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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
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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
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
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
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
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