Environmental Hazards and Human Health

1. Environmental Hazards and Human Health Chapter 17

2. 17-1 What Major Health Hazards Do We Face? • Concept 17-1 People face health hazards from biological, chemical, physical, and cultural factors, and from the lifestyle choices they make.

3. Risks Are Usually Expressed as Probabilities • Risk – a measure of the likelihood that you will suffer harm from a hazard (something that has the potential to cause harm) • Possibility – it COULD happen • Probability – how likely it is to happen We can suffer from: • Biological hazards: from more than 1,400 pathogens • Chemical hazards: in air, water, soil, and food • Physical hazards: fire, earthquake, volcanic eruption… • Cultural hazards: smoking, poor diet, unsafe sex, drugs, unsafe working conditions, and poverty • Lifestyle choices: smoking, overeating, alcohol/drug abuse

4. 17-2 What Types of Biological Hazards Do We Face? • Concept 17-2 In terms of death rates, the most serious infectious diseases are flu, AIDS, diarrheal diseases, malaria, and tuberculosis; most of these deaths occur in developing countries.

5. 17-2 What Types of Biological Hazards Do We Face? • Sources of biological hazards include bacteria, viruses, insects, plants, birds, animals, and humans. • These sources can cause a variety of health effects ranging from skin irritation and allergies to infections (e.g., tuberculosis, AIDS), cancer and so on. • This symbol is generally used as a warning, so that those potentially exposed to the substances will know to take precautions.

6. Some Diseases Can Spread from One Person to Another • Nontransmissible disease– not caused by living organisms and cannot spread from one person to another • Heart disease, cancer, asthma, diabetes • Infectious disease– caused by living organisms such as bacteria and viruses • Malaria, tuberculosis, measles • Transmissible (contagious or communicable disease) – it can be spread from person to person • Influenza, HIV

7. The World’s Seven Deadliest Infectious Diseases Kill 12.5 Million People Each Year • WHO estimates that the world’s seven deadliest infections kill 12.5 million people a year (34,200/day) • Most deaths are poor people in developing countries • Most deaths are preventable

8. Infectious Diseases Are Still Major Health Threats • Since 1950, death from infectious diseases have declined due to: • Better health care • Antibiotics • Vaccines • Infectious diseases spread through: air, water, food, body fluids • Epidemic – large scale outbreak of an infectious disease in an area or a country • Pandemic – a global epidemic

9. Science Focus:Genetic Resistance to Antibiotics Is Increasing • Infectious bacteria are becoming genetically resistant to widely used antibiotics due to: • Genetic resistance: the few bacteria that survives the antibiotics are stronger and more able to resist the antibiotics in the future – population evolves. • Overuse of antibiotics: A 2000 study found that half of the antibiotics used to treat humans were prescribed unnecessarily. • Other factors: • Rapid spread of bacteria around the world by human travel • Overuse of pesticides (crops) and antibiotics (livestock)

10. Some Viral Diseases Kill Large Numbers of People • Viruses are not treatable with antibiotics. • Influenza, 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.

11. Some Viral Diseases Kill Large Numbers of People • Acquired immune deficiency syndrome (AIDS) caused by human immunodeficiency virus (HIV) is the second biggest killer virus worldwide. • Kills 2.1 million people a year (25 million so far) • 2.5 million newly infected people a year • Virus itself doesn’t kill you • Weakened immune system • Killed by a secondary infection • No vaccine to prevent or cure AIDS • Expensive, anti-viral drugs • Live longer

12. Case Study: Malaria – Death by Parasite-Carrying Mosquitoes • Malaria • Caused by Plasmodium sp. carried by Anopheles mosquitoes • It infects and destroys red blood cells, intense fever, abdominal pains, vomiting, headaches • Malaria on the rise since 1970 • Drug resistant Plasmodium • Insecticide resistant mosquitoes • Effect of global warming • AIDS patients particularly vulnerable

13. Solutions: Infectious Diseases, Ways to Prevent or Reduce Their Occurrence

14. 17-3 What Types of Chemical Hazards Do We Face? • Concept 17-3 There is growing concern about chemicals that can cause birth defects and cancers and disrupt the human immune, nervous, and endocrine systems.

15. 17-3 What Types of Chemical Hazards Do We Face? • A toxic chemicalcan cause temporary or permanent harm or death. • A hazardous chemicalis a chemical that is flammable, explosive, or one that irritates the eyes, skin or lungs. • Chemical hazard labels indicate specific risks • Scale from 0 (no risk) to 4 (highest risk)

16. Some Chemicals Can Cause Cancers, Mutations, and Birth Defects • Mutagens – chemicals or forms of radiation that cause or increase the frequency of mutations (changes) in DNA. • UV radiation, radioactive decay, bromine • Teratogens – chemicals that cause harm or birth defects to a developing fetus or embryo. • ethyl alcohol, lead, mercury, phthalates, thalidomide • Carcinogens – chemicals or types of radiation that can cause or promote cancer. • benzene, PCB’s, radon, MANY chem. in cigarette smoke

17. Some Chemicals May Affect Our 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 nervous system • Endocrine system: complex network of glands that release minute amounts of hormones into the bloodstream

18. Some Chemicals May Affect Our Immune, Nervous, and Endocrine Systems • Hormonally active agents (HAAs) are a class of chemical that mimic the body’s natural hormones • Disrupt growth, metabolism, and reproduction • Hormone blockers • Gender benders • Thyroid disrupters

19. Science Focus: Mercury’s Toxic Effects • Mercury is a teratogen and potent neurotoxin • Interferes with nervous system and brain function • 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? • Inhalation: vaporized Hg or particulates of inorganic salts • Eating fish with high levels of methylmercury

20. Cycling of Mercury in Aquatic Environments

21. Solutions: Mercury Pollution

22. 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.

23. 17-4 How Can We Evaluate and Deal with Chemical Hazards? • Concept 17-4A Scientists use live laboratory animals, non-animal tests, case reports of poisonings, and epidemiological studies to estimate the toxicity of chemicals, but these methods have limitations. • Concept 17-4B Many health scientists call for much greater emphasis on pollution prevention to reduce our exposure to potentially harmful candidates.

24. Many Factors Determine the Harmful Health Effects of a Chemical • Toxicity – how harmful a substance can be…its ability to cause injury, illness, death. • Factors determining the harm caused by exposure to a chemical include: • Dose – the amount of a substance that has been inhaled, ingested, or absorbed • High dosage, low dosage • Frequency of exposure – how often does it occur • Frequent, infrequent • Length of exposure– how long the exposure lasts • Short-term, long-term

25. Many Factors Determine the Harmful Health Effects of a Chemical • Age is an important factor…very young and/or very old are much more at risk. • One’s genetic makeupalso influences one’s sensitivity to a toxic chemical. • A related factor is how well the body’s detoxification system (liver, kidneys lungs) works.

26. Many Factors Determine the Harmful Health Effects of a Chemical • The properties of the chemical can also determine the harm caused: • Solubility: • Water-soluble – can move throughout our environment, water supply, and bodies • Fat-soluble – can penetrate our body’s membranes and can be stored in our tissues • Persistence: its resistance to be broken down • How long does it stay in an active for in the environment

27. Many Factors Determine the Harmful Health Effects of a Chemical • Certain chemical interactions can either increase or decrease the harmful effects of a toxin: • Antagonistic interaction– certain vitamins or minerals can reduce the harm done by some kinds of toxic chemicals • Synergistic interaction– certain chemicals can increase the negative effects of other chemicals • The two chemicals together can be worse than either one of them separately

28. Many Factors Determine the Harmful Health Effects of a Chemical • Other related terms: • Bioaccumulation – the tendency to be absorbed and stored within certain tissues or organs • Low concentrations over long periods of time can become high levels in particular tissues • Biomagnification – the accumulation of chemicals as they pass through the food chain • Organisms at the top of the food chain have higher levels of toxins in their tissues

29. Estimating Human Exposure to Chemicals and Measuring Their Effects • Estimating human exposure to chemicals and their effects is very difficult because of the many and often poorly understood variables involved.

30. Many Factors Determine the Harmful Health Effects of a Chemical • Response – the type and amount of health damage done by exposure to toxic chemicals • Acute exposure – short duration or single event exposure • Chronic exposure – repeated, or continuous exposure over extended periods of time (or a lifetime) • Acute effect– an immediate, rapid, and reversible response to exposure that is usually brief and low dosage • dizziness, coughing, vomiting, irritated eyes • Chronic effect – a permanent or long lasting consequence from an exposure that is either high dosage or long-term • kidney or liver damage, damage to central nervous system, cancer, or death

31. Case Study: Protecting Children from Toxic Chemicals • 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. • Children’s developing bodies (especially the nervous system) are more susceptible to damage done by chemicals.

32. Scientists Use Live Lab Animals and Non-animal Tests to Estimate Toxicity • Dose-response curve: plotting the toxicity of a test chemical on certain organisms (usually rats or mice) • Median lethal dose (LD50) – the dose that can kill 50% of the animals tested • Median lethal concentration (LC50) – the concentration that can kill 50% of the animals tested

33. Why Do We Know So Little about the Harmful Effects of Chemicals? • Under existing laws, most chemicals are considered innocent until proven guilty, and estimating their toxicity is difficult, uncertain, and expensive. • “Toxicologists know a great deal about a few chemicals, a little about many, and next to nothing about most.” • 100,000 registered synthetic chemicals • 10% thoroughly screened for toxicity • 2% tested for carcinogen, teratogen, or mutagen determination • Federal and state governments do not regulate about 99.5% of the commercially used chemicals in the U.S.

34. Pollution Prevention and the Precautionary Principle • Some scientists and health officials say that preliminary but not conclusive evidence that a chemical causes significant harm should spur preventive action (precautionary principle). • A new product is considered harmful until it can be proved to be safe • Manufacturers contend that wide-spread application of the precautionary principle would make it too expensive to introduce new chemicals and technologies.

35. 17-5 How Do We Perceive Risks and How Can We Avoid the Worst of Them? • Concept 17-5 We can reduce the major risks we face if we become informed, think critically about risks, and make careful choices.

36. Comparative Risk Analysis: Most Serious Ecological and Health Problems

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

38. Number of Deaths per Year in the World from Various Causes • Number of deaths per year in the world from various causes. Red numbers show deaths in terms of the number of fully loaded 200-passenger jumbo jets crashing every day of the year with no survivors.

39. Comparison of Risks People Face in Terms of Shorter Average Life Span • Comparisons of risks people face expressed in terms of shorter average life span.

40. Annual Deaths in the U.S. from Tobacco Use and Other Causes in 2004