Environmental Hazards and Human Health

Core Case Study: The Global HIV/AIDS Epidemic According to the World Health Organization (WHO), in 2005 about 42 million people worldwide (1.1 million in the U.S.) were infected with HIV. There is no vaccine for HIV – if you get AIDS, you will eventually die from it. Drugs help some infected people live longer, but only a tiny fraction can afford them.

Animation: HIV Replication PLAY ANIMATION

Core Case Study: The Global HIV/AIDS Epidemic AIDS has reduced the life expectancy of sub-Saharan Africa from 62 to 47 years – 40 years in the seven countries most severely affected by AIDS. Projected age structure of Botswana's population in 2020. Figure 18-2

Core Case Study: The Global HIV/AIDS Epidemic The virus itself is not deadly, but it cripples the immune system, leaving the body susceptible to infections such as Kaposi’s sarcoma (above). Figure 18-1

RISKS AND HAZARDS Risk is a measure of the likelihood that you will suffer harm from a hazard. We can suffer from: Biological hazards: from more than 1,400 pathogens. Chemical hazards: in air, water, soil, and food. Physical hazards: such as fire, earthquake, volcanic eruption… Cultural hazards: such as smoking, poor diet, unsafe sex, drugs, unsafe working conditions, and poverty.

Video: Germs in Pakistan PLAY VIDEO From ABC News, Human Biology in the Headlines, 2006 DVD.

BIOLOGICAL HAZARDS: DISEASE IN DEVELOPED AND DEVELOPING COUNTRIES Diseases not caused by living organisms cannot spread from one person to another (nontransmissible disease), while those caused by living organisms such as bacteria and viruses can spread from person to person (transmissible or infectious)

Video: Polio Scare PLAY VIDEO From ABC News, Environmental Science in the Headlines, 2005 DVD.

Transmissible Disease Pathway for infectious disease in humans. Figure 18-4

Transmissible Disease WHO estimates that each year the world’s seven deadliest infections kill 13.6 million people – most of them the poor in developing countries. Figure 18.5 Global outlook: the World Health Organization estimates that each year the world’s seven deadliest infectious diseases kill 13.6 million people—most of them poor people in developing countries. This amounts to about 37,300 mostly preventable deaths every day. Figure 18-5

Case Study: Growing Germ Resistance to Antibiotics Rabidly producing infectious bacteria are becoming genetically resistant to widely used antibiotics due to: Genetic resistance: Spread of bacteria around the globe by humans, overuse of pesticides which produce pesticide resistant insects that carry bacteria. Overuse of antibiotics: A 2000 study found that half of the antibiotics used to treat humans were prescribed unnecessarily.

Video: The Problem with Pork PLAY VIDEO From ABC News, Environmental Science in the Headlines, 2005 DVD.

Case Study: The Growing Global Threat from Tuberculosis The highly infectious tuberculosis (TB) kills 1.7 million people per year and could kill 25 million people 2020. Recent increases in TB are due to: Lack of TB screening and control programs especially in developing countries due to expenses. Genetic resistance to the most effective antibiotics.

Viral Diseases Flu, HIV, and hepatitis B viruses infect and kill many more people each year then highly publicized West Nile and SARS viruses. The influenza virus is the biggest killer virus worldwide. Pigs, chickens, ducks, and geese are the major reservoirs of flu. As they move from one species to another, they can mutate and exchange genetic material with other viruses.

Video: Bird Flu PLAY VIDEO From ABC News, Environmental Science in the Headlines, 2005 DVD.

Video: Mask of Technology PLAY VIDEO From ABC News, Human Biology in the Headlines, 2006 DVD.

Viral Diseases HIV is the second biggest killer virus worldwide. Five major priorities to slow the spread of the disease are: Quickly reduce the number of new infections to prevent further spread. Concentrate on groups in a society that are likely to spread the disease. Provide free HIV testing and pressure people to get tested. Implement educational programs. Provide free or low-cost drugs to slow disease progression.

Malaria – Death by Mosquito Malaria kills about 2 million people per year and has probably killed more than all of the wars ever fought! Female mosquito bites infected human, ingesting blood that contains Plasmodium gametocytes Merozoites enter blood-stream and develop into gametocytes causing malaria and making infected person a new reservoir Plasmodium develops in mosquito Figure 18.7 Science: the life cycle of malaria. Plasmodium parasites circulate from mosquito to human and back to mosquito. Sporozoites penetrate liver and develop into merozoites Female mosquito injects Plasmodium sporozoites into human host Stepped Art Fig. 18-7, p. 423

Case Study: Malaria – Death by Mosquito Economists estimate that spending $2-3 billion on malaria treatment may save more than 1 million lives per year. Figure 18-6

Case Study: Malaria – Death by Mosquito Spraying insides of homes with low concentrations of the pesticide DDT greatly reduces the number of malaria cases. Under international treaty enacted in 2002, DDT is being phased out in developing countries.

Animation: Life Cycle of Plasmodium PLAY ANIMATION

Ecological Medicine and Infectious Diseases Mostly because of human activities, infectious diseases are moving at increasing rates from one animal species to another (including humans). Ecological (or conservation) medicine is devoted to tracking down these connections between wildlife and humans to determine ways to slow and prevent disease spread.

CHEMICAL HAZARDS A toxic chemical can cause temporary or permanent harm or death. Mutagens are chemicals or forms of radiation that cause or increase the frequency of mutations in DNA. Teratogens are chemicals that cause harm or birth defects to a fetus or embryo. Carcinogens are chemicals or types of radiation that can cause or promote cancer.

CHEMICAL HAZARDS A hazardous chemical can harm humans or other animals because it: Is flammable Is explosive An irritant Interferes with oxygen uptake Induce allergic reactions.

Effects of Chemicals on the Immune, Nervous, and Endocrine Systems Long-term exposure to some chemicals at low doses may disrupt the body’s: Immune system: specialized cells and tissues that protect the body against disease and harmful substances. Nervous system: brain, spinal cord, and peripheral nerves. Endocrine system: complex network of glands that release minute amounts of hormones into the bloodstream.

Case Study: A Black Day in Bhopal, India The world’s worst industrial accident occurred in 1984 at a pesticide plant in Bhopal, India. An explosion at Union Carbide pesticide plant in an underground storage tank released a large quantity of highly toxic methyl isocyanate (MIC) gas. 15,000-22,000 people died Indian officials claim that simple upgrades could have prevented the tragedy.

TOXICOLOGY: ASSESSING CHEMICAL HAZARDS Factors determining the harm caused by exposure to a chemical include: The amount of exposure (dose). The frequency of exposure. The individual person who is exposed. The effectiveness of the body’s detoxification systems. The person’s genetic makeup.

TOXICOLOGY: ASSESSING CHEMICAL HAZARDS Typical variations in sensitivity to a toxic chemical within a population, mostly because of genetic variation. Figure 18.10 Science: typical variations in sensitivity to a toxic chemical within a population, mostly because of differences in genetic makeup. Some individuals in a population are very sensitive to small doses of a toxin (left), and others are very insensitive (right). Most people fall between these two extremes (middle). Figure 18-10

TOXICOLOGY: ASSESSING CHEMICAL HAZARDS Estimating human exposure to chemicals and their effects is very difficult because of the many and often poorly understood variables involved. Figure 18.11 Science: estimating human exposure to chemicals and their effects is very difficult because of the many and often poorly understood variables involved. QUESTION: Which three of these factors do you think make you more vulnerable to the harmful effects of chemicals? Figure 18-11

TOXICOLOGY: ASSESSING CHEMICAL HAZARDS Children are more susceptible to the effects of toxic substances because: Children breathe more air, drink more water, and eat more food per unit of body weight than adults. They are exposed to toxins when they put their fingers or other objects in their mouths. Children usually have less well-developed immune systems and detoxification processes than adults.

TOXICOLOGY: ASSESSING CHEMICAL HAZARDS Under existing laws, most chemicals are considered innocent until proven guilty, and estimating their toxicity is difficult, uncertain, and expensive. Federal and state governments do not regulate about 99.5% of the commercially used chemicals in the U.S.

RISK ANALYSIS Scientists have developed ways to evaluate and compare risks, decide how much risk is acceptable, and find affordable ways to reduce it. Figure 18.12 Science: comparative risk analysis of the most serious ecological and health problems according to scientists acting as advisers to the EPA. Risks under each category are not listed in rank order. (Data from Science Advisory Board, Reducing Risks, Washington, D.C.: Environmental Protection Agency, 1990) Figure 18-12

RISK ANALYSIS Estimating risks from using many technologies is difficult due to unpredictability of human behavior, chance, and sabotage. Reliability of a system is multiplicative: If a nuclear power plant is 95% reliable and human reliability is 75%, then the overall reliability is (0.95 X 0.75 = 0.71) 71%.

RISK ANALYSIS Figure 18.A Annual deaths in the United States from tobacco use and other causes in 2003. Smoking is by far the nation’s leading cause of preventable death, causing more premature deaths each year than all the other categories in this figure combined. (Data from U.S. National Center for Health Statistics and Centers for Disease Control and Prevention and U.S. Surgeon General) Annual deaths in the U.S. from tobacco use and other causes in 2003. Figure 18-A

RISK ANALYSIS Figure 18.13 Global outlook: number of deaths per year in the world from various causes. Numbers in parentheses give these deaths in terms of the number of fully loaded 400-passenger jumbo jets crashing every day of the year with no survivors. Because of sensational media coverage, most people have a distorted view of the largest annual causes of death. QUESTION: Which three of these items are most likely to shorten your life span? (Data from World Health Organization) Number of deaths per year in the world from various causes. Parentheses show deaths in terms of the number of fully loaded 400-passenger jumbo jets crashing every day of the year with no survivors. Figure 18-13

Perceiving Risk Most individuals evaluate the relative risk they face based on: Degree of control. Fear of unknown. Whether we voluntarily take the risk. Whether risk is catastrophic. Unfair distribution of risk. Sometimes misleading information, denial, and irrational fears can cloud judgment.

RISK ANALYSIS Comparisons of risks people face expressed in terms of shorter average life span. Figure 18.14 Global outlook: comparison of risks people face, expressed in terms of shorter average life span. After poverty and gender, the greatest risks people face come mostly from the lifestyle choices they make. These are merely generalized relative estimates. Individual responses to these risks can differ because of factors such as genetic variation, family medical history, emotional makeup, stress, and social ties and support. QUESTION: Which three of these items are most likely to shorten your life span? (Data from Bernard L. Cohen) Figure 18-14