Toxicology: Chemical Risks

1. Toxicology: Chemical Risks Ch 17 APES

2. CHEMICAL HAZARDS • A toxic chemical can cause temporary or permanent harm or death. • Mutagens • chemicals or forms of radiation that cause or increase the frequency of mutations in DNA. • Type of carcinogen • Carcinogens • chemicals or types of radiation that can cause or promote cancer. • Teratogens • chemicals that cause harm or birth defects to a fetus or embryo. • Allergens • Chemicals that cause allergic reactions. Can cause abnormally high response of the immune system

4. Mutagens • Ionizing Radiation • Gamma, X and UV • Radioactive decay • PAH – polycyclic aromatic hydrocarbons If affect sperm/egg can be passed down to children • Cystic Fibrosis, Down Syndrome, Sickle Cell Benzo[a]pyrene

5. Carcinogen • Asbestos (synergistic with smoking tobacco) • Acrylamide • Dioxins • BPA (bisphenol-A), PCB • Many chemicals in cigarette smoke • Viruses- HPV • Key factors in cancer risk: • #1 Smoking (30%) • #2 Diet (30%) • Phytochemicals in fruits and vegetables prevent cancers. • Not being overweight can prevent cancers • #3 Industrial Chemicals (30%) • Occupational (15), Environmental (10) • #4 Genetic (10%)

6. Teratogen • PCB’s (polychlorinated biphenyl ) • Herbicides • Thalidimide • Acutane (acne medicine) • Heavy Metals • Arsenic, lead, cadmium, mercury • Alcohol

7. Endocrine Disrupters • Chemicals that interfere with the normal functions of hormones. • Found in drinking water from sewage, farming, & pesticides that mimic animal hormones • Growth hormones in cattle etc., human birth control pills • Many male fish, amphibians, and reptiles becoming feminized: • Low sperm count • Testes that produce both egg and sperm • Examples: DDT, Atrazine (herbicide)

9. Effects of Chemicals on the Immune, Nervous, and Endocrine Systems • Endocrine Disruptors • p235 • Reduced penis size, female shellfish with male organs, decreased fertility rates, decreased sperm counts and endometirosis, early puberty Figure 18-9

10. CHEMICAL HAZARDS • A hazardous chemical can harm humans or other animals because it: • Is flammable • Is explosive • An irritant • Interferes with oxygen uptake • Induce allergic reactions.

11. Effects of Chemicals Immune, Nervous, and Endocrine Systems • Chronic vs. Acute • Long-term exposure to some chemicals at low doses may disrupt the body’s: • Immune system: affect cells and tissues that protect the body against disease and harmful substances. Synthetic Pesticides, PCB • Nervous system: brain, spinal cord, and peripheral nerves. DDT, Heavy Metals – Pb, Hg, Cd • Endocrine system: complex network of glands that release minute amounts of hormones into the bloodstream. DDT, BPA, PCB, Dioxin, Pthalates, diethylstilbestrol (DES)

12. Industrial Disasters • Bhopal, India – • The world’s worst industrial accident occurred in 1984 at a pesticide plant in Bhopal, India. • An explosion at Union Carbide pesticide plant in an underground storage tank released a large quantity of highly toxic methyl isocyanate (MIC) gas. • 15,000-22,000 people died • Indian officials claim that simple upgrades could have prevented the tragedy. • Minamata, Japan – methylmercury, caused Minimata Disease • Love Canal – Industrial Waste near town and site turned school. NIAGARA FALLS, N.Y

13. Toxicity • Measurement of how harmful a substance is • Chemical or ionizing radiation • Depends on • Dose • Exposure • Age • Genetic Make-up of Individual • Detoxification System • Solubility • Persistence • Bioaccumulation • Biomagnification • Chemical Interactions

14. Dose-Response Studies • Expose organism to different amounts of a chemical and observe a variety of responses to: • Mortality (most common; i.e. LD-50) • Changes in behavior • Changes in reproduction • Measured as a concentration of a chemical in air, water or food. • Also measured as a dose – the amount of chemical absorbed/consumed by an organism • Because of their short duration (1-4 days) called acute studies.

15. Dose-Response Studies • Count how many die after exposure to each concentration • Data usually exhibits an S-shaped curve • Lowest dose no mortality • Threshold – dose at which effect can be detected • LD50 – measurement useful in comparing harmful effects of different chemicals • Important in assessing the toxicity of new chemicals to determine if the new chemical is more or less lethal • LD50 can be different among species and rats and mice are usually used to test LD50 in humans. Extrapolate to account for mass differences.

16. Toxicity - Dose • LD50 • Median lethal dose • The amount of chemical in 1 dose that kills 50% of animals within a 14 day period • Poison - LD50 of 50mg/kg of body weight

18. Toxicity - Dose • “The dose makes the poison” Paracelsus, 1540 • Supertoxic(dioxin, nerve gas and botulism toxin) • Extremely toxic (nicotine) • Very toxic (mercury salts, codeine) • Toxic (lead salts, caffeine, DDT) • Moderately Toxic (methyl alcohol, aspirin) • Slightly Toxic (ethyl alcohol, soap) • Essentially nontoxic (water)

19. Toxicity - Exposure • Methods of Exposure • Ingestion • Inhalation • Through Skin • How often and for how long? • Acute vs. Chronic

20. TOXICOLOGY: Exposure • Estimating human exposure to chemicals and their effects is very difficult because of the many and often poorly understood variables involved. Figure 18-11

21. Persistence • Bioacculumlation and Biomagnification • Lipid soluble • POP – persistent organic pollutants • PCB, Dioxin, DDT • Heavy Metals – methyl mercury, tetraethyl lead • Algal Blooms – “red tide” makes mussels toxic.

22. Fig. 11-4 p. 231 DDT and Bioaccumulation(absorbed or stored in organs) and Biomagnification (through a food chain)

23. TOXICOLOGY: genetic make-up • Typical variations in sensitivity to a toxic chemical within a population, mostly because of genetic variation. Figure 18-10

24. Other Studies • Chronic Studies: • Toxicology studies conducted over a long period of time. • Goal is to examine the long-term effects of chemicals on survival and impacts on reproduction • Retrospective vs. Prospective Studies: • Epidemiology – understanding the causes of disease in humans & wildlife • Retrospective Studies – monitor people who have been exposed to a chemical in the past. Ex: Bhopal, India – still monitoring people who were exposed. • Prospective Studies – monitor people who might be exposed to chemicals.