BESC 201 10 7 2013 Lecture 16 Outline of Last Lecture I Environmental Health Outline of Current Lecture II Toxic Substances and Their Effects on Organisms III Toxic Substances and Their Effects on Ecosystems Current Lecture 10 7 2013 Toxicology is the study of chemical hazards Toxicology the science that examines the effects of poisonous chemicals on humans and other organisms Toxicity the degree of harm a chemical substance can inflict Toxicant a toxic substance or poison the dose makes the poison Environmental Toxicology deals specifically with toxic substances that come from or are discharged from the environment People face environmental health hazards indoors Cigarette smoke and radon are leading indoor hazards and are the top two causes of lung cancer Polybrominated Diphenyl Ethers PBDEs used as fire retardants in computers televisions plastics and furniture and evaporate at slow rates Risks must be balanced against rewards It is important to keep in mind that artificially produced chemicals have played a crucial role in giving us the standard of living seen today Toxic Substances and Their Effects on Organisms Toxins toxic chemicals manufactured in the tissues of living organisms Synthetic chemicals are all around us and in us Every one of us carries traces of hundreds of industrial chemicals in our bodies Our exposure to synthetic chemicals begins in the womb as substances our mothers ingested while pregnant were transferred to us o Born pre polluted Silent Spring changed public attitudes toward synthetic chemicals These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Brought insecticide dichlorodiphenyl trichloroethance DDT to the public s attention Developing countries with tropical climates use it to control disease vectors and malaria represents a greater health threat than do toxic effects of the pesticide It is possible that pesticide laden food can be imported back into the United States in what has been called a circle of poison Not all toxic substances are synthetic and not all synthetic chemicals are toxic It would be a mistake to assume that all artificial substances are unhealthy and that all natural substances are healthy Toxic substances come in different types Carcinogens substances or types of radiation that cause cancer Difficult to identify because there may be a long lag time between exposure to the agent and the detectable onset of cancer Mutagens substances that cause genetic mutations in the DNA of organisms Teratogens affect development of human embryos in the womb and can cause birth defects Neurotoxins assault the nervous system Famous case of neurotoxin poisoning occurred in Japan where a chemical factory dumped mercury waste into Minamata Bay people ate the fish contaminated with mercury and suffered Some toxic substances weaken the immune system Allergens overactivate the immune system causing an immune response when one is not needed Allergens are not universally considered toxicants because they affect some people but not others and because one s response does not necessarily correlate with the degree of exposure Pathway Inhibitors toxicants that interrupt vital biochemical processes by blocking one or more steps in important biochemical pathways Endocrine Disruptors toxic substances that interfere with the endocrine system The endocrine system consists of chemical messengers hormones that travel through the bloodstream at extremely low concentrations and have many vital functions Some substances can have multiple effects by being a carcinogen mutagen and endocrine disruptor Organisms have natural defenses against toxic substances Barriers such as skin scales feathers and fur are the first line of defense against toxic substances because they help the body resist uptake from the surrounding environment Organisms possess biochemical pathways that use enzymes to detoxify harmful chemicals Individuals vary in their responses to hazards The U S Environmental Protection Agency EPA typically set human chemical exposure standards for adults and extrapolate downward for infants and children The type of exposure can affect the response Acute Exposure high exposure for short periods of time Chronic Exposure low exposure over long periods of time Incidents of acute exposure are easier to recognize because they often stem from discrete events Toxic Substances and Their Effects on Ecosystems Cascading impacts can cause changes in the composition of the biological community and threaten ecosystem functioning Airborne substances can travel widely Because so many substances are carried by the wind synthetic chemicals are ubiquitous worldwide even in seemingly pristine areas Pesticide Drift pesticides carried by air currents to sites far away from agricultural fields Some toxicants persist The rate at which a given substance degrades depends on its chemistry and on factors such as temperature moisture and sun exposure Persistent synthetic chemicals exist in our environment today because we have designed them to persist Most toxic substances degrade into simpler compounds called breakdown products Toxicants may concentrate in water Toxic substances are not evenly distributed in the environment and they move about in specific ways Once concentrated in waters toxicants can move long distances through aquatic systems and affect a diversity of ecosystems Toxic substances may accumulate and move up the food chain Bioaccumulation fat and oil soluble toxicants accumulate in fatty tissues of animals Toxic substances that bioaccumulate in an organism s tissues may be transferred to other organisms as predators consume prey Biomagnification each individual predator consumes many individuals from the trophic level beneath it so with each step up the food chain concentrations of toxicants become magnified Toxic substances can threaten ecosystem services Toxicants can alter the biological composition of ecosystems and the manner in which organisms interact with one another and their environment