A Guide to Mercury Contamination in Fish

The effects of mercury pollution can pose serious health risks to the entire population, but for children and pregnant women in particular.

For decades, seeing mercury in our everyday lives has been a regular occurrence. Indeed, manufacturers have been using it for years in products such automotive light switches, thermometers, and even dental fillings. To be sure, this form of mercury, known as "metallic mercury," really doesn't bring much of a direct health risk; industrial mercury pollution does. Industrial mercury pollution occurs when mercury is released into the air by chemical facilities, power plants, and the like, then comes to rest in lakes, rivers, and oceans. There, it begins to collect in the fish at levels that pose significant health risks to humans. Those with the potential to be most effected by this toxic mercury buildup are children and women who are pregnant or in their childbearing years.

More About Mercury in Fish

As mercury settles in local waters, bacteria in the water begin to absorb it. As they absorb it, they convert it to methyl mercury. This is where things start to get serious for humans. Not only are humans quite vulnerable to the effects of methyl mercury, but our bodies absorb it very easily. Too easily, really.

As the methyl mercury is absorbed by smaller fish, it starts its trek up the food chain. Larger fish eat smaller fish. Then even larger fish eat the large fish. As this happens, the levels of mercury begin to accumulate, rather than break down, creating even higher concentrations of mercury in larger fish. Humans eat those larger predatory fish.

Commonly contaminated fish include:

• mackerel
• shark
• swordfish
• tuna

Some of these fish can have mercury concentrations in their bodies that outpace their surrounding habitats by 10,000 times!

More About Mercury in Humans

It's these very common—and very contaminated—fish that present risks to humans upon consumption. It is very easy for humans to unknowingly ingest the mercury, since it is invisible and has no odor. Further, since it collects in the meat of fish, you can't remove it by removing certain parts of the fish.

After consumption, mercury starts to affect the brain and nervous system. It is known as a neurotoxin.

As mentioned, mercury can have the most pronounced effects on children, pregnant women, and women of childbearing age. This is because of the way children grow. During the infant and toddler years, especially, brain development is happening at a very rapid rate. As such, it needs to absorb nutrients at a rate much higher than adults. So it is rapidly absorbing mercury, as well. Among infants, and even developing fetuses, this kind of exposure and absorption can lead to a host of ill effects, including, but not limited to:

• blindness
• deafness
• cerebral palsy
• mental retardation

Because the rate of absorption is so rapid in children, even lower levels of mercury can affect development in the following ways:

• learning disabilities
• shorter attention spans
• delayed walking
• delayed talking

Mercury poisoning affects adults differently, with its own menu of adverse effects, including:

• numbness in fingers and toes
• tremors
• memory loss
• blood pressure deregulation
• fertility issues
• loss of visions

While it is not fully conclusive yet, some recent studies suggest that mercury exposure may also cause heart disease.

More About Mercury and Diets High in Fish

The most recent numbers, in January 2003, from the Center for Disease Control (CDC) showed that 17% of women who are of childbearing age have a high enough concentration of mercury in their blood to result in adverse effects during fetal development.

Still, there is promising news. Those with high levels of mercury in their blood can lower these levels by simply reducing the consumption of mercury-contaminated fish. This process, however, can take six months or more to start showing results. Looking at the big picture, though, with a remedy so simple and the enduring results so positive, six months doesn't seem like that long of a wait.