10
Environmental Health and
Toxicology
PowerPoint® Slides prepared by
Jay Withgott and April Lynch
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
This lecture will help you understand:
• Environmental health
hazards
• Environmental health goals
• Synthetic and natural
toxicants
• The study of hazards and
their effects
• Risk assessment and risk
management
• Policy and regulation
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Central Case: Alligators and Endocrine
Disruptors at Lake Apopka, Florida
• Biologist Louis Guillette found alligators with
reproductive abnormalities in a Florida lake.
• The lake had been contaminated with pesticides.
• Research revealed that chemicals in the lake were
disrupting the animals’ reproductive hormones.
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Environmental health
• Assesses environmental factors that influence human
health and quality of life
• Seeks to prevent adverse effects on human health and
ecological systems
• Contains environmental toxicology within its scope
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Environmental health hazards
Types include:
•
Physical hazards (floods, blizzards, landslides,
radon, UV exposure)
•
Chemical hazards (disinfectants, pesticides)
•
Biological hazards (viruses, bacterial infections)
•
Cultural or lifestyle hazards (drinking, smoking,
bad diet, crime in neighborhood)
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Environmental health hazards
LE 10-1
Physical hazard
Biological hazard
Chemical hazard
Cultural hazard
Infectious disease
In communicable or transmissable disease, a pathogen
attacks a host,
either directly or through a vector (e.g., mosquito that
transfers a malaria parasite to hosts)
… and the pathogen can be transmitted from one host
to another.
Infectious disease causes 25% of deaths in the world
and nearly half of deaths in developing nations.
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Infectious disease
LE 10-2
4.0
Other
Respiratory and
digestive diseases
7.9%
10.0%
5.2%
Injuries
Infectious
diseases
14.9 million
26.1%
9.1%
12.5%
Cardiovascular
diseases
29.3%
Cancers
Annual deaths (millions)
Maternal
and
perinatal
conditions
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
Respiratory AIDS
infections
(influenza,
pneumonia, etc.)
Leading causes of death across the world, 2004
Diarrheal
diseases
TB
Malaria Childhood
diseases
(measles,
Pertussis,
tetanus, etc.)
Leading causes of death by infectious disease, 2004
Many health hazards also exist indoors
• Substances in plastics and consumer products
• Lead in paint and pipes
• Radon
• Asbestos
• PBDE fire retardants
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Toxicology
…is the study of poisonous substances and their effects on
humans and other organisms.
• Toxicologists assess and compare toxic agents, or
toxicants, for their toxicity, the degree of harm a
substance can inflict.
• Environmental toxicology focuses on effects of chemical
poisons released into the environment.
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Environmental toxicology
Toxicants are studied that come from or are discharged into
the environment and their:
• Health effects on humans
• Effects on animals
• Effects on ecosystems
Animals are studied:
• For their own welfare
• As “canaries in a coal mine” to warn of effects
on humans
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Synthetic chemicals are everywhere in our
environment
• Many thousands have been produced and released.
• Some persist for long time periods or travel great
distances.
• Of the 100,000 synthetic chemicals on the market today,
very few have been thoroughly tested for harmful effects.
• 2002 USGS study: 80% of U.S. streams contain up to 82
wastewater contaminants, including antibiotics,
perfumes, detergents, drugs, steroids, disinfectants, and
so forth.
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Rise of synthetic chemicals
• There has been widespread synthetic chemical production
since WWII.
• People were largely unaware of the health risks of many
toxicants.
The potent
insecticide DDT
was sprayed
widely in public
areas, even on
people.
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Silent Spring and Rachel Carson
• Carson’s 1962 book alerted the public that DDT and
other pesticides could be toxic to animals and people.
• Further research led the EPA to ban DDT in 1973.
• These developments were central to the modern
environmental movement.
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Types of toxicants
• Carcinogens: cause cancer
• Mutagens: cause mutations in DNA
• Teratogens: cause birth defects
• Allergens: cause unnecessary immune response
• Neurotoxins: damage nervous system
• Endocrine disruptors: interfere with hormones
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Endocrine disruption
• Some chemicals, once inside the bloodstream, can
“mimic” hormones.
• If molecules of the chemical bind to the sites
intended for hormone binding, they cause an
inappropriate response.
• Thus these chemicals disrupt the endocrine
(hormone) system.
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LE 10-4
Hormone
Response
Receptor
Cell membrane
Inside cell
Normal hormone binding
Hormone mimic
Hormone
Receptor
Cell membrane
Hormone mimicry
Response
(identical
to that
caused by
hormone)
Inside cell
Endocrine disruption
• The hormone system is geared to working with tiny
concentrations of hormones …
• … so, it can respond to tiny concentrations of
environmental contaminants.
• Have chemicals in the environment acted as endocrine
disruptors in humans?
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Frogs, people, and atrazine
Frogs show reproductive
abnormalities in response to
small doses of the herbicide
atrazine, researcher Tyrone
Hayes has found.
Others suggest that atrazine may
have effects on humans as well.
The fierce criticism from
atrazine’s manufacturer reflects
the high stakes in environmental
toxicology.
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Declining sperm counts?
A 1992 study summarized results of sperm count studies
worldwide since 1938. Data showed a significant decrease
in men’s sperm counts over 50 years.
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LE 10-6a
Declining sperm count in humans, based on 61 studies
Testicular cancer
Others hypothesize that endocrine disruptors are behind
the rise in testicular cancer in many nations.
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LE 10-6b
Denmark
Norway
Germany
Finland
Sweden
Estonia
Increasing incidence of testicular cancer
Toxicants move in specific ways
Synthetic chemicals take many routes in traveling through
the environment.
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LE 10-7
Industry and manufacturing
Home
Work
Medical facilities Agriculture: crops,
and public spaces rangeland, feedlots
Soil
Water: surface
and groundwater
Humans
Genes, womb,
breast milk
Non-human biota
Human fetuses and babies
Air
Toxicants concentrate in water
• Surface water and groundwater can accumulate toxicants.
• Runoff from large areas of land drains into water bodies,
becoming concentrated.
• Toxicants in groundwater or surface water reservoirs used
for drinking water pose potential risks to human health.
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Airborne toxicants
• Volatile chemicals can travel long distances on
atmospheric currents.
• PCBs are carried thousands of miles from developed
nations of the temperate zone up to the Arctic, where they
are found in tissues of polar bears and seals.
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Persistence
• Some chemicals are more stable than others, persisting in
the environment.
• DDT and PCBs are persistent.
• Bt toxin in GM crops is not persistent.
• Temperature, moisture, sun exposure, and so forth, affect
the rate of degradation.
• Most toxicants degrade into simpler breakdown products.
Some of these are also toxic.
• (DDT breaks down to DDE, also toxic.)
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Poisons accumulate in tissues
• The body may excrete, degrade, or store toxicants.
• Fat-soluble ones are stored.
DDT is persistent and fat soluble,
… so it builds up in tissues: bioaccumulation.
• Bioaccumulated chemicals may be passed on to animals
that eat the organism—up the food chain…
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Poisons move up the food chain
At each trophic level, chemical concentration increases:
biomagnification.
DDT concentrations increase from plankton to fish to
fish-eating birds.
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LE 10-8
DDT concentration
(parts per million)
Osprey
25 ppm
Large fish
2 ppm
Small fish
0.5 ppm
Zooplankton
0.04 ppm
Water
0.000003 ppm
Not all toxicants are synthetic
• Although toxicology tends to focus on manmade chemicals, it’s important to keep in mind
that there are plenty of natural toxicants.
• Many are toxins produced by animals or plants
for protection against predators and pathogens.
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Studying effects of hazards
Toxicologists study effects in several major ways:
• Wildlife toxicology studies
• Human epidemiological studies
• Dose-response studies in the lab
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Approaches in environmental health research
Human studies rely on:
• Case history = observation and analysis of individual
patients
• Epidemiological studies = long-term, large-scale
comparisons of different groups of people
• Animal testing
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Epidemiology
• Advantages:
Realistic
All real-life factors included
• Disadvantages: Statistically correlational only;
does not prove causation
Takes many years to get results
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Mixing toxicology with anthropology
Mexican children were tested for pesticide effects.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
From The Science behind the Story
LE 10-SBS
4-year-olds
5-year-olds
Drawings by children in the foothills
4-year-olds
Drawings by children in the valley
5-year-olds
Dose-response analysis
• Dose-response analysis is a method of determining the
toxicity of a substance by measuring response to different
doses.
• Lab animals are used.
• Mice and rats breed quickly and give data relevant to
humans because they share mammal physiology with us.
• Responses to doses are plotted on a dose-response curve.
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Dose-response curve
Threshold = dose at
which response begins
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LD50 = dose
lethal to 50%
of test animals
Dose-response curve
• Dose-response curves allow us to predict effects of higher
doses.
• By extrapolating the curve out to higher values, we can
predict how toxic a substance may be to humans at
various concentrations.
• In most curves, response increases with dose.
But this is not always the case;
the increase may not be linear.
With endocrine disruption, it may decrease.
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Factors affecting toxicity
• Not all people are equal. Sensitivity to a toxicant can
vary with sex, age, weight, and so forth.
• Babies, older people, or those in poor health are more
sensitive.
• Type of exposure:
• acute = high exposure in short period of time
• chronic = lower amounts over long period of time
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Mixtures of toxicants
• Substances may interact when combined together.
• Mixes of toxicants may cause effects greater than the sum
of their individual effects.
These are called synergistic effects.
• A challenging problem for toxicology:
There is no way to test all possible combinations!
• (And the environment contains complex mixtures of many
toxicants.)
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Risk
• Risk = the mathematical probability that some
harmful outcome will result from a given action,
event, or substance
• Probability = a quantitative description of the
likelihood of a certain outcome
“Harmful outcome” could be defined as injury,
death, environmental damage, or economic loss
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Perception differs from reality
Our perception of risks tends not to match statistical reality.
smoking
plane
crash
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Risk assessment
• Analyzes risks quantitatively
• Measures and compares risks involved in different
activities or substances
• Helps identify and prioritize serious risks
• Helps determine threats posed to humans, wildlife,
and ecosystems
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Risk management
• Considers risk assessments in light of social,
economic, and political needs and values
• Weighs costs and benefits, given both scientific and
nonscientific concerns
• Results in decisions whether or not to reduce or
eliminate risk
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Risk assessment and risk management
inform policy
Following risk management, policy decisions are made.
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LE 10-11
Hazard
identification
Scientific results
and measurement
of probability
Political, social,
economic, and
ethical considerations
Risk
assessment
Risk
management
Scientific data on
Information, opinion, and lobbying from
Toxicity
characterization
Extent of
exposure
Private
citizens
Industry and
manufacturing
Policy
Nonprofit
Interest
groups
Philosophical approaches
• “Innocent until proven guilty”:
Assume harmless until shown to be harmful
• Precautionary principle:
Assume harmful until shown to be harmless
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Implications for product testing
• “Innocent until proven guilty”:
• Industry can introduce any products it wants.
• Government bears the burden of proof to show if
products are dangerous.
• Precautionary principle:
• Industry cannot introduce a product until it is very
thoroughly tested and shown convincingly to be
harmless.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Implications for product testing
• Industry has pressured government to take an
“innocent-until-proven-guilty” approach.
• Environmental advocates have pressured government
to follow the precautionary principle.
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LE 10-12
Sequence of events
“Innocent until proven
guilty” approach
Precautionary
principle approach
Industrial research and
development
Pre-market testing by
industry, government,
and academic
scientists
Limited testing; all
products brought to market
Rigorous testing; only the safest
products brought to market
Some products harm
human health
Minimal impact on
human health
Rigorous testing demanded
Limited testing required
Consumer use of
products
Post-market testing by
industry, government,
and academic scientists
Regulations and bans
of unsafe products
Unsafe products recalled
Consumer use of safe
products
Federal agencies and risk management
• In the United States, most risk management is
conducted by federal and state agencies.
• Particularly:
Environmental Protection Agency
and
Food and Drug Administration
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Policy on toxicants
Key agencies and products they regulate:
• Food and Drug Administration (FDA)
- food, additives, cosmetics, drugs, medical devices
• Environmental Protection Agency (EPA)
- pesticides, industrial chemicals, and any synthetic
chemicals not covered by other agencies
• Occupational Health and Safety Administration (OSHA)
- workplace hazards
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EPA regulation: Pesticides
• Pesticides to be introduced to market in the United States
need to be registered with the EPA.
• Registration involves risk assessment and risk
management.
• The EPA assesses research from the manufacturer along
with any outside research.
• The EPA can set restrictions on use, or even ban a
product.
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EPA regulation: Industrial chemicals
• The EPA is charged with monitoring 75,000 industrial
chemicals.
• There are too many chemicals and not enough time,
people, or resources.
• Only 10% of chemicals on the market are thoroughly
tested.
• Only 2% are screened for carcinogens, mutagens, and
teratogens.
• <1% are government regulated.
• ~0% are tested for endocrine, nervous, or immune effects.
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International policy on toxicants
• The EU has proposed legislation to require 30,000
chemicals to be tested and registered, and 1,500
hazardous chemicals to be restricted.
• Stockholm Convention, 2001: international treaty to
phase out 12 persistent organic pollutants (POPs), “the
dirty dozen”
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Viewpoints: Industry or government?
Warren
Porter
“Given the inherent
inadequacies of the testing
process and the uncertainty of
the economic impacts, both
government and industry
should share the
responsibility of testing to
ensure public safety.”
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Marian
Stanley
“Manufacturers often
voluntarily conduct new
studies to support the
continued safe use of their
chemicals. … It is important
that the EPA and
manufacturers work together
in evaluating chemicals.”
Conclusion
• International agreements are a hopeful sign that
governments will control environmental hazards.
• But solutions may come more easily when they do not
arise from government regulation alone.
• Consumer choice can influence industry if consumers
have accurate information.
• But we will never attain complete knowledge of risks.
• A safer future depends on knowing risks, phasing out
harmful substances, and replacing them with safer ones.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
QUESTION: Testing Your Comprehension
Which causes birth defects?
a. Allergen
b. Mutagen
c. Carcinogen
d. Teratogen
e. Endocrine disruptor
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QUESTION: Testing Your Comprehension
Which causes birth defects?
d. Teratogen
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QUESTION: Testing Your Comprehension
Which statement is NOT correct regarding the insecticide
DDT?
a. It was criticized in the book Silent Spring.
b. It helps fight malaria.
c. It is persistent and bioaccumulates.
d. It has no toxic breakdown products.
e. Its use was banned by the EPA.
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QUESTION: Testing Your Comprehension
Which statement is NOT correct regarding the insecticide
DDT?
d. It has no toxic breakdown products.
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QUESTION: Testing Your Comprehension
Epidemiological studies… ?
a. Can prove a certain toxicant causes a
certain effect.
b. Search for statistical association between
hazard and effect.
c. Are rapidly completed.
d. Take place with lab animals.
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QUESTION: Testing Your Comprehension
Epidemiological studies… ?
b. Search for statistical association between
hazard and effect.
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QUESTION: Testing Your Comprehension
Which statement is FALSE?
a. Babies are more sensitive to toxicants than 30year-olds.
b. Synergistic effects can occur with mixtures of
chemicals.
c. Chronic exposure occurs over a short period of
time.
d. Some doses may elicit no measurable response.
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QUESTION: Testing Your Comprehension
Which statement is FALSE?
c. Chronic exposure occurs over a short period of
time.
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QUESTION: Seeking Solutions
Describe some environmental hazards you think you may
be living with indoors. How do you think you may have
been affected by indoor or outdoor environmental
hazards? What steps do you plan to take to deal with these
toxicants in your own life?
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QUESTION: Seeking Solutions
Do you feel laboratory-bred animals should be used in
experiments on toxicology? Why or why not? Can you
envision any alternatives?
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QUESTION: Viewpoints
In testing new synthetic chemicals, should we follow the
“innocent-until-proven-guilty” approach, or the
precautionary principle?
a. “Innocent-until-proven-guilty” approach
b. Precautionary principle
c. A hybrid of both approaches
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings