Toxicology & risk


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Toxicology & risk

  1. 1. <ul><li>Environmental Health, Risk and Toxicology </li></ul>
  2. 2. Alligators and Endocrine Disruptors at Lake Apopka, Florida <ul><li>Biologist Louis Guillette found alligators with reproductive abnormalities in a Florida lake. </li></ul><ul><li>The lake had been contaminated with pesticides. </li></ul><ul><li>Research revealed that chemicals in the lake were disrupting the animals’ reproductive hormones. </li></ul>
  3. 3. Environmental health <ul><li>Environmental health: </li></ul><ul><li>Assesses environmental factors that influence human health and quality of life. </li></ul><ul><li>Seeks to prevent adverse effects on human health and ecological systems. </li></ul><ul><li>Contains environmental toxicology within its scope. </li></ul>
  4. 4. Environmental health hazards <ul><li>Synthetic and natural toxicants are only one type of environmental health threat. Others are: </li></ul><ul><ul><li>• Physical hazards (floods, blizzards, landslides, radon, UV exposure) </li></ul></ul><ul><ul><li>• Chemical hazards (disinfectants, pesticides) </li></ul></ul><ul><ul><li>• Biological hazards (viruses, bacterial infections) </li></ul></ul><ul><ul><li>• Cultural or lifestyle hazards (drinking, smoking, bad diet, crime in neighborhood) </li></ul></ul>
  5. 6. Infectious disease <ul><li>In communicable or transmissable disease, a pathogen attacks a host, </li></ul><ul><ul><li>either directly or through a vector (e.g., mosquito that transfers a malaria parasite to hosts) </li></ul></ul><ul><ul><li>… and the pathogen can be transmitted from one host to another. </li></ul></ul><ul><li>Infectious disease causes 25% of deaths in the world </li></ul><ul><li>and nearly half of deaths in developing nations. </li></ul>
  6. 7. Infectious disease 2nd-leading cause of death worldwide 6 diseases account for 80% of infectious disease deaths
  7. 8. Many health hazards exist indoors <ul><li>Substances in plastics and consumer products </li></ul><ul><li>Lead in paint and pipes </li></ul><ul><li>Radon </li></ul><ul><li>Asbestos </li></ul><ul><li>PBDE fire retardants </li></ul>
  8. 9. Toxicology <ul><li>The study of poisonous substances and their effects on humans and other organisms </li></ul><ul><li>Toxicologists assess and compare toxic agents, or toxicants , for their toxicity , the degree of harm a substance can inflict. </li></ul><ul><li>Analagous to a pathogenicity or virulence of the biological hazards that spread infectious disease. </li></ul><ul><li>Environmental toxicology focuses on effects of chemical poisons released into the environment. </li></ul>
  9. 10. Environmental toxicology <ul><li>Studies toxicants that come from or are discharged into the environment, and: </li></ul><ul><ul><li>Health effects on humans </li></ul></ul><ul><ul><li>Effects on animals </li></ul></ul><ul><ul><li>Effects on ecosystems </li></ul></ul><ul><li>Animals are studied: </li></ul><ul><ul><li>For their own welfare </li></ul></ul><ul><ul><li>As “canaries in a coal mine” to warn of effects on humans </li></ul></ul>
  10. 11. Synthetic chemicals are everywhere in our environment <ul><li>Many thousands have been produced and released. </li></ul><ul><li>Some persist for long time periods or travel great distances. </li></ul><ul><li>2002 USGS study: 80% of U.S. streams contain up to 82 wastewater contaminants, include antibiotics, perfumes, detergents, drugs, steroids, disinfectants, etc. </li></ul>
  11. 12. Synthetic chemicals <ul><li>Of the 100,000 synthetic chemicals on the market today, very few have been thoroughly tested for harmful effects. </li></ul>
  12. 13. Synthetic chemicals are numerous
  13. 14. Rise of synthetic chemicals <ul><li>Widespread synthetic chemical production after WWII </li></ul><ul><li>People are largely unaware of the health risks of many toxicants. </li></ul>The potent insecticide DDT was sprayed widely in public areas, even on people.
  14. 15. Silent Spring and Rachel Carson <ul><li>Carson’s 1962 book alerted the public that DDT and other pesticides could be toxic to animals and people. </li></ul><ul><li>Further research led the EPA to ban DDT in 1973. </li></ul><ul><li>These developments were central to the modern environmental movement. </li></ul>
  15. 16. Types of toxicants <ul><li>Carcinogens : cause cancer </li></ul><ul><li>Mutagens: cause mutations in DNA </li></ul><ul><li>Teratogens: cause birth defects </li></ul><ul><li>Allergens: cause unnecessary immune response </li></ul><ul><li>Neurotoxins: damage nervous system </li></ul><ul><li>Endocrine disruptors: interfere with hormones </li></ul>
  16. 17. Types of toxicants: Teratogens <ul><li>The drug thalidomide, used to relieve nausea during pregnancy, turned out to be a potent teratogen, and caused thousands of birth defects before being banned in the 1960s . </li></ul><ul><li>“ Thalidomide baby” Butch Lumpkin learned to overcome his deformed arms and fingers to become a professional tennis instructor. </li></ul>
  17. 18. Endocrine disruption <ul><li>Some chemicals, once inside the bloodstream, can “mimic” hormones. </li></ul><ul><li>If molecules of the chemical bind to the sites intended for hormone binding, they cause an inappropriate response. </li></ul><ul><li>Thus these chemicals disrupt the endocrine (hormone) system . </li></ul>
  18. 19. Endocrine disruption <ul><li>The hormone system is geared to working with tiny concentrations of hormones … </li></ul><ul><li>… so, it can respond to tiny concentrations of environmental contaminants. </li></ul><ul><li>Have chemicals in the environment acted as endocrine disruptors in humans? </li></ul>
  19. 20. Frogs, people, and atrazine <ul><li>Frogs show reproductive abnormalities in response to small doses of the herbicide atrazine, researcher Tyrone Hayes has found. </li></ul><ul><li>Others suggest that atrazine may have effects on humans as well. </li></ul><ul><li>The fierce criticism from atrazine’s manufacturer reflects the high stakes in environmental toxicology. </li></ul>
  20. 21. Declining sperm counts? <ul><li>A 1992 study summarized results of sperm count studies worldwide since 1938. Data showed a significant decrease in men’s sperm counts over 50 years. </li></ul>
  21. 22. Testicular cancer <ul><li>Others hypothesize that endocrine disruptors are behind the rise in testicular cancer in many nations. </li></ul>
  22. 23. Toxicants take many routes through the environment
  23. 24. Toxicants concentrate in water <ul><li>Surface water and groundwater can accumulate toxicants. </li></ul><ul><li>Runoff from large areas of land drains into water bodies, becoming concentrated. </li></ul><ul><li>Toxicants in groundwater or surface water reservoirs used for drinking water pose potential risks to human health. </li></ul>
  24. 25. Airborne toxicants <ul><li>Volatile chemicals can travel long distances on atmospheric currents. </li></ul><ul><li>PCBs are carried thousands of miles from developed nations of the temperate zone up to the Arctic, where they are found in tissues of polar bears and seals. </li></ul>
  25. 26. Transport to the Arctic: “Global distillation”
  26. 27. Persistence <ul><li>Some chemicals are more stable than others, persisting for longer in the environment. </li></ul><ul><ul><li>DDT and PCBs are persistent. </li></ul></ul><ul><ul><li>Bt toxin in GM crops is not persistent. </li></ul></ul><ul><li>Temperature, moisture, sun exposure, etc., affect rate of degradation. </li></ul><ul><li>Most toxicants degrade into simpler breakdown products . Some of these are also toxic. </li></ul><ul><ul><li>(DDT breaks down to DDE, also toxic.) </li></ul></ul>
  27. 28. Poisons accumulate in tissues <ul><li>The body may excrete, degrade, or store toxicants. </li></ul><ul><li>Fat-soluble ones are stored. </li></ul><ul><ul><li>DDT is persistent and fat soluble, </li></ul></ul><ul><ul><ul><li>… so builds up in tissues: bioaccumulation . </li></ul></ul></ul><ul><li>Bioaccumulated chemicals may be passed on to animals that eat the organism—up the food chain… </li></ul>
  28. 29. Poisons move up the food chain <ul><li>At each trophic level, chemical concentration increases: biomagnification . </li></ul><ul><li>DDT concentrations increase from plankton to fish to fish-eating birds. </li></ul>
  29. 30. All toxicants are not synthetic <ul><li>Although toxicology tends to focus on man-made chemicals, it’s important to keep in mind that there are plenty of natural toxicants. </li></ul><ul><li>Many are toxins produced by animals or plants for protection against predators and pathogens. </li></ul>
  30. 31. Studying effects of hazards <ul><li>Toxicologists study effects in several major ways: </li></ul><ul><ul><li>• Wildlife toxicology studies </li></ul></ul><ul><ul><li>• Human epidemiological studies </li></ul></ul><ul><ul><li>• Dose-response studies in the lab </li></ul></ul>
  31. 32. Wildlife toxicology <ul><li>Determine causes of mortality in die-off events (e.g., toxoplasma) </li></ul><ul><li>or </li></ul><ul><li>Test animals in the lab for response to toxicants </li></ul><ul><li>or </li></ul><ul><li>Correlate chemical presence and animal presence in the field </li></ul>
  32. 33. Human epidemiology <ul><li>Human studies rely on: </li></ul><ul><li>Case history = observation and analysis of individual patients </li></ul><ul><li>Epidemiological studies = long-term, large-scale comparisons of different groups of people </li></ul><ul><li>Animal testing </li></ul>
  33. 34. Human epidemiology <ul><li>Advantages: Realistic </li></ul><ul><li> All real-life factors included </li></ul><ul><li>Disadvantages: Statistically correlational only; does not prove causation </li></ul><ul><li> Takes many years to get results </li></ul>
  34. 35. Mixing toxicology with anthropology <ul><li>Children were tested for pesticide effects. </li></ul>Drawings by nonexposed children Drawings by exposed children
  35. 36. Dose-response analysis <ul><li>Method of determining toxicity of a substance by measuring response to different doses </li></ul><ul><li>Lab animals are used. </li></ul><ul><li>Mice and rats breed quickly, and give data relevant to humans because they share mammal physiology with us. </li></ul><ul><li>Responses to doses are plotted on a dose-response curve . </li></ul>
  36. 37. Dose-response curve LD 50 = dose lethal to 50% of test animals Threshold = dose at which response begins
  37. 38. Dose-response curve <ul><li>Dose-response curves allow us to predict effects of higher doses. </li></ul><ul><li>By extrapolating the curve out to higher values, we can predict how toxic a substance may be to humans at various concentrations. </li></ul><ul><li>In most curves, response increases with dose. </li></ul><ul><li>But this is not always the case; the increase may not be linear. </li></ul><ul><li>With endocrine disruption, it may decrease . </li></ul>
  38. 39. Factors affecting toxicity <ul><li>Not all people are equal. Sensitivity to toxicant can vary with sex, age, weight, etc. </li></ul><ul><li>Babies, older people, or those in poor health are more sensitive. </li></ul><ul><li>Type of exposure: </li></ul><ul><ul><li>acute = high exposure in short period of time </li></ul></ul><ul><ul><li>chronic = lower amounts over long period of time </li></ul></ul>
  39. 40. Mixtures of toxicants <ul><li>Substances may interact when combined together. </li></ul><ul><li>Mixes of toxicants may cause effects greater than the sum of their individual effects. </li></ul><ul><li>These are called synergistic effects . </li></ul><ul><li>A challenging problem for toxicology: There is no way to test all possible combinations! </li></ul><ul><li>(And the environment contains complex mixtures of many toxicants.) </li></ul>
  40. 41. Policy on toxicants <ul><li>Key agencies and products they regulate: </li></ul><ul><li>Food and Drug Administration (FDA) </li></ul><ul><ul><li>food, additives, cosmetics, drugs, medical devices </li></ul></ul><ul><li>Environmental Protection Agency (EPA) </li></ul><ul><ul><li>pesticides, industrial chemicals, and any synthetic chemicals not covered by other agencies </li></ul></ul><ul><li>Occupational Health and Safety Administration (OSHA) </li></ul><ul><ul><li>workplace hazards </li></ul></ul>
  41. 42. Risk <ul><li>Risk = the mathematical probability that some harmful outcome will result from a given action, event, or substance </li></ul><ul><li>Probability = a quantitative description of the likelihood of a certain outcome </li></ul><ul><li>Harmful outcome could be defined as injury, death, environmental damage, economic loss, etc. </li></ul>
  42. 43. Perceiving Risk <ul><li>Most individuals evaluate the relative risk they face based on: </li></ul><ul><ul><li>Degree of control. </li></ul></ul><ul><ul><li>Fear of unknown. </li></ul></ul><ul><ul><li>Whether we voluntarily take the risk. </li></ul></ul><ul><ul><li>Whether risk is catastrophic. </li></ul></ul><ul><ul><li>Unfair distribution of risk. </li></ul></ul><ul><li>Sometimes misleading information, denial, and irrational fears can cloud judgment. </li></ul>
  43. 44. Perception different from reality <ul><li>Our perception of risks tends not to match statistical reality. </li></ul>smoking plane crash
  44. 45. RISK ANALYSIS <ul><li>Annual deaths in the U.S. from tobacco use and other causes in 2003. </li></ul>Figure 18-A
  45. 46. RISK ANALYSIS <ul><li>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. </li></ul>Figure 18-13
  46. 47. Risk assessment <ul><li>Analyzes risks quantitatively </li></ul><ul><li>Measures and compares risks involved in different activities or substances </li></ul><ul><li>Helps identify and prioritize serious risks </li></ul><ul><li>Helps determine threats posed to humans, wildlife, ecosystems </li></ul>
  47. 48. Implications for product testing <ul><li>“ Innocent until proven guilty”: </li></ul><ul><ul><li>Industry can introduce any products it wants. </li></ul></ul><ul><ul><li>Government bears the burden of proof to show if products are dangerous. </li></ul></ul><ul><li>Precautionary principle: </li></ul><ul><ul><li>Industry cannot introduce a product until it is very thoroughly tested and shown convincingly to be harmless. </li></ul></ul>
  48. 49. Implications for product testing <ul><li>Industry has pressured government to take an “innocent-until-proven-guilty” approach. </li></ul><ul><li>Environmental advocates have pressured government to follow the precautionary principle. </li></ul>
  49. 50. “ The dirty dozen” POPs <ul><li>Aldrin (insecticide) </li></ul><ul><li>Chlordane (insecticide) </li></ul><ul><li>DDT (insecticide) </li></ul><ul><li>Dieldrin (insecticide) </li></ul><ul><li>Dioxins (industrial by-product) </li></ul><ul><li>Endrin (insecticide) </li></ul><ul><li>Furans (industrial by-product) </li></ul><ul><li>Heptachlor (insecticide) </li></ul><ul><li>Hexachlorobenzene (fungicide, industrial by-product) </li></ul><ul><li>Mirex (insecticide, fire retardant) </li></ul><ul><li>PCBs (industrial chemical) </li></ul><ul><li>Toxaphene (insecticide) </li></ul>
  50. 51. Conclusion <ul><li>International agreements are a hopeful sign that governments will prevent environmental hazards. </li></ul><ul><li>But solutions can come more easily when they do not arise from government regulation alone. </li></ul><ul><li>Consumer choice can influence industry if consumers have scientific information. </li></ul><ul><li>But we will never attain complete knowledge of risks. </li></ul><ul><li>A safer future depends on knowing risks, phasing out harmful substances, and replacing them with safer ones. </li></ul>