First published July 2007, updated March 2010

Mercury is a cumulative heavy metal poison that can be absorbed by the through the skin, our digestive system and our lungs. Mercury destroys the central nervous system and many other organs. Sufficient exposure can result in brain damage, insanity and death. Mercury is a persistent toxin in the environment.

Remember the Mad Hatter from Alice in Wonderland or ever heard the term "mad as a hatter"? It has its origins in fact - hatmakers were using mercuric nitrate right up until the 1940's and many of them did indeed go mad. Even today, mercury remains in soil and river sediment in areas where hat making factories using mercury operated.

Mercury compounds are far more toxic than the element itself. Dimethyl mercury, is so toxic that a small amount can kill. In a case in 1997, a chemistry professor died as a result of a couple of drops of Dimethyl mercury being spilled on her hand - she was even wearing latex gloves at the time. The mercury in our thermometers is silver, whereas Dimethyl mercury is a colorless liquid with a weak, sweet odor A severely toxic dose is as little as 0.1mL. Thankfully the use of Dimethylmercury is mostly limited to toxicology experiments, but mercury can change from one form to another in the environment.

Mercury and fish

Issues relating to mercury hazards have had a great deal of media coverage of late, particularly in relation to the consumption of fish. Research by the U.S. Geological Survey (USGS) determined all fish tested from 291 freshwater streams across the United States was tainted by mercury, with over 66 percent having levels higher than those set by the Environmental Protection Agency as being a concern for fish-eating mammals and over a quarter of fish were contaminated at levels above those set as the safe threshold for human consumption

Long living carnivorous fish are especially prone to containing high levels of mercury given how many other fish they eat during their lives - the mercury in the smaller fish becomes concentrated in the bodies of fish that feed upon them; building up over time.

While "safe" fish vary from country to country; species most likely to contain high levels of mercury include marlin, swordfish, snapper and tuna, carnivorous freshwater species, plus species caught in areas close to heavy industry. For more information about recommendations for fish consumption, contact your local seafood authorities.

But mercury is more than just about fish - how does it get into them in the first place and what can we do to reduce the amount getting into the environment?

Human sources of mercury

While mercury occurs naturally in the environment, the majority of atmospheric mercury vapor is attributed to human activity. Mercury vapor is a byproduct of mercury mining and refining of course, but also many other sources.

Here's some other common sources of mercury that we can avoid and or reduce:

Coal fired power generation - Coal-fired power plants are the single largest source of mercury air pollution, making up approximately 40 percent of all mercury emissions. Atmospheric mercury returns to the Earth through various forms of precipitation and dry deposition. Once in waterways it can transform into methylmercury, where it can accumulate in the tissues of aquatic organisms. Ingested methylmercury is easily absorbed by the gastrointestinal tract in humans.

By cutting down our electricity consumption and implementing some simple electricity saving tips or by installing solar power, we can all play a role in reducing the amount of atmospheric mercury generated in instances where our power is sourced wholly or in part by coal fired generation.

Cigarette smoke - I guess the answer is simple here as to what to do about it. Damn, reason number 1076 I really should give it up. It's not lost on me that I'm so concerned about the environment, yet I smoke. Such is the insanity of addiction. Tobacco's environmental impact is of course far more than just mercury emissions.

Batteries - Still often found in button cell batteries in the form of Mercury oxide. Check the labels before purchasing as it should be stated on the packaging if the battery contains mercury.

Amalgam fillings - Need to get a tooth filled? Check with your dentist if amalgam is going to be used. Amalgam fillings contain a high level of mercury (50%) and should be avoided. Alternatives are gold, composites and ceramics. The use of amalgam in some countries is now illegal.

Fluorescent Light Bulbs - old style fluorescent lights and even CFL's (compact fluourescent lamps) contain mercury. CFL's contain a minimal amount, but it's important to dispose of them properly - contact your local council for information on recycling options or the location of a hazardous waste drop-off center.

Necklaces/Jewelry - Some jewelry can contain mercury, so ask questions before purchasing items; particularly cheaper imported pieces.

Thermometers - The liquid in thermometers containing mercury is usually silver in color, while in alcohol thermometers it's red. Mercury thermometers should not be disposed of in the trash - again, contact your local council for advice as to where and how you can dispose of them safely. If you still have mercury thermometers, it's really worthwhile getting rid of them, particularly if you have kids. I remember breaking one as a child and being totally mesmerized by the droplets - I was about to start playing with it, but my parents thankfully intervened. Curiosity and sheer stupidity has nearly killed this cat on many, many, many occasions :).

Barometers - see above

Paint - Up until 1990 in the USA, mercury was used in around a third of latex (water based) paints as a preservative and pesticide and it may still be in use in some countries. Some oil based paints may also contain mercury, but this should be clearly stated on the label. If you have old paints laying around, these should also really go to a hazardous waste drop-off center.

Other products that may contain mercury are switches, solvents, dyes and pigments, pottery and art objects and cosmetics.

Dealing with a mercury spill

The number one rule for dealing with a mercury spill is to *never* use a vacuum cleaner - this will put mercury into the air. You shouldn't use a broom either, as it will create more droplets and you should certainly never dispose of it down a drain. The EPA has quite a detailed guide on cleaning up mercury spills, so I'd rather refer to you to their site - the page is well worth bookmarking.