Transcript toxicity
Risk and Toxicology Chapter 19 The Ebola virus causes a form of hemorrhagic fever, and was first recognized in Africa in 1976. The virus is transmitted through direct person-to-person contact and is one of the most virulent viruses known, with a mortality rate usually over 90%. TEM. TOXICITY AND HEALTH A toxin is any substance that is inhaled, ingested, or absorbed at sufficient dosages that it damages a living organism, and the toxicity of a toxin is the degree to which it is biologically harmful. Almost any substance that is inhaled, ingested or absorbed by a living organism can be harmful when it is present in large enough quantities—even water. In order for a substance to be harmful, all of the following must be considered: Dosage amount over a period of time Number of times of exposure Size and/or age of the organism that is exposed Ability of the body to detoxify that substance Organism's sensitivity to that substance (due, for example, to genetic predisposition, or previous exposure) Synergistic effect more than one substance combines to cause a toxic effect that's greater than any one component Five major factors can affect the harm caused by a substance. a. Solubility. Water-soluble toxins can move throughout the environment. Oil- or fat-soluble toxins (generally organic compounds) can penetrate the membranes surrounding an organism’s cells and accumulate in the body. b. Persistence of a substance is also important. Some substances resist breakdown and remain in the environment a long time and can have long-lasting harmful effects. c. Bioaccumulation is a third factor. Molecules are absorbed and stored in the body at higher than normal levels. d. Biomagnification is where toxins accumulate at greater levels as they are moved up from one trophic level to the next higher one. e. Chemical interactions can decrease or multiply the harmful effects of a toxin. An antagonistic interaction reduces the harmful effect, while a synergistic interaction multiplies the harmful effects Bioaccumulation within species Biomagnification within the food chain What is Toxicity? How is it Measured? Substances are usually tested for toxicity using a dose-response analysis. In a dose-response analysis, an organism is exposed to a toxin at different concentrations, and the dosage that causes the death of the organism is recorded. The information from a set of organisms is graphed and the resulting curve referred to as a dose-response curve. The dosage of toxin it takes to kill 50 percent of the test animals is termed LD50, and this value can be determined from the graph. A high LD50 indicates that a substance has a low toxicity, while and a low one indicates high toxicity. A poison is any substance that has an LD50 of 50 mg or less per kg of body weight. Dose-Response Curve Types of dose-response curves The dosage at which a negative effect occurs is referred to as the threshold dose. Two more terms you should know for the test are acute effect and chronic effect. An acute effect is an effect caused by a short exposure to a high level of toxin; a snake bite, for example, causes an acute effect. A chronic effect is that which results from long-term exposure to low levels of toxin; an example of this would be long-term exposure to lead paint in a house. What have we been exposed to? Industrial Chemicals Impact of Pesticides - Development Everyday chemicals – Smoking, asbestos, indoor air pollution “SickBuilding Syndrome” Examples from the Big Screen: Civil Action & Erin Brockovich There are three major types of potentially toxic agents. a. Mutagens are chemicals or ionizing radiation that cause or increase the frequency of random mutations in the DNA molecules. It is generally accepted that there is no safe threshold for exposure to harmful mutagens. b. Teratogens are chemicals that cause harm or birth defects to a fetus or embryo. Alcohol and thalidomide are examples of teratogens. c. Carcinogens are chemicals or ionizing radiation that cause or promote cancer. Major Pollution Events (Disasters): Bhopal Times Beach (dioxin) Love Canal Exxon Valdez (Alaska) , BP Gulf Oil Spill Chernobyl, Japan's Nuclear Reactor Disaster after 2011 Quake More Recent: Amazon Crude (Chevron) – 60 seconds – Politics of Pollution China’s cost of growth Table 9-1 Toxicity Ratings and Average Lethal Doses for Humans Toxicity Rating LD50 (milligrams per kg of body weight)* Average Lethal Dose† Examples Supertoxic Less than 0.01 Less than 1 drop Extremely toxic Less than 5 Less than 7 drops Nerve gases, botulism toxin, mushroom toxins, dioxin (TCDD) Very toxic 5–50 7 drops to 1 teaspoon Toxic 50–500 1 teaspoon to 1 ounce Moderately toxic 500–5,000 Slightly toxic 5,000–15,000 1 pint to 1 quart Essentially nontoxic 15,000 or greater More than 1 quart 1 ounce to 1 pint Potassium cyanide, heroin, atropine, parathion, nicotine Mercury salts, morphine, codeine Lead salts, DDT, sodium hydroxide, sodium fluoride, sulfuric acid, caffeine, carbon tetrachloride Methyl (wood) alcohol, ether, phenobarbital, amphetamines (speed), kerosene, aspirin Ethyl alcohol, Lysol, soaps Water, glycerin, table sugar *Dosage that kills 50% of individuals exposed †Amounts of substances in liquid form at room temperature that are lethal when given to a 70.4-kg (155-pound) human Pathogens An infection is the result of a pathogen invading our body, and disease occurs when the infection causes a change in the state of health. For example, HIV, the virus that causes the disease AIDS, infects the body and typically has a long residence time before it causes a change in the state of health; in the form of the disease called AIDS. There are five main categories of pathogens. • Viruses (and other subcellular infectious particles, such as prions) • Bacteria - Anthrax • Fungi • Protozoa – Malaria -Lifecycle • Parasitic worms – Examples Top Ten Killer Germs Pathogens are bacteria, virus, or other microorganisms that can cause disease. Pathogens can attack directly or via a carrier organism (called a vector). One example of a pathogen that relies on a vector is the bacteria that causes Rocky Mountain spotted fever; it is within the bodies of ticks, and when ticks bite humans, the bacteria is injected and causes the disease. Hot Zones Bioterrorism & antibiotic resistant disease The degree of likelihood that a person will become ill after exposure to a toxin or pathogen is called risk. Many environmental, medical, and public health decisions are based on potential risk. Calculating risk is referred to as risk assessment, and risk management uses strategies to reduce the amount of risk. The public health department is an organization that makes use of risk assessment and management; for example, they decide who can receive the flu shot each year. If the risk of getting the flu is high for a particular year, most of the population is encouraged to have the shot; however, if the risk seems small or the predicted flu stains are mild, only older people and the immunocompromised are advised to have the flu shot.