Content of non-mercury-associated selenium in human tissues

Recent studies have shown that at a higher mercury (Hg) burden, the molar r atio of selenium (Se) and Hg in tissues tends to approximate 1 : 1 by the f ormation of biologically largely inert adducts. From the toxicological stan dpoint, this trapping of free Hg is welcome. However, this binding of Se to Hg reduces the portion of Se in tissues, which is available for the format ion of essential selenoenzymes like glutathione peroxidase, type I deiodase , and so forth and could result in a relative deficiency of Se. Therefore, we tried to determine the concentration of non-Hg-associated Se in several human tissues. As there is no proved trace method for the speciation of non -Hg-bound and Hg-bound Se in tissues, the total concentrations of Hg and Se were determined and the portion of non-Hg-associated Se was calculated by the difference of the molar concentrations of Se and Hg. For this investiga tion, the following tissues were obtained by autopsy from 133 adults: kidne y cortex, thyroid gland, liver, spleen, cerebrum cortex, and pituitary glan d. In no case was an occupational Hg burden known. The results confirm the assumption of a 1:1 association of Hg and Se in human tissues. The mean con centration of non-Hg-bound Se was calculated to 576 mug/kg in the kidney co rtex, 363 mug/kg in the thyroid gland, 308 mug/kg in the liver, 205 mug/kg in the spleen, 111 mug/kg in the cerebrum cortex, and 545 mug/kg in the pit uitary gland. In none of the cases under investigation in any tissue was th e molar Se/Hg ratio below 1. This means that a total deficiency of non-Hg-b ound Se could not be seen in this normal population, even at a higher Hg bu rden. Nevertheless, at a suboptimal Se supply like in Germany, any reductio n of the part of Se, which is available for the formation of essential sele no-enzymes, should be avoided. Therefore, any additional Hg burden such as from dental amalgam should to be considered critically. The different distr ibution of Hg and Se in the body confirms that there is a controlled hierar chy in the Se supply of different organs, which tries to prevent a Se defic iency in organs with essential seleno-enzymes like the thyroid gland even u nder an suboptimal Se supply.