14- Toxicology

14- Toxicology - Toxicology and Environmental Health...

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Unformatted text preview: Toxicology and Environmental Health Environmental Problems Biol 1305 Environmental Hazards Environmental health = assesses environmental factors that influence human health and quality of life n Natural and human-caused factors are both considered Physical hazards = occur naturally in our environment n n n 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. Environmental Hazards Chemical = synthetic chemicals such as pesticides, disinfectants, pharmaceuticals n Harmful natural chemicals also exist Biological = result from ecological interactions n n n Viruses, bacteria, and other pathogens Infectious (communicable, or transmissible) disease = other species parasitize humans, fulfilling their ecological roles We can’t avoid risk, but we can reduce the likelihood of infection Environmental hazards Cultural = result from the place we live, our socioeconomic status, our occupation, our behavioral choices n Smoking, drug use, diet and nutrition, crime, mode of transportation Four types of environmental hazards cultural physical chemical biological Disease is a major focus of environmental health Despite our technology, disease kills most of us Disease has a genetic and environmental basis n n Cancer, heart disease, respiratory disorders Poverty and poor hygiene can foster illnesses Infectious diseases Infectious diseases kill 15 million people per year n n Half of all deaths in developing countries Developed countries have better hygiene, access to medicine, and money Vector = an organism that transfers pathogens to a host Many diseases are increasing Tuberculosis, acquired immunodeficiency syndrome (AIDS), and the West Nile virus Our mobility spreads diseases Diseases are evolving resistance to antibiotics Climate change will expand the range of diseases To predict and prevent diseases, experts deal with complicated interrelationships Indoor Environmental Hazards Radon = a highly toxic, radioactive gas that is colorless and undetectable n Can build up in basements Lead poisoning = from lead pipes n Damages organs; causes learning problems, behavior abnormalities, and death Asbestos = insulates, muffles sounds, and resists fire n Asbestosis = scarred lungs may cease to function A recently recognized hazard Polybrominated diphenyl ethers (PBDEs) = has fire-retardent properties n n n n Used in computers, televisions, plastics, and furniture Persist and accumulate in living tissue Endocrine disruptors = compounds that mimic hormones and interfere with the functioning of animals’ endocrine (hormone) systems Affect brain and nervous system development, and may cause cancer Toxicology = the study of the effects of poisonous substances on humans and other organisms Toxicity = the degree of harm a toxicant can cause n “The dose makes the poison” = toxicity depends on the combined effect of the chemical and its quantity Toxicant = any toxic agent Environmental toxicology Deals with toxic substances that come from or are discharged into the environment Studies the health effects on humans, other animals, and ecosystems n n Focus mainly on humans, using other animals as test subjects Can serve as indicators of health threats Don’t forget, chemicals have given us our high standard of living Toxic agents in the environment The environment contains countless natural chemicals that may pose health risks But, synthetic chemicals are also in our environment n Every human carries traces of industrial chemicals 80% of U.S. streams contain at least trace amounts of 83 wastewater contaminants Very few chemicals have been thoroughly tested 100,000 chemicals are on the market today n 72,000 industrial n 8,700 food additives n 2,000 new chemicals introduced per year We don’t know the effects, if any, they have Silent Spring began public debate over chemicals Rachel Carson published Silent Spring in 1962 n n Brought together studies to show DDT risks to people, wildlife, and ecosystems In the 1960s, pesticides were mostly untested and were sprayed over public areas, assuming they would do no harm The book generated significant social change Types of toxicants Carcinogens = cause cancer Mutagens = cause DNA mutations n Can lead to severe problems, including cancer Teratogens = cause birth defects Allergens = overactivate the immune system Neurotoxins = assault the nervous system Endocrine disruptors = interfere with the endocrine (hormone) system Endocrine disruption may be widespread Theo Colburn wrote Our Stolen Future in 1996 n n n Synthetic chemicals may be altering the hormones of animals This book integrated scientific work from various fields Shocked many readers and brought criticism from the chemical industry Evidence for hormone disruption Frogs also have gonadal abnormalities n Male frogs became feminized from atrazine concentrations well below EPA guidelines PCB-contaminated human babies were born weighing less, with smaller heads Male sperm counts are dropping Scientists attribute the shocking drop in men’s sperm counts to endocrine disruptors n The number and motility of sperm has dropped 50% since 1938 Testicular cancer, undescended testicles, and genital birth defects are also increasing Endocrine disruption research is controversial is inherent in Research results are uncertain, which any young field Negative findings pose economic threats to chemical manufacturers n n Banning a top-selling chemical could cost a company millions of dollars Bisphenol-A, found in plastics, can cause birth defects, but the plastics industry protests that the chemical is safe Studies reporting harm are publicly funded, but those reporting no harm are industry funded Toxins may concentrate in water Runoff carries toxins from large land areas to small volumes of surface water Chemicals can leach into the soil Chemicals enter organisms through drinking or absorption n Aquatic organisms are effective pollution indicators Routes of chemical transport Airborne toxicants travel widely Because chemicals can travel by air, their effects can occur far from the site of chemical use Pesticide drift = airborne transport of pesticides Synthetic chemical contaminants are found globally n They appear in arctic polar bears, Antarctic penguins, and people living in Greenland Toxicants persistence Toxins can degrade quickly and become harmless n n Or, they may remain unaltered and persist for decades Rates of degradation depends on temperature, moisture, sun exposure, and microbial exposure Persistent chemicals have the greatest potential for harm Breakdown products = toxicants degrade into simpler products n May be more or less harmful than the original substance Toxicants can accumulate and biomagnify Some toxicants can be excreted or metabolized n Fat-soluble toxicants are stored in fatty tissues Bioaccumulation = toxicants build up in animal tissues Biomagnification = toxicants concentrate in top predators n Near extinction of peregrine falcons and brown pelicans Not all toxicants are synthetic Chemical toxicants also exist naturally and in our food n Don’t assume natural chemicals are all healthy and synthetic ones are all harmful Natural toxicants intake may dwarf our intake of synthetic chemicals n n Natural defenses against toxins are effective against synthetic ones, too Critics say natural toxins are more readily metabolized and excreted, and synthetic chemicals persist and accumulate Wildlife studies 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 Scientists can first measure effects in the lab, then look for correlations in the wild Conspicuous mortality events can trigger research n n Many sea otters died and washed ashore Research showed they died from parasites carried in sewage runoff containing cat litter Human studies Case histories = studying sickened individuals directly n n Autopsies Don’t tell about future risks Epidemiology = large-scale comparisons between groups of people n n Studies between exposed and unexposed people last for years Yield accurate predictions about risk Animals are used as test subjects n n Some people object to animal research New techniques (human cell cultures, bacteria, etc.) may replace some live-animal testing Dose-response analysis “The dose makes the poison” Dose-response analysis = measuring how much effect a toxicant produces at different doses n n n n Animal testing Dose = the amount of toxicant the test animal receives Response = the type or magnitude of negative effects of the animal Dose-response curve = the plot of dose given against response LD50/ED50= the amount of toxicant required to kill (affect) 50% of the subjects Threshold = the dose level where certain responses occur n Organs can metabolize or excrete low doses of a toxicant Scientists extrapolate downward from animal studies to estimate the effect on humans n Regulatory agencies set allowable limits well below toxicity levels in lab studies Individuals vary in their responses to hazards Different people respond differently to hazards n n n n 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 Standards for responses are set by the Environmental Protection Agency (EPA) n Often, standards are not low enough to protect babies The type of exposure Acute exposure = high exposure for short periods of time to a hazard n n Easy to recognize Stem from discrete events: ingestion, oil spills, nuclear accident Chronic exposure = low exposure for long periods of time to a hazard n n n Hard to detect and diagnose Affects organs gradually: lung cancer, liver damage Cause and effect may not be easily apparent Mixes may be more than the sum of their parts We can’t determine the impact of mixed hazards n They may act in ways that cannot be predicted from the effects of each in isolation Synergistic effects = interactive impacts that are more than or different from the simple sum of their constituent effects n n Mixed toxicants can sum, cancel out, or multiply each other’s effects New impacts may arise from mixing toxicants Risk assessment Risk = the probability that some harmful outcome will result from a given action n n Exposure to environmental health threats doesn’t automatically produce an effect Rather, it causes some probability (likelihood) of harm Probability entails n n n n Identity and strength of threat Chance and frequency that an organism will encounter it Amount of exposure to the threat Perceiving risks Everything we do involves some risk We try to minimize risk, but we often misperceive it n Flying versus driving We feel more at risk when we cannot control a situation n We fear nuclear power and toxic waste, but not smoking or overeating Analyzing risk quantitatively Risk assessment = the quantitative measurement of risk and the comparison of risks involved in different activities or substances n It is a way of identifying and outlining problems Several steps: n n Scientific study of toxicity Assessing an individual or population’s likely exposure to a substance, including frequency, concentrations, and length of exposure Studies are often performed by industryassociated scientists, which may undermine Risk management Combines decisions and strategies to minimize risk Scientific assessments are considered with economic, social, and political needs and values Developed nations have federal agencies to manage risk n The U.S. has the Centers for Disease Control (CDC), the EPA, and the Food and Drug Administration (FDA) Comparing costs and benefits is hard n Benefits are economic and easy to calculate The process of risk management One approach to determining safety Innocent until proven guilty approach: product manufacturers must prove a product is safe n n Benefits: now slowing down technological innovation and economic advancement Disadvantage: putting into wide use some substances that may later on turn out to be dangerous Another approach to determining safety Precautionary principle approach: the government, scientists, and the public are required to prove a product is dangerous n n n Assume substances are harmful until they are proven harmless Identifies troublesome toxicants before they are released But, this may impede the pace of technology and economic advance Philosophy affects policy Different nations use different policies; most use a mix between the “innocent until proven guilty” principle and the precautionary principle n n Europe is shifting more towards the precautionary principle Industries like the “innocent until proven guilty” approach because it allows them to produce more and make more money The EPA regulates substances Federal agencies apportion responsibility for tracking and regulating synthetic chemicals n n n FDA: food, food additives, cosmetics, drugs, and medical devices EPA: pesticides Occupational Safety and Health Administration (OSHA): workplace hazards Many public health and environmental advocates fear it isn’t enough n n n Many synthetic chemicals are not actually tested Only 10% have been tested for toxicity Fewer than 1% are government regulated International regulation Nations address chemical pollution with international treaties Stockholm Convention on Persistent Organic Pollutants (POPs) was ratified by 140 nations in 2004 n Ends the release of the 12 most dangerous POPs EU’s Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) Program n n Aims to evaluate and restrict dangerous chemicals while giving industries a streamlined regulatory system It will cost the chemical industry 2.8 – 5.2 billion euros (U.S. $3.8 – 7.0 billion), but will save more than 10 times that in health benefits ...
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