Chapter 17

Environmental Hazards and Human Health

Risks Are Usually Expressed as Probabilities

• Risk

– Probability of suffering harm from a hazard

– Probability vs. possibility

Science: Risk Assessment and Risk Management

Fig. 17-2, p. 437

We Face Many Types of Hazards

1. Biological: – Pathogen: an organism that causes disease in other

organisms

2. Chemical

3. Physical

4. Cultural

5. Lifestyle choices

Nitrates

Some Diseases Can Spread from One Person to Another

• Infectious disease – Pathogen invades the body and multiplies

• Transmissible disease – Infectious disease transmitted between people – Flu, tuberculosis, measles

• Since 1950, death from infectious diseases have declined due to – Better health care – Better sanitation – Antibiotics – Vaccines

Infectious Diseases Are Still Major Health Threats

• Infectious diseases spread through – Air

– Water

– Food

– Body fluids

• Epidemics and pandemics

Science: Pathways for Infectious Diseases in Humans

Fig. 17-3, p. 439

Major Causes of Death from Infectious Diseases in the World, 2007

Fig. 17-4, p. 439

Genetic Resistance to Antibiotics Is Increasing

• Bacteria: rapid reproduction, easily spread

• Overuse of antibiotics

• Overuse of pesticides

Genetic Resistance to Antibiotics Is Increasing

• Methicillin-resistant Staphylococcus aureus (MRSA)

– Resistant to most antibiotics

– Symptoms of MRSA

– How will it be controlled?

The Growing Global Threat from Tuberculosis

• One in ten will become sick with TB

– 1.8 million deaths each year, primarily in less-developed countries

• Why is tuberculosis on the rise?

– Not enough screening and control programs

– Genetic resistance to a majority of effective antibiotics

– Person-to-person contact has increased

– AIDS individuals are very susceptible to TB

Lung Tissue Destroyed by Tuberculosis

Fig. 17-5, p. 440

Viral Diseases Kill Large Numbers of People

• Influenza or flu virus – #1 Killer

• HIV

– #2 Killer

• Hepatitis B virus (HBV) – #3 Killer

• Emergent diseases: West Nile virus

Viral Diseases Kill Large Numbers of People

• Viruses that move form animals to humans

– West Nile virus

– Ecological medicine

• Reduce chances of infection:

1.Wash your hands

2.Avoid touching your face

3.Avoid sick people

Ecological Medicine: How Humans Get Infectious Diseases from Animals

• Human practices that encourage the spread of diseases from animals to humans

• Emerging infections – HIV

– Avian flu

– Hepatitis B

– Lyme virus

Global HIV/AIDS Epidemic

• Acquired immune deficiency syndrome (AIDS)

– caused by human immunodeficiency virus (HIV)

– Many secondary infections

• No vaccine to prevent or cure AIDS

• Expensive drugs—live longer

Global HIV/AIDS Epidemic

• 25 million deaths, so far

• #1 killer globally of women 15-49

• Most prevalent in sub-Saharan Africa

– Life expectancy dropped from 62 to 47

– Alters age structure of population

Malaria — The Spread of a Deadly Parasite

• Malaria

– Caused by Plasmodium sp. carried by Anopheles mosquitoes

– Tropical and subtropical regions

– Spread

– Symptoms

– Malarial cycle

Malaria — The Spread of a Deadly Parasite

• Malaria on the rise since 1970 – Drug resistant Plasmodium

– Insecticide resistant

mosquitoes

– Clearing of tropical forests

– AIDS patients particularly

vulnerable

Global Outlook: Distribution of Malaria

Fig. 17-6, p. 444

A Boy in Brazil’s Amazon Sleeps Under an Insecticide-Treated Mosquito Net

Fig. 17-7, p. 445

We Can Reduce the Incidence of Infectious Diseases

• Good news

– Vaccinations on the rise

– Oral rehydration therapy

• Bad news

– More money needed for medical research in developing countries

Solutions: Infectious Diseases

Fig. 17-8, p. 445

Some Chemicals Can Cause Cancers, Mutations, and Birth Defects

• Toxic chemicals – Carcinogens

• Chemicals, types of radiation, or certain viruses the cause or promote cancer

– Mutagens • Chemicals or radiation that cause mutations or increase

their frequency

– Teratogens • Chemicals that cause harm or birth defects to a fetus or

embryo

PCBs Are Everywhere—A Legacy from the Past

• Class of chlorine-containing compounds

– Very stable

– Nonflammable

– Break down slowly in the environment

– Travel long distances in the air

– Fat soluble

– Biomagnification

– Food chains and webs

• Banned, but found everywhere

Potential Pathways on Which Toxic Chemicals Move Through the Environment

Fig. 17-9, p. 447

Some Chemicals May Affect Our Immune and Nervous Systems

• Some natural and synthetic chemicals in the environment can weaken and harm

– Immune system

– Nervous system

• Neurotoxins: PCBs, arsenic, lead, some pesticides

– Endocrine system

Mercury’s Toxic Effects

• Hg: teratogen and potent neurotoxin – Once airborne, persistent and not degradable

– 1/3 from natural sources

– 2/3 from human activities

– Enters the food chain: biomagnification

• How are humans exposed? 1. Inhalation: vaporized Hg or particulates

2. Eating fish with high levels of methylmercury

3. Eating high-fructose corn syrup

Mercury’s Toxic Effects

• Effects of Hg on humans

– Damage nervous system, kidneys, lungs

– Harm fetuses and cause birth defects

• Who is most at risk?

– Pregnant women

– 75% of exposure comes from eating fish

Solutions: Mercury Pollution

Fig. 17-10, p. 449

Some Chemicals Affect the Human Endocrine System

• Glands that release hormones that regulate bodily systems and control sexual reproduction, growth, development, learning, behavior

• Hormonally active agents have similar shapes and bind to hormone receptors – Gender benders

– Thyroid disruptors

– BPA?

– Phthalates in plastics

Hormones and Hormones Mimics or Blockers

Fig. 17-11, p. 449

Many Factors Determine the Harmful Health Effects of a Chemical

• Toxicology • Toxicity dependent on

– Dose – Age – Genetic makeup – Multiple chemical sensitivity (MCS) – Solubility – Persistence – Biomagnification

Many Factors Determine the Harmful Health Effects of a Chemical

• Response

– Acute effect: immediate or rapid

– Chronic effect: permanent or long-lasting

Science: Estimating Human Exposure to Chemicals and Measuring Their Effects

Fig. 17-12, p. 452

Protecting Children from Toxic Chemicals

• Analysis of umbilical cord blood: significance

• Infants and children more susceptible – Eat, drink water, and breathe more per unit of body

weight than adults – Put their fingers in their mouths – Less well-developed immune systems and body

detoxification processes

• Fetal exposure may increase risk of autism, asthma, learning disorders

Scientists Use Live Lab Animals and Non-animal Tests to Estimate Toxicity

• Mice and rats – Systems are similar to humans

– Small, and reproduce rapidly

– Is extrapolation to humans valid?

• Dose-response curve: median lethal dose (LD50) – Nonthreshold dose-response model

– Threshold dose-response model

Scientists Use Live Lab Animals and Non-animal Tests to Estimate Toxicity

• More humane methods using animals

• Replace animals with other models – Computer simulations

– Tissue culture and individual animal cells

– Chicken egg membranes

• What are the effects of mixtures of potentially toxic chemicals?

Hypothetical Dose-Response Curve Showing Determination of the LD50

Fig. 17-13, p. 453

Toxicity Ratings and Average Lethal Doses for Humans

Table 17-1, p. 453

Science: Two Types of Dose-Response Curves

Fig. 17-14, p. 454

There Are Other Ways to Estimate the Harmful Effects of Chemicals

• Case reports and epidemiological studies

• Limitations of epidemiological studies

– Too few people tested

– Length of time

– Can you link the result with the chemical?

– Cannot be used for new hazards

Are Trace Levels of Toxic Chemicals Harmful?

• Insufficient data for most chemicals

• We are all exposed to toxic chemicals

• Are the dangers increasing or are the tests just more sensitive?

Some Potentially Harmful Chemicals Found in Most Homes

Fig. 17-15, p. 455

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

• Severe limitations estimating toxicity levels and risks

• Only 2% of 100,000 chemicals have been adequately tested

• 99.5% of chemicals used in the United States are not supervised by government

Pollution Prevention and the Precautionary Principle

• Those introducing a new chemical or new technology would have to follow new strategies – A new product is considered harmful until it can be proved to be

safe

– Existing chemicals and technologies that appear to cause significant harm must be removed

• 2000: global treaty to ban or phase out the dirty dozen persistent organic pollutants (POPs)

• 2007 REACH program in the European Union

The Greatest Health Risks Come from Poverty, Gender, and Lifestyle Choices

• Risk analysis – Risk assessment

– Risk management

– Risk communication

• Greatest health risks – Poverty

– Gender

– Lifestyle choices

Global Outlook: Number of Deaths per Year in the World from Various Causes

Fig. 17-16, p. 458

Comparison of Risks People Face in Terms of Shorter Average Life Span

Fig. 17-17, p. 459

Death from Smoking

• Most preventable major cause of suffering and premature death – Premature death of 5.4 million per year globally and

442,000 in the United States

– Could be linked to increased dementia and Alzheimer’s disease

• Nicotine: addictive

• Effects of passive smoking (secondhand smoke)

Case Study: Death from Smoking

• How to reduce smoking

– Taxes

– Classify and regulate nicotine

– Bans on smoking in public places

– Education

Normal Lung and Emphysema Lung

Fig. 17-18, p. 459

Annual Deaths in the U.S. from Tobacco Use and Other Causes

Fig. 17-19, p. 460

Most People Do a Poor Job of Evaluating Risks

1. Fear

2. Degree of control

3. Whether a risk is catastrophic or chronic

4. Optimism bias

5. Want instant gratification without thinking of future harm

http://www.livescience.com/environment/050106_odds_of_dying.html

Cause of Death Lifetime Odds

Heart Disease 1-in-5

Cancer 1-in-7

Stroke 1-in-23

Accidental Injury 1-in-36

Motor Vehicle Accident* 1-in-100

Intentional Self-harm (suicide) 1-in-121

Falling Down 1-in-246

Assault by Firearm 1-in-325

Fire or Smoke 1-in-1,116

Natural Forces (heat, cold, storms, quakes, etc.) 1-in-3,357

Electrocution* 1-in-5,000

Drowning 1-in-8,942

Air Travel Accident* 1-in-20,000

Flood* (included also in Natural Forces above) 1-in-30,000

Legal Execution 1-in-58,618

Tornado* (included also in Natural Forces above) 1-in-60,000

Lightning Strike (included also in Natural Forces above) 1-in-83,930

Snake, Bee or other Venomous Bite or Sting* 1-in-100,000

Earthquake (included also in Natural Forces above) 1-in-131,890

Dog Attack 1-in-147,717

Asteroid Impact* 1-in-200,000**

Tsunami* 1-in-500,000

Fireworks Discharge 1-in-615,488

The Probability of Suffering Harm from Various Hazards

Several Principles Can Help Us to Evaluate and Reduce Risk

1. Compare risks

2. Determine how much you are willing to accept

3. Determine the actual risk involved

4. Concentrate on evaluating and carefully making important lifestyle choices

Three Big Ideas

1. We face significant hazards from infectious diseases, malaria, and tuberculosis, and from exposure to chemicals that can cause cancers and birth defects, and disrupt the human immune, nervous, and endocrine systems.

2. Because of the difficulty in evaluating the harm caused by exposure to chemicals, many health scientists call for much greater emphasis on pollution prevention.

Three Big Ideas

3. Becoming informed, thinking critically about risks, and making careful choices can reduce the major risks we face.