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Toxicology

Toxicology. Toxicology is the study of the adverse effects of chemicals on living systems, the mechanisms underlying those effects and the conditions under which they are likely to occur.

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Toxicology

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  1. Toxicology • Toxicology is the study of the adverse effects of chemicals on living systems, the mechanisms underlying those effects and the conditions under which they are likely to occur. “All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy” Pracelsus (1493-1541). • Environmental Toxicology is the study of the effects of incidental exposure of organisms and ecosystems to toxins in the environment (air, water and food).

  2. How can we classify toxicants? Acute Toxicity: occurs due to short-term exposure to high levels of toxic substance. Generally has a sudden onset for a short period of time (usually reversible). Chronic Toxicity: occurs due tolong-term exposure to low levels of toxic substance. Resulting health effect is generally of long or permanent duration (usually irreversible).

  3. How can we classify toxicants? Local Toxicity: occurs at the site of application or exposure. E.g. Acid on the skin Systemic Toxicity: requires absorption of the toxicant by the body and distribution via the bloodstream to target organ(s). E.g. Lead ingestion and neurological effects.

  4. Note Whether the toxic effects are systemic or local, they can be acute or chronic, and reversible or irreversible. E.g. Carbon tetrachloride

  5. Toxic Substance A toxic substance produces its adverse effect by interacting with humans (or organisms) and the environment in a relationship referred to as “the toxic triangle”.

  6. The Toxic Triangle Environment HAZARD Toxic Substance Host

  7. Factors that Affect Disease Development • Characteristics of the toxic substance • Characteristics of the host • Characteristics of the environment

  8. Factors That Affect the Outcome of an Exposure to a Toxicant • Chemical properties of toxicant • Concentration of toxicant • Length of exposure • Interactions between chemicals • Additive 1+1 = 2 • Synergism 1+1=5 • Potentiation 0+2=10 • Antagonism 4+6=8; 4+0=1 • Characteristics of exposed individual E.g. age, activity level, health status

  9. Factors That Affect the Outcome of an Exposure to a Toxicant • Absorption: entry into the body • Bioavailability: the rate at which a substance enters the blood. It affects the internal dose. • Biotransformation: metabolic processes that change the structure and characteristics of a chemical • Storage • Elimination

  10. What Are Some Toxicological Effects? • Infectious or Communicable Disease • Agent • Reservoir of infection (human, animal or non-living) • Transmission via contact, a vehicle (water, air or food) or a vector (animals). • Reproductive Toxicity: occurs when toxic substances affect the male or female reproductive system. • Developmental Toxicity (teratogenesis): occurs when when mistakes occur within genes (chromosomes) or when stages of fetal development are disturbed. • Neurotoxicity: damage to the neurological system. • Immunotoxicity: suppression of the immune system or production of exaggerated immune reactions. • Cancer:a result of multiple genetic and non-genetic effects that may lead to uncontrolled proliferation of cells.

  11. Some Examples of Toxic Agents Lead Exposure sources: water (leaching of pipes), food, air and leaded-paint in old housing. Since, 1980’s uses of Pb in gasoline, paint and solder have decreased but not in other parts of the world. Health effects: • Crosses placenta barrier, excreted in breastmilk • Slows normal maturation of RBCs and may lead to anemia • Interferes w/ synthesis of hemoglobin • Impairs fertility in males and females • Nervous system and developmental effects: delayed development in children, lower IQ, behavioral problems • Can cause kidney damage

  12. Some Examples of Toxic Agents Asbestos • is used in building material, bricks, cement, insulation, brake lining, tiles, radiator covers • It is hazardous when inhaled. The fiber is deposited in airways and lung cells (particularly the ones >1/5000 in. in size). Some are cleared via the mucociliary tract, others never leave the lung. Health effects: • Asbestosis, scarring of lung tissue • Lung Cancer, risk is 20-25%. • Mesothelioma: cancer of lung or stomach lining • GI cancer: causality not well-established Asbestos remediation: Encapsulation, enclosure or removal.

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