Science Advocacy
Science Advocacy
Welcome to “chemicals and society” a new feature at UYBFS where we highlight the current understanding of the biological effects and safety of some of the most common chemicals in today’s society.
What is Mercury? Mercury is an element with an atomic number of 80. While mercury is a metal, it is a liquid at room temperature, which makes it both really cool and really useful. Mercury exists in many different forms, and the form that it’s in makes a big difference: the different forms are used for different things, and their chemistry and toxicity varies greatly. Here are the major forms of mercury and their uses:
How are people exposed to mercury?
People often worry about the obvious exposures to elemental mercury – things like broken thermometers or florescent light bulbs or dental fillings. While people are definitely exposed to mercury this way, the majority of the mercury you and I are exposed to is from the environment. Mercury enters the environment from three major sources: The first is natural; elemental mercury vapor released from volcanoes accounts for over 50% of all the mercury entering the environment. The second and third sources are human activities: coal burning power plants (again, in the form of elemental mercury vapor) and sources like industrial waste and runoff. Fortunately, environmental regulations have reduced the last source in recent years.
What are the effects of mercury?
Mercury is a dangerous neurotoxin – this will probably come as a surprise to no one. However, how “bad” it is depends greatly on what form you are exposed to and how you are exposed to it. Elemental mercury is the least toxic form, in part because is it not well absorbed through the GI tract (your stomach and intestines) or skin. Sure, if you drink a few grams of the stuff it will probably kill you, but elemental mercury is still much less dangerous than the other forms. The most dangerous way to be exposed to elemental mercury is by breathing in its vapors – this can rapidly affect the brain (causing confusion, tremors, memory loss and behavior changes), and eventually death. The same effects would occur if you cracked open a few dozen large thermometers and drank the mercury inside. Please don’t do this.
Most of the historical mercury poisonings that occurred involved mercury salts. Mercury chloride was used as a laxative, to treat syphilis, and in teething powders (!!!). You know, for infants. (What was wrong with you, old-timey people?!) Since mercury salts don’t get into the brain very well, the main toxicity concern for mercury salts is kidney damage, which can be severe and fatal. One mercury salt, mercury nitrate, was used to stabilize wool for felting in the 18th and 19th century. Persons who worked as “hatters” around this time often breathed in the elemental mercury vapors coming off the mercury nitrate they were working with, causing severe neurological damage, hence the term “mad as a hatter.”
The most dangerous forms of mercury today are the organic mercury compounds, particularly methyl mercury. When elemental mercury enters the environment from a volcano, a coal plant, or someone improperly disposing of a thermometer or a fluorescent light bulb, it generally makes it’s way into the water. Once there, it settles to the bottom of the ocean, lake, or river and it is turned into methyl mercury by the microbes in the sediment. Don’t blame the microbes – they’re just trying to get rid of the mercury around them – but this is a problem for us, because methyl mercury bioaccumulates (it’s concentrated by organisms in the food chain) and is easily absorbed when we eat it. Since it’s in the sediment under the water, eating fish is the major source for people, and this is the reason the FDA and EPA recommends that children and pregnant women only eat fish twice a week. The fish with the highest mercury levels are sharks, mackerel, swordfish, marlin, bluefin tuna, and tilefish. The safest are shrimp, salmon, and catfish. Here’s a link the detailed FDA/EPA recommendations.
Unfortunately, we know exactly what methyl mercury poisoning looks like from several large scale poisonings. In the 1950’s and 1960’s thousands of people in Minimata, Japan were diagnosed with “Minimata Disease”, which was caused by widespread mercury contamination in Minimata Bay and consumption of contaminated seafood. Affected persons had numbness, lack of coordination, plus speech and hearing issues. The most severe cases ended in paralysis, coma, and death.
While Mercury is a potent neurotoxin, it’s important to note that there is no scientific evidence at all liking it to autism. You may hear conspiracy theories about the mercury-containing thermasol preservative in vaccines causing autism, but these are completely untrue. Thermasol has never even been present in the MMR vaccine that many cite as “toxic,” and the levels of mercury in vaccines are extremely low. Plus, pharmaceutical companies have been reducing the levels of thermasol or eliminating it completely from their vaccines.
So what is the bottom line?
Mercury can be dangerous, but most people aren’t exposed to significant amounts. Unless you are cracking open thermometers or light bulbs for fun, your biggest risk comes from eating fish. There are reports of people eating so much fish they suffered from mercury poisoning (Jeremy Piven says he did it!), so follow the FDA/EPA guidelines and choose safer fish options. Also, remember that the reason we can’t eat fish every day is largely because of man-made pollution – write or call your Congress-person, or better yet the head of the EPA and let them know you want stricter regulations on coal plant emissions.
