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Environmental Health and Toxicology


Environmental Health and Toxicology Chapter 8 – PowerPoint PPT presentation

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Title: Environmental Health and Toxicology

Environmental Health and Toxicology
  • Chapter 8

  • Environmental Health Hazards
  • Global Disease Burden
  • Emergent and Infectious Diseases
  • Antibiotics and Pesticide Resistance
  • Toxicology
  • Distribution and Fate of Toxins
  • Minimizing Toxic Effects
  • Measuring Toxicity
  • Risk Assessment
  • Public Policy

  • Health - A state of complete physical, mental,
    and social well-being.
  • Disease - An abnormal change in the bodys
    condition that impairs important physical or
    psychological functions-.
  • Diet and nutrition, infectious agents, toxic
    chemicals, physical factors, and psychological
    stress all play roles in morbidity (illness) and
    mortality (death).

Global Disease Burden
  • Health agencies calculate disability-adjusted
    life years (DALYs) as a measure of disease
  • Chronic diseases now account for nearly 60 of
    the 56.5 million total deaths worldwide each
  • Progress in eliminating communicable diseases
    such as smallpox, polio, and malaria, is allowing
    people to live longer.

Disability-Adjusted Life Year
  • WHO reports communicable diseases are responsible
    for nearly half of all 1.2 billion DALYs 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.

Emergent Diseases and Infectious Diseases
  • An emergent disease is one not previously known
    or that has been absent for at least 20 years.
  • An important factor in the spread of many
    diseases is speed and frequency of modern travel.
  • Malaria is one of the most prevalent remaining
    infectious diseases.
  • SARS and Avian Flu
  • HIV/AIDS has the largest death toll from an
    emergent disease.

Ecological Diseases
  • Domestic animals and wildlife also experience
    sudden and widespread epidemics.
  • Distemper Virus (Seals)
  • Chronic Wasting Disease (Deer and Elk)
  • Transmissible Spongiform Encephalopathies
  • Black-Band Disease (Coral)

Infectious Disease Outbreaks
Antibiotic and Pesticide Resistance
  • 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

Antibiotic and Pesticide Resistance
Antibiotic Use
  • At least half of the 100 million antibiotic doses
    prescribed in the U.S every year are unnecessary
    or are the wrong drug.
  • Many people do not finish full-course.
  • More than half of all antibiotics manufactured in
    the U.S. are routinely fed to farm animals to
    stimulate weight gain.

  • Dangerous chemicals are divided into two broad
  • Hazardous - Dangerous
  • Flammable, explosive, irritant, sensitizer, acid,
  • Toxic - Poisonous
  • Can be general or very specific. Often harmful
    even in dilute concentrations.

Toxicology Contd
  • Allergens - Substances that activate the immune
  • 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.

Toxicology Contd
  • Sick Building Syndrome
  • Headaches, allergies, and chronic fatigue caused
    by poorly ventilated indoor air contaminated by
    molds, carbon monoxide, nitrogen oxides, and
    other toxic chemicals.
  • Worker absenteeism and reduced productivity.
  • EPA estimates 60 billion annual loss.

Toxicology Contd
  • 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.

Toxicology Contd
  • Mutagens - Agents that damage or alter genetic
  • Radiation
  • Teratogens - Specifically cause abnormalities
    during embryonic growth and development.
  • Alcohol - Fetal Alcohol Syndrome
  • Carcinogens - Substances that cause cancer.
  • Cigarette smoke

Endocrine Hormone Disrupters
  • Chemicals that disrupt normal endocrine hormone
  • 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

  • Strong correlation between cardiovascular disease
    and the amount of salt and fat in an individuals
  • Highly-processed foods, fat, and smoke-cured,
    high-nitrate meats appear to be associated with
  • Nearly 2/3 of all Americans are considered

  • Solubility - Chemicals are divided into two major
  • Dissolve more readily in water.
  • Dissolve more readily in oil.
  • Water-soluble compounds move rapidly through the
    environment, and have ready access to most human
  • Oil-soluble molecules generally need a carrier to
    move through the environment.

Bioaccumulation and Biomagnification
  • 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.

  • DDT is a synthetic chemical compound once used
    widely in the United States and throughout the
    world as a pesticide (a chemical substance used
    to kill weeds, insects, rodents, or other pests).
    It is probably best known for its dual nature
    although remarkably effective in destroying
    certain living things that are harmful to plants
    and animals, it can also be extremely dangerous
    to humans and the environment.
  • The abbreviation DDT stands for
    dichlorodiphenyltrichloroethane. DDT was first
    produced in the laboratory in 1873. For more than
    half a century, it was little more than a
    laboratory curiositya complicated synthetic
    (produced by scientists) compound with no
    apparent use.
  • Then, in 1939, Swiss chemist Paul Hermann Müller
    (18991965) discovered that DDT was highly
    poisonous to insects. The discovery was very
    important because of its potential for use in
    killing insects that cause disease and eat
    agricultural crops. For his work, Müller was
    awarded the Nobel Prize in medicine in 1948.
  • DDT's environmental problems arise because of two
    important properties persistence and
    lipid-solubility. The term persistence refers to
    the fact that DDT does not break down very
  • Once the pesticide has been used in an area, it
    is likely to remain there for many years. In
    addition, DDT does not dissolve in water,
    although it does dissolve in fatty or oily
    liquids. (The term lipid-solubility is used
    because fats and oils are members of the organic
    family known as lipids.)
  • Since DDT is not soluble in water, it is not
    washed away by the rain, adding to its
    persistence in the environment. But since DDT is
    lipid-soluble, it tends to concentrate in the
    body fat of animals.

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Before the dangers of DDT were known, crops and
people alike were sprayed with the chemical to
protect against bothersome insects.
DDT is used today in such African nations as
Zimbabwe and Ethiopia to control mosquitoes and
the tsetse fly. These two insects cause serious
diseases, such as malaria and sleeping sickness.
DDT saves lives when used on the tsetse fly in
Lake Kariba in Zimbabwe. But once sprayed on the
lake, DDT does not disappear very quickly.
Instead, it is taken up by plants and animals
that live in the lake. Studies have shown that
the concentration of DDT in the lake itself is
only 0.002 parts per billion. But algae in the
lake have a concentration of 2.5 parts per
Clutch of mallard eggs contaminated by DDT. The
accumulation of DDT in many birds causes
reproductive difficulties. Eggs have thinner
shells that break easily, and some eggs may not
hatch at all
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DDT The American Bald Eagle
  • The bald eagle (Haliaeetus leucocephalus) is
    currently listed as a federally threatened
    species in Washington.  In July 1999, the U.S.
    Fish and Wildlife Service published a proposal to
    delist the bald eagle under the Endangered
    Species Act. 
  • At the time the species was listed, environmental
    contaminants were cited as the primary reason for
    its decline.  Beginning in the 1940's, dichloro
    diphenyl trichloroethane (DDT) and other
    organochlorine pesticides became widely used as
  • In the late 1960's and early 1970's, it was
    determined that dichlorophenyl-dichloroethylene
    (DDE), the principal breakdown product of DDT,
    accumulated in the fatty tissues of adult female
    bald eagles and resulted in thin shells and
    reproductive failure (Wiemeyer et al. 1972, 1984
    Grier 1982). 
  • Due to the bioaccumulative and persistent nature
    of DDT and the adverse reproductive effects
    elicited by DDT, particularly on birds, its use
    was banned in the United States in 1972.

Agent Orange
  • During the Vietnam War, US military forces
    sprayed nearly 19 million gallons of herbicide on
    about 3.6 million acres of land in Vietnam and
    Laos to remove forest cover, destroy crops, and
    clear vegetation from the perimeters of US bases.
    This effort, known as Operation Ranch Hand,
    lasted from 1962 to 1971.
  • Various herbicidal (plant-killing) formulations
    were used, but most were mixtures of 2 herbicides
    known as phenoxy herbicides because of their
    chemical structures
  • 2,4-dichlorophenoxyacetic acid (2,4-D)
  • 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)
  • Each formulation was shipped in a chemical drum
    marked with an identifying colored stripe. The
    most widely used mixture contained equal parts
    2,4-D and 2,4,5-T. Because this herbicide came in
    drums with orange stripes, it was called Agent
    Orange. Today, Agent Orange is used to refer
    generally to all the phenoxy herbicides sprayed
    at the time.
  • The 2,4,5-T was contaminated with small amounts
    of dioxins, which were created unintentionally
    during the manufacturing process.
  • Dioxins are a family of biologically active
    compounds formed during the manufacturing of
    paper and some other industrial processes.
    Because they can remain in the environment for
    years, they form part of a group of chemicals
    known as "persistent organic pollutants."
  • The particular dioxin present in Agent Orange,
    2,3,7,8-tetrachlorodibenzo-p-dioxin, or TCDD, is
    unusually toxic.

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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 because these
    materials persist in the environment and have
    unexpected effects far from their original use.
  • PBDE (flame-retardants in textiles)

Chemical Interactions
  • Antagonistic Reaction - One material interferes
    with the effects, or stimulates the breakdown, of
    other chemicals.
  • Additive Reaction - Effects of each chemical are
    added to one another.
  • Synergistic Reaction - One substance multiplies
    the effect of the other.

  • Every material can be poisonous under certain
  • 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

  • Effects of waste products and environmental
    toxins reduced by eliminating via excretion.
  • Breathing
  • Kidneys
  • Urine

  • 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.

Population Sensitivity Variations
Acute vs. Chronic Effects
  • 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.

  • Factors influencing risk perception
  • Rating risks based on agendas.
  • Most people have trouble with statistics.
  • Personal experiences can be misleading.
  • We have an exaggerated view of our abilities to
    control our fate.
  • News media sensationalizes rare events.
  • Irrational fears lead to overestimation of
    certain dangers.
  • Fear of the unknown.

Accepting Risks
  • 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.

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  • Biggest problem in making regulatory decisions is
    that we are usually exposed to many sources of
    harm, often unknowingly.
  • May not be reasonable to demand protection from
    every potentially harmful contaminant in our
    environment, no matter how small the risk.

  • In setting standards for environmental toxins,
    need to consider
  • Combined effects of different exposures.
  • Individual sensitivities within population.
  • Effects of chronic and acute exposures.
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