Chapter 17

Human Health and Environmental Risks

What is Risk?

• Risk: possibility of suffering harm from a hazard

Human Health Risks

• Physical• Biological• Chemical

Leading Causes of Death Worldwide

Biological Risks

• Disease: any impaired function of the body with a characteristic set of symptoms

Biological Risks

• Infectious diseases: those caused by infectious agents, known as pathogens– Ex: pneumonia and

venereal diseases

Pathogens• Bacteria:

– Cholera– Tuberculosis– Syphilis

• Virus:– HIV/AIDS– Hepatitis– Ebola

• Protozoa:– Malaria

What causes disease?

• Infectious agents (pathogens) that spread by:– Air– Water– Food– Body fluids– Vectors (nonhuman carriers, like mosquitoes)

Biological Risks

• Chronic disease: slowly impairs the functioning of a person’s body– Ex: heart disease, cancer, diabetes– 70% of all deaths in the U.S.

• Acute disease: rapidly impairs the functioning of a person’s body– Ex: Ebola hemorrhagic fever

Leading Health Risks in the World

Historical Diseases

• Plague• Malaria • Tuberculosis

Emergent Diseases

• HIV/AIDS• Ebola• Mad Cow Disease• Bird Flu• West Nile Virus

Emergent Diseases

Pathways of Transmitting Pathogens

Chemical Risks

• Neurotoxins: chemicals that disrupt the nervous system

• Carcinogens: chemicals that cause cancer• Teratogens: chemicals that interfere with the

normal development of embryos and fetuses• Allergens: chemicals that cause allergic

reactions• Endocrine disruptors: chemicals that interfere

with the normal functioning of hormones

Cigarettes

Every year, over 400,000 smokers and almost 40,000 non-smokers die from cigarette-related illnesses. In fact, smoking kills more people than HIV, drugs, alcohol, car crashes, and homicide combined. People who work in bars and restaurants, and those who live with smokers are especially at risk for secondhand-smoke related illness.

Should cigarettes be made illegal?

Toxicology Studies

• Retrospective studies– “Looking back” – Monitoring people who have already been

exposed to a chemical to determine the effects• Prospective studies

– “Looking forward”– Monitoring people who might become exposed to

a chemical to determine the effects

Toxicology

• Dose – the amount of a substance that a person has in their body– Can be:

• Ingested• Inhaled• Injected • Absorbed

• “The dose makes the poison”

Dose-Response Studies

• LD50: the lethal dose that kills 50% of the individuals within a test population

LD50

LD50 = 5.3

Poisons

• Poisons: materials that kill at a very small dose (50 milligrams or less per kilogram of weight)

Toxicity Rating LD50

Average Lethal Dose Examples

super toxic < 0.01 less than 1 drop nerve gases, botulism, mushroom toxins, dioxin

extremely toxic

< 5 less than 7 drops potassium cyanide, heroin, atropine, parathion, nicotine

very toxic 5–50 7 drop to 1 teaspoon

mercury salts, morphine, codeine

toxic 50–500 1 teaspoon to 1 ounce

lead salts, DDT, sodium hydroxide, fluoride, sulfuric acid, caffeine, carbon tetrachloride

moderately toxic

500–5,000 1 ounce to 1 pint methyl alcohol, ether, pehobarbital, amphetamines, kerosine, aspirin

slightly toxic 5,000–15,000 1 pint to 1 quart ethyl alcohol, lysol, soapsessentially nontoxic

> 15,000 more than 1 quart water, glycerin, table sugar

Threshold

Dose-Response Studies

• ED50: effective dose that causes 50% of the individuals to display the harmful, but nonlethal, effect

Interactions• Synergistic interactions: when two (or more)

risk factors have a greater effect together than each by themselves– Ex: being exposed to asbestos and smoking gives

you a 400 times greater chance of developing lung cancer than if you experienced only one of those risks

+ =

Routes of Exposure

Toxicology

• Solubility - what can the chemical dissolve in?– Water-soluble toxins– Oil/Fat-soluble toxins

• Which do you think is generally “better” for the health of an organism?– Water is “better” since it can be diluted– Fats aren’t good since chemicals can gather

in body fat of animals

Toxicology

• Bioaccumulation: an increased concentration of a chemical within an individual organism over time– The chemical is usually stored in

body fat • Biomagnification: the increase

in a chemical concentration in animal tissues as the chemical moves up the food chain

Persistence• Persistence: how long a chemical remains in

the environment

Risk Analysis

Qualitative vs. Quantitative

• Qualitative risk assessment: judging the relative risk of various decisions (ex: low, medium, or high)

• Quantitative risk assessment: determining the probability of an event occurring using data (ex: 83% chance)

Probabilities of Death in U.S.

Risk Analysis

Risk =Probability of being exposed to a hazard

Probability of being harmed if exposedx

Chemical Regulation

Chemical Regulation

• Trade-off:– Greater safety with slower introduction of

beneficial chemicalsvs.

– Greater potential risk with a greater rate of discovery of beneficial chemicals