toxicology and human health

• Risk


  The likelihood of suffering harm from a hazard

  
• Major types of hazards

  • Cultural hazards (e.g. smoking, poor diet, driving)
  • Chemical hazards (e.g. harmful chemicals in air, water, soil and food)
  • Physical hazards (e.g. fire, tornado, earthquake)
  • Biological hazards (e.g. pathogens, pollen, venomous animals)
• Risk assessment


  The scientific process of estimating how much harm a particular hazard can cause to human health
• Risk management


  Deciding whether or how to reduce a particular risk to a certain level and at what cost

  
• Most individuals are poor at evaluating the relative risks they face, mostly because of misleading information and irrational fears
• Aflatoxin is a potent carcinogen produced by moulds in peanut butter and corn
• How to become better at risk analysis & management

  1. Carefully evaluate media presentations

  2. Compare risks

  3. Concentrate on the most serious risks over which you have some control

  4. Determine how much a life is worth and how much money should be spent per life saved
• Under 70 - US$3.7 million, Over 70 - US$1.4 million
• Cigarette smoking is the most preventable major cause of suffering and premature death among adults in Canada
• Tobacco is responsible for one in every five deaths (100 deaths per day) in Canada and costs $17.7 billion a year in health care, disability, fires related to smoking
• Taxation, banning advertising and sale, anti-smoking campaigns are used to address the issue of tobacco use
• The greatest health risk of all is poverty
• Biological hazards


  • Pathogens (bacteria, viruses, protozoa, parasites)
  • Cardiovascular disorders (31% of annual deaths worldwide)
  • Cancers (13% of annual deaths worldwide)
  • Diabetes
  • Asthma
  • Emphysema
  • Malnutrition
• Nontransmissible


  Not caused by living organisms, do not spread from one person to another
• Transmissible


  Caused by living organisms, such as bacteria and viruses, can spread from one person to another
• Life cycle of malaria

  Plasmodium parasites circulate from mosquito to human and back to mosquito

  
• Malaria


  • Kills 655,000 people per year (mostly children under age 5)
  • 1 in 5 people at risk (most of them living in poor African countries)
  • Resistance to insecticides
  • Resistance to antimalarial drugs

  
• Malaria prevention


  1. Remove stagnant water

  2. Use insecticide-treated nets

  3. Cultivate mosquito predators (biological control)

  4. Use zinc + vitamin A supplements

  5. Use DDT in endemic countries
• Toxic chemical (or poison, toxin)

  Chemical that can cause temporary or permanent harm or death to biological organisms
• Types of toxic chemicals based on biological effects

  • Mutagens (possible DNA mutations)
  • Teratogens (harm or birth defects in utero)
  • Carcinogens (promote malignant tumor growth)
  • Neurotoxic (harm to the nervous system, including behavior, paralysis, death)
  • Endocrine disruptors (affect our hormonal system)
• Toxicology


  Assessing chemical hazards
• Toxicity


  How harmful a substance is in causing injury, illness, or death to a living organism
• Factors affecting toxicity


  • Dose (how much?)
  • Frequency of exposure (how often?)
  • Personal traits (e.g. age, genes) (who?)
• "The dose makes the poison" - Paracelsus (1492 - 1541), Swiss physician and "Father of Toxicology"
• Both developing and aging organisms are more susceptible to toxicants
• Infants and children are more susceptible due to rapid physical development, elderly are more susceptible due to decreased body functions
• Genetic makeup


  Typical variations in sensitivity to a toxic chemical within a population, mostly because of differences in genetic makeup
• How to assess the toxicity of a substance

  1. Most often with laboratory tests involving living organisms

  2. Develop dose-response curves

  3. LD50 or LC50: dose or concentration resulting in 50% effects

  
• Bioaccumulation and Biomagnification of DDT


  • DDT causes thinning of egg shells in birds
  • 1962: Rachel Carson published Silent Spring, the book that pioneered the modern environmental movement
  • DDT was banned from most countries in the 1970s, and raptor populations bounced back
• Rachel Carson (1907 - 1964): marine biologist and nature writer
• In the world over the past 50 years: 1 new substance registered every 2.5 minutes in the Chemical Abstract Service (CAS) registry, the world's largest database of chemical substances
• In Canada, the legislation that regulates chemical substances available for commercial use is the Canadian Environment Protection Act (CEPA)
• Pollution prevention


  Using the precautionary principle - those proposing to introduce a new chemical or technology would bear the burden of establishing its safety, and existing chemicals that appear to have a strong chance of causing significant harm would be removed from the market until their safety can be established
• The precautionary principle could make it too expensive/almost impossible to introduce any new chemical or technology, but it may also encourage innovation in developing less harmful alternative chemicals