Risk and Toxicology What is Risk? the possibility of suffering harm from a hazard that can cause injury, disease, death, economic loss, or environmental damage expressed in terms of probability Risk Assessment vs. Risk Management risk assessment : the scientific process of estimating how much harm a particular hazard can cause to human health risk management : involves deciding whether or how to reduce a particular risk to a certain level and at what cost Four Major Types of Hazards cultural physical chemical biological Toxicology toxicity : a measure of how harmful a substance is in causing injury, illness, or death to a living organism depends on several factors: dose : the amount of a substance a person has ingested, inhaled, or absorbed through the skin frequency of exposure size of person exposed how well the bodys detox systems work genetic makeup Five Major Harm Factors 5 major factors that affect how harmful a substance is: solubility persistence bioaccumulation biomagnification chemical interactions Solubility water-soluble toxins usually inorganic can move through the environment and get into water supplies OR the solutions that surround our cells oil (fat)-soluble toxins usually organic can penetrate cell membranes and therefore can accumulate in body tissues and cells (e.g. DDT) Persistence resists breakdown can have long-lasting harmful effects Bioaccumulation when molecules are absorbed and stored in specific organs or tissues at higher than normal levels chemicals can build up to harmful levels in animals occurs in a single organism Biomagnification when levels of some potential toxins in the environment are magnified as they pass through food chains each animal in low trophic levels ingests a small amount an animal higher up eats a lot of the lower-level organisms Biomagnification Illustrated Chemical Interactions antagonistic interaction : reduces harmful effects synergistic interaction : multiplies harmful effects Types of Response response : the type and amount of health damage resulting from exposure to a chemical or other agent acute effect : an immediate or rapid harmful reaction to an exposure chronic effect : a permanent or long-lasting consequence from exposure to a single dose or to repeated sublethal doses of a harmful substance Basic Principle of Toxicology ANY chemical can be harmful if taken in large enough quantity the dose makes the poison depends on the genetic makeup of the individual Mechanisms for Reducing Harmful Effects the body can break down, dilute, or excrete small amounts of most toxins to keep them from reaching harmful levels cells can sometimes repair damage to DNA and proteins cells in some parts of the body can reproduce fast enough to replace damaged cells Toxicity Depends On what the chemical is! top 5 toxic substances are: arsenic lead mercury vinyl chloride (used to make PVC) polychlorinated biphenyls (PCBs) How Do We Estimate Toxicity? median lethal dose (LD 50 ) : the amount received in one dose that kills 50% of the animals in a test population dose-response curve : shows the effects of various dosages of a toxic agent on a group of test organisms typically use fairly high dosages Dose-Response Curve EC50 Human Health TOPIC 22 How Do We Estimate Toxicity for Humans? we use case studies and epidemiological studies i.e. accidental poisonings, overdoses, homicides, etc. we can extrapolate from high-dose studies on animals is this valid?? Chemical Hazards 3 major types of potentially toxic agents: mutagens teratogens carcinogens Mutagens chemicals or ionizing radiation that cause or increase the frequency of random mutations, or changes, in the DNA molecules found in cells most mutations are harmless harmful mutations in reproductive cells can be passed to offspring Teratogens chemicals that cause harm or birth defects to a fetus or embryo alcohol thalidomide Carcinogens chemicals or ionizing radiation that cause or promote cancer (i.e. the growth of a malignant tumor, in which certain cells multiply uncontrollably) there may be YEARS between initial exposure and the appearance of detectable symptoms metastasis : when malignant cells break off from tumors and travel in body fluids to other parts of the body Effects of Chemical Hazards on Humans effects can be seen in the: immune system nervous system endocrine system (network of glands that release hormones) Immune System chemicals (such as arsenic and dioxins), as well as ionizing radiation, can weaken the immune system makes the body vulnerable to allergens, bacteria, viruses, and protozoa Nervous System neurotoxins : inhibit, damage, or destroy nerve cells that transmit electrochemical messages throughout the body cause behavioral changes, paralysis, death e.g. PCBs, mercury Endocrine System hormones : chemicals that turn on/off bodily systems that control reproduction, growth, development, learning ability, and behavior hormone disrupters (hormonally active agents [HAAs]) hormone mimics hormone blockers thyroid disrupters Biological Hazards nontransmissable disease : caused by something other than a living organism and does not spread from one person to another e.g. cardiovascular disorders, diabetes, asthma, malnutrition transmissable disease : caused by a living organism and can spread from one person to another caused by infectious agents, or pathogens spread by vectors Types of Pathogens bacteria single-celled organisms that can replicate themselves by simple cell division viruses microscopic, noncellular infectious agents (must hijack living cells) parasites organisms that feed off other organisms protozoa a diverse assortment of microscopic or near-microscopic organisms that live as single cells or in simple colonies Epidemiological Transition as a country industrializes, deaths from childhood infectious diseases decrease and those from chronic disease of adulthood increase why? Considerations we are starting to see more genetic resistance of bacteria due to the overuse of antibiotics disease spreads more rapidly due to human travel and the trade of goods we cannot use antibiotics to deal with viruses! Most Widespread and Dangerous Viruses human immunodeficiency virus (HIV) transmitted by unsafe sex, sharing of drug needles, infected mothers to offspring before or during birth, and exposure to infected blood influenza (the flu) transmitted by the body fluids or airborne emissions of an infected person hepatitis B (HBV) transmitted in the same manner as HIV Recent Viruses that Have Received a Lot of Coverage Ebola transmitted by the blood or other body fluids of an infected person West Nile transmitted by the bite of a mosquito that has become infected by feeding on birds carrying the virus severe acute respiratory syndrome (SARS) transmitted by airborne droplets Problems with Viral Drugs drugs used to treat viruses also harm host cells vaccines stimulate the immune system to produce antibodies to ward off viral infections BUT vaccines are not available for all viruses Some Diseases are Making a Comeback! tuberculosis (TB) bacteria are transmitted through airborne droplets silent global epidemic factors: lack of screening antibiotic resistance urbanization malaria parasites are transmitted through mosquito bite infects and destroys red blood cells factors: mosquitoes are resistant to pesticides Plasmodium is resistant to drugs poverty