By Brian Cronin, Director of AquaMD

Before the days of digital thermometers, many of us grew up being poked and prodded with mercury-filled glass tubes whenever we came down with a sniffle. Nowadays, the mercury thermometer has all but gone the way of the horse and buggy with good reason: Mercury is highly toxic.

While mercury occurs naturally in the earth's crust, the vast majority of contamination occurs via human activity. What are the major sources of mercury pollution?

• Coal-burning power plants
• The incineration of hazardous waste
• Chlorine production
• Cement manufacturing
• Municipal landfills
• Metal refining
• Sewage

The EPA enforces standards called Maximum Contaminant Levels, or MCLs. The MCL for mercury is set at 2 parts per billion, a limit exceeded by only a couple of drops in an Olympic-sized swimming pool. Today, many municipalities are encouraging residents to dispose of old mercury thermometers, dry-cell batteries, fluorescent light bulbs and switches at designated disposal sites for hazardous waste.

The Health Risks

Mercury is a neurotoxin, which means that it affects the nervous system. The common term "mercury poisoning" refers to the effect of over-exposure on the human nervous system, organs and other bodily functions. In fact, the famous phrase, "Mad as a Hatter," was a direct result of this.

Once upon a time, craftsmen in the 1800s who made hats by hand were exposed to mercury in the felting process, as they rubbed mercury into cloth to preserve it. As a result, mercury poisoning commonly caused trembling, anxiety, personality shifts and dementia and the Mad Hatter was born.

Today, mercury poisoning manifests itself in many forms:

Acute Exposure: This involves exposure to high doses of mercury over a short period of time. Exposure can occur when drinking highly contaminated water, inhaling high levels of mercury vapor, or if children play with mercury. Nausea, vomiting, diarrhea and severe kidney damage may also occur.

Chronic Exposure: This form of poisoning happens when exposure to contamination occurs repeatedly or over an extended period. Eating too much contaminated fish or drinking repeatedly from a polluted water supply can lead to chronic mercury poisoning.

Nervous system damage, kidney disease, birth defects, dental problems, mood swings, mental changes, hallucinations, memory loss, nerve damage and the inability to concentrate can occur. Symptoms also include tremors, loss of dermal sensitivity, slurred speech and, in rare cases, even death and paralysis.

(Soon, I'll write about the wave of warnings concerning contaminated water supplies nationwide this past summer. Recent EPA studies show that in the United States, one of every three lakes and one-quarter of the nation's rivers contain enough pollution that people should not even think about eating fish caught in these areas -- much less ever consuming the water.)

Protect Your Family

For starters, you may want to rethink how much fish, if any, should be in your family's diet. Taking mercury exposure into consideration, the concept of fish as "brain food" takes on a whole new meaning.

Be sure to test your home's drinking water at least once a year for dangerous contaminants, like mercury. Remember, mercury is considered harmful at level higher than 2 parts per billion. There is no way to detect it, other than through analysis in a laboratory.

Be smart and be safe.