 background for teachers background information in the united states thousands of chemicals are consumed and utilized in everyday items such as food personal care products prescription drugs household cleaners and garden lawn care products the effects of many of these chemicals on humans are unknown moreover our use and disposal of these products ultimately contaminates our planet s soil water and air safeguarding public health and the quality of the environment depends on identifying the effects of these chemicals and the levels of exposure at which they may become hazardous as highschool students study the flow of matter and energy in natural systems they develop an understanding that important molecules and elements are continually recycled by studying toxicology students add to this understanding by examining that hazardous chemicals in natural systems also are passed along the food chain thus an herbicide used to kill weeds or a pesticide used to kill insects is not isolated to its target organism we are in fact all connected on this planet to each other and the risk to our own health must always be weighed against the benefit attained by using hazardous chemicals toxicology overlaps with many aspects of the sciences including biology chemistry physiology microbiology public health and pharmacology overall it is a science that studies toxins and their effect on biological systems mercury toxicology 101 routes of exposure ie how does mercury get into organisms  a human or other organism can be exposed to mercury from breathing in contaminated air from ingesting contaminated water or food or from having skin contact with mercury not all forms of mercury easily enter your body even if they come in contact with it so it is important to know which form of mercury you or a creature you are studying have been exposed to inorganic mercury or methylmercury and by which route air food or skin once it is absorbed into the bloodstream it travels rapidly to other parts of the body including the brain and kidneys toxicologists use certain terms to talk about routes of entry for toxic substances into the body you ll see these terms if you ever look at a materials safety data sheet msds for any chemical or substance  ingestion  if you were to swallow small amounts of inorganic mercury metal for example from a broken oral thermometer virtually none less than 001 of the mercury would enter your body through the stomach or intestines unless these organs were diseased even when a larger amount of mercury a half of a tablespoon was swallowed by one person very little entered the body methylmercury is the form of organic mercury that is most about 95 easily absorbed through the gastrointestinal tract after eating fish or other foods that are contaminated the methylmercury enters your bloodstream easily and travels rapidly to other parts of your body eating mercurycontaminated food is the primary pathway by which people and other organisms are exposed to mercury inhalation inorganic mercury compounds may evaporate slowly at room temperature and could enter your body easily if you were to breathe in the vapors when you breathe in mercury vapors most about 80 of the mercury enters your bloodstream directly from your lungs a small amount of the inorganic mercury can be changed in your body to metallic mercury and leave again as a mercury vapor when you exhale skin contact  only small amounts of methylmercury enter the bloodstream directly through the skin but other forms of organic mercury in particular dimethylmercury can rapidly enter the body through the skin note we won t be working with any dimethylmercury and the methylmercury in our study organisms will be tightly bound in those organisms and won t be able to move from those organisms into us by just skin contact what happens once mercury is in the body  once in your body inorganic metallic mercury can stay for weeks or months when mercury enters the brain it can be trapped in the brain for a long time metallic mercury in the blood of a pregnant woman can enter her developing child and cause developmental disabilities most metallic mercury will accumulate in your kidneys but some can also accumulate in the brain most of the metallic mercury absorbed into the body eventually leaves in the urine and feces while smaller amounts leave the body in the exhaled breath biomagnification students now have an understanding of how mercury acts as a poison within an individual organism now we will show them how mercury biomagnifies  bioaccumulation  bioaccumulation is the accumulation of higher and higher concentrations of potentially toxic chemicals in individual organisms it occurs in the case of chemicals that are ingested but cannot be broken down or excreted every time an organism eats an organism that contains mercury it takes in the mercury burden of that food item the methylmercury within the food item is a lipid soluble not water soluble chemical this means it cannot be removed from the body in urine which is waterbased instead methylmercury accumulates in different tissues within the body with every food item consumed more methylmercury is accumulated by the consumer and little of it can be excreted the methylmercury is stored in the consumer whether the consumer be an earthworm owl beetle copepod pickerel or human if any of these organisms is eaten then their body burden is in turn accumulated by their consumer if all you eat are small fish then you will accumulate all the mercury of every small fish you eat bioaccumulation of mercury depends on what an organism eats and the longevity of the organism biomagnification  biomagnification is the bioaccumulation occurring through several levels of a food chain biomagnification is the increase in concentration of a substance from one trophic level to the next biomagnification results from the fact that 1 mercury bioaccumulates within an organism and 2 organisms must consume a lot of other organisms to live biomagnification depends on what trophic level you are observing and how much mercury is present in the environment to begin with in summary although the methylmercury form of mercury is a very small fraction of the global mercury cycle it is by far the form most prevalent in the biosphere and therefore most important to us from a health perspective the  teacher s cheat sheet  includes a brief list of factors that affect how much mercury is in a system along with where it shows up in the system this list might help you as you think about how to guide your students inquiry  other resources additional background information    mercury in watersheds background background for teachers  