Chapter 11: Risk, Toxicology, and Human Health

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Chapter 11 Risk, Toxicology, and Human Health
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What is Risk?

• Risk - the possibility of suffering harm from a
  hazard that can cause injury, disease, economic
  loss, or environmental change
• Expressed in terms of probability a mathematical
  statement about how likely it is that some event
  or effect will occur.
• Risk Exposure x Harm

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How Are Risks Assessed and Managed?

• Risk Assessment
• Identifying a real or potential hazard
• Determining the probability of its occurrence
• Assessing the severity of its health,
  environmental, economic, and social impact
• Risk Management
• How serious it is compared to other risks?
• How much (if at all) the risk should be reduced?
• How can such risk reduction be accomplished?
• How much money should be spent?
• RM More controversial because there is a lack of
  information and there can be economic, health,
  and political implications

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What Are the Major Types of Hazard?

• Cultural Hazards
• Chemical Hazards
• Physical Hazards
• Biological Hazards

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Toxicity Dose and Response

• Toxicity - measures how harmful a substance is
• Dose - the amount of a potentially harmful
  substance that has been ingested, inhaled, or
  absorbed through the skin
• Whether a chemical is harmful depends on
• The size of the dose over a certain period of
  time
• How often the exposure occurs
• Who is exposed
• How well the bodys detoxification system works
• Genetic make-up of an individual

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Other Factors That Determine a Substances Harm

• Solubility - water-soluble toxins can move
  through the environment and get into the water
  supplies fat-soluble toxins can accumulate in
  the body tissues and cells
• Persistence - the chemicals resistance to
  breakdown and its long-lasting effects

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Bioaccumulation, Biomagnification, and Chemical
Interactions

• Bioaccumulation - where molecules are absorbed
  and stored in specific organs or tissues at
  higher levels than normally would be expected.
• Biomagnification - where some toxins are
  magnified as they pass through food chains and
  webs
• Chemical interactions - decrease or multiply the
  harmful effects of a toxin
• Antagonistic Interaction - can reduce the harmful
  effects
• Synergistic Interaction - can multiply the
  harmful effects

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Response

• Response - the type and amount of health damage
  that results from exposure to a chemical or other
  agent.
• Acute Effect - an immediate or rapid, harmful
  reaction to an exposure
• Chronic Effect - a permanent or long-lasting
  consequence of exposure to a harmful substance

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Should We Be Concerned About Toxic Chemicals?

• It depends on the chemical and its concentration
  - ANYTHING can be harmful if ingested in a large
  quantity
• Most chemicals have a safe, threshold level
• The human body can break down, dilute, and
  excrete
• Enzymes can repair DNA and protein molecules
• Cells reproduce quickly
• Synthetic does not mean deadly and natural does
  not mean safe

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What is Poison?

• Poison - a chemical that has an LD50 of 50 mg or
  less per kg of body weight
• Median Lethal Dose - LD50 - the amount of a
  chemical received in one dose that kills exactly
  50 of the animals in a test population (usually
  within a 14-day period)

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Case Reports

• Case Reports - provide information about people
  suffering from some adverse health effect or
  death after exposure to a chemical
• Not reliable as the actual dosage and the
  persons health status are not known
• Could include accidental poisonings, drug
  overdoses, homicides, or suicide attempts

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Epidemiological Studies

• Epidemiological Studies - the health of people
  exposed to the toxic agent are compared to the
  health of the people not exposed to the agent
• Limited
• too few people are exposed to high levels of many
  toxic substances
• it is difficult to link effect to a particular
  exposure
• cant be used to evaluate hazards from new
  technologies or chemicals to which people have
  not been exposed.

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Laboratory Experiments

• Use test animals under controlled conditions --
  good because it mimic biological interactions
  that happen in live animals
• More humane methods include
• Bacteria
• Cell and tissue cultures
• Chicken egg membranes

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Dose Response Curves

• Shows the effect of various dosages of a toxic
  agent on a group of test organisms
• Controlled by keeping organisms at the same age,
  health status, genetic make-up, and same
  environmental conditions
• Non-threshold Dose-Response Model - any dosage of
  a toxic chemical that causes harm that increases
  with the dosage
• Threshold Dose-Response Model - a threshold
  dosage must be reached before any detectable
  harmful effects occur

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Toxic and Hazardous Chemicals

• Toxic Chemicals - fatal to more than 50 of test
  animals
• Hazardous Chemicals - cause harm
• by being flammable or explosive, irritating, or
  damaging to the skin
• interfering with or preventing oxygen uptake and
  distribution
• inducing allergic reactions

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Mutagens

• Mutagens - agents that cause random mutations, or
  changes, in the DNA molecules found in cells
• Some are inherited, some are not
• More mutations are harmless as organisms have
  biochemical repair mechanisms

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Teratogens

• Teratogens - chemicals, radiation, or viruses
  that cause birth defects while the human embryo
  is growing and developing during pregnancy
• PCBs
• Thalidomide
• Steroid Hormones
• Heavy Metals - arsenic, cadmium, lead, and
  mercury

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Carcinogens

• Chemicals, radiation, or viruses that cause or
  promote the growth of a malignant tumor
• Smoke
• Diet
• Occupational exposure
• Environmental pollutants
• Inherited factors and viruses (20)
• Time Delay - often 10 - 40 years between the
  initial exposure and the appearance of any
  symptoms

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Chemicals and the Immune System

• Examples of chemicals/situations that weaken the
  immune system
• HIV
• Ionizing radiation
• Malnutrition
• Weakening the immune system leaves the body
  vulnerable to
• Allergens
• Infectious bacteria
• Viruses
• Protozoans

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Chemicals and the Nervous System

• Certain neurotoxins can attack nerve cells
• Chlorinated hyrdocarbons - DDT, PCBs, dioxins
• Organophosphate pesticides
• Formaldehyde
• Arsenic, merculry, lead, cadmium
• Industrial solvents - tricholorethylene (TCE),
  toluene, xylene

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Chemicals and the Endocrine System

• Toxins can effect
• Sexual reproduction
• Growth
• Development and behavior
• Hormonally Active Agents - mimic and disrupt the
  effects of natural hormones

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Why Do We Know So Little About the Harmful
Effects of Chemicals?

• Only 10 of 75,000 have been thoroughly screened
  for toxicity 2 adequately screened
• Most commercial products have not been screened
  and 1,000 new chemicals are introduced to the
  marketplace every year.
• Three major reasons for a lack of knowledge
• Most chemicals are considered innocent until
  proven guilty
• Not enough funds, personnel, facilities, and test
  animals
• Analyzing the effects of multiple exposures to
  various chemicals and their possible interactions
  is too difficult and expensive

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Should We Apply the Precautionary Principle?

• Would reduce the need for toxicity studies and
  exposure standards.
• Would reduce the risk posed by exposure to
  potentially hazardous chemicals and their poorly
  understood interactions

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Nontransmissible Disease

• Diseases not caused by a living organism
• Does not spread from one person to the next
• Has multiple causes
• Tend to develop slowly and progressively
• CV diseases
• Most cancers
• Diabetes
• Asthma
• Emphysema
• Malnutrition

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Transmissible Diseases

• Diseases caused by a living organism or a virus
  (pathogens)
• Can be spread from one person to the next
• Spread by food, water, body fluids, some insects,
  and non-human carriers called vectors
• Bacterium - one celled microorganisms that are
  capable of replicating itself by cell division
• Can use antibiotics to treat they have reduced
  the incidence of disease, but they have also been
  misused and bacteria have increaed their genetic
  resistance
• Virus - a microscopic, noncellular infectious
  agent DNA or RNA contains instructions for
  making more viruses

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Infectious Diseases

• Cause 1 in 4 deaths each year
• Worlds Deadliest
• Acute respiratory infections - flu, pneumonia
• AIDs
• Diarrheal Diseases
• Tuberculosis - TB
• Malaria
• Hepatitis B
• Measles
• Epidemiological Transition - when countries
  industrialize and the infectious diseases of
  childhood become less important and the chronic
  diseases become more important

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Spreading of Viral Diseases and How Viral
Diseases Are Treated

• Can adapt quickly - new flu viruses
• Transmitted through sex
• 23 of the American Population has an STD
• AIDS situation
• 40 million people worldwide have AIDs
• 15,300 new infections a day
• In sub-Saharan Africa - 20 or more of adults are
  infected with HIV within 7-10 years, those with
  HIV will develop AIDS
• 39 of Botswana adults have AIDS - their life
  expectancy has dropped 30 years
• Treating Viral Diseases
• No antibiotics
• Vaccines

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Spreading of Viral Diseases

• o Increased international air travel
• o Migration to urban areas
• o Migration to uninhabited rural areas and
  deforestation in tropical developing countries -
  exposes people to new diseases
• o Migration to suburbs in developed countries -
  more contact with forested areas
• o Hunger and malnutrition increases the number
  of children killed by infectious diseases

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Spreading of Viral Diseases Continued

• o Increased rice cultivation ideal breeding
  grounds for mosquitos and other insects that
  transmit diseases to humans
• o Global warming leads to the spread of
  diseases
• o High winds or hurricanes can transfer
  organisms and carriers of disease
• o Accidental Introduction of Insect Vectors
• o Deliberate introduction of pathogens as an act
  of bioterrorism
• o Flooding - contaminates water supplies
  creates areas of standing water and moist soil
  which are breeding grounds for mosquitoes and
  other insects

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Reducing Infectious Diseases

• o Increase research on tropical diseases and
  vaccines
• o Reduce poverty
• o Decrease malnutrition
• o Improve drinking water quality
• o Reduce unnecessary use of antibiotics
• o Educate people to take all of an antibiotic
  prescription
• o Reduce antibiotic use to promote livestock
  growth
• o Careful hand washing by all medical personnel
• o Slow global warming to reduce the spread of
  tropical diseases
• o Increase preventative health care

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How Can We Estimate Risks?

• Risk Analysis
• Risk Assessment - identifying hazards and
  evaluating their associated risks
• Comparative Risk Analysis - ranking risks
• Risk Management - determining options and making
  decisions
• Risk Communication - informing decision makers
  and the public about risks.
• Risks determined by scientists are different than
  those determined by the public

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What Are The Greatest Risks People Face?

• o Poverty
• o Voluntary choices people make about their
  lifestyle
• o Not to smoke
• o Avoid excess sunlight
• o Not drink alcohol or drink in moderation
• o Reduce consumption of foods containing
  cholesterol and saturated fats
• o Eating fruits and vegetables
• o Exercising
• o Lose excess weight
• o Drive safely
• o Cannot control
• o Gender
• o Genes
• o Social and psychological environment

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How Can We Estimate Risks for Technological
Systems

• System reliability () technological
  reliability x human reliability
• Creates tragedies
• To err is human -- all technologies rely on
  humans

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What are the Limitations of Risk Analysis?

• o Are data and models reliable?
• o Who profits and who suffers from chemicals?
• o Should we care more about short-term or
  long-term risks?
• o Should we determine acceptability or how to do
  the least damage?
• o Who should do the risk analysis?
• o Should various risks be considered?
• o How widespread is each risk?
• o Should risk levels be higher for workers than
  for the general public?
• o How much risk is acceptable? And to whom?

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How Should Risks Be Managed? How Do We Perceive
Risks?

• Includes the administrative, political, and
  economic actions taken to decide whether and how
  to reduce a particular societal risk to a certain
  level at a certain cost
• How Well Do We Perceive Risks?
• Motorcycling, smoking, hang gliding, driving
• Commercial airplane crash, killed by a handgun,
  being struck by lightening, a train crash, a
  snakebite, shark attack