Chapter 17 Human Health and Environmental Risks

1. Chapter 17 Human Health and Environmental Risks

3. Risks and Hazards • Risk = a measure of the likelihood that you will suffer harm from a hazard • We can suffer from • Physical hazards: such as fire, earthquake, volcanic eruption… • Biological hazards: from more than 1,400 pathogens. • Chemical hazards: in air, water, soil, and food, venom.

4. Biological Risks • 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) • Infectious diseases- those caused by infectious agents, known as pathogens. • Examples: pneumonia and venereal diseases

5. Biological Risks • Chronic disease- slowly impairs the functioning of a person’s body. • Acute diseases- rapidly impair the functioning of a person’s body.

6. Disease is a major focus of environmental health • Despite our technology, disease kills most of us • Disease has a genetic and environmental basis • Cancer, heart disease, respiratory disorders • Poverty and poor hygiene foster illnesses

7. Infectious diseases kill millions • Infectious diseases kill 15 million people/year • Half of all deaths in developing countries • Money lets developed countries have access to hygiene and medicine

8. Infectious and noninfectious diseases • Lifestyles in developed nations affect diseases • Smoking, obesity, etc • Public health decreases some infectious diseases • Some (AIDS) are spreading • Some develop resistance to antibiotics

10. Diseases, the environment, and society • Our mobility spreads diseases • West Nile Virus spread from Africa to all lower 48 U.S. states in 5 years • New diseases are emerging • H5N1 avian flu, H1N1 swine flu • Climate change will expand the range of diseases • To predict and prevent diseases, experts deal with complicated interrelationships • In technology, land use, and ecology

11. Killing large #s of People • Epidemic: when a pathogen causes rapid increase in disease (exceeds what is expected based on experience) • Pandemic: when an epidemic spreads through human populations across a large region, like a continent

12. Historical Diseases • Plague • Malaria • Tuberculosis

13. Emergent Diseases • HIV/AIDS-virus believed to have begun in chimps • Ebola-virus with many strains. Can be deadly • Mad Cow Disease-caused by cows being fed infected cow brain • Swine and Bird Flu-originated from bird • SARS (severe acute respiratory syndrome) • West Nile Virus-carried through mosquito

15. Chemical Risks • Neurotoxins- chemicals that disrupt the nervous system • Carcinogens- chemicals that cause cancer • Mutagens-causes damage to the genetic material • Teratogens- chemicals that interfere with the normal development of embryos or fetuses • Allergens- chemicals that cause allergic reactions, affecting the immune system • Endocrine disruptors- chemicals that interfere with the normal functioning of hormones in an animal’s body

16. Indoor environmental health hazards • Radon = a highly toxic, radioactive gas that is colorless and undetectable • It can build up in basements • Asbestos = a mineral that insulates, muffles sounds, and resists fire • Asbestosis = scarred lungs that cease to function

17. Lead poisoning • Lead poisoning = caused by lead, a heavy metal • Damages the brain, liver, kidney, and stomach • Causes learning problems, behavior abnormalities, and death • Exposure is from drinking water that flows through lead pipes or from lead paint Education led to declines in poisoning, but China still used it in toy paint until recently

18. A recently recognized hazard • Polybrominated diphenyl ethers (PBDEs) = has fire-retardant properties • Used in computers, televisions, plastics, and furniture • Persist and accumulate in living tissue • Mimic hormones and affect thyroid hormones • Also affect brain and nervous system development and may cause cancer • Concentrations are rising in breast milk • Now banned in Europe, concentrations have decreased • The U.S. has not addressed the issue

19. Toxicology studies poisonous substances • Toxicology = the study of the effects of poisonous substances on humans and other organisms • Toxicity = the degree of harm a toxicant can inflict • Toxicant = any toxic substance (poison) • “The dose makes the poison” = toxicity depends on the combined effect of the chemical and its quantity • Environmental toxicology = deals with toxic substances that come from or are discharged into the environment • Studies health effects on humans, other animals, and ecosystems

20. Balancing risks and rewards • There is a tradeoff between the risk and reward of most hazards • We must judge how these compare • We use bisphenol (BPA) despite its health risks • Are safer and affordable alternatives available? • Don’t forget, chemicals have given us our high standard of living • Food, medicine, conveniences

21. Toxic substances in the environment • The environment contains natural chemicals that may pose health risks • Toxins = toxic chemicals made in tissues of living organisms • But synthetic chemicals are also in our environment • Every human carries traces of industrial chemicals The U.S. makes or imports 250 lb of chemicals for every person in the country

22. Chemicals are in the air, water, and soil • 80% of U.S. streams contain 82 contaminants • Antibiotics, detergents, drugs, steroids, solvents, etc. • 92% of all aquifers contain 42 volatile organic compounds (from gasoline, paints, plastics, etc.) • Less than 2% violate federal health standards for drinking water Pesticides are present in streams and groundwater in levels high enough to affect aquatic life

23. Synthetic chemicals are in all of us • Every one of us carries traces of hundreds of industrial chemicals in our bodies • Including toxic persistent organic pollutants restricted by international treaties • Babies are born “pre-polluted” – 232 chemicals were in umbilical cords of babies tested • Not all synthetic chemicals pose health risks • But very few of the 100,000 chemicals on the market have been tested

24. Dose-response analysis • Dose-response analysis = measures the effect a toxicant produces or the number of animals affected • At different doses • Dose = amount of substance the test animal receives • Response = the type or magnitude of negative effects • Dose-response curve = the dose plotted against the response

25. Dose-Response Studies • 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

26. The type of exposure affects the response • Acute exposure = high exposure to a hazard for short periods of time • Easy to recognize • Stem from discrete events: ingestion, oil spills, nuclear accident, etc. • Chronic exposure = low exposure for long periods of time • More common but harder to detect and diagnose • Affects organs gradually: lung cancer, liver damage • Cause and effect may not be easily apparent

27. Dose Response Studies • Dose-response studies: expose animals or plants to different amounts of a chemical and observe a variety of responses • Acute studies: short duration experiments • Chronic studies: longer duration of experiments, goal is to examine long-term effects of chemicals including effects on survival and impact

28. LD50 Studies To determine the dose of a chemical that causes a 50% death rate, scientists expose animals to different doses to determine what proportion will die at each dose

29. Number of individuals affected Majority of population Very sensitive Very insensitive Dose (hypothetical units) Fig. 18-10, p. 430

30. Retrospective vs Prospective • Retrospective study: a study on people who have been exposed to chemicals sometime in their past • Prospective study: a study on people might be exposed to harmful chemicals in the future • Participants may be asked to track tobacco, food or alcohol intake to track future health problems

31. Human studies • Case history approach = studies individual patients • Autopsies tell us about lethal doses • Don’t tell about rare, new, or low-concentration toxins • Don’t tell about probability and risk • Epidemiological studies = large-scale comparisons between exposed and unexposed groups • Studies can last for years • Yield accurate predictions about risk • Measure an association between a health hazard and an effect – but not necessarily the cause of the effect

32. Mixes may be more than the sum of their parts • We can’t determine the impact of mixed hazards • They may act in ways that cannot be predicted from the effects of each in isolation • Mixed toxicants can sum, cancel out, or multiply each other’s effects • Synergistic effects = interactive impacts that are greater than the sum of their constituent effects • New impacts may arise from mixing toxicants • DDE may cause or inhibit sex reversal, depending on the presence of other chemicals (DDE results from breakdown of DDT)

33. Routes of Exposure

34. Some toxicants persist • Toxins can degrade quickly and become harmless • Or they may remain unaltered and persist for decades • Rates of degradation depend on the substance, temperature, moisture, and sun exposure • Breakdown products = simpler products that toxicants degrade into • May be more or less harmful than the original substance • DDT degrades into DDE, which is also highly persistent and toxic

35. Bioaccumulation • bioaccumulation- an increased concentration of a chemical within an organism over time. Occurs when an organism absorbs the toxic substance at a greater rate than the substance is lost or broken down. • Properties of substances that bioaccumulate • Long lived • Mobile • Typically fat soluble

36. Bioaccumulation The longer the half life of the substance leads to greater risk of chronic poisoning, even if levels of the toxin are not very high A classic example: DDT (dichloro-diphyny-trichloroethane. It has a half-life of 15 years. Can lead to biomagnification

37. Silent Spring began the debate over chemicals In the 1960s, untested pesticides were sprayed over public areas, with assumption they would do no harm • Rachel Carson’s Silent Spring (1962) showed DDT’s risks to people, wildlife, and ecosystems • Chemical companies challenged the book • Discrediting Carson’s personal reputation • DDT was banned in the U.S. in 1973 • But is still made in the U.S. and exported

38. DDT has rather low toxicity to humans • But • high toxicity to insects • If accidentally swallowed in large amounts, it can cause a person to become excitable, have tremors and seizures • In animals, harmful effects in reproduction and in the nervous system • Causes shell-thinning in birds, in particular carnivorous birds (raptors) such as ospreys and bald eagles

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

40. Biomagnification • Biomagnification causes accumulation of toxins in the food chain. • Predators eat contaminated prey • Pollutions accumulates at each stage of the food chain • Top consumers, including humans, are most affected

41. Biomagnification of Other Pollutants

42. Persistence • Persistence- how long a chemical remains in the environment

43. We express risk in terms of probability • Exposure to health threats doesn’t automatically produce an effect • Rather, it causes some probability (likelihood) of harm • A substance’s threat depends on its identity and strength • Chance and frequency of an encounter • An organism’s exposure and sensitivity to the threat • Risk = the probability that some harmful outcome will result from a given action, event, or substance • Probability = describes the likelihood of a certain outcome

44. Perceptions of risk may not match reality • We try to minimize risk • But perception may not match reality • Flying versus driving • We feel more at risk when we do not control a situation • We fear nuclear power and toxic waste • But not smoking or overeating Everything we do involves some risk

45. Environmental Hazard- anything in our environment that can potentially cause harm. Environmental substances include substances such as pollutants or other chemical contaminants, draining swamps, logging forests, or volcanoes and earthquakes. Hazards that are voluntary include smoking, tobacco… Hazards that are involuntary include pollution Risk Analysis

47. 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

48. Quantitative Risk Assessment • Risk assessment = the quantitative measurement of risk • Compares risks involved in different activities or substances • It identifies and outlines problems • Risk assessment has several steps: • The scientific study of toxicity • Assessing an individual or population’s exposure to the substance (frequency, concentrations, length) • Teams of scientific experts review hundreds of studies • Regulators and the public benefit from informed summaries

49. Risky Business • Risk acceptance determines how much risk can be tolerated • Risk management balances potential harms against other factors

50. Risk management • Risk management = decisions and strategies to minimize risk • Federal agencies manage risk • The U.S. has the Centers for Disease Control (CDC), the EPA, the Food and Drug Administration (FDA) • Scientific assessments are considered with economic, social, and political needs and values • Comparing costs and benefits is hard • Benefits are economic and easy to calculate • Health risks (costs) are hard-to-measure probabilities of a few people suffering and lots of people not