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Toxicology. Human Health. What Determines Whether a Chemical is Harmful?. Size of dose over a certain period of time How often an exposure occurs Who is exposed (adult or child?) How well the body can detox Genetic makeup of the individual. Harm Can Also be Affected by….

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Toxicology


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    1. Toxicology Human Health

    2. What Determines Whether a Chemical is Harmful? • Size of dose over a certain period of time • How often an exposure occurs • Who is exposed (adult or child?) • How well the body can detox • Genetic makeup of the individual

    3. Harm Can Also be Affected by… • Solubility: can the toxin get into the water supply? • Persistence: does not break down easily; long-lasting effects on people and animals • Biomagnification: some toxins are magnified as they pass through food chains • Chemical interactions: can multiply harmful effect of a toxin

    4. DDT in fish-eating birds (ospreys) 25 ppm DDT in large fish (needle fish) 2 ppm DDT in small fish (minnows) 0.5 ppm DDT in zooplankton 0.04 ppm DDT in water 0.000003 ppm, Or 3 ppt BIOACCUMULATION

    5. Toxicology Toxicology is the study of the adverse effects of chemicals on health. • toxicity is a measure of how harmful a substance is; • the amount of a potentially harmful substance that is ingested, inhaled, or absorbed through the skin is called the dose; • the resulting type & amount of damage to health are called the response; • two types of responses: • acute effect: immediate or rapid harmful reaction, e.g., dizziness, rash, death; • chronic effect: permanent or long–lasting consequence, e.g., asthma, kidney damage, heart disease;

    6. Determining Toxicity • Laboratory investigations (usually with test animals); • LD50 is the median lethal dose, the amount of a chemical received that kills 50% of animals (usually rats or mice) in a test population (usually 60–200 animals) within a 14–day period; • a poisonis legally defined as a chemical that has an LD50 of 50 milligrams or less per kilogram of body weight.

    7. Toxicity Rating Examples

    8. Mutagens, Teratogens, & Carcinogens • Mutagens: agents that cause random mutations (changes) in DNA. Example: mutations in sperm or egg cells can be passed on and cause bipolar disorder, cancer, hemophilia, Down Syndrome, etc. • Most mutations are harmless (DNA repair enzymes)

    9. Mutagens, Teratogens, & Carcinogens • Teratogens: chemicals, radiation, or viruses that cause birth defects during the first 3 months of pregnancy Examples: PCBs, steroid hormones, heavy metals (lead, mercury)

    10. Mutagens, Teratogens, & Carcinogens • Carcinogens: chemicals, radiation, or viruses that cause the growth of a cancerous (malignant) tumor—cells multiple uncontrollably and may spread by metastasis to other parts of the body • Examples: Cigarette smoke, occupational exposure, environmental pollutants, inheritance

    11. Children and Chemical Exposure • Children more susceptible to chemicals • Weigh less than adults • Bodies are still developing • Play on floors and lawns • Exposed to cleaning products and pesticides • Put things into their mouths • Diagram • Children in foothills not exposed to pesticides • Children in valley were exposed

    12. Chemical Testing

    13. How Concerned Should We Be? Most chemicals have threshold levels of exposure below which we are safe because… • Human body has ways of breaking down and diluting toxins • Cells have enzymes that repair damaged DNA • Some cells can reproduce fast enough to replace damaged cells

    14. 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.

    15. TOXICOLOGY: ASSESSING CHEMICAL HAZARDS • Some scientists and health officials say that preliminary but not conclusive evidence that a chemical causes significant harm should spur preventive action (precautionary principle). • Manufacturers contend that wide-spread application of the precautionary principle would make it too expensive to introduce new chemicals and technologies.

    16. How Would You Vote? • Should we rely more on the precautionary principle as a way to reduce the risks from chemicals and technologies? • a. No. Assuming that every chemical or technology is a serious health or environmental threat will lead to wasteful over-regulation, high costs and hinder the development of critically needed pesticides, plastics, and other commercial products. • b. Yes. Preventing the commercialization of harmful chemicals and technologies is better than dealing with the high costs of medical treatments and environmental damage.

    17. RISK ANALYSIS • Annual deaths in the U.S. from tobacco use and other causes in 2003. Figure 18-A