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Lead stays in the body for different periods of time, depending on where it is. Half of the lead in the blood will be excreted in 25 days (this is called the "half-life"). In soft tissues, it takes 40 days for half of the lead to be excreted. In bones and teeth it takes much longer, up to 10 years or longer. Since lead is stored in the body, a person can get poisoned from exposure to just small amounts of lead over a long period of time (chronic exposure). You do not need to get exposed to just large doses of lead to be poisoned (acute exposure). It can take months or years for the body to get rid of lead. A person will continue to be exposed to lead internally even after the actual exposure to lead stops. How is Lead Measured in the Body? Blood tests to measure the amount of lead circulating in the body were developed over 60 years ago. The results are measured in micrograms of lead per deciliter of blood (the symbols used are ug/dl or mcg/dl).

 Mercury >>>Approximately one half of the mercury absorbed from a single dose will be eliminated within two months, but it can take several months to remove all traces of mercury. The body gets rid of mercury through the urine and the feces. "Chelation" therapy is used when mercury levels are extremely high. Factors that determine the severity of the health effects from mercury exposure include: dose, duration of exposure, age of the person exposed (the fetus is most susceptible), route of exposure (inhalation, ingestion or skin contact), and the health and nutritional status of the person involved.