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Unit VI: Our Health and Our Future Chapter 20: The Environment & Human Health 20-1 Pollution and Human Health Pollution causes illness in 2 main ways: 1. directly – poisoning us 2. indirectly – many infectious diseases spread in polluted environments (ex. cholera, malaria) • WHO = World Health Organization Toxicology: study of the harmful effects of substances on organisms • Toxic: poisonous Know This Table • Toxicity: How dangerous is it? – Almost any chemical is harmful if ingested (taken in) in large enough amounts – Is the concentration of any particular chemical in the environment high enough to be harmful? • Dose: amount of a harmful chemical to which a person is exposed – Response: damage to health that results from exposure to a given dose – Persistent Chemicals: break down slowly in the environment (ex. DDT) • More people likely to come into contact • More likely to remain in the body – Dose-Response Curve: the relative effect of various doses of a drug or chemical on an organism – Threshold Dose: less than = no bad effect. greater than = worse effects Epidemiology: study of the spread of diseases • Epidemiologists – try to find the origins and preventive measures of outbreaks • Risk Assessment: estimate of the risk posed by an action or substance – Used to form government regulations on substances (by the EPA – Environmental Protection Agency) Pollution from Natural Sources • Usually become hazardous when concentrated above normal levels • Ex. Radon – gas seeps from granite bedrock into buildings people unknowingly breathe it in cause cancer • Particulates: particles in the air small enough to breathe into the lungs (ex. dust, soot) – Can cause lung irritation – making conditions like bronchitis and emphysema worse – Some natural sources: dust storm, volcanic eruption, wildfires • Heavy Metals – occur naturally in rocks and soil (ex. arsenic, cadmium, lead) – Most cause nerve damage when ingested beyond threshold dose Most Pollutants come from Human Activities • Only about 10% of commercial chemicals have been tested for their toxicity – About 1,000 new chemicals are introduced every year • Recent Improvements – U.S. regulations have helped reduce our exposure • Burning Fuels – in vehicles, home furnaces, power plants, factories – Creates an enormous amount of air pollutants (ex. carbon monoxide, many particulates) – Gasoline & Coal burning contribute to many premature deaths each yr. from asthma, heart disease & lung disorders – It may be possible to predict an area’s death rate based on the amount of pollution • Pesticides: chemicals designed to kill unwanted organisms (insects, fungi, weeds) – Allow us to grow more food by reducing pest damage – :( Often dangerous to humans in large doses – Most in the U.S. break down quickly in the environment into harmless substances – Organophosphates: pesticides that replaced persistent pesticides like DDT • BUT… are very toxic causing nerve damage and perhaps cancer – Persistent Chemicals – still used in many developing countries • Pose greatest risk to children – internal organs are still developing, eat & drink more in relation to body weight than adults • Industrial Chemicals – Exposed to low levels every day – Especially in new buildings w/ new furnishings – In building materials, carpets, cleaning fluids, furniture, etc. – Older buildings often have lead-based paint (directly linked to brain damage & learning disabilities) – Often not known to be toxic until used for many years • Ex. PCBs (polychlorinated biphenyls) – oily fluids used as insulation in electrical transformers – don’t break down in the environment – children in the womb can develop learning problems and IQ deficits – pregnant women warned not to eat fish from the Great lakes – adults develop memory loss • Waste Disposal – much of our pollution is a byproduct of inadequate waste disposal – Methods have improved – Many old landfills are leaking – Many communities still release raw sewage into a river or the ocean after heavy rains – Laws are not always enforced – Radioactive Waste - US government has not decided how to dispose of waste from nuclear power plants • Most is stored in barrels at or near the plants • Small quantities of radioactive elements leak into nearby waterways 20-2 Biological Hazards • Pathogens: organisms that cause disease (cause most of the diseases that have an environmental component) • Host: an organism in which a pathogen lives all or part of its life The Most Deadly Infections Diseases Worldwide Waterborne Disease • Almost 75% of infectious diseases are transmitted through water • Vectors: organisms that transmit diseases to people (i.e. mosquitoes) • Widespread construction of irrigation canals and dams has increased the habitat for vectors • Cholera & Dysentery – enter the water in human feces, cause dehydration by diarrhea & vomiting – Cause most of the infant mortality around the world • Malaria: caused by parasitic protists, transmitted by mosquitoes, no effective vaccine exists Environmental Change & Disease • Soil Erosion spreads pathogens, parasites, and chemicals in polluted soil • Antibiotic Resistance – Large quantities fed to livestock – Salmonella, E. coli and other bacteria live in livestock and evolve resistance to antibiotics – Misuse of antibiotics in humans has led to drug-resistant strains of pneumonia and tuberculosis (TB) • Malaria: mosquitoes that transmit it live in warm places – Global warming may increase the range of malaria – Historically combated with pesticides – mosquitoes have evolved resistance – Newer methods involve spraying growth regulators Environmental Change & Disease • Emerging Viruses: previously unknown viruses – Ex. AIDS (acquired immune deficiency syndrome) – caused by HIV (human immune deficiency virus), hanta virus, Ebola virus, West Nile virus – Not many effective drugs to fight viral diseases – Main defense is vaccinations • But… vaccines are very specific and viruses evolve rapidly Environmental Change & Disease • Cross-Species Transfers: pathogens move from one species to another (on the rise) – HIV & West Nile have lived for centuries in some species w/ little damage – Some ecologists think the way we are altering the environment & destroying habitats ensure that diseases like these will become more common in the future. – Examples • Hanta Virus – carried by rodents – cause internal bleeding • Influenza (flu) – highly contagious – The Greatest Threat to Human Health (as predicted by epidemiologists): • Outbreak of a new, very virulent strain of flu virus – spread rapidly through crowded urban populations