Mercury

Two types of mercury are present in the body: organic and inorganic. While both types are poisonous, organic mercury, 80% to 90% of which is methylmercury, is usually considered more of a hazard.

Normally, the body’s total burden of mercury comes from the diet.

Mercury absorption is dependent on the form. Mercury vapor is almost completely absorbed by the lungs; however, pure liquid mercury will pass through the gastrointestinal tract almost completely unabsorbed. The body efficiently absorbs methylmercury from dietary sources. Methylmercury also accumulates in the body following conversion of inorganic (elemental or salt forms) mercury to methylmercury.

The distribution of mercury in the body depends greatly on the type absorbed. Inorganic mercury coming from industrial exposure predominantly deposits in the kidneys, while organic mercury from the diet will deposit in the brain.

The primary dietary source of methylmercury is seafood. Mercury is common in the aquatic food chain. The highest levels can be found in the most common aquatic foods: tuna, salmon, swordfish, halibut, trout, pike, bass, eel, and most invertebrates.

The FDA issued a warning that two cans of tuna per week would put an individual over the mercury exposure limit (10 ug/L).  Additionally, the FDA has issued warnings to women to limit their seafood intake during pregnancy. Other individuals susceptible to methylmercury poisoning are those who consume significant amounts of sushi containing species such as tuna or swordfish.

Environmental sources of mercury come from industrial applications, as mercury is incorporated into consumer products. Individuals working in these industries are at risk. Individuals working with dental amalgams containing mercury are also at risk of exposure.

The half-life varies depending upon the type of mercury present. Inorganic mercury has a half-life of 18 to 24 days, while methylmercury is reported to have a half-life of 52 days. The extended half-life of mercury compounds is attributed to their accumulation in body tissues, predominantly liver, kidney, and brain. Regardless of the type of mercury present, the extended half-life will result in significant accumulation if there is chronic exposure.

This greatly depends on the type of mercury absorbed. Inorganic mercury is generally excreted through urine, while organic mercury is excreted through feces. Both types will show up in the bloodstream. Therefore, if symptoms of mercury exposure are present, blood would be the first specimen of choice. If a blood test is positive, a follow-up test using a 24-hour urine sample would help differentiate organic versus inorganic mercury exposure.

For workplace exposure, random urine collections are easiest and help to eliminate the possibility of an elevated result due to seafood.

The test provides only a “total” mercury concentration, whether performed on blood or serum. Based on symptoms and lifestyle, however, it should not be difficult to determine the source/type of mercury to which the patient was exposed.