Interactions between selenium and mercury in mice: marked retention in the lung after inhalation of metallic mercury

The distribution of 203Hg after inhalation of radioactive metallic mercury (4.3 mumol 203Hg0/kg body wt. for 1 h) was studied in saline (control) and selenite (10 mumol/kg body wt. intraperitoneally, i.p.) pretreated male C57BL mice by means of whole-body autoradiography and scintillation counting. Selenite pretreatment did not apparently change the immediate uptake and distribution of 203Hg (presumably inorganic Hg after oxidation in the different organs) but markedly increased the retention time in the whole body. The most marked retention was seen in the lungs where the selenite-pretreated animals had 200 times higher concentration as compared to control animals 14 days after inhalation. In other organs the corresponding value ranged between 1 (brain) and 12 (spleen). Selenite-pretreated and control animals showed the same low rate of exhalation of 203Hg after the inhalation period, while the latter animals eliminated significantly more through the urine and faeces (measured only during the first 24 h). When inversely radioactive selenite (75Se-selenite) was injected i.v. into animals 1 h earlier exposed to non-radioactive Hg0 (by inhalation), the lung concentration of 75Se after 24 h was 4 times higher than that of control animals. When radioactive mercury was injected i.v. in the form of 203HgCl2 (4.3 mumol/kg body wt.), selenite (10 mumol/kg body wt., i.p.) increased the retention time in the body, more so than after 203Hg0 inhalation. In this case the mercury was retained especially in the serum, red pulp of the spleen and liver (reticulo-endothelial system). 75Se-selenite injected i.v. after i.p. administration of non-radioactive HgCl2 in the same doses as above similarly accumulated more in serum, spleen and liver as compared to control animals. It is presumed that while injected selenite and inorganic mercury (Hg2+) interact strongly in the serum, increasing each other's uptake and retention especially in the reticulo-endothelial system, inorganic mercury retained in various organs after oxidation of Hg0 upon inhalation interacts with selenium mainly intracellularly. This occurs especially in the lungs, where initially high concentrations of mercury are found after inhalation.