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CH 8 - Environmental Health &
Toxicology
In some parts of Eastern Europe and the former USSR, up
to 90% of all children suffer from environmentally linked
diseases.
What is Health?
• The World Health Organization defines
health: state of complete physical, mental, &
social well-being –
not just absence of disease.
• Disease - a deleterious change in the body’s
condition in response to an environmental factor
(nutrition, chemicals, biological agents, etc)
• Morbidity – illness or disease
• Mortality – death rate
Eg: Tuberculosis
Deforestation
causes insect
vectors to
move to cities
Morbidity and Quality of Life
• Death rates do not tell everything about
burden of disease.
• What is the total social burden of diseases?
– Total economic and social consequences of
diseases are difficult to obtain.
• Disability-Adjusted Life Year (DALY) combines
premature deaths and loss of healthy life resulting
from illness or disability.
Morbidity and Quality of Life
in Poor Households
(DisabilityAdjusted Life
Years)
Disruption to quality
of life & economic
productivity caused
by premature deaths
& loss of healthy life
caused by
illness/disability.
• Problems occurring
when people live in
crowded conditions--eg,
developing countries
(90% DALY losses),
poverty)
• New global megacities where managing
human generated
wastes is poor
Elephantiasis –
caused by parasitic
worm
At any given time, about 2 billion people suffer from
worms, protozoans, and other internal parasites.
Emergent Diseases
• An emergent disease is one never known
before, OR has been absent for at least 20
years.
– An important factor in the spread of many
diseases is speed and frequency of modern
travel.
• Foot and Mouth Disease
• Ebola
Recent outbreaks of lethal infectious
diseases
At least 30 new infectious diseases have appeared in the past two
decades while many well-known have reappeared in more virulent, drugresistant forms.
Factors Contributing to the Spread
of Contagious Diseases
• High population densities
• Settlers pushing into remote areas
• Human-caused environmental change
(elimination of predators increasing rodents,
use of fertilizers, pesticides etc)
• Speed and frequency of modern travel
• Contact with water or food contaminated
with human waste
Emerging Ecological Diseases
• Domestic animals and wildlife also
experience sudden and widespread
epidemics.
– Distemper (Seals)
– Chronic Wasting Disease (Deer and Elk)
• Transmissible Spongiform Encephalopathies
– Black Band Disease (Coral)
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, flesh-eating
bacteria
Toxic Chemicals
• Hazardous chemicals – dangerous (eg, flammables,
explosives, irritants, acids, etc)
• Toxins – poisonous, kills cells
• Allergens – activate the immune system
• Mutagens – chemicals or radiation that damage/alter
genetic material (DNA)
• Teratogens - chemicals or other factors that cause
abnormalities during embryonic growth &
development
• Carcinogens – substances that cause cancer (out of
control cell growth)
Toxins:
Movement,
Distribution,
Fate
Movement, fate
of chemicals in
the environment
(processes that
modify, remove
or sequester
compounds)
Many routes of synthetic chemicals traveling through the environment
(Brennan & Withgott 2005)
Toxins: Movement, Distribution, Fate
Movement
via
Solubility
- water
- oil
Routes by
which
chemicals
enter body
determine
toxicity
Bioaccumulation and Biomagnification
• Bioaccumulation –
selective absorption
& storage of
molecules; dilute
toxins in the
environment can
reach dangerous
levels inside cells
and tissue
• Biomagnification the effects of toxins
are magnified
through food webs
“DDT - Powerful Insecticide, Harmless to
Humans” common statement in the 1950s
???????
Pesticides and Child Development in Mexico’s Yaqui Valley
• Elizabeth Guillette
(anthropologist) –
1994
• Valley farmers
used pesticides but
foothill farmers
continued
traditional farming
•Valley children
were far behind
foothill children
developmentally in:
Coordination
Physical
endurance
Long-term
memory
Fine-motor
skills
(Brennan & Withgott 2005)
Peregrine falcons disappeared from the eastern US in
1960s due to excess pesticide use
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 – belief in 1800s, arsenic
(Napoleon)
• Liver - primary site of detoxification
• Tissues and organs - high cellular
reproduction rates replace injured cells down side: tumors, cancers possible
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
A Typical Dose/Response Curve
LD50 - the dose
of a toxin that is
lethal to half the
test population
Acute Lethal Doses for Some Toxic Organic Chemicals
mouse
rat
It is useful to group materials according to their
relative toxicity.
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:
– a single exposure to a very toxic substance,
OR
– continuous or repeated sublethal exposure to
a toxin
Risk Assessment and
Acceptance
• Risk
probability of harm X probability of exposure
• A number of factors influence how we perceive
relative risks associated with different situations
(interests as industrialist vs environmentalist,
understanding probability, personal experience, our
abilities to control our fate, news media biases, fear
of technology).
• Accepting risks - we go to great lengths to avoid
some dangers, while gladly accepting others
McKinney & Schoch
Establishing Public Policy
In setting standards for environmental
toxins, we need to consider:
• Combined effects of exposure to many
different sources of damage (synergistic
effects of different toxins, eg smoking &
asbestos effects on lung cancer rates)
• Different sensitivities of members of the
population
• Effects of chronic as well as acute exposures
Regulatory Decisions – EPA framework
The Science Specific to the
Problem
Other Factors Not
Specific to the Problem
Summary:
• Environmental Health Hazards
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Infectious Organisms
Emergent Diseases
Antibiotics and Pesticide Resistance
Toxic Chemicals
Distribution and Fate of Toxins
Minimizing Toxic Effects
Measuring Toxicity
Risk Assessment
Public Policy