Environment Task Force Newsletter
Ohio State University Extension
Spring, 1998, v1 #4

Mercury in Fish Isn't Likely to Cause 'Mad Fish Eaters'

Joe Heimlich, State Extension Environmental Specialist

Many people fear that larger levels of methylmercury (MeHg) in fish can be toxic to those who eat the fish. Luckily, most studies show that while this is a legitimate concern, most fish eaters are not at risk.

Mercury is a naturally occurring element in the Earth's crust and is used in disinfectants, antiseptics, diuretics, preservatives and scores of other processes and items. The human body is able to adapt to the mercury found in the natural environment.

However, human activities such as coal burning, incineration and industrial emissions release mercury into the environment where it eventually is washed into streams, lakes, rivers and oceans. In the water, mercury can be methylated (converted) by organisms and concentrated in fish. This bioaccumulation of methylmercury currently is the subject of debate.

Mad hatters

In the 19th century, concentrated mercury fumes drove hat makers mad and coined the term "mad hatters." Repeated exposure to high levels of mercury can harm the central nervous system and cause sudden mood swings for no apparent reason, shaky hands, difficulty walking, slurred speech, hallucinations, memory loss and a loss of concentration. Kidney damage and birth defects also are possible.

The dose makes the poison

To be categorized as unsafe, the level of MeHg in fish would have to be uniformly high in all fish eaten, and the amount of fish that would need to be eaten before mercury levels become dangerous is far greater than most of us eat.

However, caution is suggested for pregnant women in communities that eat a lot of fish.

For most of us, the bottom line is that the value of eating fish--a good source of protein low in saturated fat--far outweighs the low risk of mercury poisoning. For more information about mercury levels and fish consumption, interested people should check with their local health department.