Mercury is a toxic heavy metal that poses a significant health concern when it accumulates in the body. Human exposure occurs mainly through three forms: organic mercury (methylmercury), inorganic mercury salts, and elemental mercury vapor. The most common exposure route for the general population is through the consumption of fish and shellfish contaminated with methylmercury, which bioaccumulates up the aquatic food chain. Other sources can include occupational exposure to mercury vapor or, historically, certain medical or dental materials. When exposure is suspected based on symptoms or history, specific testing can determine the body burden and guide necessary interventions.
Testing for Recent Exposure (Blood and Urine)
Testing the blood and urine offers a snapshot of recent mercury exposure, but the interpretation depends heavily on the form of mercury involved. Blood testing is primarily used to assess exposure to methylmercury. This form of mercury is readily absorbed from the gastrointestinal tract, concentrates in red blood cells, and has a half-life in the blood of about 50 days, making the blood test a good indicator of exposure over the last few weeks. A high blood mercury level usually suggests a recent or ongoing diet high in contaminated seafood.
Urine testing, conversely, is generally a better indicator of exposure to elemental or inorganic mercury. Exposure to these forms often occurs through inhalation of mercury vapor, such as in an industrial setting or from a large spill, or through contact with inorganic mercury salts. The body metabolizes these forms, and they are then excreted primarily through the kidneys into the urine. Methylmercury is poorly excreted in the urine, making a urine test unreliable for assessing dietary methylmercury exposure.
Elemental and inorganic mercury levels in the blood decrease relatively quickly, often by half within a few days, as the metal moves into organs like the kidneys and brain. Therefore, blood testing for these forms must be done shortly after a suspected acute exposure to be meaningful. Urine levels, which reflect the body’s attempt to excrete these forms, may remain elevated for a longer period following a high-level exposure.
Assessing Long-Term Exposure (Hair and Nails)
Hair analysis is often utilized to assess exposure that occurred over several months, particularly for methylmercury. As mercury circulates in the bloodstream, it binds to sulfur-containing proteins, like keratin, which is the main structural component of hair. Once incorporated into the hair shaft as it grows, the mercury remains stable, providing a historical record of exposure.
This process allows for a segmented analysis, where each centimeter of hair from the scalp can represent approximately one month of past exposure. This timeline is useful for reconstructing the pattern of methylmercury intake, as 80 to 90 percent of the mercury found in hair is methylmercury. Hair analysis is generally not used for inorganic mercury exposure, as that form is not readily incorporated into the keratin structure.
Nail testing is a supplementary method that also relies on the binding of mercury to keratin, similar to hair. While not routinely tested, mercury is present in nails, and they can offer an additional matrix for assessing longer-term cumulative exposure.
Understanding What Your Test Results Mean
Mercury test results are typically reported in units such as micrograms per liter (µg/L) for blood and urine, or micrograms per gram (µg/g) for hair. Interpretation requires comparing the measured value to established reference ranges, which represent the levels found in the general, unexposed population. For instance, whole blood mercury levels are usually below 2.0 µg/dL in individuals with low fish intake, and urine levels are often below 10 µg/L.
These reference ranges are not necessarily thresholds for toxicity, but rather indicators of unusual exposure. Elevated results suggest that an individual has been exposed to more mercury than the average person, but the level at which clinical symptoms appear varies widely. Pregnant women represent a special population, as the World Health Organization recommends monitoring hair mercury and notes that levels above 10 µg/g may increase the risk of neurological defects in the fetus.
If test results indicate significantly elevated mercury levels, the primary course of action is to identify and eliminate the source of exposure. For organic mercury, this often means adjusting dietary habits, specifically reducing consumption of high-mercury fish. In cases of severe or symptomatic poisoning, a medical professional may recommend chelation therapy.
Chelating agents are specific drugs that bind to the metal in the body, which then facilitates its removal via urine or feces. This treatment is only approved for confirmed heavy metal poisoning and must be administered under strict medical supervision due to the potential for side effects, including the loss of beneficial minerals.