Chapter 17Human Health and Environmental Risks

ObjectivesAP Standard: Impacts on the Environment and Human Health

1. Hazards to human health-Environmental risk analysis; acute and chronic effects; dose-response relationships; air pollutants; smoking and other risks

2. Hazardous chemicals in the environment-Types of hazardous waste; treatment/disposal of hazardous waste; cleanup of contaminated sites; biomagnification; relevant laws

•Identify 3 major categories of human health risk

•List the major historical and emerging infectious diseases

•Name 5 major types of toxic chemicals

•Distinguish between dose-response, retrospective, and prospective studies

•Factors that determine the chemical concentrations organisms experience

•Factors involved in risk analysis

•Two major chemical regulation philosophies

Categories of human health risks

1. Physical – natural disasters, UV radiation from the sun, exposure to radioactive substances like radon

2. Biological – diseases

3. Chemical – exposure to chemicals such as arsenic, mercury, lead, pesticides, etc.

Biological Risks• Cause the most human deaths (~75% worldwide)

• Infectious diseases – diseases caused by pathogens

• Examples: tuberculosis, pneumonia and STDs

• Six types of illnesses account for 94% of deaths

• Epidemic vs. pandemic

Biological Risks• All diseases fall into 2 categories:

1. Chronic diseases slowly impairs the functioning of a person’s body

• Examples: heart disease and cancer

2. Acute diseases rapidly impairs the functioning of a person’s body

• Example: Ebola hemorrhagic fever

Biological Risk Factors• WHO determined that risk factors vary greatly between

developed and developing nations:

Biological Risk Factors

Historical Diseases1. Plague (bubonic plague or Black Death)

• Caused by Yersinia pestis bacterium

• Carried by fleas

• Estimated to have killed ¼ to ⅓ of Europe’s population in the 1300’s

Historical Infectious Diseases2. Malaria

• Caused by several species from the protist genus Plasmodium

• Carried by mosquitoes

• Each year, 300-350 million people are infected, and 1 million (mostly children) die from it

3. Tuberculosis

• Caused the facultative aerobic bacterium Mycobacterium tuberculosis

• Highly contagious, spread by coughing bacteria into air where it can live for several hours

• Estimated that 1/3 of world’s population is infected

• Kills 2 million annually

Emergent Infectious Diseases• Since the 1970’s, world has averaged one emergent disease per

year:

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

Toxicology• Study of chemical risks

• Very complex due to large numbers of chemicals released into the environment and their potential direct and synergistic effects

• Five categories:

1. Neurotoxins - chemicals that disrupt the nervous system of animals

• Insecticides, lead, mercury

Toxicology2. Carcinogens - chemicals that cause cancer by either

interfering with cells’ normal metabolic processes or cause damage to genetic material (mutagens)

• Asbestos, radon, formaldehyde, and chemicals found in tobacco

3. Teratogens - chemicals that interfere with the normal development of embryos or fetuses

• Thalidomide (1950-1960), alcohol (FAS)

Toxicology4. Allergens - chemicals that cause allergic reactions

• Overreaction of the immune system; difficulty breathing and death

• Ex: peanuts, milk, penicillin, codeine, etc.

5. Endocrine disruptors - chemicals that interfere with the normal functioning of hormones in an animal’s body

• Hormones are slow acting, but long lasting; bind to specific cell receptors

• Wastewater may contain hormones from livestock operations, birth control pill residue, and pesticides that mimic animal hormones = problems with fish, reptiles and amphibians

Dose-Response Studies• A dose-response relationship describes how the likelihood and

severity of adverse health effects (the responses) are related to the amount and condition of exposure to an agent (the dose provided)

• Expose animals and plants to varying concentrations of chemicals, then observe responses in behavior, reproduction or mortality

• Acute studies last 1-4 days; chronic studies often last from birth to age of reproduction (tadpoles)

• LD50 - lethal dose that kills 50% of the individuals

• ED50 - effective dose that causes 50% of the animals to display the harmful but nonlethal effect

Testing Standards• Effects of chemicals on humans and wildlife is regulated by EPA

• Toxic Substances Control Act of 1976 gives the EPA authority to regulate many chemicals except food, cosmetics, and pesticides

• Pesticides are regulated under the Federal Insecticide, Fungicide, and Rodenticide Act of 1996

• 10 million species of organisms; scientists can’t test on every species, so they use a representative group:

• Bird, mammal, fish, invertebrate

• What’s missing and why is this a problem today?

• EPA uses LD50 and ED50 values to to determine safe concentrations in the environment

• For most animals, take LD50 and divide by 10

• For humans, standards are usually more conservative

• Estimating the effect of chemicals on humans is a major challenge

• An alternative to dose-response examines large human or other animal populations exposed to chemicals (included in epidemiological studies)

1. Retrospective studies monitor people who have been exposed to chemicals in the past

2. Prospective studies monitor people who might be exposed in the future (e.g. food, alcohol and tobacco study of population over 40 years)

• Synergistic interactions - when two risks come together and cause more harm that one would. For example, the health impact of a carcinogen such as asbestos can be much higher if an individual also smokes tobacco.

Routes of Exposure

Solubility, Bioaccumulation, and Biomagnification

• Movement of a chemical in the environment depends upon its solubility

• Water soluble – pervasive in ground and surface waters

• Fat soluble – found in high concentrations in in soil and fat tissues of animals

• Bioaccumulation- an increased concentration of a chemical within an organism over time

• Biomagnification- the increase in a chemical concentration in animal tissues as the chemical moves up the food chain

• Persistence- how long a chemical remains in the environment

Risk Analysis

Qualitative Risk Assessment

Making a judgment of the relative risks of various decisions

Probability- the statistical likelihood of an event occurring and the probability of that event causing harm

Quantitative Risk Assessment

The approach to conducting a quantitative risk assessment is:

Risk= probability of being exposed to a hazard X probability of being harmed if exposed

Stockholm Convention In 2001, a group of 127 nations gathered in

Stockholm, Sweden, to reach an agreement on restricting the global use of some chemicals

12 chemicals were to be banned, phased out, or reduced

These include DDT, PCBs, and certain chemicals that are by-products of manufacturing processes.

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