<p>
	<b>BACKGROUND INFORMATION</b></p>
<p>
	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&rsquo;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.</p>
<p>
	As high-school 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.</p>
<p>
	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.</p>
<h3>
	<a name="TOC-Mercury-Toxicology-101"></a>Mercury Toxicology 101</h3>
<p>
	<i><b>Routes of exposure (i.e. how does mercury get into organisms?) </b></i></p>
<p>
	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 &ndash; you&rsquo;ll see these terms if you ever look at a Materials Safety Data Sheet (MSDS) for any chemical or substance:</p>
<p>
	<b>Ingestion</b>: If you were to swallow small amounts of <b>inorganic mercury</b> metal&ndash;for example, from a broken oral thermometer&ndash;virtually none (less than 0.01%) 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. <b>Methylmercury </b>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 mercury-contaminated food is the primary pathway by which people (and other organisms) are exposed to mercury.</p>
<p>
	<b>Inhalation: Inorganic mercury</b> 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.</p>
<p>
	<b>Skin contact:</b> Only small amounts of <b>methylmercury </b>enter the bloodstream directly through the skin, but other forms of organic mercury (in particular dimethylmercury) can rapidly enter the body through the skin. <b>Note: we won&rsquo;t be working with any dimethylmercury, and the methylmercury in our study organisms will be tightly bound in those organisms, and won&rsquo;t be able to move from those organisms into us by just skin contact. </b></p>
<p>
	<i><b>What happens once mercury is in the body? </b></i></p>
<p>
	Once in your body, inorganic metallic mercury can stay for weeks or months. When mercury enters the brain it can be &quot;trapped&quot; 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.</p>
<h3>
	<a name="TOC-Biomagnification"></a>Biomagnification</h3>
<p>
	Students now have an understanding of how mercury acts as a poison within an individual organism. Now we will show them how mercury &ldquo;biomagnifies.&rdquo;</p>
<ul>
	<li>
		<i>Bioaccumulation</i>: 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.
		<ul>
			<li>
				Every time an organism eats an organism that contains mercury, it takes in the mercury burden of that food item.</li>
			<li>
				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 water-based). Instead, methylmercury accumulates in different tissues within the body.</li>
			<li>
				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&ndash; 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.</li>
			<li>
				Bioaccumulation of mercury depends on what an organism eats and the longevity of the organism.</li>
		</ul>
	</li>
	<li>
		<i>Biomagnification</i>: Biomagnification is the bioaccumulation occurring through several levels of a food chain.
		<ul>
			<li>
				Biomagnification is the increase in concentration of a substance from one trophic level to the next.</li>
			<li>
				Biomagnification results from the fact that 1.) mercury bioaccumulates within an organism and 2.) organisms must consume a lot of other organisms to live.</li>
			<li>
				Biomagnification depends on what trophic level you are observing, and how much mercury is present in the environment to begin with.</li>
		</ul>
	</li>
</ul>
<p>
	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.</p>
<p>
	The <a href="http://participatoryscience.org/sites/default/files/2_teachers cheat sheet_0.pdf">&quot;Teacher&#39;s Cheat Sheet&quot;</a> 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 <u>how to guide your students&rsquo; inquiry</u>.</p>
<p>
	<font size="4">OTHER RESOURCES</font></p>
<h3>
	<a name="TOC-Additional-Background-Information"></a>Additional Background Information</h3>
<div>
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