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Risk, Toxicity, and Human Health. Annual death in US in 2000. Cigarette smoking. Kills 13,400 people per day, 560 per hour, 1 every 6 seconds
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Cigarette smoking • Kills 13,400 people per day, 560 per hour, 1 every 6 seconds • WHO – tobacco helped kill 70 million people between 1950 – 2002, more than twice the 30 million people killed in battle in all wars during the 20th century.
Risk is the possibility of suffering harm from a hazard that can cause injury, disease, economic loss, or environmental damage. • Hazard – danger
Major types of Hazards • Cultural hazards such as unsafe working condition, smoking, poor diet, drug, drinking, driving, criminal assault, unsafe sex, and poverty. • Chemical hazards from harmful chemicals in the air, water, soil, and food.
Physical hazards such as ionizing radiation, fires, earthquakes, volcanic eruption, floods, tornadoes, and hurricanes. • Biological hazards from pathogens (bacteria, viruses, and parasites), pollen and other allergens, and animals such as bees and poisonous snakes.
Toxicity • Measures how harmful a substance is. • This depends on several factors : • Dose • Frequency of exposure • Who is exposed • How well the body’s detoxification system work (liver, lungs, kidneys) • Genetic makeup
Substance factors • Solubility. Water soluble toxin (usually inorganic compound) can get into water supplies, and Fat soluble toxin (usually organic compounds) can accumulate in body tissues and cells. • Persistence. Many chemicals such as chlorofluorocarbons, chlorinated hydrocarbons, and plastics are used widely because of their persistence or resistance to breakdown. However this persistence also means they can have long lasting effects on the health of wildlife and people.
Substance factors • Bioaccumulation – some molecules are absorbed and stored in specific organs or tissues at higher than normal levels. • Biomagnification – levels of some toxins in the environment are magnified as they pass through food chains and webs. Examples : pesticides DDT (fat soluble organic compound). Stored in body fat, such chemicals can be passed along to offspring during gestation or egg laying and as mothers nurse their young.
Chemical reactions • Antagonistic interaction – can reduce harmful effects. Example : vitamin E and A apparently interact to reduce the body’s response to some cancer-causing chemicals. • Synergistic interaction – multiplies harmful effects. Example : workers exposed to tiny fibers of asbestos increase their chances of getting lung cancer 20-fold. But asbestos workers who also smoke have a 400-fold increase in lung cancer rates.
Response – the type and amount of health damage that result from exposure to a chemical or other agent. • Acute effect – is an immediate or rapid harmful reaction to an exposure-ranging from dizziness or a rash to death. • Chronic effect – is a permanent or long lasting consequences of exposure to a harmful substance. Example : kidney or liver damage.
Basic concept of toxicity is that any synthetic or natural chemical (even water) can be harmful if ingested in a large enough quantity. Example : drinking 100 cups of strong coffee can exposed to lethal dosage of caffeine. Downing 100 tablets of aspirin or 1 liter of pure alcohol (ethanol) would kill most people.
Chemical Hazards • Toxic chemicals – are substances fatal to more than 50% of test animals at given concentration. • Hazardous chemicals – are flammable or explosive, irritate or damage the skin or lungs, interfere with oxygen uptake, or induce allergic reactions.
Types of toxic agents • Mutagens – that cause random mutations, or changes, in the DNA molecules found in cells. • Teratogens – that cause birth defects while the human embryo is growing and developing during pregnancy. • Carcinogens – that cause or promote the growth of a malignant (cancerous) tumor, in which certain cells multiply uncontrollably. • Metastasis – when malignant cells break off from tumors and travel in body fluids to other parts of the body. • 10-40 years may elapse between the initial exposure to a carcinogen and the appearance of detectable symptoms. Smoking, drinking, eating, and other lifestyle habits today of teenagers and young adults could lead to some form of cancer before age 50.
If you take care of your body on the first 40 years of your life, your body will take care of you on the next 40 years of your life.
Hormonal Active Agents • Hormone mimics – are chemicals similar to estrogens (female sex hormones). They disrupt the endocrine system by attaching to estrogen receptor molecules. • Hormone blockers – disrupt the endocrine system by preventing natural hormones such as androgens (male sex hormones) from attaching to their receptors.
Example • Lake Michigan fish contaminated with endocrine disrupters (DDT, PCBs) failed to reproduce. Reduced penis size in test animals and in 118 boys born to women exposed to PCBs in 1979 spill in Taiwan. • Michigan State University, 1999 – female rats exposed to PCBs were reluctant to mate, could lower sex drive in women. • Estrogen mimics called PBBs got into cattle feed in Michigan, then to beef. Pregnant women ate beef (breast milk contain PBBs) had sons with undersize penises and malformed testicles.
“Toxicologist know a great deal about a few chemicals, a little about many, and next to nothing about most.” Risk assessment expert Joseph Rodricks.
US National Academy of Sciences – 10% of at least 75,000 chemicals in commercial use have been thoroughly screened for toxicity, and only 2% have been adequately tested to determine whether they are carcinogens, teratogens, or mutagens. Hardly any of the chemicals in commercial use have been screened for damage to the nervous, endocrine, and immune systems.
Federal and state governments do not regulate about 99.5% of the commercially used chemicals in US because : • Under laws, most chemicals are considered innocent until proven guilty • Not enough funds, personnel, facilities, and test animals. • Analyzing the combined effects of multiple exposures to various chemicals and the possible interactions of such chemicals is too difficult and expensive. Example : studying three chemical interactions of 500 most widely used industrial chemicals take 20.7 million experiments.
Biological Hazards • Nontransmissible Diseases – is not caused by living organisms, does not spread from one person to another, and tends to have multiple causes and develop slowly. Examples are cardiovascular (heart and blood vessel disorders), most cancers, diabetes, asthma, emphysema, and malnutrition.
Transmissible disease – is caused by living organism (such as bacterium, virus, protozoa, or parasite) and can spread from one person to another. These infectious agents are called pathogens. They are spread by air, water, food, body fluids, some insects, and other non human carriers (such as mosquitoes) called vectors.
As a country industrializes, it usually makes an epidemiological transition in which deaths from the infectious diseases of childhood decrease and those from the chronic diseases of adulthood (heart disease and stoke, cancer, and respiratory conditions) increase.
Since 1950, we have greatly reduced the incidence of infectious diseases and the death rates from such diseases, because : • Better health care • Antibiotics – for bacterial diseases • Vaccines – for viral diseases
Challenge • Infectious diseases still cause about 1 every 4 deaths each year – mostly in developing countries • Disease carrying bacteria have developed genetic immunity to widely used antibiotics. • Many disease transmitting species of insects (such as mosquitoes) have become immune to widely used pesticides that once helped control their populations.
War against infectious bacteria • A few bacteria in the colony have mutant genes that make them immune to the drug. A single mutant can pass such traits on to most of its offspring, which can amount to 16,777,216 in only 24 hours. • Bacteria can become genetically resistant to antibiotics they have never been exposed to. When a resistant and a nonresistant bacterium touch one another, they can exchange a small loop of DNA called a plasmid. This enables them to transfer genetic resistance to a disease from one organism to another.
Spread of harmful bacteria around the globe by human travel and the trade of goods. • Overuse of antibiotics (160). Half of antibiotics used to treat humans are prescribed unnecessarily. In many countries antibiotics are available without prescriptions, which promotes unnecessary use. • Overuse of pesticides is also a problem because it increases populations of pesticide resistant insects and other carriers of bacterial diseases.
Widespread use of antibiotics for livestock and dairy animals to control disease and to promote animal growth. Resistant strain as in animals can spread to humans through contact with infected animals or water and through food webs. 70,000 die/year from mostly preventable infections in hospitals.
Ways to prevent or reduce the incidence of infectious diseases • Increase research on tropical diseases and vaccines • Reduce poverty • Decrease malnutrition • Improve drinking water quality • Reduce unnecessary use of antibiotics • Educate people to take all of an antibiotic prescription
Reduce antibiotic use to promote livestock growth • Careful hand washing by all medical personnel • Immunize children against major viral diseases • Oral rehydration for diarrhea victims • Global campaign to reduce HIV/AIDS.
