence
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Some chemical compounds are very
unstable and degrade rapidly under most
conditions, thus their concentrations decline
quickly after release.
Others are more persistent.
 Stability can cause problems because
these materials persist in the environment
and have unexpected effects far from their
original use.
- PBDE (flame-retardants in textiles)
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Chemical Interactions
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Antagonistic Reaction - One material
interferes with the effects, or stimulates the
breakdown, of other chemicals.
Additive Reaction - Effects of each chemical
are added to one another.
Synergistic Reaction - One substance
multiplies the effect of the other.
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MECHANISMS FOR MINIMIZING
TOXIC EFFECTS
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Every material can be poisonous under
certain conditions.
 Most chemicals have a safe threshold
under which their effects are insignificant.
Metabolic Degradation
 In mammals, the liver is the primary site of
detoxification of both natural and
introduced poisons.
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Excretion
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Effects of waste products and environmental
toxins reduced by eliminating via excretion.
 Breathing
 Kidneys
- Urine
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MEASURING TOXICITY
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Animal Testing
 Most commonly used and widely accepted
toxicity test is to expose a population of
laboratory animals to measured doses of
specific toxins.
- Sensitivity differences pose a problem.
 Dose Response Curves
 LD50 - Dose at which 50% of the test
population is sensitive.
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LD50
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Population Sensitivity Variations
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Acute vs. Chronic Effects
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Acute Effects - Caused by a single exposure
and result in an immediate health problem.
Chronic Effects - Long-lasting. Can be result
of single large dose or repeated smaller
doses.
 Very difficult to assess specific health
effects due to other factors.
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RISK ASSESSMENT
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Factors influencing risk perception:
 Rating risks based on agendas.
 Most people have trouble with statistics.
 Personal experiences can be misleading.
 We have an exaggerated view of our
abilities to control our fate.
 News media sensationalizes rare events.
 Irrational fears lead to overestimation of
certain dangers.
- Fear of the unknown.
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Accepting Risks
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Most people will tolerate a higher probability
of occurrence of an event if the harm caused
by that event is low.
 Harm of greater severity is acceptable only
at low levels of frequency.
- EPA generally assumes 1 in 1 million is
acceptable risk for environmental
hazards.
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ESTABLISHING PUBLIC POLICY
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Biggest problem in making regulatory
decisions is that we are usually exposed to
many sources of harm, often unknowingly.
May not be reasonable to demand protection
from every potentially harmful contaminant in
our environment, no matter how small the
risk.
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ESTABLISHING PUBLIC POLICY CONT’D
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In setting standards for environmental toxins,
need to consider:
 Combined effects of different exposures.
 Individual sensitivities within population.
 Effects of chronic and acute exposures.
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