Chapter 17

Human Health and Environmental Risks

Warm-Up

1. What are the leading causes of death worldwide?2. How is the economic development of a country

related to disease?3. Rank the following in order of highest probability of

death to lowest probability:A. Airplane accidentB. DrowningC. Motor vehicle accidentD. Heart diseaseE. Firearm assault

(1 in 5,051)

(1 in 1,008)

(1 in 314)

(1 in 84)

(1 in 5)

What is Risk?

• Risk: possibility of suffering harm from a hazard

Human Health Risks

• Physical – harm caused by environmental factors – Natural disasters– Sunburn

• Biological – harm caused by diseases– Malaria– Influenza

• Chemical – harm caused by chemicals– Arsenic– Pesticides

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

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 Studies

• Epidemiology: field of science that seeks to understand the causes of illness and disease

• Retrospective and prospective studies allow researchers to determine the effects of chemicals on individuals

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

• Exposing organisms to different doses of a chemical and then observing their response allows scientists to determine how chemicals affect living things

• Response: the effect that a substance has on an organism (ex: mortality, change in behavior, etc.)

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

Dose-Response StudiesDose (hypothetical units) Percent Mortality

1 0%2 0%3 4%4 10%5 40%6 60%7 90%8 96%9 100%

10 100%

LD50

LD50 = 5.3

Do The Math

• If the LD50 of a pesticide is 20 mg/kg for a mouse, what amount would be considered safe to ingest for a human?

• (Calculate the “safe” amount by taking the LD50 and dividing it by 1,000)

20 mg/kg ÷ 1000 = 0.02 mg/kg• Calculate the maximum amount that a 80 kg

man could ingest and still be considered “safe”80 kg × 0.02 mg/kg = 1.6 mg

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

• These effects that change the behavior of the individuals or cause harm are called sublethal effects

• The LD50 and ED50 values for mice are often divided by 1,000 to determine the safe value for humans

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

Do The Math

If the element Strogenium has an LD50 of 40 mg/kg, how big of a dose is necessary to kill a 30 kg goat?

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)

• Judgments based on perception, not on actual data

• 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

Risk Analysis

• What is riskier: flying on a plane for 1,000 miles per year or eating 40 tablespoons of peanut butter per year?– The probability of a plane crash is low, but the

probability of dying if the plane crashes is high– The probability of eating peanut butter is high, but

the probability of developing cancer from the peanut butter is low

– Both behaviors produce a risk of 1 in 1 million

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

Concentration Practice Problems

1. How much is 6 ppm in ppb?

2. What concentration is 4,000 ppt in ppm?

6

1,000,000

1,000

1,000

6,000

1,000,000,0006,000 ppbx = =

4,000

1,000,000,000,000

1,000,000

1,000,000

0.004

1,000,0000.004 ppm÷ = =