Transcript Chapter 8: Environmental Health and Toxicology

Chapter 8: Environmental Health and
Toxicology
Hong Kong residents concerned about SARS
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Chapter Eight Topics
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Environmental Health
Toxicology
Movement, Distribution, and Fate of Toxins
Mechanisms for Minimizing Toxic Effects
Measuring Toxicity
Risk Assessment and Acceptance
Establishing Public Policy
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Part 1: 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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What is Health?
• The World Health Organization (WHO)
defines health as a state of complete
physical, mental, and social wellbeing.
• Disease - a deleterious change in the
body's condition in response to an
environmental factor
• Morbidity - illness
• Mortality - death
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At any given time, about 2 billion people suffer from
worms, protozoans, and other internal parasites. 6
West Nile Virus 2001
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West Nile Virus 2002
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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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Part 2: Toxicology
Toxicology: The study of toxins (poisons) and their
effects on living systems.
What does toxic mean?
Environmental Wisdom…visit
http://www.dhmo.org
What does Toxic mean
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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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Fig. 8.6
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Hazardous and Toxic Chemicals
• Allergens formaldehyde
• Immune system
depressants - PCBs?
• Neurotoxins - lead, DDT
• Mutagens
• Teratogens - alcohol
• Carcinogens
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Part 3: 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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"DDT - Powerful Insecticide, Harmless to Humans"
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Part 4: 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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Part 5: 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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Part 6: Risk Assessment
and Acceptance
• Risk - the probability of harm times the
probability of exposure
• A number of factors influence how we
perceive relative risks associated with
different situations.
• Accepting risks - we go to great lengths
to avoid some dangers, while gladly
accepting others
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Part 7: Establishing Public Policy
In setting standards for environmental toxins,
we need to consider:
• Combined effects of exposure to many different
sources of damage
• Different sensitivities of members of the
population
• Effects of chronic as well as acute exposures
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Regulatory Decisions
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