Environmental Health and Toxicology

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Environmental Health and Toxicology

• Chapter 9

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Outline

• Environmental Health Hazards
• Infectious Organisms
• Antibiotics and Pesticide Resistance
• Toxic Chemicals
• Movement and Fate of Toxins
• Minimizing Toxic Effects
• Measuring Toxicity
• Risk Assessment

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ENVIRONMENTAL HEALTH HAZARDS

• Health - A state of complete physical, mental,
  and social well-being.
• Disease - A deleterious change in the bodys
  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).

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Infectious Organisms

• For most of human history, the greatest health
  threats have been pathogenic organisms (causes
  disease) 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.

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Morbidity and Quality of Life

• 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.
• Judges the total impact of the disease rather
  than the of people dying

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Disability-Adjusted Life Year

• WHO reports communicable diseases are responsible
  for nearly half of all 1.4 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

• An emergent disease is one never known before, or
  has been absent for at least 20 years (i.e.
  Ebola)
• An important factor in the spread of many
  diseases is the speed and frequency of modern
  travel (i.e. Foot and Mouth Disease)
• ways viruses spread
• -epidemic
• -change host
• -mutate

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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 Use

• At least half of the 100 million antibiotic doses
  prescribed in the US 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 US are routinely fed to farm animals to
  stimulate weight gain.

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Toxic Chemicals

• 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.
• Dangerous because they react or interfere with
  specific cell functions

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Toxic Chemicals

• 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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Toxic Chemicals

• 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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Toxic Chemicals

• 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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US Age-Adjusted Cancer Death Rates
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Natural and Synthetic Toxins

• 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.

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MOVEMENT, DISTRIBUTION, AND FATE OF TOXINS

• Solubility - One of most important
  characteristics in determining the movement of a
  toxin
• Characteristics of chemicals that determine their
  environmental risks
• Solubility
• Reactivity
• Persistence
• Toxicity

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• If a substance is toxic, its toxicity is highly
  dependant on its form and where it is present in
  the environment
• Chemicals are divided into two major groups
• Those that dissolve more readily in water.
  (polar)
• Those that dissolve more readily in oil.
  (nonpolar) stay in body longer
• Water soluble compounds move rapidly through the
  environment, and have ready access to most human
  cells.

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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.
• Importanceaccumulate nutrient minerals
• 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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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 as toxic effects may
  be stored for long period of time and spread to
  unintended victims.
• (DDT is stored in fat)

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Bioaccumulation
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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 exacerbates
  the effect of the other.

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MECHANISMS FOR MINIMIZING TOXIC EFFECTS

• Every material can be poisonous under certain
  conditions. (the dose makes the poison)
• 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
  dies. (lethal dose of 50 of the population)

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Population Sensitivity Variations
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• Threshold level of toxicity
• The dose (level) below which no toxic effects are
  observed and/or above which toxic (lethal)
  effects are apparent

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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

• 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.
• EPAs standards for toxic exposure does not take
  into account the natural env.

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• In setting standards for environmental toxins, we
  need to consider
• 1) combined effects of exposure to many different
  sources of damage
• 2) different sensitivities of members of the
  population
• 3) effects of chronic and acute exposure

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