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TOXICOLOGY AND HUMAN HEALTH © 2011 Pearson Education, Inc. The four types of environmental hazards • Physical hazards = occur naturally in our environment - Earthquakes, volcanoes, fires, floods, droughts - We can’t prevent them, but we can prepare for them - We increase our vulnerability by deforesting slopes (landslides), channelizing rivers (flooding), etc. - We can reduce risk with better environmental choices • Chemical hazards = synthetic chemicals such as pharmaceuticals, disinfectants, pesticides - Harmful natural chemicals (e.g., venom) also exist © 2011 Pearson Education, Inc. • Biological hazards = result from ecological interactions - Viruses, bacteria, and other pathogens - Infectious disease = species parasitize humans, fulfilling their ecological roles - Vector = an organism that transfers a pathogen to a host - We can’t avoid risk, but we can reduce infection • Cultural = result from where we live, our socioeconomic status, our occupation, our behavioral choices - We can minimize some, but not all, of these hazards - Smoking, drug use, diet and nutrition, crime, mode of transportation - Health factors (e.g., living near toxic waste) are often correlated with poverty © 2011 Pearson Education, Inc. Four types of environmental hazards © 2011 Pearson Education, Inc. Disease is a major focus of environmental health • Despite our technology, disease kills most of us • Disease has a genetic and environmental basis - Cancer, heart disease, respiratory disorders - Poverty and poor hygiene foster illnesses © 2011 Pearson Education, Inc. Infectious diseases kill millions • Infectious diseases kill 15 million people/year - Half of all deaths in developing countries • Money lets developed countries have access to hygiene and medicine © 2011 Pearson Education, Inc. Health workers fight disease • The best way to reduce disease? Improve the basic living conditions of the poor - Food security, sanitation, clean drinking water • Expanded access to health care - Health clinics, immunizations, pre- and postnatal care • Education campaigns work in rich and poor nations - Public service and governments give advice - Packaging and ads advise us on smoking, etc. - Sex and reproductive health education slows population growth and spread of HIV/AIDS © 2011 Pearson Education, Inc. Toxicology studies poisonous substances • Toxicology = the study of the effects of poisonous substances on humans and other organisms - Toxicity = the degree of harm a toxicant can inflict - Toxicant = any toxic substance (poison) - “The dose makes the poison” = toxicity depends on the combined effect of the chemical and its quantity • Environmental toxicology = deals with toxic substances that come from or are discharged into the environment - Studies health effects on humans, other animals, and ecosystems © 2011 Pearson Education, Inc. Toxic substances in the environment • The environment contains natural chemicals that may pose health risks • Toxins = toxic chemicals made in tissues of living organisms or synthetically by humans - Every human carries traces of industrial chemicals The U.S. makes or imports 250 lb of chemicals for every person in the country © 2011 Pearson Education, Inc. Examples: Indoor environmental toxins • Radon = a highly toxic, radioactive gas that is colorless and undetectable - It can build up in basements • Asbestos = a mineral that insulates, muffles sounds, and resists fire - Asbestosis = scarred lungs that cease to function © 2011 Pearson Education, Inc. Chemicals are in the air, water, and soil • 80% of U.S. streams contain 82 contaminants - Antibiotics, detergents, drugs, steroids, solvents, etc. • 92% of all aquifers contain 42 volatile organic compounds (from gasoline, paints, plastics, etc.) - Less than 2% violate federal health standards for drinking water Pesticides are present in streams and groundwater in levels high enough to affect aquatic life © 2011 Pearson Education, Inc. Lead poisoning • Lead poisoning = caused by lead, a heavy metal - Damages the brain, liver, kidney, and stomach - Causes learning problems, behavior abnormalities, and death • Exposure is from drinking water that flows through lead pipes or from lead paint Education led to declines in poisoning, but China still used it in toy paint until recently © 2011 Pearson Education, Inc. Synthetic chemicals are in all of us • Every one of us carries traces of hundreds of industrial chemicals in our bodies - Including toxic persistent organic pollutants restricted by international treaties • Babies are born “pre-polluted” – 232 chemicals were in umbilical cords of babies tested • Not all synthetic chemicals pose health risks - But very few of the 100,000 chemicals on the market have been tested © 2011 Pearson Education, Inc. A recently recognized hazard • Polybrominated diphenyl ethers (PBDEs) = has fireretardant properties - Used in computers, televisions, plastics, and furniture - Persist and accumulate in living tissue - Mimic hormones and affect thyroid hormones - Also affect brain and nervous system development and may cause cancer • Concentrations are rising in breast milk - Now banned in Europe, concentrations have decreased - The U.S. has not addressed the issue © 2011 Pearson Education, Inc. Case: Poison in the bottle: is bisphenol A (BPA) safe? • BPA causes cancer, nerve damage, and miscarriages - In extremely low doses • It is in hundreds of products - Cans, utensils, baby bottles, laptops, toys • BPA leaches into food, water, air, and bodies - 93% of Americans have it in their bodies © 2011 Pearson Education, Inc. Bisphenol A mimics estrogen • BPA mimics estrogen, a female hormone - Effects occur at lower levels than set by regulatory agencies • Researchers, doctors, and consumer advocates want regulation - The chemical industry insists it is safe • Some countries and states have banned it - Many companies are removing it voluntarily © 2011 Pearson Education, Inc. Toxicants come in different types • Carcinogens = cause cancer - Hard to identify because of the long time between exposure and onset of cancer • Mutagens = cause DNA mutations - Can cause cancer • Teratogens = cause birth defects in embryos • Neurotoxins = assault the nervous system • Allergens = overactivate the immune system • Endocrine disruptors = affect the endocrine (hormone) system © 2011 Pearson Education, Inc. Endocrine disruptors mimic hormones • Hormones stimulate growth, development, sexual maturity • Synthetic chemicals - Block hormones - Mimic hormones © 2011 Pearson Education, Inc. Many products mimic female hormones • Bisphenol A binds to estrogen receptors • Phthalates in plastics disrupt hormones - Toys, perfumes, makeup - Birth defects, cancer, reproductive effects - In the bodies of everyone in the U.S. © 2011 Pearson Education, Inc. Toxins may concentrate in water • Runoff carries toxins from land to surface water • Chemicals in the soil can leach into groundwater - Contaminating drinking water • Chemicals enter organisms through drinking or absorption - Aquatic organisms (fish, frogs, etc.) are good pollution indicators • Contaminants in streams and rivers enter drinking water and the air © 2011 Pearson Education, Inc. Routes of chemical transport © 2011 Pearson Education, Inc. Airborne substances can travel widely • Chemicals can travel by air - Their effects can occur far from the site of use • Pesticide drift = airborne transport of pesticides • Synthetic chemicals are found globally - In arctic polar bears, Antarctic penguins, and people in Greenland © 2011 Pearson Education, Inc. Some toxicants persist • Toxins can degrade quickly and become harmless - Or they may remain unaltered and persist for decades - Rates of degradation depend on the substance, temperature, moisture, and sun exposure • Breakdown products = simpler products that toxicants degrade into - May be more or less harmful than the original substance - DDT degrades into DDE, which is also highly persistent and toxic © 2011 Pearson Education, Inc. Toxicants can accumulate and biomagnify • Toxicants in the body can be excreted, degraded, or stored - Fat-soluble toxicants are stored in fatty tissues • Bioaccumulation = toxicants build up in animal tissues • Biomagnification = concentrations of toxicants become magnified - Near extinction of peregrine falcons and bald eagles © 2011 Pearson Education, Inc. Not all toxicants are synthetic • Toxic chemicals also exist naturally and in our food - Don’t assume natural chemicals are all healthy and synthetic ones are all harmful • Some scientists feel that natural toxicants dwarf our intake of synthetic chemicals - Natural defenses are effective against synthetics • Environmentalists say synthetic toxins: - Are harder to metabolize and excrete - Persist and accumulate - Enter people in ways other than in food © 2011 Pearson Education, Inc. Wildlife studies integrate field and lab work • Museum collections provide data from times before synthetic chemicals were used • Measurements from animals in the wild can be compared to controlled experiments in the lab Alligators and frogs show reproductive abnormalities due to endocrine disruption from pesticides © 2011 Pearson Education, Inc. Human studies • Case history approach = studies individual patients - Autopsies tell us about lethal doses - Don’t tell about rare, new, or low-concentration toxins - Don’t tell about probability and risk • Epidemiological studies = large-scale comparisons between exposed and unexposed groups - Studies can last for years - Yield accurate predictions about risk - Measure an association between a health hazard and an effect – but not necessarily the cause of the effect © 2011 Pearson Education, Inc. Manipulative experiments show causation • Animals are used as test subjects • Mammals share evolutionary history - Substances that harm rats and mice probably harm us • Some people object to animal tests - Medical advances would be far more difficult without them • New techniques may replace some live-animal testing - Human cell cultures, bacteria, etc. © 2011 Pearson Education, Inc. Dose-response analysis • Dose-response analysis = measures the effect a toxicant produces or the number of animals affected - At different doses • Dose = amount of substance the test animal receives • Response = the type or magnitude of negative effects • Dose-response curve = the dose plotted against the response © 2011 Pearson Education, Inc. Dose response curves • LD50/ED50= the amount of toxicant required to kill (affect) 50% of the subjects - A high number indicates low toxicity • Threshold dose = the level where certain responses occur - Organs can metabolize or excrete low doses of a toxicant Scientists extrapolate downward from animal studies to estimate the effect on humans © 2011 Pearson Education, Inc. Individuals vary in their responses to hazards • Different people respond differently to hazards - Affected by genetics, surroundings, etc. - People in poor health are more sensitive - Sensitivity also varies with sex, age, and weight - Fetuses, infants, and young children are more sensitive • The Environmental Protection Agency (EPA) sets standards for responses based on adult responses - Often, standards are not low enough to protect babies © 2011 Pearson Education, Inc. The type of exposure affects the response • Acute exposure = high exposure to a hazard for short periods of time - Easy to recognize - Stem from discrete events: ingestion, oil spills, nuclear accident, etc. • Chronic exposure = low exposure for long periods of time - More common but harder to detect and diagnose - Affects organs gradually: lung cancer, liver damage - Cause and effect may not be easily apparent © 2011 Pearson Education, Inc. Perceptions of risk may not match reality Everything we do involves some risk • We try to minimize risk - But perception may not match reality - Flying versus driving • We feel more at risk when we do not control a situation - We fear nuclear power and toxic waste - But not smoking or overeating © 2011 Pearson Education, Inc. Analyzing risk quantitatively • Risk assessment = the quantitative measurement of risk - Compares risks involved in different activities or substances - It identifies and outlines problems • Risk assessment has several steps: - The scientific study of toxicity - Assessing an individual or population’s exposure to the substance (frequency, concentrations, length) • Teams of scientific experts review hundreds of studies - Regulators and the public benefit from informed summaries © 2011 Pearson Education, Inc. Risk management • Risk management = decisions and strategies to minimize risk • Federal agencies manage risk - The U.S. has the Centers for Disease Control (CDC), the EPA, the Food and Drug Administration (FDA) • Scientific assessments are considered with economic, social, and political needs and values • Comparing costs and benefits is hard - Benefits are economic and easy to calculate - Health risks (costs) are hard-to-measure probabilities of a few people suffering and lots of people not © 2011 Pearson Education, Inc. EPA regulation is only partly effective • The Toxic Substances Control Act (1976) = the EPA monitors chemicals made in or imported into the U.S. - The EPA can ban substances that pose excessive risk • Many health advocates think the TSCA is too weak - Of 83,000 chemicals, only five have been restricted - To push for more testing, toxicity must already be proven, but testing is minimal • Only 10% of chemicals have been tested for toxicity - Fewer than 1% are regulated - Almost none have been tested for endocrine, nervous, or immune system damage © 2011 Pearson Education, Inc. FIFRA (1974) • The Federal Insecticide, Fungicide, and Rodenticide Act - Charges the EPA with “registering” new pesticides manufacturers want to market • The EPA asks the manufacturer to provide information on safety assessments - The EPA examines ingredients, use, etc. to determine risks to people, other organisms, water, or air - It approves, denies, or sets limits on the chemical’s sale and use and approves language used on the label • Hazardous chemicals are approved if economic benefits outweigh hazards © 2011 Pearson Education, Inc. The Stockholm Convention on Persistent Organic Pollutants (POPs) • Enacted in 2004 and ratified by over 150 nations • POPs = toxic, persistent chemicals - Bioaccumulate and biomagnify - Can travel long distances • The “dirty dozen” = the 12 most dangerous POPs • The Stockholm Convention sets guidelines for phasing out these chemicals - Encouraging transition to safer alternatives © 2011 Pearson Education, Inc.