Thus, at best, a stool test might indicate that mercury entered the gastrointestinal tract, but it could not provide an accurate measurement of either exposure or what was absorbed into the body. Hair Analysis Hair mercury levels are not an accurate indicator of mercury exposure. Hair testing has never been standardized to provide meaningful information. It gets there from food, water, and air. Mercury can be accurately measured in blood and also in urine, which is a distillate of the blood serum.
Hair is similar to the outer layer of the skin and has no blood supply.
Thus the amount of mercury in hair does not reflect the concentration in the rest of the body. Measurements of blood and urine from thousands of people have never shown high levels of mercury in the general population. Only workers with high work exposure have shown abnormal levels in blood and urine, but these are not in the toxic range. Hair grows at different rates in different individuals and its composition is quite variable. However, the amount of a substance absorbed into the hair is influenced by surface area and hair composition.