Ever wonder where the mad hatter in Alice in Wonderland got his madness? It may have actually come from the metal mercury.

Years ago, the process of hat making included dipping the felt into mercury to make it easier to mold the felt to the hat. Great for the hat, not so great for the hatter because the mercury often would make the hatter go "insane."

While we no longer have to worry about being exposed to toxic amounts of mercury during our hat-making hours, we do need to be cognizant of the mercury in our food supply. With all the madness surrounding the recent recommendation of fish consumption for health benefits, we should know the risks over-consumption may pose to us as well.

Mercury can be found in our food supply in foods ranging from potatoes to meat. However, current concerns about the safety of fish have come up in the medical community. Specifically, if you are pregnant, may become pregnant, nursing or are a small child (note: this does not include someone's "mental age"), you should avoid fish high in mercury because it may affect brain development. Such sources of fish include shark, swordfish, mackerel and tilefish.

In addition, it is advised that healthy individuals should consume no more than seven micrograms of mercury a day.

Shark and swordfish have been tested to contain levels of over 130 micrograms per five-ounce serving, well above the advised amount. While one or two servings once in a while probably won't kill you, you may want to limit your intake of such fish.

Being in the middle of Pennsylvania, many people may not consume fish often. However, canned tuna fish also contains fairly high amounts of mercury. One six-ounce can of tuna may contain over 30 micrograms of mercury. In addition, the albacore tuna variety typically contains more mercury than light tuna because the individual fish used for each type have different feeding habits. Typically, fish that are higher up on the food chain contain higher amounts of mercury because they eat the smaller fish and their mercury content bioconcentrates. Fish containing smaller amounts of mercury include salmon, catfish, pollock and shrimp.

Why do we suddenly have to worry about the safety of our fish? As our technology has increased over the years, so has our search for materials to utilize. Unfortunately, these materials often turn out to be unsafe. For instance, mercury has been added to marine paint to prevent the growth of algae on boats. However, it can leach into our water supply. In addition, coal, petroleum and natural gas are all sources of mercury. While we may not be able to fix these sources of contamination right away, we can begin to protect ourselves by being educated consumers.

Exposure to large doses of mercury in a short time period can cause numbness, difficulty speaking, inability to concentrate and vision and hearing loss.

Long-term effects of exposure include seizures and mental retardation. None of these consequences seem particularly worth a can of tuna or a shark steak, although depending on how it is marinated...

The bottom line is that if you eat too much of these types of fish, you may suffer the health consequences later on. However, that doesn't mean you should avoid these fish completely, unless you want to. Just being aware of how much "high mercury content" fish we eat may be enough to help ward off the mad hatter inside us all.