Distribution and Elimination of Ingested Mercuric Oxide in Mice

Abstract

Neutron-activated mercuric oxide was administered by gavage to female BALB/c mice. Counts of 197Hg and 203Hg in the whole body, urine, and feces were followed for up to 36 days. Elimination of mercury fitted a 3-compartment model. Nonpregnant mice eliminated approximately 87.5% of the dose at a fast rate (t1-2 = 9 hours), 12% at an intermediate rate (t>1/2 = 2 days), and 0.5% at a slow rate (t1/2 = 15 days). Each half-time was approximately 7 times shorter than the corresponding half-time fitted to published data on rats. Mice were also faster than humans in eliminating the ingested mercury. Pregnancy slowed down the intermediate rate of elimination. The total administered dose was recovered from feces and urine in a 9:1 ratio. Organ weights and mercury burdens were measured after serial sacrifice. Peak concentrations were reached within two days, with highest levels in kidneys followed by placentae and livers. In brains, peak concentrations were delayed and low. Subsequent losses of mercury differed widely in rate constants, with fastest overall rates in the brain, intestine, and integument, followed in order by whole body, liver, and kidneys. Ten days after dosing, mercury concentration ratios of placenta to 17-day old fetus were 20:1; 11 days after dosing, and with less than 2% of body burden remaining, while body concentration ratios of mother to neonate were 4:1. The data indicated that mice eliminated mercuric salts faster than had been reported for rats or humans, and that rapid elimination coupled with a placental barrier shielded fetuses from equlibrating with the peak concentrations of mercury found in dams after a single dose.