Environmental Health and Toxicology

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Environmental Health and Toxicology

• Chapter 8

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Outline

• 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

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ENVIRONMENTAL HEALTH HAZARDS

• 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).

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Global Disease Burden

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

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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.

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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.

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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)

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Infectious Disease Outbreaks
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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
  antibiotics.

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Antibiotic and Pesticide Resistance
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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.

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Toxicology

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

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Toxicology Contd

• 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.

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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.

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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.

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Toxicology Contd

• 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

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Endocrine Hormone Disrupters

• 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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Diet

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

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DISTRIBUTION AND FATE OF TOXINS

• Solubility - Chemicals are divided into two major
  groups
• 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
  cells.
• Oil-soluble molecules generally need a carrier to
  move through the environment.

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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.

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Biomagnification
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DDT

• 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
  easily.
• 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
million.
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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
  insecticides. 
• 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.

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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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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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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.

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MECHANISMS FOR MINIMIZING TOXIC EFFECTS

• 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

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MEASURING TOXICITY

• 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.

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LD50
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Population Sensitivity Variations
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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.

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RISK ASSESSMENT

• 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.

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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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ESTABLISHING PUBLIC POLICY

• 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.

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ESTABLISHING PUBLIC POLICY CONTD

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