What is mercury and where does it come from?

Mercury is a shiny, white silver heavy metal that is liquid at room temperature. It forms a colorless, odorless vapor and is released to the environment by both natural and human actions. Mercury occurs naturally in volcanoes, mercury deposits, and even wildfires. Most natural mercury exists as the solid mineral cinnabar in mercury deposits and is bound up and harmless until it is mined for human use. Mercury is also contained in fossil fuels, like coal and oil, and it can be released when those fuels are burned to generate electricity or for other purposes.

When mercury is removed from the earth, it can enter our environment.  Once in the environment, mercury does not break down, and it is very hard to control, due to its unique properties as a solid, liquid, and gas.  Mercury may travel long distances, or stay nearby, depending on a variety of environmental factors.  Scientists refer to the mercury in any given local area or region as a “pool” which may build up in fish, move from place to place, or even become buried in underwater sediments.  When mercury is released it becomes part of the mercury that is now circulating in the environment -- part of what is called the global pool.  Its disposition in the environment will dictate whether it is “available” to contribute to human or wildlife exposure and ultimately, whether it is a risk to human health.

To reduce mercury levels, it is necessary to focus on controllable sources.  Some of the more common controllable emissions and releases of mercury include chlorine-manufacturing plants, coal combustion, waste incineration, mining, cement manufacture and pulp and paper production.

How does mercury get into our bodies?

Mercury exposure in humans results primarily from eating fish contaminated with methylmercury. Nearly 85 percent of adults in the United States consume seafood at least once a month, and 40 percent eat it on a weekly basis. Certain ethnic and Native American groups and recreational anglers consume seafood at much higher rates and are at higher risk.  Albacore tuna, one of America's most commonly eaten fish, and fresh tuna steaks have high mercury levels as do other predatory fish such as swordfish. Other sources of mercury include dental fillings, and vaccines.

How does mercury affect adults?

Adults who consume high levels of mercury can also experience a variety of toxic effects, mostly related to the nervous system and the brain, which control sensory and motor activities. Behavior, memory, and learning processes can be adversely affected by mercury contamination, and new studies show that the cardiovascular and reproductive systems also can be damaged.

Why is mercury such a problem for children?

Mercury is dangerous to humans because, when ingested, it can cause a variety of serious health disorders, especially in children. Methylmercury can travel across the placenta from the mother to the fetus, meaning exposure to the dangerous poison begins in the womb during a baby's most vulnerable developmental period. Not only can children and fetuses be harmed by lower concentrations of mercury than adults but, because they are in a more active development stage, they are especially vulnerable to mercury's toxic effects.

• A United States Environmental Protection Agency (EPA) scientist estimates that one out of every six pregnant American women has enough mercury in her blood to cause neurological damage to her developing baby.
• Each year, hundreds of thousands of babies are born with enough mercury to pose developmental risks.

How does it affect marine-life?

Much of the mercury released as pollution to our air and water will eventually make its way to the ocean. This can occur when mercury is directly deposited over our oceans, or when mercury is deposited on land, and enters our waterways as runoff.  Methylmercury levels in fish don’t only affect humans who eat them, but have also been found to harm the fish. Methylmercury can lower fish reproduction rates and hinder their development. It can also affect survival of larvae and alter competitive abilities.

Those species at the top of the marine food chain tend to accumulate the most mercury. For example, data show that whales, dolphins and sharks, among other species have very high levels of mercury in their bodies. It is difficult to observe toxic effects on marine animals in the wild.  However, toxic effects have been observed in some wildlife that consumes fish, such as otters, Florida panther, and birds. The observed effects include impaired behavior, reproduction and development and at high levels of exposure, even death. 

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