Chapter 19 – The Environment and
Human Health
Hong Kong residents concerned about SARS
DDT vs. Malaria
• Malaria is one of the most important
diseases
• Major issues in Africa
• 20% of children under 5 years old died from malaria
• DDT was developed and was effective
in controlling mosquitoes that vectored
malaria
• Helped eradicate malaria from many regions of
world
• DDT affects wildlife
2013 Pearsonin
Education,
Inc. regions
– Reduced use,©banned
some
"DDT - Powerful Insecticide, Harmless to Humans"
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Introduction to Public Health
• Measuring public health
– Population level statistics
• Life expectancy at birth
– Worldwide 67 years (1950: 46 years)
• Mortality rate
– Infant mortality
» Percentage of infants that die before age 1
» Worldwide 4.9% (1950: 15.3%)
© 2013 Pearson Education, Inc.
Introduction to Public Health
• Hazards and risks
– May be immediate or delayed
• Grouped into four categories
–
–
–
–
Physical
Chemical
Biological
Cultural
– Latent consequences
• Delayed effects
– Exposure to radiation
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Introduction to Public Health
• Risk perception and reality
– Human perception differs from reality
– Key factors influence risk perception
•
•
•
•
•
Myth of zero risk
Public awareness
Risk–risk tradeoffs
Control
Risk and time
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Environmental Health
In some parts of Eastern Europe and the former USSR, up
to 90 % of all children suffer from environmentally linked
diseases.
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At any given time, about 2 billion people suffer from
worms, protozoans, and other internal parasites.10
Physical Hazards in the Environment
• Geological hazards
– Earthquakes, tsunamis, volcanoes
• Weather hazards
– Hurricanes/typhoons
– Floods
• Fire in the environment
– Wildfires
© 2013 Pearson Education, Inc.
Chemical Hazards in the
Environment
• Toxicology: The study of toxins
(poisons) and their effects on living
systems.
– Scientific discipline that studies chemical
poisons and effect on human health
• Dose-response curves
• Toxicity threshold
• Median lethal dose (LD50)
• The dose makes the poison
• Acute exposure
© 2013 Pearson Education, Inc.
Chemical Hazards in the
Environment
• Human vulnerability to toxins
• Effects of toxins depend on various
factors
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–
–
–
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Genetics
Environmental cause
Age
Health
Socioeconomic status
© 2013 Pearson Education, Inc.
Chemical Hazards in the
Environment
• Toxin transport and fate
• Impact of certain toxins depends on
movement through environment
–
–
–
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Persistence
Volatility
Solubility in water
Uptake and fate in other organisms
• Bioaccumulation
• Body burden
© 2013 Pearson
Education, Inc.
– Persistent organic
pollutants
(POPs)
Movement, Distribution, and
Fate of Toxins
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Bioaccumulation and Biomagnification
• Bioaccumulation dilute toxins in the
environment can
reach dangerous
levels inside cells
and tissue
• Biomagnification the effects of toxins
are magnified
through food webs
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Persistence
• 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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Minimizing Toxic Effects
• Every material can be poisonous under
some conditions.
• Taken in small doses, most toxins can
be broken down or excreted before they
do much harm.
• Liver - primary site of detoxification
• Tissues and organs - high cellular
reproduction rates replace injured cells down side: tumors, cancers possible
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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
• Effects of waste products and
environmental toxins reduced by
eliminating via excretion.
– Breathing
– Kidneys
• Urine
• Feces
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Measuring Toxicity
Animal Testing
• Most commonly used and widely accepted
• Expensive - hundreds of thousands of dollars to
test one toxin at low doses
• Time consuming
• Often very inhumane
• Difficult to compare toxicity of unlike chemicals
or different species of organisms
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A Typical Dose/Response Curve
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LD50 - the dose
of a toxin that is
lethal to half the
test population
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Acute Versus Chronic Doses and Effects
• Acute effect - immediate health effect
caused by a single exposure to a toxin
(can be reversible)
• Chronic effect - long lasting or
permanent health effect caused by (1) a
single exposure to a very toxic
substance or (2) continuous or
repeated sub lethal exposure to a toxin
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Chemical Hazards in the
Environment
• Kinds of toxins
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–
–
–
–
–
Corrosive toxins
Asphyxiants
Carcinogens
Teratogens
Allergens
Neurotoxins
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Endocrine Disruptors
• 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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Chemical Hazards in the
Environment
• Toxin testing and regulation
– Contains both ethical and practical challenges
– EPA charged to monitor over 75,000 industrial
chemicals
– Most chemicals assumed to be nontoxic until
proved otherwise
• Model organisms
– Used to test effects of chemicals for humans
© 2013 Pearson Education, Inc.
Biological Hazards in the
Environment
• Infectious disease and the environment
– Environmental factors influence populations of
disease agents and vectors
• Population size, movement, climate, water quality
– Pathogens
– Virulence
– Anthroponosis
– Disease only in humans
– Zoonosis
– Disease shared by animals and humans
© 2013 Pearson Education, Inc.
Brown Recluse
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Biological Hazards in the
Environment
• Respiratory disease
– Influenza
• Avian flu
• H1N1
• Diarrheal disease
– Most from poor sanitation and polluted water
– Most die from dehydration
• Cholera, cryptosporidium
© 2013 Pearson Education, Inc.
Biological Hazards in the
Environment
• Blood-borne diseases
– HIV
– Malaria
• Transmitted by mosquitoes
• Caused by parasite Plasmodium
• Evolutionary change
– Coevolution between pathogen and hosts
– Tends to diminish disease severity
• Sickle-cell and malaria
© 2013 Pearson Education, Inc.
Biological Hazards in the
Environment
• Landscape change
– Altered landscapes and waterways provide
habitats for disease agents
• Climate change
– Global warming altering habitats
– Allows disease organisms and agents to expand
range
© 2013 Pearson Education, Inc.
Factors Contributing to the Spread of
Contagious Diseases
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•
•
•
•
High population densities
Settlers pushing into remote areas
Human-caused environmental change
Speed and frequency of modern travel
Contact with water or food
contaminated with human waste
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Antibiotic and Pesticide Resistance
• Indiscriminate use of antibiotics and
pesticides - perfect recipe for natural
selection
• Protozoan that causes malaria now
resistant to most antibiotics, and
mosquitoes have developed resistance
to many insecticides
• Drug resistance: TB, Staph A, flesheating bacteria
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