Chapter 17 Human Health and Environmental Risks

Three categories of human health risks physical biological chemical

Biological Risks Infectious diseases- those caused by infectious agents, known as pathogens. Examples: pneumonia and venereal diseases

Biological Risks Chronic disease- slowly impairs the functioning of a person’s body. Acute diseases- rapidly impair the functioning of a person’s body.

Historical Diseases Plague Malaria Tuberculosis

Emergent Diseases HIV/AIDS Ebola Mad Cow Disease Bird Flu West Nile Virus

Transmissible diseases Caused by living organisms Bacterium, virus, protozoan, or parasite = pathogen 1) vectors: nonhuman carriers 2) bacterium: one celled microorganism 3) virus: noncellular, infectious agent, a strand of nucleic acid (either DNA or RNA) wrapped in a protein coat virus must invade host cell and take over cell’s DNA to make more viruses

80% of all illnesses in developing countries are caused by waterborne infectious diseases e.g. diarrhea, hepatitis, cholera Note: when bacteria are treated with penicillin, survivors have mutant genes that make them immune to medication---> natural selection Epidemiological transition: industrialized, less infectuous, more chronic

Viral Diseases e.g. HIV, flu, hepatitus B, ebola, West Nile, rabies From , flu epidemic killed million people (massive epidemic = pandemic) Due to AIDS, life expectancy among 700 million in sub-Saharan Africa: 62-->42 years

Viral Diseases Once a viral infection starts, it is harder to fight than bacteria or protozoan infections 1) antibiotics are useless and increases resistance of bacteria 2) preventative vaccines are the only effective weapon

Tuberculosis Infects 9 million per year. Kills 1.7 million per year. Bacterium spreads by airborne droplets (coughing, talking) Half of infected people don’t know they are Most strains are genetically resistant to almost all previously effective antibiotics

Malaria - 2nd only to tuberculosis as a global health problem 45% of world population lives in regions where malaria is present Symptoms: chills, weakness, anemia Kills about 1 million people per year Spread by: anopheles mosquito bites person infected with plasmodium parasite (protozoa), mosquito later bites uninfected person, spreading disease Parasite invades red blood cells ---> decreases body’s ability to transport O 2 (anemia) ---> lower resistance

Malaria Spread of malaria was cut by draining swamps, spraying with insecticide, treating parasite with drugs Since 1970, disease has come back, mosquito became resistant to insecticides and parasite became resistant to drugs Spread is increasing because irrigation and hydropower has led to more breeding places, global warming has led to increased range

Chemical Risks Neurotoxins- chemicals that disrupt the nervous system Carcinogens- chemicals that cause cancer Teratogens- chemicals that interfere with the normal development of embryos or fetuses Allergens- chemicals that cause allergic reactions Endocrine disruptors- chemicals that interfere with the normal functioning of hormones in an animal’s body

Chemical Hazards Mutagens chemicals or radiation that causes mutations in DNA affects future generations may cause tumors in exposed person Teratogens chemicals, radiation or viruses that cause birth defects while embryo is growing (especially first 3 months) e.g. PCB’s, thalidomide (sleeping pill, never approved in US), mercury, etc

Chemical Hazards Carcinogens chemicals, radiation or viruses that cause growth of malignant tumors cancer can be spread by metastasis: malignant cells break off from tumors and travel in body fluids to other parts

Endocrine system set of glands that release hormones into the bloodstream 1) hormones control sexual reproduction, growth, behavior, mix of estrogens and androgens determines sex 2) hormones (key and lock) connect with receptor molecule and move onto nucleus to execute message

Endocrine Disrupters (human-made chemicals,DDT, PCBs) 1) thyroid disrupters cause growth, brain, weight, behavior disorders 2) more than 60 chemicals (HAAs) are identified e.g. dioxins (chlorinated hydrocarbons) are produced when chlorine compounds are incinerated (found in Agent Orange, defoliant used in Vietnam) e.g. PCB’s, pesticides, lead and mercury 3) can be biomagnified

Toxicology study of health affects caused by chemicals 1) toxicity: how harmful a chemical is 2) dose: amount of substance or radiation taken into body [acute (one dose), chronic (lifetime of doses)] 3) response: type and amount of damage to health a) acute effect: immediate, rapid reaction to dose b) chronic: permanent or long lasting result

Dose-Response Studies LD50- lethal dose that kills 50% of the individuals ED50- effective dose that causes 50% of the animals to display the harmful but nonlethal effect

Dose synergistic effects (antagonistic effects) e.g. NO 2, O 3 react synergistically with allergens LD50 dose required to kill 50% of test population a) poison: chemical with an LD50 of 50 mg or less per kg of body weight EPA lists top 5 toxic substances: arsenic, lead, mercury, vinyl chloride (PVC), PCBs

Dose-response curve Shows effects of various doses of a toxic agent on a group of test organisms Requires a controlled experiment (test group vs control group) To save time and money, high doses are used and results are extrapolated to lower doses (and to human response, which is controversial)

© 2004 Brooks/Cole – Thomson Learning Effect Dose Nonlinear dose-response Linear dose-response No threshold Effect Threshold level Dose Usually used

Synergistic interactions- when two risks come together and cause more harm that one would. For example, the health impact of a carcinogen such as asbestos can be much higher if an individual also smokes tobacco.

Routes of Exposure

Bioaccumulation bioaccumulation- an increased concentration of a chemical within an organism over time

Bioaccumulation (typically occurs in organisms low on food chain) a) toxins accumulate in fat cells over time b) biological half-life: time required for 1/2 of chemical to be removed c) water soluble toxins pass through in urine

Biomagnification (high on food chain) a) each consumer ingests toxins accumulated by each organism lower on the food chain e.g. 10 minnows eat toxin. small fish eats 10 minnows. big fish eats 10 small fish. human eats big fish and the equivalent of 1000 minnows worth of toxin. DDT ---> zooplankton ---> insects ---> spiders --- > mice ---> falcon

Biomagnification Biomagnification- the increase in a chemical concentration in animal tissues as the chemical moves up the food chain.

Methods to determine toxicity (public health threat) 1) case reports (anecdotal info on rxn to chemical) 2) lab study (done on test animals) a) metabolites: products of body’s rxn to chemical 3) epidemiology a) study of human populations exposed to chemicals or diseases b)why do some get sick, others don’t

Hormesis Some substances that can kill us at high doses can be beneficial at low doses (digitalis)

Epidemiology Study of patterns of disease or toxicity to find out why some people get sick and others do not. Not useful for predicting affects of new technologies, substances or diseases. Because of uncertainty, standards for exposure to toxic chemicals or radiation are set at levels 100 to 1,000 times lower than estimated harmful levels

Epidemiological transition In 1994, 23 million people died of all causes 39% ---> heart attacks and strokes 24% cancer 5% infectious diseases (pneumonia, flu, aids) 4% accidents (2% auto)

Persistence Persistence- how long a chemical remains in the environment

Risk Analysis

Qualitative Risk Assessment Making a judgment of the relative risks of various decisions Probability- the statistical likelihood of an event occurring and the probability of that event causing harm

Quantitative Risk Assessment The approach to conducting a quantitative risk assessment is: Risk= probability of being exposed to a hazard X probability of being harmed if exposed

Stockholm Convention In 2001, a group of 127 nations gathered in Stockholm, Sweden, to reach an agreement on restricting the global use of some chemicals 12 chemicals were to be banned, phased out, or reduced These include DDT, PCBs, and certain chemicals that are by-products of manufacturing processes.