Transcript Understanding Our Environment

Chapter 8 Outline:
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Environmental Health Hazards
 Infectious Organisms
 Antibiotics and Pesticide Resistance
 Toxic Chemicals
Movement and Fate of Toxins
Minimizing Toxic Effects
Measuring Toxicity
Risk Assessment
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
ENVIRONMENTAL HEALTH HAZARDS
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Health - A state of complete physical, mental,
and social well-being.
Disease - A harmful change in the body’s
condition in response to an environmental
factor.
 Diet and nutrition, infectious agents, toxic
chemicals, physical factors, and
psychological stress all play roles in
morbidity (illness) and mortality (death).
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Infectious Organisms
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For most of human history, the greatest health
threats have been pathogenic organisms and
accidents or violence.
 Infectious diseases are still responsible for
about 24% of all disease-related deaths.
- Majority of these deaths in poorer
countries with poor nutrition, sanitation,
and vaccination programs.
 AIDS now largest single cause of
communicable death in the world.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Morbidity and Quality of Life
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Death rates do not tell everything about
burden of disease.
 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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Disability-Adjusted Life Year
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WHO reports communicable diseases are
responsible for nearly half of all 1.4 billion
DALY’s lost each year.
 About 90% of all DALY losses occur in
developing world where one-tenth of all
health care dollars are spent.
- Malnutrition exacerbates many diseases.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Emergent Diseases
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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 the speed and frequency of
modern travel.
- Hand, Foot and Mouth Disease
(humans)
- Foot and Mouth (cattle)
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Antibiotic and Pesticide Resistance
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Protozoan parasite that causes malaria is
now resistant to most antibiotics, while the
mosquitoes that transmit it have developed
resistance to many insecticides.
 Short life spans.
- Speeds up natural selection and
evolution.
 Human tendency to overuse pesticides
and antibiotics.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Toxic Chemicals
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Dangerous chemicals are divided into two
broad categories:
 Hazardous - Dangerous
- Flammable, explosive, irritant, acid,
caustic.
 Toxic - Poisonous
- Can be general or very specific. Often
harmful even in dilute concentrations.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Toxic Chemicals
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Allergens - Substances that activate the
immune system.
 Antigens - Allergens that are recognized as
foreign by white blood cells and stimulate
the production of specific antibodies.
- Other allergens act indirectly by binding
to other materials so they become
antigenic.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Toxic Chemicals
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Neurotoxins - Special class of metabolic
poisons that specifically attack nerve cells.
 Different types act in different ways
- Heavy Metals kill nerve cells.
- Anesthetics and Chlorinated
Hydrocarbons disrupt nerve cell
membranes.
- Organophosphates and Carbamates
inhibit signal transmission between nerve
cells.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Toxic Chemicals
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Mutagens - Agents that damage or alter
genetic material.
 Radiation
Teratogens - Specifically cause abnormalities
during embryonic growth and development.
 Alcohol - Fetal Alcohol Syndrome
Carcinogens - Substances that cause cancer.
 Cigarette smoke
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Natural and Synthetic Toxins
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Many natural chemicals are very dangerous
while many synthetic chemicals are relatively
harmless.
 Both plants and animals produce
chemicals similar to neurotransmitters,
hormones, and regulatory molecules.
- Arsenic and cyanide are both natural.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
MOVEMENT, DISTRIBUTION,
AND FATE OF TOXINS
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Solubility - One of most important
characteristics in determining the movement of
a toxin.
Chemicals are divided into two major groups:
- Those that dissolve more readily in water.
- Those that dissolve more readily in oil.
 Water soluble compounds move rapidly
through the environment, and have ready
access to most human cells.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Bioaccumulation and Biomagnification
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Cells have special mechanisms for
Bioaccumulation - Selective absorption and
storage.
 Dilute toxins in the environment can build
to dangerous levels inside cells and
tissues.
Biomagnification - Toxic burden of a large
number of organisms at a lower trophic level
is accumulated and concentrated by a
predator at a higher trophic level.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Persistence
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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 as toxic
effects may be stored for long period of
time and spread to unintended victims.
- (DDT)
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Bioaccumulation
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Chemical Interactions
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Synergistic Reaction - One substance
exacerbates the effect of the other.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
MECHANISMS FOR MINIMIZING
TOXIC EFFECTS
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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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
MEASURING TOXICITY
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Animal Testing
 Most commonly used and widely accepted
toxicity test is to expose a population of
laboratory animals to measured doses of
specific toxins.
- Sensitivity differences pose a problem.
 Dose Response Curves
 LD50 - Dose at which 50% of the test
population is sensitive.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Population Sensitivity Variations
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Acute vs. Chronic Effects
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Acute Effects - Caused by a single exposure
and result in an immediate health problem.
Chronic Effects - Long-lasting. Can be result
of single large dose or repeated smaller
doses.
 Very difficult to assess specific health
effects due to other factors.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Accepting Risks
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Most people will tolerate a higher probability
of occurrence of an event if the harm caused
by that event is low.
 Harm of greater severity is acceptable only
at low levels of frequency.
- EPA generally assumes 1 in 1 million is
acceptable risk for environmental
hazards.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
ESTABLISHING PUBLIC POLICY
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It is difficult to separate the effects of multiple
hazards and evaluate their risks accurately,
especially when exposures are near the
threshold of measurement and response.
 May not be reasonable to mandate
protection, no matter how small the risk,
from every potentially harmful contaminant
in our environment.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Summary:
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Environmental Health Hazards
 Infectious Organisms
 Antibiotics and Pesticide Resistance
 Toxic Chemicals
Movement and Fate of Toxins
Minimizing Toxic Effects
Measuring Toxicity
Risk Assessment
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.