Chapter 18

Risk, Toxicology, and Human Health

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?

DeathsCause of Death

Tobacco use 440,000

Alcohol use

Accidents

Pneumonia andinfluenza

Suicides

Homicides

Hard drug use

AIDS

150,000

95,600 (41,800 auto)

67,000

28,300

16,100

15,600

14,400

© 2004 Brooks/Cole – Thomson Learning

Annual Deaths in the U.S.

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

How Are Risks Assessed?

1. What is the hazard?2. How likely is the event?3. 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:

1. Number of people/animals exposed2. How long they were exposed3. Age, health, sex, interaction with other chemicals, etc.

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?

© 2004 Brooks/Cole – Thomson Learning

Hazard identificationWhat is the hazard?

Probability of riskHow likely is the event?

Consequences of riskWhat is the likelydamage?

Risk Assessment Risk Management

Comparative risk analysisHow does it comparewith other risks?

Risk reductionHow much shouldit be reduced?

Risk reduction strategyHow will the riskbe reduced?

Financial commitmentHow much moneyshould be spent?

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

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

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

DDT in fish-eatingbirds (ospreys)

25 ppm

DDT in largefish (needle fish)2 ppm

DDT in smallfish (minnows)0.5 ppm

DDT inzooplankton0.04 ppm

DDT in water0.000003 ppm,Or 3 ppt

BIOACCUMULATION

© 2004 Brooks/Cole – Thomson Learning

Verysensitive

Majorityof population Very

insensitive

0 20 40 60 80

Dose (hypothetical units)

Nu

mb

er o

f in

div

idu

als

affe

cted

Variations in sensitivity due to genetic makeup

Response

Response: type and amount of health damage that results from exposure

Acute effect: immediate harmful reactionEx: dizziness or rash

Chronic effect: permanent, long-lasting consequence

Ex: kidney or liver damage

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

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

100

75

50

25

02 4 6 8 10 12 14 16

Per

cen

tag

e o

f p

op

ula

tio

n k

illed

by

a g

iven

do

se

Dose (hypothetical units)

LD50

© 2004 Brooks/Cole – Thomson Learning

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

How Are Lab Experiments Used to Estimate Toxicity? Use live laboratory animals Cost $200,000-$2 million per substance Dose-response curve—shows the effects

of different doses of a toxin on a group of test organisms

Controlled experiments-compare test group to control group

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

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

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)

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)

What are Carcinogens?

Carcinogens: chemicals, radiation, or viruses that cause the growth of a cancerous (malignant) tumor—cells multiple uncontrollably and may spread by metastasis to other parts of the body

Cigarette smoke, occupational exposure, environmental pollutants, inheritance

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

Hormone

Receptor

Cell

Normal Hormone Process Hormone Mimic Hormone Blocker

Estrogen-like chemical Antiandrogen chemical

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”

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

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.

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)

Figure 11-8Page 236

Viruses HIV(AIDS)

Hepatitis B

Smallpox

Ebola

On this scale, a human hair would be 6 meters (20 feet) wide

1 micrometer

Bacteria Vibrio cholerae(cholera)

Myobacteriumtuberculosis

(tuberculosis)

Treponema pallidum (syphilis)

6 micrometers

Protozoa

Plasmodium(malaria)

10 micrometers

The viral geneticmaterial uses thehost cell's DNA toreplicate againand again.

Each new copy ofthe virus directs thecell to make it aprotein shell.

The new viruses emerge fromthe host cell capable of infectingother cells. This process oftendestroys the first cell.

The virus attaches to thehost cell. The entire virusmay enter or it may injectits genetic material,or genome.

Virus

Cell membrane

Host cell

North America940,000 (20,000)

Caribbean420,000 (30,000)

Latin America1.4 million (80,000)

Western Europe560,000 (6,800)

North Africa& Middle East440,000 (30,000)

Sub-Saharan Africa28.1 million (2-3 million)

Eastern Europe& Central Asia1 million (23,000)

South &Southeast Asia6.1 million (400,000)

East Asia & Pacific1 million (35,000)

Australia &New Zealand15,000 (120)

40 Million people infected with HIV in 2001. Numbers in ( ) are # of deaths in 2001

• HIV immune suppression facilitates active TB development

• AIDS can lead to job loss and poverty

HIV/AIDS

• Malnutrition weakens body and may facilitate HIV transmission and progress

• Malnutrition may facilitate development of active TB

Malnutrition TB

• TB can lead to job loss and malnutrition because of lack of money

• Active TB facilitates HIV replication and speeds up HIV progression

Figure 11-12Page 243

Malaria-free areas Malaria largely eliminated Malaria transmission areas

Anopheles mosquito (vector)in aquatic breeding area

1. Femalemosquito bitesinfected human,ingesting bloodthat containsPlasmodiumgametocytes

4. Parasite invadesblood cells, causingmalaria and makinginfected persona new reservoir

3. Mosquito injects Plasmodiumsporozoites into human host

2. Plasmodiumdevelops inmosquito

eggs

larvapupa

adult

Increase research on tropical diseases and vaccines

Reduce poverty

Decrease malnutrition

Improve drinkingwater quality

Reduce unnecessary use of antibiotics

Educate people totake all of an antibiotic prescription

Reduce antibiotic use to promote livestock growth

Careful hand washing by all medicalpersonnel

Slow global warming to reduce spread of tropical diseases to temperate areas

Increase preventative health care

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 Ecological Problems• Acid deposition • Pesticides • Airborne toxic chemicals • Toxic chemicals, nutrients, and sediment in surface waters

Medium-Risk Problems• Coastal water contamination• Solid waste and litter• Pesticide risks to farm workers• Water pollution from sewage plants

Low-Risk Ecological Problems • Oil spills • Groundwater pollution• Radioactive isotopes• Acid runoff to surface waters• Thermal pollution

Low-Risk Problems • Air pollution from vehicles • Pesticide residues in foods• Global climate change • Drinking water contamination

Hazard Shortens average life span in the United States by

7-10 yearsPoverty

Born male

Smoking

Overweight (35%)

Unmarried

Overweight (15%)

Spouse smoking

Driving

Air pollution

Alcohol

Drug abuse

AIDS

Drowning

Pesticides

Fire

Natural radiation

Medical X rays

Oral contraceptives

Toxic waste

Flying

Hurricanes, tornadoes

Living lifetime near nuclear plant

7.5 years

6 years

5 years

2 years

1 year

7 months

5 months

4 months

4 months

3 months

2 months

1 month

1 month

8 days

5 days

5 days

4 days

1 day

1 day

10 hours

Flu

Air Pollution

6 years

5 months

1 month

© 2

004

Bro

oks

/Co

le –

Th

om

son

Lea

rnin

g

How Can We Estimate Risks?

1. Identify hazards2. Rank risks (comparative risk analysis)3. Make decisions to reduce risks4. Communicating to the public about risks

Most widely used method is benefit-cost analysis

How Well Do We Perceive Risks?

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