ENS 201 Chapter 8, Spring 2008

Environmental Health and Toxicology Chapter 8 To wish to become well is a part of becoming well. Seneca Outline: • Environmental Health Hazards  Infectious Organisms  Antibiotics and Pesticide Resistance  Toxic Chemicals • Movement and Fate of Toxins • Minimizing Toxic Effects • Measuring Toxicity • Risk Assessment Environmental Health • Health  A state of complete physical, mental, and social well-being • Disease  A deleterious change in the body’s condition in response to an environmental factor • Morbidity (illness) and mortality (death) are caused by:  Diet & nutrition, infectious agents, toxic chemicals, physical factors, and psychological stress • Environmental health focuses on external factors (natural, social, cultural, & social) that cause disease Infectious Organisms • Pathogens (disease-causing organisms):  Include viruses, bacteria, protozoans (single-celled animals), and parasitic worms  Cause communicable or Infectious diseases  Responsible of 1/3 of all disease-related mortality  Raging mainly in poorer countries with poor nutrition, sanitation, and vaccination programs • Pathogenic organisms and accidents or violence  the greatest health threats for most of human history • AIDS is now the leading cause of communicable death in the world Photos of influenza viruses, Giardia, and Guinea worm Antibiotic and Pesticide Resistance • A large number of disease-causing insects & microbes have acquired resistance against pesticides & antibiotics Why?  Natural selection & evolution – speeded up by the short life spans  Human tendency to overuse & unsafe use of pesticides and antibiotics • Example: The parasite that causes malaria is now resistant to most antibiotics, while the mosquitoes that transmit it have developed resistance to many insecticides How Microbes Acquire Antibiotic Resistance Antibiotic Use and Misuse • What leads to selection of resistant microorganisms? • Misuse  Not finishing full-course of treatment  Unnecessary or wrong drug • Overuse  Large quantities of antibiotics are routinely fed to farm animals to stimulate weight gain Harmful Chemicals • Two broad categories:  Hazardous - Dangerous - Flammable, explosive, irritant, acid, caustic  Toxic - Poisonous - Can be general or very specific - Often harmful even in dilute concentrations Toxic Chemicals • Allergens  Substances that activate the immune system  Are recognized as foreign by white blood cells and stimulate the production of specific antibodies  E.g.: Formaldehyde Toxic Chemicals • Endocrine disrupters (environmental estrogens or androgens)  Substances that disrupt normal hormone functions  Include dioxins and PCBs (Polychlorinated Biphenyl's): - Interfere with normal growth, development and physiology - Developmental abnormalities - Sexual dysfunction: reproductive health problems in females and feminization of males - Picogram concentrations (trillionths of a gram per liter) of environmental eustrogens or androgens can exert health effects Toxic Chemicals • Neurotoxins - Special poisons that specifically attack nerve cells • Different neurotoxins act in different ways - Heavy Metals: kill nerve cells - Anesthetics: disrupt nerve cell membranes - Pesticides (organophosphates, carbamates, & chlorinated hydrocarbons): inhibit signal transmission between nerve cells Toxic Chemicals • Mutagens - Agents that damage or alter genetic material (radiation, chemicals)  May trigger cancer (later in life)  Leads to birth defects during embryonic growth • Teratogens - Specifically cause abnormalities during embryonic growth and development  Alcohol - Fetal Alcohol Syndrome • Carcinogens - Substances that cause cancer (2nd leading cause of deaths worldwide).  E.g.: Cigarette smoke MOVEMENT, DISTRIBUTION, AND FATE OF TOXINS • Solubility - One of most important characteristics in determining the movement of a toxin through:  The environment  Through the body to its site of action • Chemicals are divided into two major groups:  Those that dissolve more readily in water (water soluble): - Move rapidly through the environment & have ready access to most human cells  Those that dissolve more readily in oil Movement & Fate of Chemicals in the Environment Routes of exposure to toxins and hazardous environmental factors Bioaccumulation and Biomagnification • Bioaccumulation:  Selective cellular absorption, storage, & buildup of a toxin to dangerous levels inside cells & tissues • Biomagnification:  Toxic burden of a large number of organisms at a lower trophic level is accumulated and concentrated by a predator at a higher trophic level - The effect of toxins are magnified in the environment through food webs Bioaccumulation & Biomagnification Persistence • Some chemical are very unstable and degrade rapidly under most conditions =>  Their concentrations decline quickly after release • Others are more persistent  Stability can cause problems as toxic effects may be stored for long period of time and spread to unintended victims - (DDT) Mechanisms for Minimizing Toxic Effects • Every material can be poisonous under certain conditions  Most chemicals have a safe threshold under which their effects are insignificant • Metabolic Degradation  In humans, the liver is the primary site of detoxification of both natural and introduced poisons • Excretion  Waste products of metabolism & environmental toxins can be excreted from the body via the lungs (by breathing) & the kidneys (by urine). MEASURING TOXICITY • Animal Testing  Most commonly used and widely accepted toxicity test is to expose a population of laboratory animals to measured doses of specific toxins under controlled conditions - Sensitivity differences pose a problem  Dose Response Curves  LD50 - Dose at which 50% of the test population is sensitive Establishing Public Policy • It is difficult to separate the effects of multiple hazards and evaluate their risks accurately, especially when exposures are near the threshold of measurement and response  May not be reasonable to mandate protection, no matter how small the risk, from every potentially harmful contaminant in our environment Natural systems loaded with toxic chemicals Unpolluted Ecosystems