Transcript Document

Environmental Hazards and
Human Health
Chapter 17
17-1 What Major Health Hazards Do We Face?
 Concept 17-1 People face health hazards from
biological, chemical, physical, and cultural
factors, and from the lifestyle choices they make.
Risks Are Usually Expressed as Probabilities
 Risk – a measure of the likelihood that you will suffer
harm from a hazard (something that has the potential
to cause harm)
• Possibility – it COULD happen
• Probability – how likely it is to happen
We can suffer from:
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Biological hazards: from more than 1,400 pathogens
Chemical hazards: in air, water, soil, and food
Physical hazards: fire, earthquake, volcanic eruption…
Cultural hazards: smoking, poor diet, unsafe sex, drugs,
unsafe working conditions, and poverty
 Lifestyle choices: smoking, overeating, alcohol/drug abuse
17-2 What Types of Biological Hazards
Do We Face?
 Concept 17-2 In terms of death rates, the most
serious infectious diseases are flu, AIDS, diarrheal
diseases, malaria, and tuberculosis; most of these
deaths occur in developing countries.
17-2 What Types of Biological Hazards
Do We Face?
 Sources of biological hazards include bacteria,
viruses, insects, plants, birds, animals, and humans.
 These sources can cause a variety of health effects
ranging from skin irritation and allergies to infections
(e.g., tuberculosis, AIDS), cancer and so on.
 This symbol is generally used as a warning, so that those potentially
exposed to the substances will know to take precautions.
Some Diseases Can Spread from
One Person to Another
 Nontransmissible disease – not caused by living
organisms and cannot spread from one person to another
• Heart disease, cancer, asthma, diabetes
 Infectious disease – caused by living organisms such as
bacteria and viruses
• Malaria, tuberculosis, measles
• Transmissible (contagious
or communicable disease)
– it can be spread from
person to person
• Influenza, HIV
The World’s Seven Deadliest Infectious
Diseases Kill 12.5 Million People Each Year
 WHO estimates that
the world’s seven
deadliest infections kill
12.5 million people a
year (34,200/day)
• Most deaths are
poor people in
developing countries
• Most deaths are
preventable
Infectious Diseases Are Still
Major Health Threats
 Since 1950, death from infectious diseases have
declined due to:
• Better health care
• Antibiotics
• Vaccines
 Infectious diseases spread through: air, water, food,
body fluids
 Epidemic – large scale outbreak of an infectious
disease in an area or a country
 Pandemic – a global epidemic
Science Focus:
Genetic Resistance to Antibiotics Is Increasing
 Infectious bacteria are becoming genetically resistant
to widely used antibiotics due to:
• Genetic resistance: the few bacteria that survives the
antibiotics are stronger and more able to resist the
antibiotics in the future – population evolves.
• Overuse of antibiotics: A 2000 study found that half of
the antibiotics used to treat humans were prescribed
unnecessarily.
• Other factors:
• Rapid spread of bacteria around the world by human travel
• Overuse of pesticides (crops) and antibiotics (livestock)
Some Viral Diseases Kill Large
Numbers of People
 Viruses are not treatable with antibiotics.
 Influenza, HIV, and hepatitis B viruses infect and
kill many more people each year then highly
publicized West Nile and SARS viruses.
• The influenza virus is the biggest killer virus worldwide.
• Pigs, chickens, ducks, and geese are the major
reservoirs of flu. As they move from one species to
another, they can mutate and exchange genetic
material with other viruses.
Some Viral Diseases Kill Large
Numbers of People
 Acquired immune deficiency syndrome (AIDS)
caused by human immunodeficiency virus (HIV)
is the second biggest killer virus worldwide.
• Kills 2.1 million people a year (25 million so far)
• 2.5 million newly infected people a year
• Virus itself doesn’t kill you
• Weakened immune system
• Killed by a secondary infection
• No vaccine to prevent or cure AIDS
• Expensive, anti-viral drugs
• Live longer
Case Study:
Malaria – Death by Parasite-Carrying Mosquitoes
 Malaria
• Caused by Plasmodium sp. carried by Anopheles
mosquitoes
• It infects and destroys red blood cells, intense fever,
abdominal pains, vomiting, headaches
 Malaria on the rise since 1970
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Drug resistant Plasmodium
Insecticide resistant mosquitoes
Effect of global warming
AIDS patients particularly vulnerable
Solutions: Infectious Diseases, Ways to
Prevent or Reduce Their Occurrence
17-3 What Types of Chemical Hazards
Do We Face?
 Concept 17-3 There is growing concern about
chemicals that can cause birth defects and cancers
and disrupt the human immune, nervous, and
endocrine systems.
17-3 What Types of Chemical Hazards
Do We Face?
 A toxic chemical can cause temporary or permanent
harm or death.
 A hazardous chemical is a chemical that is flammable,
explosive, or one that irritates the eyes, skin or lungs.
 Chemical hazard labels indicate specific risks
• Scale from 0 (no risk) to 4 (highest risk)
Some Chemicals Can Cause Cancers,
Mutations, and Birth Defects
 Mutagens – chemicals or forms of radiation that
cause or increase the frequency of mutations
(changes) in DNA.
• UV radiation, radioactive decay, bromine
 Teratogens – chemicals that cause harm or birth
defects to a developing fetus or embryo.
• ethyl alcohol, lead, mercury, phthalates, thalidomide
 Carcinogens – chemicals or types of radiation that
can cause or promote cancer.
• benzene, PCB’s, radon, MANY chem. in cigarette smoke
Some Chemicals May Affect Our Immune,
Nervous, and Endocrine Systems
 Long-term exposure to some chemicals at low doses
may disrupt the body’s:
• Immune system: specialized cells and tissues that
protect the body against disease and harmful substances
• Nervous system: brain, spinal cord, and peripheral
nervous system
• Endocrine system: complex network of glands that
release minute amounts of hormones into the bloodstream
Some Chemicals May Affect Our Immune,
Nervous, and Endocrine Systems
 Hormonally active agents (HAAs) are a class of
chemical that mimic the body’s natural hormones
 Disrupt growth, metabolism, and reproduction
• Hormone blockers
• Gender benders
• Thyroid disrupters
Science Focus:
Mercury’s Toxic Effects
 Mercury is a teratogen and potent neurotoxin
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Interferes with nervous system and brain function
Once airborne, persistent and not degradable
1/3 from natural sources
2/3 from human activities
Enters the food chain: biomagnification
 How are humans exposed?
• Inhalation: vaporized Hg or particulates of
inorganic salts
• Eating fish with high levels of methylmercury
Cycling of Mercury in Aquatic Environments
Solutions: Mercury Pollution
Case Study:
A Black Day in Bhopal, India
 The world’s worst industrial accident occurred in
1984 at a pesticide plant in Bhopal, India.
• An explosion at Union Carbide pesticide plant in an
underground storage tank released a large quantity of
highly toxic methyl isocyanate (MIC) gas.
• 15,000-22,000 people died
• Indian officials claim that simple upgrades could have
prevented the tragedy.
17-4 How Can We Evaluate and Deal with
Chemical Hazards?
 Concept 17-4A Scientists use live laboratory
animals, non-animal tests, case reports of
poisonings, and epidemiological studies to estimate
the toxicity of chemicals, but these methods have
limitations.
 Concept 17-4B Many health scientists call for much
greater emphasis on pollution prevention to reduce
our exposure to potentially harmful candidates.
Many Factors Determine the Harmful Health
Effects of a Chemical
 Toxicity – how harmful a substance can be…its
ability to cause injury, illness, death.
 Factors determining the harm caused by exposure to a
chemical include:
• Dose – the amount of a substance that has been
inhaled, ingested, or absorbed
• High dosage, low dosage
• Frequency of exposure – how often does it occur
• Frequent, infrequent
• Length of exposure – how long the exposure lasts
• Short-term, long-term
Many Factors Determine the Harmful Health
Effects of a Chemical
 Age is an important factor…very young and/or very
old are much more at risk.
 One’s genetic makeup also
influences one’s sensitivity
to a toxic chemical.
 A related factor is how well the body’s
detoxification system (liver, kidneys lungs) works.
Many Factors Determine the Harmful Health
Effects of a Chemical
 The properties of the chemical can also determine
the harm caused:
• Solubility:
• Water-soluble – can move throughout our environment,
water supply, and bodies
• Fat-soluble – can penetrate our body’s membranes and
can be stored in our tissues
• Persistence: its resistance to be broken down
• How long does it stay in an active for in the environment
Many Factors Determine the Harmful Health
Effects of a Chemical
 Certain chemical interactions can either increase or
decrease the harmful effects of a toxin:
 Antagonistic interaction – certain vitamins or
minerals can reduce the harm done by some kinds
of toxic chemicals
 Synergistic interaction – certain chemicals can
increase the negative effects of other chemicals
• The two chemicals together can be worse than either one
of them separately
Many Factors Determine the Harmful Health
Effects of a Chemical
 Other related terms:
 Bioaccumulation – the tendency to be absorbed
and stored within certain tissues or organs
• Low concentrations over long periods of time can become
high levels in particular tissues
 Biomagnification – the accumulation of chemicals
as they pass through the food chain
• Organisms at the top of the food chain have higher levels
of toxins in their tissues
Estimating Human Exposure to Chemicals
and Measuring Their Effects
 Estimating human
exposure to
chemicals and their
effects is very
difficult because of
the many and often
poorly understood
variables involved.
Many Factors Determine the Harmful Health
Effects of a Chemical
 Response – the type and amount of health damage
done by exposure to toxic chemicals
• Acute exposure – short duration or single event exposure
• Chronic exposure – repeated, or continuous exposure
over extended periods of time (or a lifetime)
• Acute effect – an immediate, rapid, and reversible
response to exposure that is usually brief and low dosage
• dizziness, coughing, vomiting, irritated eyes
• Chronic effect – a permanent or long lasting consequence
from an exposure that is either high dosage or long-term
• kidney or liver damage, damage to central nervous system,
cancer, or death
Case Study:
Protecting Children from Toxic Chemicals
 Children are more susceptible to the effects of toxic
substances because:
• Children breathe more air, drink more water, and eat more
food per unit of body weight than adults.
• They are exposed to toxins when they put their fingers or
other objects in their mouths.
• Children usually have less well-developed immune systems
and detoxification processes than adults.
• Children’s developing bodies (especially the nervous
system) are more susceptible to damage done by chemicals.
Scientists Use Live Lab Animals and
Non-animal Tests to Estimate Toxicity
 Dose-response curve: plotting the toxicity of a test
chemical on certain organisms (usually rats or mice)
• Median lethal dose (LD50) – the dose that can kill
50% of the animals tested
• Median lethal concentration (LC50) – the
concentration that can kill 50% of the animals tested
Why Do We Know So Little about the Harmful
Effects of Chemicals?
 Under existing laws, most chemicals are considered
innocent until proven guilty, and estimating their
toxicity is difficult, uncertain, and expensive.
 “Toxicologists know a great deal about a few chemicals,
a little about many, and next to nothing about most.”
 100,000 registered synthetic chemicals
• 10% thoroughly screened for toxicity
• 2% tested for carcinogen, teratogen, or mutagen determination
 Federal and state governments do not regulate about
99.5% of the commercially used chemicals in the U.S.
Pollution Prevention and the
Precautionary Principle
 Some scientists and health officials say that
preliminary but not conclusive evidence that a
chemical causes significant harm should spur
preventive action (precautionary principle).
• A new product is considered harmful until it can be
proved to be safe
 Manufacturers contend that widespread application of the
precautionary principle would
make it too expensive to introduce
new chemicals and technologies.
17-5 How Do We Perceive Risks and How Can
We Avoid the Worst of Them?
 Concept 17-5 We can reduce the major risks
we face if we become informed, think critically
about risks, and make careful choices.
Comparative Risk Analysis:
Most Serious Ecological and Health Problems
The Greatest Health Risks Come from
Poverty, Gender, and Lifestyle Choices
 Most individuals evaluate the relative risk they
face based on:
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Degree of control
Fear of unknown
Whether we voluntarily take the risk
Whether risk is catastrophic
Unfair distribution of risk
 Sometimes misleading information, denial, and
irrational fears can cloud judgment.
Number of Deaths per Year in the World
from Various Causes
 Number of deaths per year in
the world from various causes.
Red numbers show deaths in
terms of the number of fully
loaded 200-passenger jumbo
jets crashing every day of the
year with no survivors.
Comparison of Risks People Face in Terms of
Shorter Average Life Span
 Comparisons of risks people
face expressed in terms of
shorter average life span.
Annual Deaths in the U.S. from Tobacco Use
and Other Causes in 2004