Risk, Toxicology, and Human Health

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Chapter 11

• Risk, Toxicology, and Human Health

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Key Questions

• What types of hazards do humans face?
• What chemical hazards do humans face?
• What types of diseases threaten people in
  developing and developed countries?
• How can risks be estimated and reduced?

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Deaths
Cause of Death
Tobacco use
440,000
Alcohol use
150,000
Accidents
95,600 (41,800 auto)
Pneumonia and influenza
67,000
Suicides
28,300
Annual Deaths in the U.S.
Homicides
16,100
Hard drug use
15,600
AIDS
14,400
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What Is a Risk?

• The possibility of suffering harm from a hazard
  that can cause injury, disease, economic loss, or
  environmental damage
• Expressed in terms of probability
• Risk Exposure x Harm

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How Are Risks Assessed?

• What is the hazard?
• How likely is the event?
• How much damage is it likely to cause?
• Example to assess the risk of exposure to a
  toxic chemical, you must look at the following
• Number of people/animals exposed
• How long they were exposed
• Age, health, sex, interaction with other
  chemicals, etc.

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How Are Risks Managed?

• How serious is the risk compared to other risks?
• How much should the risk be reduced?
• How can the risk be reduced?
• How much money will be needed?

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Risk Assessment
Risk Management
Hazard identification What is the
hazard? Probability of risk How likely is the
event? Consequences of risk What is the
likely damage?
Comparative risk analysis How does it
compare with other risks? Risk reduction How
much should it be reduced? Risk reduction
strategy How will the risk be reduced? Financial
commitment How much money should be spent?
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What Are the Major Types of Hazards?

• Cultural Hazards unsafe working conditions, poor
  diet, smoking, poverty
• Chemical Hazards harmful chemicals in the air,
  water, soil, food (human body contains about 500
  synthetic chemicals whose health effects are
  unknown)
• Physical Hazards fire, earthquake, flood
• Biological Hazards allergens, bacteria, viruses,
  bees, poisonous snakes

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What Determines Whether a Chemical is Harmful?

1. Size of dose over a certain period of time
2. How often an exposure occurs
3. Who is exposed (adult or child?)
4. How well the body can detox
5. Genetic makeup of the individual

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Harm Can Also be Affected by

• Solubility can the toxin get into the water
  supply?
• Persistence does not break down easily
  long-lasting effects on people and animals
• Bioaccumulation molecules are absorbed and
  stored in organs or tissues at a high level
• Biomagnification some toxins are magnified as
  they pass through food chains
• Chemical interactions can multiply harmful
  effect of a toxin

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DDT in fish-eating birds (ospreys) 25 ppm
DDT in large fish (needle fish) 2 ppm
DDT in small fish (minnows) 0.5 ppm
DDT in zooplankton 0.04 ppm
DDT in water 0.000003 ppm, Or 3 ppt
BIOACCUMULATION
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Variations in sensitivity due to genetic makeup
Majority of population
Very insensitive
Very sensitive
Number of individuals affected
0
20
40
60
80
Dose (hypothetical units)
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Response

• Response type and amount of health damage that
  results from exposure
• Acute effect immediate harmful reaction
• Ex dizziness or rash
• Chronic effect permanent, long-lasting
  consequence
• Ex kidney or liver damage

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How Concerned Should We Be?

• Most chemicals have threshold levels of exposure
  below which we are safe because
• Human body has ways of breaking down and diluting
  toxins
• Cells have enzymes that repair damaged DNA
• Some cells can reproduce fast enough to replace
  damaged cells

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What is a Poison?

• Poison chemical that has an LD50 of 50
  milligrams or less per kilogram of body weight
• LD50 amount of a chemical that kills exactly 50
  of animals

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How Do We Estimate Toxicity?

• Case reports accidental poisonings, drug
  overdoses, suicide attempts, etc.
• Epidemiological studies experiments where
  healthy people are exposed to a toxin

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How Are Lab Experiments Used to Estimate Toxicity?

• Use live laboratory animals
• Cost 200,000-2 million per substance
• Dose-response curveshows the effects of
  different doses of a toxin on a group of test
  organisms
• Controlled experiments-compare test group to
  control group

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Dose-response Models

• Nonthreshold dose-response model any dosage of a
  toxic chemical causes harm that increases with
  dosage
• Threshold dose-response model threshold dosage
  must be reached before any harmful effects occur

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What are Toxic and Hazardous Chemicals?

• Toxic chemicals substances that are fatal to
  more than 50 of test animals
• Hazardous chemicals cause harm by being
  explosive, damaging to skin or lungs, interfering
  with oxygen, or causing allergic reaction

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What are Mutagens?

• Mutagens agents that cause random mutations
  (changes) in DNA.
• Example mutations in sperm or egg cells can be
  passed on and cause bipolar disorder, cancer,
  hemophilia, Down Syndrome, etc.
• Most mutations are harmless (DNA repair enzymes)

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What are Teratogens?

• Teratogens chemicals, radiation, or viruses that
  cause birth defects during the first 3 months of
  pregnancy
• Examples PCBs, steriod hormones, heavy metals
  (lead, mercury)

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What are Carcinogens?

• Carcinogens chemicals, radiation, or viruses
  that cause the growth of a cancerous (malignant)
  tumorcells multiple uncontrollably and may
  spread by metastasis to other parts of the body
• Cigarette smoke, occupational exposure,
  environmental pollutants, inheritance

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How Can Chemicals Harm the Immune, Nervous, and
Endocrine System?

• Long-term exposure can affect these systems
• Immune System specialized cells and tissues that
  protect against disease and harmful substances by
  forming antibodies
• Diseases such as HIV can weaken the immune
  system, leaving body vulnerable to allergens,
  bacteria, and viruses.
• Nervous System (brain, spinal cord, nerves)-many
  poisons are neurotoxins which attack nerve cells
  (DDT, PCBs, pesticides, lead, arsenic)
• Endocrine System (hormones for reproduction,
  growth, development, behavior)-hormonally active
  agents mimic and disrupt the effects of natural
  hormones

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Hormone
Estrogen-like chemical
Antiandrogen chemical
Receptor
Cell
Normal Hormone Process
Hormone Mimic
Hormone Blocker
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What is the Precautionary Approach?

• When we are uncertain about the harmfulness of
  chemicals, decision makers should act to prevent
  harm to humans and the environment
• better safe than sorry

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What Are Nontransmissable Diseases?

• Nontransmissable disease not caused by living
  organisms and does not spread from one person to
  another
• Example heart and blood disorders, asthma,
  malnutrition

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What Are Transmissable Diseases?

• Transmissable Disease caused by living organisms
  (bacteria, parasite, etc.) and can be spread from
  person to person
• Pathogens infectious agents-spread by air,
  water, food, body fluids, some insects, etc.

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Top 7 Deadliest Infectious Diseases

1. Acute respiratory infection (pneumonia, flu)
2. AIDS (virus)
3. Diarrheal diseases (bacteria and virus)
4. Tuberculosis (bacteria)
5. Malaria (parasite)
6. Hepatitis B (virus)
7. Measles (virus)

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Figure 11-8Page 236
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The virus attaches to the host cell. The entire
virus may enter or it may inject its genetic
material, or genome.
Virus
Cell membrane
Host cell
The viral genetic material uses the host cell's
DNA to replicate again and again.
Each new copy of the virus directs the cell to
make it a protein shell.
The new viruses emerge from the host cell capable
of infecting other cells. This process
often destroys the first cell.
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Eastern Europe Central Asia 1 million (23,000)
North America 940,000 (20,000)
Western Europe 560,000 (6,800)
East Asia Pacific 1 million (35,000)
North Africa Middle East 440,000 (30,000)
Caribbean 420,000 (30,000)
South Southeast Asia 6.1 million (400,000)
Latin America 1.4 million (80,000)
Australia New Zealand 15,000 (120)
Sub-Saharan Africa 28.1 million (2-3 million)
40 Million people infected with HIV. Numbers in
( ) are of deaths
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HIV/AIDS

• HIV immune
• suppression
• facilitates active
• TB development
• AIDS can lead to job
• loss and poverty

Malnutrition
TB

• Malnutrition weakens
• body and may
• facilitate HIV
• transmission
• and progress
• Malnutrition may
• facilitate development
• of active TB

• TB can lead
• to job loss and
• malnutrition
• because of
• lack of money
• Active TB facilitates
• HIV replication
• and speeds up
• HIV progression

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Figure 11-12Page 243
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Anopheles mosquito (vector) in aquatic breeding
area
eggs
adult
larva
pupa
1. Female mosquito bites infected
human, ingesting blood that contains Plasmodium ga
metocytes
4. Parasite invades blood cells, causing malaria
and making infected person a new reservoir
2. Plasmodium develops in mosquito
3. Mosquito injects Plasmodium sporozoites into
human host
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Increase research on tropical diseases and
vaccines Reduce poverty Decrease
malnutrition Improve drinking water
quality Reduce unnecessary use of
antibiotics Educate people to take all of an
antibiotic prescription Reduce antibiotic use
to promote livestock growth Careful hand
washing by all medical personnel Slow global
warming to reduce spread of tropical diseases
to temperate areas Increase preventative
health care
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Scientists (Not in rank order in each category)
Citizens (In rank order)
High-Risk Health Problems Indoor air
pollution Outdoor air pollution Worker
exposure to industrial or farm chemicals
Pollutants in drinking water Pesticide residues
on food Toxic chemicals in consumer
products High-Risk Ecological Problems Global
climate change Stratospheric ozone depletion
Wildlife habitat alteration and destruction
Species extinction and loss of biodiversity
High-Risk Problems Hazardous waste sites
Industrial water pollution Occupational
exposure to chemicals Oil spills
Stratospheric ozone depletion Nuclear
power-plant accidents Industrial accidents
releasing pollutants Radioactive wastes
Air pollution from factories Leaking
underground tanks
Medium-Risk Problems Coastal water
contamination Solid waste and litter
Pesticide risks to farm workers Water pollution
from sewage plants
Medium-Risk Ecological Problems Acid deposition
Pesticides Airborne toxic chemicals
Toxic chemicals, nutrients, and sediment in
surface waters
Low-Risk Problems Air pollution from vehicles
Pesticide residues in foods Global climate
change Drinking water contamination
Low-Risk Ecological Problems Oil spills
Groundwater pollution Radioactive isotopes
Acid runoff to surface waters Thermal pollution
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Hazard
Shortens average life span in the United States by
Poverty
7-10 years
Born male
7.5 years
Smoking
6 years
Overweight (35)
6 years
Unmarried
5 years
Overweight (15)
2 years
Spouse smoking
1 year
Driving
7 months
Air pollution
5 months
Alcohol
5 months
Drug abuse
4 months
Flu
4 months
AIDS
3 months
Air Pollution
2 months
Drowning
1 month
Pesticides
1 month
Fire
1 month
Natural radiation
8 days
Medical X rays
5 days
Oral contraceptives
5 days
Toxic waste
4 days
Flying
1 day
1 day
Hurricanes, tornadoes
Living lifetime near nuclear plant
10 hours
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How Can We Estimate Risks?

• Identify hazards
• Rank risks (comparative risk analysis)
• Make decisions to reduce risks
• Communicating to the public about risks
• Most widely used method is benefit-cost analysis

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How Well Do We Perceive Risks?

• Most of us do poorly in assessing the risks from
  the hazards that surround us